1
IS HUMAN INFORMATION PROCESSING CONSCIOUS?
Max Velmans, Department of Psychology, Goldsmiths College, University of London, Lewisham Way, London,
SE14 6NW,
England.
Behavioral and Brain Sciences, 1991, 14(4):651-669 (target article, accompanied by 36 commentaries)
KEY WORDS: consciousness, information processing, conscious process, preconscious process, unconscious
process, focal-attentive process, attention, brain, mind, functionalism, reductionism, psychological
complementarity.
ABSTRACT: Investigations of the function of consciousness in human information processing have focused
mainly on two questions: (1) where does consciousness enter into the information processing sequence and
(2) how does conscious processing differ from preconscious and unconscious processing. Input analysis is
thought to be initially "preconscious," "pre-attentive," fast, involuntary, and automatic. This is followed by
"conscious," "focal-attentive" analysis which is relatively slow, voluntary, and flexible. It is thought that
simple, familiar stimuli can be identified preconsciously, but conscious processing is needed to identify
complex, novel stimuli. Conscious processing has also been thought to be necessary for choice, learning and
memory, and the organization of complex, novel responses, particularly those requiring planning, reflection,
or creativity. The present target article reviews evidence that consciousness performs none of these
functions. Consciousness nearly always results from focal-attentive processing (as a form of output) but
does not itself enter into this or any other form of human information processing. This suggests that the
term "conscious process" needs re-examination. Consciousness appears to be necessary in a variety of tasks
because they require focal-attentive processing; if consciousness is absent, focal-attentive processing is
absent. Viewed from a first-person perspective, however, conscious states are causally effective. Firstperson accounts are complementary to third-person accounts. Although they can be translated into thirdperson accounts, they cannot be reduced to them.
In the words of George Miller (1987), "Consciousness is a word worn smooth by a million tongues". Its most
common meanings are "awareness," "knowledge," and a "state of wakefulness." In the analysis that follows,
it is "consciousness" in the sense of "awareness" that is of primary concern.
Much of human information processing seems to involve awareness (e.g. perception, imagery, and emotion).
From a Darwinian standpoint, it is reasonable to assume that consciousness (in this sense) might have some
function. Cognitive psychologists accordingly have devoted considerable effort to determining what the
functions of consciousness might be. This effort has focused mainly on two questions:
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(1) Where does consciousness enter into human information processing?
(2) How does conscious processing differ from preconscious and unconscious processing?
The experimental literature dealing with these questions is both extensive and complex1, and there are many
divergent theories.2 Nonetheless, there is consensus on some points. Awareness of a stimulus is thought to
be preceded by preconscious information processing. The physical features of well-learnt verbal stimuli, for
example, are thought to be analyzed preconsciously (La Berge, 1975, 1981; Posner, 1978; Shiffrin &
Schneider, 1977) in the first 250 msec. (Posner & Snyder, 1975; Neeley, 1977). Libet, Wright, Feinstein &
Pearl (1979) review evidence that similar periods are required for preconscious processing of tactile stimuli
for at least 200 msec. for suprathreshold stimuli, ranging up to 500 msec. for threshold stimuli.
Suprathreshold stimuli applied to the skin, for example, are masked by electrical stimuli applied directly to
the somatosensory cortex, up to 200 msec. after the skin stimuli have arrived at the cortical surface (a
situation which could not arise if the skin stimuli had already entered awareness).
It is also thought that not all stimuli are selected for further "focal-attentive processing"; only those that
enter consciousness (Broadbent, 1958; Mandler, 1985; Norman, 1969; Posner, 1978; Shiffrin & Schneider,
1977). The relationship between attention and consciousness is therefore a close one. Indeed, many
psychologists explicitly or tacitly assume that "preconscious" processing is identical to "pre-attentive"
processing, whereas "conscious" processing is identical to "focal-attentive" processing (e.g. Mandler, 1975,
1985; Miller, 1987).
These assumptions are tempting. If they are justified, studies of "focal-attentive" processing become studies
of "conscious" processing by definition. And "focal-attentive" processing, unlike "awareness," is easily
understood in information processing terms. In the present target article, however, I do not take these
assumptions for granted.
1
See Baars (1989), Carr & Bacharach (1976), Dixon (1971, 1981), Holender (1986), Kihlstrom (1987), and
Mandler (1975, 1986) for reviews.
2
For example, consciousness is thought to be necessary for the analysis of novel stimuli or novel stimulus
arrangements (Posner & Snyder, 1975; Bjork, 1975). According to Mandler (1975, 1985), consciousness
allows us to choose amongst competing input stimuli. Other theorists have assumed that conscious
processing is necessary for a stimulus to be remembered (James, 1890; Underwood, 1979; Waugh and
Norman, 1965) and for the production of anything other than an automatic, well-learnt response, e.g. for a
voluntary response that is flexible or novel, or for a response that requires monitoring (feedback) or planning
(Romanes, 1895; Mandler, 1975,1985; Shiffrin & Schneider, 1977; Underwood, 1982). According to some
theorists consciousness enables us to interact with our environment in a "reflective" rather than an
automatic fashion (Mandler, 1975,1985; Dixon, 1981). There are many further views (see recent discussions
in Baars, 1989; Blakemore & Greenfield, 1987; Marcel & Bisiach, 1988). Baars (1989), for example, suggests
no less than eighteen different functions for consciousness in human information processing!
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In the psychological literature, experimental investigations of the role of consciousness in human information
processing have dealt largely with input analysis. Currently, "preconscious," "pre-attentive" analysis is
thought to be involuntary, inflexible and automatic, and restricted to accessing the memory traces of simple,
well-known stimuli. Conscious, focal-attentive processing is thought to be voluntary and flexible, and
therefore required for the analysis of novel stimuli or novel stimulus arrangements. In sections 1.1 to 1.4 we
examine the evidence for this view.
In sections 2.1 to 2.5 I develop an alternative view, citing evidence that preconscious analysis may extend to
(novel) phrases and sentences and that consciousness of such material arises only after input analysis is
complete. In sections 3 to 8, I question the many other ways consciousness has been claimed to enter into
information processing, for example, in stimulus selection (following stimulus analysis), in learning and
memory, and in the control of responses, including planning and creativity. I also re-examine the relationship
of awareness to focal-attentive processing. Finally, in sections 9.1 to 9.3, we look more closely at what is
meant by a "conscious process" and consider what the experimental studies of "conscious processing" imply,
both for models of human information processing and for philosophy of mind.
1. Preconscious vs. conscious analysis of input stimuli.
1.1 Early studies of preconscious stimulus analysis, using a shadowing task.
Many early explorations of pre-attentive analysis used a "shadowing task," in which one message is
presented through headphones to a subject's left ear while a different message is simultaneously presented
to the subject's right ear. The subject is asked to attend to only one of the messages and to repeat aloud
what he hears. Afterwards, however, he is questioned about the nonselected message.3 Cherry (1953), for
example, found that if subjects shadowed the message presented to one ear they were unable to report the
meaning of the message in the other ear, or even be sure that it was in English, though they could report
some of its physical characteristics. Subjects always noticed, for example, whether the nonselected message
was in a male or a female voice, or whether it was speech or a 400 Hz tone. If the nonselected message was
played backwards (on tape), they sometimes noticed that the reversed speech was "queer." Cherry
concluded that certain physical and statistical properties of the nonselected message were analyzed but not
its meaning.
On the basis of this and other evidence, Broadbent (1958) proposed the existence of a "bottleneck" in the
human information processing system. The physical properties of the many stimuli arriving at the sense
organs are simultaneously analyzed (in parallel "channels") in an automatic, preconscious fashion. However,
the channel used for the analysis of meaning has a limited capacity. Consequently, stimuli do not receive an
analysis for meaning unless they are fully attended to (i.e., selected for entry into this "limited capacity
decision channel") and it is only if they receive full (focal) attention that they enter consciousness, in which
case they can be reported.
3
Processes that are accompanied by consciousness are at the focus of attention. It appears that
consciousness is closely linked to that aspect of focal-attentive processing which makes information generally
available throughout the processing system.
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Further evidence of the inability to report words outside the focus of attention was provided by Moray
(1959), who presented English words up to 35 times in the nonselected ear while words were shadowed in
the other ear and found that subjects were unable to recall the nonselected words even though they knew
they would be asked to recall them at the end of the shadowing task.
Some additional findings, however, indicated a more extensive analysis of nonselected input than that
revealed by subjects' reports. Although they could report little about the nonselected messages, if those
messages were preceded by the subjects' own names, they switched attention to them on 51% of the trials
(Moray, 1959). Similarly, Treisman (1960) found that if the message in a shadowing task was suddenly
switched from the shadowed ear to the nonselected ear, subjects made a corresponding (albeit temporary)
switch in what they shadowed on 6% of the trials.
Thus, a pertinent stimulus, outside the focus of attention, can attract attention. But if preconscious analysis
is restricted to the physical properties of a stimulus, how can this be? As Norman (1969) pointed out, if we
could not determine the significance of stimuli outside the focus of attention it would be difficult to know
when we needed to switch attention to them. In any case, the fact that a subject cannot report a message
he has been specifically instructed to ignore (during shadowing) does not guarantee that he has not analyzed
it.
1.2 Preconscious semantic analysis outside the focus of attention.
Later studies accordingly examined the analysis of stimuli outside the focus of attention by the subtler
technique of assessing their influence on the attended message. Lewis (1970) found that the speed at which
attended-to words were shadowed was influenced by the presence of semantically related words in the
nonselected ear, but not by the presence of unrelated words. Corteen and Wood (1972) found that words
previously associated with electric shocks continued to produce changes in galvanic skin response even when
presented to the nonselected ear in a shadowing task, and that this occurred also with words which were
semantically related to the conditioned word. Similar findings have been obtained by Corteen and Dunn,
1974; Forster & Govier, 1978; Von Wright, Anderson & Stenman, 1975; but not by Wardlaw & Kroll, 1976.
Mackay (1973), furthermore, found that disambiguating words presented to the nonselected ear tended to
bias the meanings of ambiguous, shadowed sentences in the attended ear.
Such studies have often been cited as evidence that under some circumstances the preconscious processing
of stimuli outside the focus of attention includes the analysis of meaning. Indirect effects of the kind
mentioned above, however, appear to be sensitive to small perturbations in experimental design.
Consequently, in recent years the interpretation of these studies has become controversial (see Holender,
1986).
The Lewis (1970) study, for example, was repeated by Treisman, Squire & Green (1974), using a list of 10
dichotically presented word pairs. They replicated Lewis's findings for related pairs when these occurred
early in the list (position 3) but not when they occurred later in the list (position 7). This may indicate that
when subjects are accustomed to the shadowing task they no longer analyze the nonselected message, in
which case Lewis's findings may have resulted from subjects, unaccustomed to shadowing, switching their
focal attention to the nonselected ear. Alternatively, it may be that once subjects are accustomed to the
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shadowing task, their speed of responding to shadowed words is no longer influenced by the results of
analyses that continue to take place on the nonselected ear.
The various replications of Corteen & Wood's (1972) study indicate that their results are reliable. However,
the findings are subject to more than one interpretation. Dawson & Schell (1982), in a similar study, found
that if subjects were told beforehand that they would be required to name the conditioned word in the
nonselected ear, they could sometimes (but not always) do so. According to Holender (1986), this suggests
that subjects had been momentarily aware of the nonselected, conditioned words in the earlier studies—a
possibility admitted by Corteen (1986). Dawson & Schell's procedure, however, required subjects to divide
their attention. It is therefore not strictly comparable to earlier studies where subjects were simply asked to
shadow the message in the attended ear. Nevertheless, their finding highlights the difficulty of assessing the
awareness of nonselected words in dichotic listening studies.
Mackay's (1973) finding that single, concurrent words in the nonselected ear disambiguated sentences in the
selected ear was replicated by Newstead & Dennis (1979). However, if the critical words were embedded in
sentences, the disambiguating effect did not occur. Again, according to Holender (1986), this implies that
isolated words in the nonselected ear momentarily attract attention, leading to focal-attentive switching and
conscious identification—an effect which does not occur if the words form part of a relatively continuous
stimulus presented to the nonselected ear. Holender accordingly argues that such findings do not
demonstrate semantic analysis without conscious identification.
It seems unlikely, however, that focal-attentive switching can account for the findings of Groeger (1984a,
1984b). Groeger examined the effects of threshold words (presented to nonselected channels) on attended
messages and found these to differ from the effects of the same words (similarly presented) at subthreshold
levels. In one study, subjects were asked to complete sentences in the attended ear such as "She looked ---in her new coat," with one of two completion words, e.g. "smug" or "cosy." Simultaneous with the attended
sentence, the word "snug" was presented to the nonselected ear either at threshold or at various
subthreshold levels. With "snug" presented at threshold level, subjects tended to choose "smug" as the
completion word, indicating that they had some awareness of the physical structure of the cue. Below
threshold, however, subjects tended to choose "cosy" as the completion word, which indicates semantic
analysis (of the cue) without awareness.
One cannot assume from the findings above that semantic analysis of nonselected messages always takes
place in dichotic listening studies, or that when it does, it makes no demand on limited processing resources
(see section 2.4). Moreover, in dichotic listening studies it is often difficult to be certain that subjects have
no awareness of stimuli presented to the nonselected ear. Nevertheless, such studies have produced diverse
evidence of semantic analysis of nonselected words, under conditions where subjects claim to have no
awareness of those words and are unable to report them afterwards. This suggests that under some
circumstances a preliminary analysis for meaning can take place outside the focus of attention, without
reportable consciousness.
But, if this is so, what are the limits of preconscious, nonfocal-attentive analysis? Even if one assumes that
under some circumstances input stimuli not at the focus of attention receive an initial, preconscious analysis
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for meaning, there must be some limits on the processing of such stimuli, for there are limits on the tasks
one can perform with them. In any case, only some of these stimuli actually enter consciousness.
1.3 A "two-process" theory of preconscious vs. conscious input analysis.
In the "late-selection" model of attention proposed by Posner and Boies (1971), simultaneous processing of
input stimuli in different channels proceeds in a parallel, automatic, preconscious fashion, without mutual
interference, up to the point where each stimulus is identified. This matches each stimulus to its long-term
memory trace, which includes information relating to meaning (see also Norman, 1969; Posner, 1978;
Shiffrin & Schneider, 1977). Processing above and beyond this (e.g. rehearsing an item, or choosing an
appropriate output response to it) requires a limited capacity central processor, and only information that
makes use of this processor enters consciousness. Indeed, Posner & Warren (1972) suggest that the use of
the limited capacity central processor "becomes the central definition of a conscious process and its non-use
is what is meant by a process being automatic."
By virtue of its limited capacity, information in this processor can only be processed in serial fashion and is
susceptible to interference from other, competing tasks. Posner & Warren accordingly argue that
susceptibility to interference provides one way of ascertaining which processes are conscious by
experimental means (see Posner & Klein, 1973).
Posner and Snyder (1975) developed this "two-process" view in somewhat greater detail. Drawing on a
theory proposed by Collins and Quillian (1969), they suggested that preconscious, pre-attentive processing
produces a fast, automatic, "spreading activation" in the central nervous system (a parallel process). This
activates not only memory traces of a given stimulus word but also related traces that share some of its
features. However, this process has no effect on unrelated traces.
Limited capacity central processing, by contrast, only occurs after such spreading activation; it is relatively
slow and serial in nature, and cannot operate without intention and awareness. Awareness that a given
stimulus has been presented creates expectations about which stimuli are likely to follow and which stimuli
are unlikely or unexpected.
In short, the processing of a given stimulus may affect the processing of subsequent stimuli. Meyer,
Schvaneveldt & Ruddy (1975), for example, found that processing a given word may "prime" (facilitate) the
recognition of a subsequent, semantically related target word. In a task where subjects had to decide
whether a given string of letters was a word or a non-word, subjects responded to a word more quickly if the
immediately preceding string was a semantically related word than if it was a nonrelated word. For example,
reaction time to "nurse" is faster if it is preceded by the word "doctor" than if it is preceded by the word
"bread."
According to the "two-process" view, the effects of such "lexical priming" are complex. If the target follows
the prime within 250 msec. or less, conscious processing has insufficient time to operate. Spreading
activation should facilitate the recognition of target words semantically related to the prime, producing
faster recognition times, while recognition times for words unrelated to the prime remain unaffected. If the
interval between target and prime increases beyond 250 msec. conscious processing also operates and
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expectations about future target words have time to develop. These should speed the recognition of
expected target words but slow the recognition of unexpected words. The effects of "lexical priming,"
therefore, depend on (a) the interval between the prime and target word (b) the semantic relatedness
between the prime and target word and (c) whether the subject, having perceived the prime, expects the
target word.
These rather complex effects were investigated by Neeley (1977) using a "lexical priming" task similar to that
devised by Meyer, Schvaneveldt & Ruddy (1975). As expected, priming words decreased the reaction time to
related target words (e.g. bird → robin) at short interstimulus intervals (250 msec.) but had no effect on the
reaction time to unrelated target words (e.g. bird → arm). Nor, at short interstimulus intervals, did subjects'
expectations about likely target words have any effect. However, as the interval between the prime and
target words increased from 250 msec. to 750 msec, reaction time to expected target words decreased
progressively, whereas reaction time to unexpected target words progressively increased.
Neeley then introduced an experimental condition which appeared to clearly dissociate the effects of
preconscious spreading activation from those of conscious expectation. In this condition, subjects were told
to expect words that were semantically unrelated to the prime. Given the prime "body," for example, they
were told to expect a target word relating to a "building" (such as "door"). At short interstimulus intervals
(250 msec.) conscious expectations did not have time to operate, and as one would predict if spreading
activation were operating in isolation, the prime "body" had no effect on the reaction time to these
semantically unrelated target words. At longer interstimulus intervals, however, conscious expectations did
appear to have an influence. As the interstimulus interval increased, the reaction time to the expected (but
semantically unrelated) target words progressively decreased.
A similar dissociation was produced by giving subjects a target word that was semantically related to the
prime under these conditions. For example, the prime "body," might be followed by the target word "heart"
(which is semantically related to the prime) although subjects were expecting a target word relating to
"building." In this situation, spreading activation from the prime "body" appeared to facilitate the
recognition of the semantically related word "heart," speeding the reaction time to the target by around 40
msec. (at 250 msec. interstimulus intervals). At longer interstimulus intervals, however, the expectation of a
target word relating to "building" appeared to progressively inhibit recognition of the word "heart" (i.e. to
oppose the effects of spreading activation); so at 750 msec. intervals, reaction time to the unexpected target
word was around 40 msec. slower than normal.
Neeley concluded that his findings provide strong support for Posner and Snyder's "two-process" theory; an
initial preconscious identification process accesses not only the memory traces of the input stimulus but also
those of semantically related stimuli; this is followed by a conscious identification process that not only
facilitates the recognition of expected stimuli but also inhibits the recognition of unexpected stimuli (but see
Underwood, 1977).
1.4 Current ways of distinguishing preconscious from conscious input analysis.
In recent years, theories of how attentional resources are devoted to input analysis have continued to
develop. La Berge (1981) and Kahneman & Treisman (1984), for example, review evidence that the
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processing of visual stimuli which are not at the focus of attention may, to varying degrees, demand
attentional resources (see section 2.4)—a finding similar to that obtained with acoustic stimuli in dichotic
listening studies, but inconsistent with "late selection" theories.4
There is also reason to believe that different forms of attention may have to be devoted to different stages
of input analysis. La Berge (1981), for example, suggests that attention has to be devoted to physical
features in the process of searching for a target input stimulus, and both La Berge (1981) and Kahneman &
Treisman (1984) propose that attentional resources may be needed to integrate the set of features at the
location found by the search. Kahneman & Treisman (1984) go on to suggest that some attentional limits
may turn out to be failures in the dissemination of the results of input analysis to other information
processing modules rather than failures in input processing itself. Kahneman & Treisman (1984) note,
however, that the question of how attentional resources are allocated is in principle distinguishable from the
question of what is or is not conscious.5 For present purposes, the latter distinction is the crucial one.
As should be apparent from the foregoing review, there is considerable disagreement about how the
distinction between preconscious and conscious analysis should be framed. It seems clear, however, that
consciousness of an input occurs relatively late in the information processing sequence. It also appears that
words in both nonselected and attended channels can be analyzed for meaning in the absence of any ability
to report them; this indicates that semantic analysis is possible without consciousness.6
According to current theory, "preconscious" analysis nevertheless differs from "conscious" analysis. For
example, if Posner & Snyder (1975) and Neeley (1977) are right, "preconscious" analysis activates memory
traces of input stimuli and traces of semantically related stimuli, but has no effect on traces of unrelated
stimuli. By contrast, "conscious" analysis both facilitates the activation of semantically related stimuli and
inhibits the activation of unrelated stimuli. The above findings also appear to be consistent with the view
that "preconscious" analysis is fast and automatic in the sense of being involuntary and inflexible (but not
automatic in the sense of being free of processing capacity restraints)—whereas "conscious" analysis is
relatively slow, flexible and voluntary.
Preconscious analysis is accordingly thought to be both
rudimentary and limited (Posner and Snyder, 1975; Bjork, 1975; Underwood, 1979). Bjork, for example,
asserts that without the involvement of the conscious central processor, "nothing happens in the system
beyond the formation of input traces." If this were true, conscious analysis would play a crucial role in the
adaptive activities of the brain for it would be required for the processing of any novel stimulus (i.e., any
stimulus that did not already have a long-term memory trace) and for the processing of novel stimulus
arrangements. For example, preconscious analysis might suffice to identify the meanings of well-known
4
Posner & Snyder (1975) for example, claim that all inputs receive an initial, automatic, parallel analysis for
meaning that is essentially free of processing capacity limitations.
5
One method of operationalizing this distinction is suggested by Nissen & Bullemer (1987), discussed in
section 4.4.
6
This assumes that subjective reports provide a valid basis for assessing whether or not an item enters
consciousness, an issue to which we return in section 2.2.
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individual words, but conscious analysis would be required to identify the complex meanings of novel
phrases and sentences. This is not supported by the evidence, however.
2. Does consciousness enter into input analysis?
2.1 Preconscious analysis of complex messages outside the focus of attention.
Evidence that phrases and sentences can be analyzed outside the focus of attention has been found by
Treisman (1964a). In one experiment, she asked subjects who were bilingual in English and French to
shadow passages of English prose presented to one ear in a female voice. Simultaneously, a different prose
passage in English, French, German, Czech, reversed English, and a French translation of the shadowed
message, were presented to the other ear in a male voice. Treisman found that subjects always noticed the
male voice (replicating Cherry, 1953). In addition, however, just under half the subjects recognised the
French translation. Treisman concluded that the physical characteristics of the voice in the nonselected ear
were always analyzed, but the meaning of the prose passage in the nonselected ear was not always fully
analyzed.
On the other hand, many subjects did recognise the meaning of the French translation, indicating that
preconscious analysis of connected prose is possible outside the focus of attention. Indeed, in another
experiment Treisman (1964b) found that the better the subject knew the language in the nonselected ear,
the more difficult it was to reject. Whereas monolingual subjects could easily shadow the English prose
passage, bilinguals found the task more difficult, often giving a response in mixed English and French.
As Holender (1986) notes, shadowing tasks are very attention demanding, so it is unlikely that subjects in this
task voluntarily switched their attention to a (continuous) message in the nonselected ear, which they had
been instructed to ignore. It would seem, therefore, that complex messages can be analyzed outside the
focus of attention (preconsciously) although there are individual differences in the extent to which this is
normally done, depending on how skilled subjects are at identifying the nonselected input.
Further evidence of preconscious analysis of complex, nonselected messages was found by Lackner and
Garrett (1973), who presented ambiguous sentences to one "attended" ear, while disambiguating sentences
were presented, simultaneously, to the subject's other ear. For example, if "Visiting relatives can be a bore,"
was the attended sentence, it might be paired with "I hate relatives who visit often," in the nonselected ear.
Subjects were asked to paraphrase each attended-to sentence immediately (if possible, before it ended).
The sentences in the nonselected ear were presented at intensity levels 5 to 10 dB below those of the
attended sentences and subjects could produce no systematic information about them. Nevertheless, the
meanings of nonselected sentences biased subjects' paraphrases of sentences in the attended ear. In the
situation above, for example, the attended sentence tended to be paraphrased as, "Relatives who visit can
be boring," rather than, "It can be boring to visit relatives."
According to Lackner and Garrett, at least a phrasal analysis of nonselected sentences would have been
required (in most of the material they used) to disambiguate the meaning of the attended sentences; for
example, in the non attended sentence above, at least "relatives who visit" would have had to be analyzed.
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Holender (1986) goes further, pointing out that disambiguation occurred even if the disambiguating portion
of the nonselected sentence followed the ambiguous portion of the relevant sentence. This implies that a
complete syntactic and semantic analysis of the nonselected sentence took place. Moreover, the product of
this analysis had to be integrated with the analysis of the attended sentence in order to yield a particular
interpretation of it—a task demanding considerable processing resources.
One can go further still. Although human speech perception is not yet fully understood, the processes
involved are thought to be both "productive" (indefinitely novel) and complex–so complex, in fact, that they
surpass the capabilities of the most sophisticated present-day machines. According to current theory,
speech perception involves various levels of analysis (phonemic, syntactic and semantic) interacting in a
dynamic, flexible, interactive fashion, incorporating both "data-driven" and "cognitively-driven" processing
(see section 2.3). If this is so, the analysis of nonselected spoken phrases and sentences is unlikely to be
restricted to inflexible, "data-driven" processing.7
The findings of Treisman (1964a; 1964b) and Lackner & Garrett (1973) demonstrate that the analysis of
messages outside the focus of attention can extend to spoken phrases and sentences, involving syntactic and
semantic analysis of potentially novel word combinations. If so, preconscious, nonfocal-attentive analysis
cannot be restricted to a relatively inflexible, data-driven analysis of simple, well-learnt stimuli. It is therefore
misleading to think of the processing of stimuli in the non-selected ear as non-attended or even as preattentive in dichotic listening tasks of the kind described above. Even when subjects are instructed to
shadow or paraphrase a message in one ear and ignore the message in the other ear, the non-selected
message may be subject to sophisticated analysis. In this sense, the rejected message is receiving attentional
resources (allocated to input analysis), although it may not enter consciousness, alter long-term memory or
be available as a response. In short, rather than speaking of "pre-attentive" processing (versus "focalattentive" processing) in such divided attention tasks, it seems more accurate to speak of "preliminary
attention" (versus "focal attention")—a suggestion consistent with the "filter" model of selective attention
advocated by Treisman and her associates (reviewed in Kahneman & Treisman, 1984).
7
It should be noted that this interpretation of the findings is quite different from that given by Holender
(1986). According to Holender, the disambiguation which occurred in Lackner & Garrett's study was so
complex that it would have been impossible without "focal-attentive switching" to the nonselected ear, in
which case the analysis of nonselected sentences must have been conscious. This question cannot be settled
by fiat, however. If subjects had consciously analyzed the meanings of the sentences in the nonselected ear
and had consciously integrated their meanings with those of the relevant, ambiguous sentences, it is difficult
to understand why they could give no systematic information about nonselected sentences when asked.
Such ignorance would not obtain, after all, for a context sentence presented at similar intensity, but to the
attended ear, prior to the target, ambiguous sentence. Holender concedes, furthermore, that focal-attentive
switching in Treisman's studies was unlikely. Her findings therefore also suggest that complex messages can
be analyzed outside the focus of attention. If such messages are pertinent, they may subsequently attract
focal attention and intrude into consciousness, which is why bilingual subjects (in Treisman, 1964b) often
found it difficult to prevent giving a shadowing response in mixed English and French.
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Once relabeled, the "preliminary attention"/"focal attention" distinction remains a useful one. Stimuli that
are preconsciously analyzed, identified and then ignored, for example, appear to be treated differently from
stimuli that are selected for focal-attentive processing and subsequently enter consciousness. It remains
possible, furthermore, that once stimuli are at the focus of attention they are analyzed in a different,
"conscious" way.
2.2 Preconscious semantic analysis in the attended channel.
In psychological tasks, the "attended" channel is operationally defined by combining instructions to subjects
to attend in a given way with appropriate forms of stimulus presentation. For example, the subject might be
asked to focus on material in one ear rather than the other, or to fixate a particular point on a screen, and
then the stimulus is presented to the point of focus. In the current literature, the analysis of stimuli in
nonselected channels is thought to be "preconscious" and the analysis of stimuli in the attended channel is
thought to be "conscious."
It has to be borne in mind, however, that most models of selective attention assume that input stimuli
receive some initial, preconscious analysis (preliminary attention) whether or not they are in the attended
channel. This applies to both early-selection models (e.g. Broadbent, 1958) and late-selection models (e.g.
the "two-process" model of Posner & Snyder, 1975, discussed above). Stimuli in the attended channel differ
in that they are normally selected for further "focal-attentive processing" and it is only when this happens
that they enter consciousness. In principle, therefore, it might be possible for input in an attended channel
to be preconsciously analyzed without being subject to "conscious" focal-attentive analysis—for example, if
the input is "masked" before it can be fully analyzed, as in the studies of "masked priming" discussed below.
In the "priming" studies of Schvaneveldt, et al. (1975) and Neeley (1977), both the prime and the target are
presented suprathreshold and both are potentially available to consciousness. But in "masked priming"
studies the prime is followed by a masking stimulus, and at certain prime-mask intervals this prevents the
prime from entering consciousness (according to subjective reports). It may nevertheless continue to
influence the subject's response to the following target, providing evidence for at least some analysis (of the
prime) in the absence of reportable consciousness.
As with the dichotic listening studies discussed above, the effects of masked priming appear to be extremely
sensitive to small perturbations in experimental design, producing extensive discussion in the literature of
methodological issues, and controversy over the reliability and interpretation of experimental results.8 For
example, Holender (1986) reviews evidence that when masked priming effects occur, subjects remain able to
make judgements about the prime (via some form of discriminative response) despite their claim not to have
seen it—evidence, he argues, that introspective reports of whether or not the prime enters consciousness
are unreliable (see also Lupker, 1986).
8
See Holender (1986) & BBS open peer commentary, and Dagenbach, Carr & Wilhelmsen (1989), for a
summary.
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12
Cheesman & Merikle (1986) agree that the prime-mask interval at which subjects claim they cannot see the
prime (the "subjective" threshold) must be distinguished from the shorter interval at which subjects cannot
make a better than chance judgement about the prime (the "objective" threshold). Contrary to Holender's
interpretation, however, they point out that it is the "subjective" threshold rather than the ability to make a
discriminative response that relates directly to what is consciously experienced. They also suggest that if a
prime presented above the subjective threshold has a qualitatively different effect from one presented
below that threshold, this would provide strong support for the claim that the subjective threshold defines
the transition between two different perceptual states (i.e. between perceptual processing which is
accompanied by consciousness and processing which is not; see also discussion of Groeger, 1984b, above).
Such effects have been demonstrated by Cheesman & Merikle (1984, 1986), Dagenbach, et al.(1989), Forster
& Davis (1984), and Marcel (1980, 1983 experiment 5). Marcel (1980), for example, used polysemous primes
(with multiple meanings) embedded within three word sequences, each beginning with a context word
followed by the polysemous prime, and ending with a target (for example, "save - bank - money," or "save bank - river"). In one condition, the primes were presented unmasked, at an exposure duration of 500 msec.
In this suprathreshold condition, selective priming of the target occurred; for example, in the above three
word sequences, the cued meaning of the prime "bank" facilitated the response to the target "money," but
not "river." In the other condition, the primes were presented for 10 msec. and followed by a pattern mask
at an interval set to produce chance detection of the prime. With masked primes, unselective priming
occurred; for example, in the above sequences, the word "bank" primed both "money" and "river."
These findings indicate that semantic analysis of familiar stimuli in the attended channel can take place
without reportable consciousness. Hence, consciousness cannot be necessary for such analysis. At the same
time, processing which is accompanied by awareness (of the stimulus) appears to differ from processing
which is not accompanied by awareness. Marcel's findings, for example, appear to support Posner &
Snyder's "two-process" theory. They suggest that when a polysemous word in the attended channel is first
analyzed, simultaneous activation of its multiple meanings takes place preconsciously. Once focal-attentive
processing operates, one meaning is selected and the subsequent entry of the word into consciousness is
accompanied by inhibition (or deactivation) of inappropriate meanings. Similar effects have also been
observed with polysemous words in connected speech (Pynte, Do & Scampa, 1984; Swinney, 1979, 1982).
Masked priming studies, however, do not enable one to dissociate entry into consciousness from the effects
of focal-attentive processing. Masking that prevents entry into consciousness is also likely to disrupt focalattentive processing. The different effects of primes above and below the "subjective" threshold may
therefore be due not to entry into consciousness as such, but to the operation (or nonoperation) of focalattentive processing.9
9
Entry of the stimulus into consciousness (being aware of the stimulus) might accompany, or be a product
of focal-attentive processing without exerting a causal influence on focal-attentive processing. Hence, I do
not take it for granted that the effects of focal-attentive processing and entry into consciousness are one and
the same (see section 7).
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13
Such studies do demonstrate that the identification of well-known stimulus words in the attended channel is
initially preconscious. Moreover, there is evidence from studies of speech perception that even if awareness
does accompany input analysis (of connected speech in the attended channel), that awareness follows input
analysis and consequently cannot enter into it.
2.3 Preconscious analysis of complex messages in the attended channel.
Marslen-Wilson (1984) reviews evidence that the analysis of words in attended-to connected speech is both
"data-driven" and "cognitively driven," combining knowledge of the stimulus with knowledge of its context.
For example, in Grosjean's (1980) word recognition task, successively larger fragments of a word were
presented. If the words were presented in isolation, subjects required fragments of 333 msec. (on average)
to identify them (total word length was in excess of 400 msec.). But if the words were presented in normal
verbal contexts, a fragment of 199 msec. (on average) was sufficient to identify them. In a related
experiment, Marslen-Wilson and Tyler (1980) found that the average reaction time to detect target words (in
context) was 273 msec, although their mean length was 370 msec. Allowing around 75 msec. execution time
(the time to press a button) this again suggests a word identification time of around 200 msec.
Now, a word fragment of 200 msec. is large enough to contain just the first two phonemes and, according to
Marslen-Wilson (1984), these convey useful information. Assuming a dictionary of 20,000 American-English
words, knowledge of the first phoneme reduces the set of possible words to a median of 1,033, knowledge
of the first two phonemes reduces the set size to a median of 87, and so on (Kucera and Francis, 1967). In
this way, sensory analysis (a largely "data-driven" process) contributes to word identification. After two
phonemes, however, a large number of possible words remain (a median of 87). Hence subjects who can
identify the word on the basis of the first two phonemes must use their knowledge of the context to decide
which of the remaining words is the correct one (a "cognitively driven" process).
On the basis of this and other evidence Marslen-Wilson (1984) concludes that to cope with a complex
acoustic waveform developing over time the speech processing system moves the analysis of the sensory
signal as rapidly as possible to a domain where all possible sources of information (semantic as well as
phonemic) can be brought to bear on its further analysis and interpretation—a process of "on-line interactive
analysis" of considerable sophistication and flexibility.
The stimuli to be identified in these experiments are in the attended channel. Yet if words (in context) are
identified within 200 msec., this confluence of data-driven and cognitively driven processing cannot be
conscious, for according to the evidence reviewed earlier (Libet, et al., 1979; Posner and Snyder, 1975;
Neeley, 1977), consciousness of a given stimulus does not arise until at least 200 msec. after the stimulus
arrives at the cortical projection areas, i.e. after the identification of a word (in context) has been achieved!
In these experiments spoken words in the attended channel are therefore analyzed in preconscious fashion.
Indeed, it is by no means clear that the analysis of words in the attended channel is different from the
analysis of words in nonselected channels. In either case, pattern-recognition may be flexible and dynamic,
combining data-driven and cognitively driven processing; and there seems to be little doubt that pattern
recognition is preconscious in both cases.
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Rather than consciousness entering into input analysis of well-known stimuli, consciousness of those stimuli
appears to follow sophisticated, preconscious analysis and identification. If this is the case, "conscious" focalattentive processing cannot be necessary for the analysis and identification of such stimuli even when they
occur in novel, complex combinations. This may seem counterintuitive. It is, however, easy to illustrate.
Consider how one silently reads the following sentence: The forest ranger did not permit us to enter the
reserve without a permit.
Note that on its first occurrence, the word "permit" was (silently) pronounced with the stress on the second
syllable (permit) while on its second occurrence the stress was on the first syllable (permit). But how did you
know?
Clearly, the syntactic and semantic analysis required to determine the appropriate meaning of the word
"permit" must have taken place prior to the allocation of the stress pattern, and this, in turn, must have
taken place prior to the phonemic image entering awareness.
Note too, that while reading, one is not conscious of any pattern recognition processing to identify individual
words or of any syntactic or semantic analysis being applied to the sentence. Nor is one aware of the
processing responsible for the resulting covert speech (with the appropriate stress patterns on the word
"permit"). In this case, not just an individual word, but an entire attended-to sentence appears to be
processed in preconscious fashion.
2.4 Input analysis is largely involuntary.
Note finally that the analysis of well-known stimuli proceeds in a largely involuntary fashion, whether or not
the stimuli are in the attended channel. Even if one "consciously attends" to a given stimulus, it may be
difficult to prevent certain analyses from being carried out; in this sense, the analysis is automatic.
This point was demonstrated by Stroop (1935), who observed that subjects instructed to name the colour in
which a word is printed found the task far more difficult if the word was itself a colour name, but of a
different colour. For example, subjects presented with the word "red" printed in orange cannot restrict their
analysis to the colour of the print (orange) because they cannot prevent themselves from reading the word
("red"). Eventually, a subject may adopt some artificial strategy to avoid reading the word, for example,
squinting to avoid seeing the letters. Even with extended practice, however, the task remains difficult (in
comparison say, to naming colour patches, or simply reading a colour word—see Jensen, 1965).
On the basis of this and other evidence, Kahneman (1973) concludes that "subjects cannot prevent the
perceptual analysis of irrelevant attributes of an attended object." Even if a stimulus is consciously attended
to, what is analyzed may not be under conscious voluntary control. However, an "involuntary" process is not
necessarily "inflexible" (see above).10 Nor need it be "effortless" (Regan, 1981). Recent studies of the Stroop
10
See also Carr, Davidson & Hawkins, 1978; Brown, Carr & Chaderjian, 1987, for evidence that visual analysis of verbal input stimuli
may be, to some extent, under strategic control.
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effect indicate that while input analysis may be automatic in the sense of "involuntary," it nevertheless draws
on limited processing resources (Kahneman & Treisman, 1984).
In one study, for example, Kahneman & Chajcyk (1983) found that subjects took longer to name the colour of
a centrally fixated colour bar if a conflicting colour word was presented either above or below it. This
"Stroop" effect was not as great as when subjects were asked to name the ink in which a conflicting colour
word was printed, indicating that the effect depends, in part, on whether or not the conflicting information is
spatially integrated with the fixated stimulus (see also Dyer, 1973; Gatti & Egeth, 1978). Kahneman
&
Chajcyk found the Stroop effect was further diluted by a neutral word, presented simultaneously with the
conflicting colour word, to the opposite side of the bar. They accordingly conclude that the two irrelevant
words were competing for limited processing resources.
Nevertheless, unless subjects have advance information about the precise location of the irrelevant
information, they cannot avoid processing it (Kahneman & Treisman, 1984). Processing remains automatic in
the sense of being outside conscious voluntary control - again calling into question the role of consciousness
in input analysis.
2.5 Automatic, flexible, preconscious analysis of familiar input stimuli.
The evidence reviewed in sections 2.1 to 2.4 suggests that current ways of distinguishing "preconscious"
from "conscious" analysis require re-examination. Conventionally, "preconscious," "pre-attentive" analysis
is thought to be automatic (in the sense of being involuntary), and restricted to simple, familiar stimuli whose
long-term memory traces are accessed in data-driven (albeit resource-limited) fashion. By contrast,
"conscious," "focal-attentive" analysis is voluntary and flexible (involving cognitively-driven as well as datadriven processing).
If preconscious analysis (in nonselected channels) can deal with the syntactic and semantic analysis required
to identify the meanings of phrases and sentences involving potentially novel word combinations, then it
cannot be restricted to simple, familiar stimuli. The on-line analysis of speech is one of the most
sophisticated of human pattern recognition tasks, involving both cognitively driven and data driven
processing. Hence, while preconscious analysis might be automatic (in the sense of being involuntary) it
cannot be inflexible.
Input analysis of phrases and sentences in the attended channel appears to be similarly automatic
(involuntary) and flexible. It is also largely preconscious, casting doubt on the assumption that input in the
attended channel is subject to "conscious," "focal attentive" analysis. Consciousness of familiar stimuli,
rather than entering into input analysis, appears to follow it, in human information processing.
3. Preconscious selection and choice.
However, input analysis and identification are merely the first stages of human information processing.
While many inputs may be simultaneously analyzed and identified preconsciously, only some receive our full
focal attention. Those that do need to be selected from competing stimuli according to their interest or
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16
importance. Perhaps, as Mandler (1975, 1985) and Miller (1987) suggest, consciousness makes it possible to
select and choose.
Consider how such selections are made. Prior to being selected for focal-attentive processing, input stimuli
do not enter consciousness. The information on which such choices are based must therefore be
represented in the CNS in preconscious fashion. What is important to attend to at any given moment also
requires continuous updating, for in a constantly changing world, that which is of primary importance may
itself be in continuous flux and change.
But are assessments of relative importance conscious? If so, it is odd that we are not normally aware of
making them. Rather, the detailed operation of such selection procedures, still under investigation within
cognitive psychology, can only be inferred.11
Carr & Bacharach (1976), for example, review evidence for the existence of preconscious input selection in
the form of perceptual tuning of input analyzers by prior conceptual or structural stimulus information.
Some of this tuning is long-term and is manifest, for example, in the characteristic tendency to analyze visual
scenes in terms of conceptually meaningful relations among stimulus components. This process may be
likened to a "parsing" of the scenes in accordance with a form of "visual grammar" (Biederman, 1972;
Biederman, Glass & Stacey, 1973; Biederman, Rabinowitz, Glass & Stacey, 1974). Other tuning is temporary.
Preconscious, semantic priming effects (discussed in sections 1.3 and 2.2) may be regarded as cases of this
kind.
Hence, it is reasonable to assume that some selective processes are preconscious. This does not, of course,
rule out the possibility of a subsequent "conscious voluntary choice" amongst stimuli which have been
preconsciously selected for focal-attentive processing and which now require some response. Carr &
Bacharach (1976) argue, for example, that input selection must be distinguished from task selection.
Whereas input selection is preconscious, task selection is under conscious, voluntary control.
Yet, even a "conscious voluntary choice" may have preconscious neural antecedents. It has been known for
some time that voluntary acts are preceded by a slow negative shift in electrical potential (recorded at the
scalp) known as the "readiness potential," and that this shift can precede the act by up to one second or
more (Deecke, Grozinger & Kornhuber, 1976; Gilden, Vaughan & Costa, 1966; Kornhuber & Deecke, 1965).
In itself, this says nothing about the relation of the readiness potential to the experienced wish to perform an
act. To address this, Libet (1985) developed a procedure which enabled subjects to note the instant they
experienced a wish to perform a specified act (a simple flexion of the wrist or fingers) by relating the onset of
the experienced wish to the spatial position of a revolving spot on a clock face, thereby giving it a "clock
time." Recorded in this way, the experienced wish (to flex the wrist or fingers) was preceded by a
preconscious readiness potential by around 550 msec. (for spontaneous acts involving no preplanning).
11
See Carr & Bacharach, 1976; Dixon, 1981, p.259, for an initial review of some of the factors involved.
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This suggests that conscious volition may be one output from the (prior) cerebral processes that actually
select a given response. Hence, conscious volition may be no more necessary for such a (preconscious)
choice than the consciousness of a stimulus is necessary for the (prior) pattern recognition of that stimulus
(see Libet, 1985 and accompanying BBS open peer commentary, and Harnad, 1982, for a more detailed
discussion).
4. Consciousness, learning and memory.
4.1 Is consciousness necessary for learning?
The experiments above suggest that input analysis and selection can take place preconsciously. However,
subjects in these experiments were required to process known stimuli, using well-established skills. To some
extent, such "automaticity" needs to be acquired. Hence, consciousness may be essential when novel stimuli
or skills are being learnt.
According to La Berge (1981), learning to identify simple patterns may involve different attentional
processes. To identify a new pattern as a coherent unit may require one to combine outputs from various
feature detectors to form an integrated, higher-order perceptual code. Attaching a name to a pattern or
investing it with meaning may require one to form associations between relatively distinct representational
systems (for example, associations between visual codes and phonemic or semantic codes). Such learning
usually requires focal attention, and focal-attentive processing is usually accompanied by consciousness.
However, consciousness of the input stimulus, of the associations being formed, and so forth, result from
focal-attentive processing. The integration of feature analyzers into a higher order perceptual code, and the
formation of associations between different cerebral representational systems, are processes to which we
have no introspective access, which would normally be explained in entirely neurophysiological terms!
In his analysis of what the functions of consciousness might be, Baars (1989) agrees that its contribution to
learning is a mystery. As he notes,
"To learn anything new we merely pay attention to it. Learning occurs "magically" - we merely allow
ourselves to interact consciously with algebra, with language....etc., and somehow, without detailed
conscious intervention, we acquire the relevant knowledge and skill. But we know that learning cannot
be a simple, unitary process in its details ... all forms of learning involve specialised components of
knowledge and acquisition strategies."
Baars nevertheless concludes that consciousness (in some unspecified fashion) facilitates learning. All that
one can infer from the above, however, is that focal-attentive processing facilitates learning. While
consciousness accompanies such processing, the details of such processing are not under conscious control.
Similar arguments apply, furthermore, if one thinks of "learning" in terms of the updating of (or transfer of
information to) long-term memory.
4.2 Is consciousness necessary for encoding in long-term memory?
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On intuitive grounds, it is difficult to envisage how, without consciousness, one could update long-term
memory, for if one has never experienced an event, how could one remember it? How could an event which
is not part of one's psychological present become part of one's psychological past?
It is important to distinguish the contents of consciousness (which in the theories of James, 1890, and Waugh
and Norman, 1965, are identified with the contents of "primary memory") and contents of long-term
memory (or "secondary memory") from the processes which encode information, transfer it between
primary and secondary memory, search for and retrieve it, and so on. Such processes are no more conscious
(accessible to introspection) than are the other ones discussed above. Furthermore, preconscious contents
may influence the way the contents of consciousness are interpreted and, consequently, remembered. In
dichotic listening studies, for example, words and sentences in the nonselected ear may influence the
interpretation of sentences in the attended ear (Lackner and Garrett, 1973; MacKay, 1973). But how about
memory of the preconscious contents themselves? It is the accepted wisdom (backed by numerous
experiments) that unless preconscious contents are selected for focal-attentive processing and enter
consciousness, they are quickly lost from the system (within 30 seconds). Words and sentences presented to
the nonselected ear in dichotic listening studies, for example, cannot usually be remembered.
It appears, however, that preconscious processing can affect the memory trace of an input stimulus even if
that stimulus cannot later be explicitly recognised or recalled. Eich (1984), for example, required subjects to
shadow a passage presented to one ear while word pairs were presented to the other ear. The second
member of each pair was a homophone (a phoneme string corresponding to more than one word, e.g. FAIR,
FARE), and the first member of each pair cued its less common usage (e.g. taxi - FAIR). The shadowing task
reduced recognition of the homophones to chance levels in a subsequent recognition test. Nevertheless, in a
subsequent spelling test, subjects were more likely to produce the cued (less common) interpretation of the
homophones. Moreover, recent studies of hypnosis (discussed below) indicate that information may be able
to enter long-term memory and be recalled, without first entering consciousness.
4.3 The hidden observer.
In hypnotically induced anaesthesia subjects may report experiencing no pain, although they exhibit normal
physiological responses to painful stimuli, that is, painful stimuli are processed by the central nervous system
despite appearing to be neither experienced nor remembered. Under some circumstances, however, a
"hidden observer" within the subject may be fully cognizant of what is going on (see Hilgard, 1986 and
reviews in Kihlstrom, 1984; Oakley & Eames, 1985).
One way to elicit this phenomenon is to inform a subject, before hypnosis, that some part of him will
continue to monitor everything that happens during hypnosis even if he is not aware of it. During hypnosis
one can then ask to speak to this "hidden observer," in which case subjects frequently begin to speak and act
as if they were no longer hypnotised (although they are still under hypnosis).
According to Oakley & Eames (1985),
"Two reports may thus be taken from a hypnotised subject. In hypnotic analgesia, for instance, it is
possible for a subject to smile benignly and, despite physiological evidence to the contrary, to fail to
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experience pain in a hand which is plunged into icy water. The hidden observer, however, when called
upon, leaves the experimenter in no doubt as to the severity of the pain in the affected hand and will
give a pain rating, either verbally or in the form of 'automatic writing' with the nonimmersed hand,
which matches that given in the waking state under the same conditions ..... The absence of pain is
nonetheless real to the hypnotised subject. Transfer of a similar dissociation to the waking state is
possible in some types of chronic pain, and therapies which aim to relegate pain to the hidden
observer, by setting up selective mechanisms in consciousness which deny pain information entry into
self-awareness, are successful in a proportion of individuals.... Some hypnotic subjects are able to
achieve, upon suggestion, a level of anaesthesia and local analgesia sufficient to allow painful surgical
procedures to be carried out without apparent discomfort or distress, and often with reduced bleeding
and salivation. In these subjects physiological indices of pain may also be absent ....One hypnotised
subject, Mrs D., underwent an operation to remove a ganglion in her left wrist and a foreign body in
her right index finger. In a later interview, also under hypnosis, she was able to recall the people in the
operating theatre, the numbness in her arms and the fact that she had asked for, and been given, a
drink of water during the operation. During the surgical procedures, she had thought mainly of a
holiday, and had experienced the sun shining as she sailed in a pedal-craft. She had known that the
operation was taking place but had felt nothing of it. A suggestion designed to call the hidden observer,
however, produced a different story. The thermocautery was 'so hot...It was burning...it was agony...as
bad as the incision'." (p240)
The hidden observer phenomenon has been replicated on many occasions (see reviews cited above).
According to some investigators, however, the phenomenon arises from subjects' attempts to comply with
what is demanded of them under hypnosis instructions, rather than from any special hypnotised state
(Spanos, 1986, 1988; Wagstaff, 1981, 1987). Spanos & Hewitt (1980), for example, exposed highly
suggestible hypnotic subjects in one experimental group to the same procedures used by Hilgard & Hilgard
(1975) for eliciting hidden reports (suggesting that the hidden observer would remain aware of what was
going on) and replicated the finding that the hidden observer felt high levels of pain, although overtly, the
hypnotised subject experienced reduced pain. However, a second highly suggestible group was told that
their hidden part was hidden so deeply that it would be even less aware of what was being experienced than
their overt part—and these hidden observers, correspondingly, reported lower levels of pain than the overt
pain.
As Spanos (1986) notes, this in itself may merely indicate that different suggestions produce different
amounts of dissociation from the pain experience. Spanos, Gwynn & Stam (1983) however, found that if a
given subject received no prior indication of how much pain the hidden observer should feel, he could be
made to report greater, less, or the same hidden pain (relative to the overt pain) if he were sequentially
exposed to instructions that explicitly called for each of these patterns of responding—a clear demonstration
that hidden observer reports may be influenced by the demand characteristics of the experimental situation.
Nogrady, McConkey, Laurence & Perry (1983), however, found that the proportion of hypnotised subjects
who gave hidden observer reports was little influenced by whether or not there was pressure to produce
such reports from the hypnotist, varying from around 42 per cent with little pressure to around 50 per cent
with extreme pressure. By contrast, a group of subjects instructed to simulate hypnosis gave no hidden
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20
observer reports when under little pressure, but under extreme pressure the proportion giving such reports
rose to 75 per cent.
Accordingly, it remains possible that genuine dissociation effects also occur. It seems unlikely, for example,
that subjects undergoing surgery under hypnotic analgesia are simply lying about their lack of pain to please
the medical staff! And comments from some hypnotised subjects indicate that they believe some inner
dissociation to be taking place. Colman (1987) cites the case of a subject under hypnotic analgesia whose
whole body moved when exposed to a normally painful electric shock. When questioned about this, she
said, "I don't feel anything, but she seems uncomfortable"—even though no hidden observer instructions
were given in this experiment (in Sutcliffe, 1961). Similar reports occurred in a hidden observer experiment
by Knox, Morgan & Hilgard (1974). In the words of one subject, "The hidden observer is more aware and
reported honestly what was there. The hypnotised part of me just wasn't aware of the pain" (see Bowers,
1976; Colman, 1987; for further discussion of this point). Whether hypnotism should be thought of as a
special state, or some combination of social compliance (Spanos, 1986, 1988) with conventional coping
strategies such as selective inattention, relaxation, etc. (Wagstaff, 1987) remains controversial. However, if
subjects' hidden observer reports are to be believed, it is possible for painful stimuli to enter long-term
(episodic) memory without first entering consciousness—evidence that entry into consciousness is not
necessary for long-term memory updates.
4.4 Implicit learning and memory.
Much learning and memory has to do not with individual stimuli occurring in a single episode but with
recurring stimulus patterns.
On any given occasion, the stimuli themselves may be present to
consciousness, but the fact that they form a recurring pattern may not. Being exposed to successive
exemplars of recurring patterns, however, may produce learning of those patterns, whether or not there is
any intention to learn and, indeed, in the absence of any explicit knowledge of the pattern being learnt. The
evidence for this has been extensively reviewed by Schacter (1987) and Reber (1989), and we need not
recount it here. One series of experiments initiated by Nissen & Bullemer (1987), however, is particularly
relevant to our present concerns, in that they claim to have examined implicit learning (of a given stimulus
pattern) under conditions that operationally separated the contribution of conscious awareness (of that
pattern) from focal-attentive processing.
Nissen & Bullemer (1987) devised a serial reaction time task in which a light appeared at one of four
locations arranged horizontally on a video monitor. Below each light location was a key, and on each trial
subjects were required to press the key corresponding to the location of the light. Trials were presented in
blocks of 100, consisting either of 10 repetitions of a fixed 10 trial sequence or 10 presentations of 10
randomly ordered trials.
In their initial experiment with normal subjects, eight such blocks were presented and subjects were allowed
to devote their full attention to the task. Subjects given the fixed sequence had a steadily improved reaction
time. After only six presentations of the sequence their group performance was significantly better than that
of subjects given the randomly ordered trials and by the end of the eighth block there was a 50% reduction in
their reaction time. Those given the randomly ordered trials showed little improvement. The improved
reaction time, therefore, reflected the learning of the fixed sequence rather than any general characteristics
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of the experimental task. Subjects who learned the sequence also became aware of what they had learnt.
When asked, they said they had noticed the sequence and were able to describe it by pointing to the
successive locations in which the lights had appeared.
In their second experiment, Nissen & Bullemer used a divided attention task to examine the contribution of
focal-attentive processing to implicit learning of the sequence. As before, normal subjects had to press a
sequence of keys in response to a sequence of lights; the sequence for one group was fixed, whereas for the
other group it was randomly ordered. In addition either a high or a low tone occurred at the beginning of
each trial and subjects were asked to count the number of times a low tone occurred, reporting the total at
the end of each block. After four such blocks, knowledge of the sequence was assessed using a "generate"
task. This time, rather than responding to the appearance of a light, subjects had to press a button
corresponding to where they expected the next light to appear—and accuracy rather than reaction time was
the variable of interest.
Under these conditions, no significant difference in reaction time appeared between the fixed and random
sequence groups, even after four blocks. The groups also performed similarly in subsequent attempts to
generate the sequence—indicating that under divided attention conditions no learning of the fixed sequence
had occurred.
Taken together, these experiments demonstrate the necessity of focal-attentive processing for implicit
sequence learning in this particular serial reaction-time task. In themselves, however, the experiments do
not dissociate focal-attentive processing from consciousness. When subjects focused their attention on
successive presentations of the fixed sequence (in experiment 1) they also became more aware of the
sequence (and they were able to describe it by pointing).
According to Nissen & Bullemer, a further experiment comparing normal subjects with amnesic (Korsakoff's
syndrome) patients did dissociate focal-attentive processing from consciousness. In this experiment all
subjects were given the serial reaction-time task and were allowed to devote their full attention to the task.
On this occasion, all subjects were given four fixed sequence blocks, followed by four randomly ordered
blocks. Although amnesic patients responded more slowly than normals, both groups showed a steady
improvement in reaction time over blocks 1 to 4. Both groups also showed a sharp increase in reaction time
as they were transferred to a random sequence in block 5—clear evidence that the improved reaction time
over blocks 1 to 4 resulted, in part, from sequence learning and not solely from increased familiarity with the
task.
When questioned after block 8, all the normal subjects reported that they had noticed a repeating sequence
and five (out of eight) commented spontaneously after block 5 that the pattern was no longer present. By
contrast, none of the amnesic patients either reported noticing a repeating sequence or spontaneously
remarked on any change.
Nissen & Bullemer conclude that sequence learning in amnesics must have involved (focal) attentive
processing, because in divided attention tasks with normals, sequence learning does not take place. At the
same time, sequence learning in amnesics did not appear to be manifest in awareness, because amnesics
reported neither the presence of a fixed sequence nor its absence, when it changed.
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It should be noted that Nissen & Bullemer's conclusion is based on the assumption that amnesics reliably
report what they experience—a justifiable assumption with normal subjects that, with amnesics, cannot be
taken for granted. However, implicit sequence learning (with the same task) has also been found in healthy
young adults (Willingham, Bullemer & Nissen, 1989). Nor are the effects transitory. In a further study by
Nissen, Willingham & Hartman (1989), amnesic patients showed normal retention of the learned sequence
(without reported awareness) over an interval of one week. Sequence learning without reported awareness
has also been demonstrated in normal subjects injected with scopolamine, a drug that blocks the action of
acetylcholine (Nissen, Knopman & Schacter, 1987) and in normal subjects (with focal-attention, but without
reported awareness) using verbal stimuli (Hartman, Knopman & Nissen, 1989). Similar effects also occur in
some (but not all) patients with Alzheimer's disease (Knopman & Nissen, 1987).
Given this, it seems unlikely that learning novel stimulus patterns requires prior consciousness (of the pattern
being learnt).
5. Consciousness and the control of action.
Perhaps if one is searching for some essential function of consciousness one needs to look at how action is
controlled by the organism rather than at analysis, selection and storage of input, or a simple intention to
respond. It is commonly thought, for example, that a reflex or well learnt response may be performed in an
unconscious, automatic fashion—whereas an adaptive response to the environment requires awareness of
that environment, particularly if the required response is novel or complex.
This view is supported by the fact that interaction with the environment is usually accompanied by
awareness of the environment, of one's own action and, perhaps, of the interaction between the two.
Nevertheless, there is reason to doubt that adaptive interaction requires consciousness for its operation.
5.1 Preconscious response.
Suppose a tactile stimulus is applied to the skin and one is required to press a button as soon as one feels it.
It takes only a few milliseconds for the skin stimulus to reach the cortical surface. According to Libet et al.
(1979), awareness of the stimulus takes longer to develop (up to around 500 msec. for a threshold stimulus).
Yet, as Harth (1982) notes, one typically requires only around 100 msec. to react to such a stimulus. If so,
one can signal the presence of the stimulus by pressing a button about 400 msec. before the skin stimulus
enters awareness!
Nonetheless, we have the subjective impression that we respond after feeling
something touching the skin. According to Libet et al. (1979), this arises out of the way consciousness is
"constructed" by the brain. The subjective occurrence of the skin stimulus is "referred backwards in time" to
the instant it first projects onto the cortical surface—to an arrival time recorded in the brain by an early
evoked potential, which acts as a "time marker" for input stimuli of this kind.
Libet et al. arrived at this
view by comparing how subjects experienced the relative time of occurrence of stimuli both with and
without such early time markers. For example, threshold skin stimuli (which have early time markers) were
judged to be roughly simultaneous with electrical stimuli applied directly to the postcentral gyrus (which
have no time markers) applied 500 msec. after the tactile stimuli were applied to the skin. And, if they were
applied at the same time, the skin stimuli were judged to precede the postcentral gyrus stimuli.
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On the other hand, electrical stimuli applied directly to the ventroposteromedial nuclei of the thalamus do
produce early time markers. The subjective timing of these stimuli accordingly resembled that of external
skin stimuli. For example, they were judged to be roughly simultaneous with skin stimuli applied at the same
time, but to precede postcentral gyrus stimuli applied at the same time. To be judged simultaneous with
postcentral gyrus stimuli, the thalamic stimuli had to be delayed by around 500 msec.
The claim that
input stimuli are referred backwards in time is a radical one, and remains controversial (see BBS open peer
commentary on Libet, 1985; Harnad, 1982). However, if the findings are correctly interpreted, they
demonstrate a clear dissociation between cerebral information processing and awareness of that processing.
In short, the conviction that consciousness enters into cerebral information processing may not be a reliable
indicator that it does so.
Pressing a button in response to a tactile stimulus is of course a relatively simple task; a more complex task,
such as overt identification of a stimulus, or overt discrimination between two stimuli may not be possible
without awareness. This too is in doubt, however.
5.2 Overt identification and discrimination without awareness.
In some "masked priming" studies subjects seem able to make discriminative judgments about stimuli
without awareness of those stimuli (see section 2.2). This also occurs in the remarkable phenomenon of
"blindsight."
Weiskrantz (1986) describes an extensive series of tests carried out on a subject (D.B.) whose right visual
cortex (the striate cortex) had been removed and who was consequently blind in his left hemifield. He could
nevertheless make discriminative responses to stimuli presented to that field. In one study, Weiskrantz,
Warrington, Sanders & Marshall (1974) required the subject to fixate a point in the centre of a screen while a
random series of X's and O's was presented to the blind hemifield. As expected, the subject reported that he
could see nothing. When persuaded to guess, however, he made a correct identification on 27 out of 30
trials; in another series of tests with vertical and horizontal stripes, the subject guessed correctly on all 30
occasions.
In other studies Marcel (1982) reports that although cortically blind subjects have no phenomenal
experience of an object in their blind hemifield they can preadjust their hands appropriately to the size,
shape, orientation, and 3-D location of that object when forced to try to grasp it (see also Perenin &
Jeannerod, 1978; Torjussen, 1978; Stoerig, Hubner & Poppel, 1985). It is interesting that a similar
phenomenon, "blind-touch," has been reported in the somatosensory domain. Paillard, Michel & Stelmach
(1983) describe a patient with hemi-anaesthesia caused by a cortical lesion in the sensorimotor cortex who
could locate touch stimuli applied to her hand, but had no awareness of being touched.
Campion, Latto & Smith (1983) have argued that blindsight findings may be artifactual; it may be, for
example, that the striate is not completely damaged in patients exhibiting some residual visual functioning.
Weizkranz (1988) agrees that prior to post-mortem, one cannot rule this out. However, he points out that
this possibility is far-fetched in blindsight cases where complete unilateral hemispheric decortication obtains
(Perenin & Jeannerod, 1978).
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Campion et al also suggest that residual vision might have arisen from stray light originating from the
stimulus and diffused onto intact regions of the visual field, to produce a subtle form of stimulation of which
the subjects remained unaware. Weiskrantz (1983, 1986, 1988) reviews various sources of evidence against
this. For example, one naturally occurring control for stray light was provided by the optic disk of subject
D.B., which fell within his blind hemifield. Within the optic disc, nerve fibers penetrate the retina and no
receptors exist. In this region, therefore, the eye is truly blind. Accordingly, when a spot of light (suitably
adjusted for intensity and contrast) was projected onto D.B.'s optic disc, he could not see it and his ability to
guess whether or not it was present remained at chance. Hence, the spot could not have been a source of
stray light; when it was directed to the blind hemifield just adjacent to his optic disc D.B. still maintained he
could not see it, but his ability to guess whether or not it was present was very good. This provided clear
evidence that "blindsight" is not an artifact.12
Hence, under exceptional circumstances, it seems possible not only to analyze a visual stimulus but also to
make an appropriate, overt identification response to it, without any accompanying visual awareness.
5.3 Unconscious control of complex, novel, motor adjustments.
The above findings deal with identification responses to stimuli that do not enter awareness. Responses of
this kind, however, require little monitoring or feedback of the kind needed to adapt the movement of
muscles and limbs to novel, complex or changing situations. According to some theorists (e.g. Underwood,
1982), this is what consciousness provides.
It is clear that not all forms of feedback in the central nervous system require consciousness for their
operation. Homeostatic mechanisms controlling body temperature, blood sugar levels and so forth operate
in an entirely unconscious fashion, as do the various forms of proprioceptive feedback that signal the
positions of limbs and muscles. Consciousness seems to arise whenever we are called upon to make some
novel adjustment to an external situation (a point noted by Romanes, 1895). In such situations, according to
Mandler (1975), consciousness may perform a "troubleshooting" function. One might, for example, be
driving a car in more or less automatic fashion, but if the brakes suddenly fail, consciousness is immediately
directed towards "getting repair work under way."
Yet, even in these situations the question of what consciousness contributes to adaptive interaction remains.
Dixon (1981) notes that there are cases where emergency adjustments need to be made too quickly for
(relatively slow) conscious processing to operate, for example, when a driver needs to make an immediate
response to avoid the sudden threat of an accident. The manipulation of steering wheel, accelerator and
brake may take place with a very high level of competence and accuracy. Yet, after the event, the driver may
exclaim (quite truthfully) "I don't know how I missed him." In this situation, complex muscular adjustments
to a novel, rapidly changing situation appear to take place prior to the advent of consciousness. Anecdotal
accounts of the need for consciousness in situations where complex or novel motor adjustments are
required are therefore inconclusive. Whereas emergency situations demand one's full focal attention and
whereas focal attention is usually accompanied by consciousness, it does not follow that consciousness is
12
A similar control and result has also been reported by Stoerig et al. (1985).
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necessary for complex motor adjustments to be made. Indeed, one might ask, even if consciousness has
time to emerge and one is conscious of the task demanding one's attention, just how "conscious" is
"conscious control"?
One has no awareness whatsoever of the myriad motor commands issuing from the central nervous system
that travel down efferent fibers and innervate the muscles, nor of the complex motor programming that
allow muscular co-ordination and control. In speech, for example, the tongue may make as many as 12
adjustments of shape per second—adjustments which need to be precisely co-ordinated with other rapid,
dynamic changes within the articulatory system. According to Lenneberg (1967), "Within one minute of
discourse as many as 10 to 15 thousand neuromuscular events occur." Yet only the results of this activity
(the overt speech) normally enter consciousness.
5.4 Unconscious planning.
Unconscious motor control might of course be the result of prior conscious activity. For example, Popper
(1972) and Mandler (1975) suggest that consciousness is necessary for short and long term planning,
particularly where one needs to create some novel plan or novel output response. In the case of speech
production, for example, the control of the articulatory system might be unconscious but planning what to
say might be conscious, particularly if one is expressing some new idea, or expressing some old idea in a
novel way.
The planning and execution of speech has been subject to considerable experimental examination. Speech
production seems to involve various complex levels of organization. According to Bock (1982), these can be
roughly divided into six, relatively distinct "arenas": a referential arena in which some nonlinguistic coding of
thought is transformed into a format that can be used by the linguistic system, a semantic arena in which the
propositional relations formed within the referential arena are meshed with lexical concepts, a syntactic
arena responsible for structuring lexical items into conventional surface grammatical forms, a phonological
arena in which lexical items are mapped onto phonological representations, a phonetic arena that translates
phonological codes into codes suitable for entry into motor programs (e.g. target vocal-tract configurations),
and a motor assembly arena responsible for the actual compiling and running of the motor programs.
These levels of organization are commonly thought to be hierarchically arranged, with communicative
intentions being translated into a syntactic form with a given lexical content, in a largely top-down fashion
(Dell, 1986; Foss & Hakes, 1978; Garrett, 1982; Liberman, Cooper, Shankweiler & Studdert-Kennedy, 1967;
Schaffer, 1984).13 As noted above, articulatory control (motor programming and execution) is largely
unconscious. According to Bock, syntactic planning by skilled speakers is also relatively automatic and
13
Bock (1982) reviews evidence that factors affecting lexical retrievability (e.g. semantic and phonological
priming) are also associated with certain syntactic modifications in sentences, suggesting that the production
system might be subject to bottom-up as well as top-down influences.
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outside conscious voluntary control. Planning what to say and translating nonverbal conceptual content into
linguistic forms, however, requires effort.14 Could it be that such planning is conscious? Let us see.
A number of theorists have argued that periods of conceptual, semantic and syntactic planning are
characterized by gaps in the otherwise relatively continuous stream of speech (Goldman-Eisler, 1968;
Boomer, 1970). The neurologist John Hughlings Jackson, for example, suggested that the amount of planning
required depends on whether the speech is "new" speech or "old" speech. Old speech (well known phrases,
etc.) requires little planning and is relatively continuous. New speech (saying things in a new way) requires
planning and is characterized by hesitation pauses. Fodor, Bever & Garrett (1974) point out that breathing
pauses also occur (gaps in the speech stream caused by the intake of breath)—and breathing pauses do not,
in general, coincide with hesitation pauses.
Breathing pauses nearly always occur at the beginnings and ends of major linguistic constituents (such as
clauses and sentences); they therefore appear to be co-ordinated with the syntactic organization of such
constituents into a clausal or sentential structure. Hesitation pauses tend to occur within clauses and
sentences and appear to be associated with the formulation of ideas, deciding which words best express
one's meaning, and so on.
Accordingly, in assessing whether the planning of what to say is conscious, it is instructive to examine what
one experiences during a hesitation pause (where we have good reason to infer such planning to be taking
place). This simple thought experiment reveals that during a hesitation pause one might experience a certain
sense of effort (perhaps the effort to put something in an appropriate way), but nothing is revealed of the
processes which formulate ideas, translate these into a form suitable for expression in language, search for
and retrieve words from memory, assess which words are most appropriate, and so on. In short, no more is
revealed of conceptual or semantic planning in hesitation pauses than is revealed of syntactic planning in
breathing pauses. The fact that a process demands effort does not ensure that it is conscious. Indeed, there
is a sense in which one is only aware of what one wants to say after one has said it!
Nor is the situation any different if one expresses one's thoughts in covert speech through the use of
phonemic imagery. Covert speech and overt speech bear a similar relation to the planning processes that
produce them. In neither case are the complex antecedent processes available to introspection.
Furthermore, overt and covert speech are, in principle, "productive," in that one can produce an indefinitely
large number of sentences, including sentences which have never been produced before. Consequently, the
unconscious planning of speech must involve, at least to some extent, the planning of novel responses.
It could be argued, however, that merely saying something in a new way does not require genuine creativity.
After all, how often does one express a genuinely new idea? Perhaps it is in the creation of a novel idea that
consciousness plays some essential role.
14
According to Bock (1982), processing in the referential domain draws heavily on working memory
capacity.
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6. Consciousness and creativity.
Studies of creativity in both artists and scientists indicate that creative thought usually requires a preparation
period, an incubation period, and a consolidation period (Patrick, 1955; Ghiselin, 1952; Thomson, 1966; Platt
& Baker, 1969; Bowers, 1984).
As Thomson (1966) points out, "No intuitions come without hard work." Preparation in creative writing
might require an initial idea to be reworked or rewritten. In science, a period of data collection and analysis
may be followed by an initial formulation of a theory, or an initial attempt to deal with unresolved problems.
Such efforts require one's focal attention and are duly accompanied by consciousness (of what is being read,
written, reworked, and so on).
It should be clear from the discussions of overt and covert speech above that one can become conscious of
one's thoughts (on a given issue) without consciousness having entering into the formulation of such
thoughts. Moreover, if a creative "leap of imagination" is necessary, this initial processing may not lead to
success; an additional incubation period may be required. This period is characterized by the absence of
conscious effort. One might simply turn one's attention elsewhere or, indeed, "sleep on the problem." After
such an incubation period a creative solution may suddenly emerge into consciousness, without warning
and, apparently, without effort. As the poet Stephen Spender observes, "Everything is work except
inspiration" (see Ghiselin, 1952). There are, for example, a number of well documented cases of intuitive
insight emerging in dreams.
Famous examples include Henri Poincare's proof that there are no
mathematical functions such as Fuchsian functions (Thomson, 1966), Otto Loewi's discovery of how to do a
fundamental experiment on the chemical transmission from the vagus nerve to the frog's heart (Popper &
Eccles, 1976) and Auguste Kekule's discovery that benzene forms a closed hexagonal ring (Hein, 1966—but
see Browne, 1988).
There are many more examples of such intuitive insights in science (Platt and Baker, 1969). In general, such
insights need to be followed by a further consolidation period. Like the preparation period, this engages
focal attention with its accompanying conscious contents. Yet the heart of the creative act (the conceptual
reorganization required to make the intuitive leap) is associated with the incubation period, in which
processes not accompanied by consciousness dominate (see Thomson, 1966 and Bowers, 1984 for a
discussion). Creativity, therefore, cannot be one of the special functions of consciousness.
7. Does consciousness enter into subsequent information processing?
In the tasks discussed above, when consciousness appears, it follows the information processing to which it
relates and does not enter into it. It remains possible, however, that what enters consciousness has an effect
on subsequent information processing. From a first-person perspective, there seems to be little doubt that
prior conscious states influence subsequent conscious states; for example, one thought may lead to another,
or to a feeling, or to an action, and so forth.
From a third-person perspective, however, things look very different. As noted earlier, consciousness
normally accompanies focal-attentive processing. Conversely, when consciousness is absent, focal-attentive
processing is usually absent.
This simple point explains why processing which is accompanied by
consciousness may have effects (on subsequent tasks) very different to nonconscious processing (for
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example, in the studies of priming and masked priming discussed above). It also explains why some tasks
appear to require consciousness for their successful completion (they require focal-attentive processing).
In the analysis of input, for example, focal-attentive processing not only enables an item to enter
consciousness, but also to update long-term memory in a way that allows potential recognition or recall.
Information not given focal-attentive processing, on the other hand, is either inaccessible or lost from the
system. Focal-attentive processing also activates traces related to the input and inhibits traces not related to
the input, whereas non focal-attentive processing simply produces activation of related traces (see sections
1.3 and 2.2).
But this does not establish that the conscious states which accompany focal-attentive processing themselves
enter into subsequent information processing. According to Mandler (1985), however, they do so. Mandler
suggests that while information must be at a certain level of activation in order to become conscious, once it
does so it will receive additional activation, which is mediated by consciousness, resulting in further
enhancement. Such information is then more likely to be utilized in subsequent thoughts and actions, a
desirable consequence, given that it relates most closely to current concerns. As he notes,
"The proposal can easily be expanded to account for some of the phenomena of human problem
solving. I assume that activation is necessary but not sufficient for conscious construction and that
activation depends in part on prior conscious constructions. The search for problem solutions and the
search for memorial targets (as in recall) typically have a conscious counterpart, frequently expressed
in introspective protocols. What appear in consciousness in these tasks are exactly those points in the
course of the search when steps toward the solution have been taken and a choice point has been
reached at which the immediate next steps are not obvious. At that point the current state of world is
reflected in consciousness. That state reflects the progress toward the goal as well as some of the
possible steps that could be taken next. A conscious state is constructed that corresponds to those
aspects of the current search that do (partially and often inadequately) respond to the goal of the
search. Consciousness at these points truly depicts waystations toward solutions and serves to restrict
and focus subsequent pathways by selectively activating those that are currently within the conscious
construction." (p77 - italics added)
The sense in which the present analysis differs, on this point, from that of Mandler can be gleaned from the
final sentence of the quotation. As noted earlier, items enter consciousness only if they are (or have recently
been) subject to focal-attentive processing. Accordingly, what enters consciousness during problem solving
"truly depicts waystations toward solutions" for the reason that such conscious contents reflect the state of
progress of focal-attentive processing. If "two-process" theory is correct, focal-attentive processing also
activates (or inhibits) subsequent representational states.
Given this, it is not clear what additional activation mediated by consciousness would achieve. Only
information selected for focal-attentive processing enters consciousness. According to "activation" theories
of attention, this will only occur if it is already more activated than competing, less relevant information—in
which case no additional, "consciousness-mediated activation" would be required to ensure its prominence
in subsequent activity.
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8. How consciousness relates to focal-attentive processing.
It is important to remember in this regard that in its ordinary usage "consciousness" refers to something
other than "focal-attentive processing." It refers primarily to "awareness," whereas "focal-attentive
processing" refers to a functional subdivision within an information processing model of the brain. Focalattentive processing is thought to be a necessary condition for conscious awareness. Operationally, however,
they are distinct (Nissen & Bullemer, 1987; Kahneman & Treisman, 1984).
Conscious contents are typically investigated by the use of subjective reports (of subjective experience)—
usually verbal reports, although various other means of communicating experience exist (Ericsson & Simon,
1984; Pope & Singer, 1978). By contrast, human information processing and functional divisions within such
processing are typically inferred from performance measures such as reaction time, error score, and so forth.
In principle, therefore, it might be possible to obtain evidence of focal-attentive processing in the absence of
awareness (of what is being processed). In practice, however, a complete dissociation of consciousness from
focal-attentive processing is difficult to achieve, as the disruption of consciousness is also likely to interfere
with at least some aspects of (normal) focal-attentive processing.
For example, blindsighted subjects direct their attention to an input stimulus, identify its properties and
make appropriate identification responses, but are unable to experience the stimulus to which they attend
(Weiskrantz, 1986). Such subjects, however, need to be forced to make decisions about stimuli they believe
they cannot see, indicating that information about the stimulus is not readily available to all parts of the
information processing system. Similarly, Marcel (1986) found that blindsight patients make no attempt to
grasp a glass of water in their blind field even when thirsty, suggesting that information about the input
remains dissociated from systems subserving voluntary control.
In "masked priming" experiments, the mask may interfere not only with consciousness of the prime but also
with the usual inhibition of traces which do not relate to the prime (Marcel, 1980) and with other
consequences of focal-attentive processing (Marcel, 1983 experiment 5; Forster & Davis, 1984; Cheesman &
Merikle, 1984,1986; Dagenbach, et al, 1989).
In hypnotic analgesia, the "hidden observer" claims to remember pain, which the hypnotised patient, in
surgery, says he does not experience—suggesting that focal-attentive processes required to update longterm memory are partially dissociated from those subserving conscious experience. The absence of
experienced pain, however, may be accompanied by an absence of physiological indices of pain and by
reduced bleeding and salivation (Oakley & Eames, 1985), indicating that information about the painful input
may not be readily available to other parts of the system (as with the cases of blindsight and visual masking
discussed above). Similarly, in implicit learning and memory studies, information which is not present to
consciousness at the time of learning (according to subjective reports) may update long-term memory but
may not be available for later explicit recognition and recall (Reber, 1989; Nissen & Bullemer, 1987).
Even partial dissociations provide useful information, however, in that they enable one to be more precise
about what aspect of focal-attentive processing might relate most closely to consciousness. The above
findings, for example, suggest that the processing required for information to enter consciousness may also
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be required to make that information generally available to other parts of the system. As Kahneman &
Treisman (1984) suggest, the dissemination of currently processed information to other information
processing modules may be one of the functions of focal-attentive processing.
This view is also similar to one that has recently been developed, in depth, by Baars (1989). According to
Baars, the principle function of consciousness is to enable information to be "broadcast" throughout the
central nervous system. If the above arguments are correct, however, this is not the function of
consciousness. Rather, the processes which enable information to be integrated into a particular conscious
state also enable that information to be broadcast to other parts of the system. Consciousness results from
such focal-attentive processing but does not enter into it.
9. General discussion.
9.1 Is human information processing conscious?
In the above examples, we have ranged over all the main phases of human information processing—from
information encoding, storage, retrieval, and transformation to output. We have considered the role of
consciousness in the analysis and selection of stimuli, in learning and memory, and in the production of
voluntary responses, including those requiring planning and creativity.
In one sense, each of these tasks may be "conscious" (if it is at the focus of attention). We may be conscious
of the stimuli that we analyze and select for more detailed attention, conscious of what we learn and commit
to memory, and conscious of the responses we make to such stimuli. When the required responses are
complex or novel we may be aware of devoting effort to planning and monitoring their execution. In
reflective thought or problem solving we may have some awareness of internal processing in the form of
thoughts, emotions, images, and so forth. Whether consciousness is necessary for such processing,
however, is a different matter.
Some processes operate either with or without accompanying awareness, including aspects of input analysis,
memory, and overt response. Consequently, these cannot require awareness for their operation. More
important, there is a sense in which the execution of none of these tasks is "conscious" (even if they are at
the focus of attention, and are accompanied by awareness).
The detailed information processing required to analyze and select amongst stimuli, or to encode them in
memory is not, by and large, available to introspection, nor is there any awareness of the processing required
to execute a response. Rather, one becomes aware of a stimulus only after one has analyzed and selected it,
and aware of one's own response only after one has executed it. This applies not only to simple, automatic
responses (such as pressing a button or detecting a stimulus) but also to complex, novel, voluntary responses
(such as the production of "new" speech).
In similar fashion, awareness of "inner responses" follows the processing required to produce them. For
example, covert speech results from the antecedent processing involved in thinking, problem solving,
remembering, silent reading, and so forth. This applies equally to the "intuitive insights" which are the
product of the creative process.
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As noted earlier, conscious contents that follow given forms of information processing cannot be thought of
as entering into that processing. Nor does consciousness as such enter into subsequent information
processing. Rather, it is the focal-attentive processing which provides (at least some of) the necessary
conditions for conscious awareness that also influences the course of subsequent processing operations.
If consciousness does not enter into human information processing, then the very notion that some of this
processing is "conscious" needs re-examination. In retrospect, a process might be said to be "conscious" in
three distinct senses. It might be "conscious"
(a) in the sense that one is conscious of the process
(b) in the sense that the operation of the process is accompanied by consciousness (of its results ) and
(c) in the sense that consciousness enters into or causally influences the process.
Some processes (problem solving, thinking, planning, and so on) are conscious in sense (a) but only in so far
as their detailed operation is accessible to introspection. Many processes (input analysis, motor control,
thinking, planning, etc.) are conscious in sense (b), in so far as they engage focal-attentive processing.
However, no human information processing is conscious in sense (c).
The theoretical implications of this are far-reaching. If consciousness does not enter into human information
processing then processes which allow adaptive functioning in the human brain must be distinguished from
accompanying awareness. If so, information processing models (and other models) that deal solely with
how input is transformed into behavioural output remain seriously incomplete, for they do not contain
consciousness within their workings.15
9.2 Some implications for the philosophy of mind.
The above conclusions also have consequences for the philosophy of mind. These cannot be fully dealt with
in the space available for this target article. A brief outline, however, may provide a useful basis for
discussion.
It should be apparent that the dissociation of awareness from cerebral functioning poses problems for
reductionist theories of consciousness. It is inconsistent with the functionalist view that consciousness
simply is (ontologically identical to) a mode of functioning of the brain. 16 Nor is it consistent with physicalism
(the view that consciousness is ontologically identical to a physical state of the brain) 17--unless one is willing
to accept that some cerebral states exist that neither have a function in themselves nor influence the
development of subsequent, functional, cerebral states or processes. The exclusion of consciousness from
15
This applies equally to recent alternatives to information processing models, such as parallel distributed processing.
Philosophical functionalists such as Dennett (1978) argue that consciousness has functional aspects which are ontologically
identical to the contents of a hypothetical memory buffer "M." In similar fashion, cognitive psychologists have assumed the
contents of consciousness to be identical to the contents of "primary memory" or some similar short-term store (James, 1890;
Waugh and Norman, 1965); Posner and Warren (1972) define a "conscious process" to be one that makes use of the "limited
capacity central processor"; others view "conscious processing" and "focal-attentive processing" to be one and the same (Miller,
1987; Mandler, 1975), and so forth.
17
A recent, sophisticated defense of physicalism is given by Searle (1987).
16
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cerebral functioning is equally inconsistent with emergent interactionism (the view that consciousness
emerges from cerebral activity but then supervenes over the activity from which it emerges—see Sperry,
1985) and with interactionist forms of dualism (the view that a disembodied consciousness engages in
reciprocal interaction with the brain—see, e.g. Popper & Eccles, 1976; Eccles, 1980, 1987).
But what alternatives remain? According to the behaviourists, one should simply exclude consciousness
from psychological science, and recently, some philosophers have questioned whether consciousness is a
genuine phenomenon (Dennett, 1988; Rey, 1988). Unfortunately for such views, consciousness has been
subject to extensive scientific investigation.
From an experimenter's perspective, the contents of a subject's consciousness may not be directly
observable, but they may nevertheless be inferred to be a form of output accompanying certain forms of
information processing. Accordingly, the physical, psychological and neurophysiological determinants of
these contents have been extensively explored in perception, psychophysics, sensory physiology and many
other domains of the psychological and brain sciences, along with the processes which enable those contents
to be formed into an integrated whole (see Blumenthal, 1977, for a review). In recent years, moreover, there
has been a renewed interest in structured subjective reports and other methods of phenomenological
enquiry (Ericsson & Simon, 1984; Pope & Singer, 1978). There has also been extensive investigation of how
processes that are accompanied by consciousness differ from processes that are not, revealing major
functional subdivisions in human information processing. Ultimately, such studies may enable one to specify,
in information processing terms, what the necessary and sufficient conditions for consciousness may be—
conditions which are linked, in the present analysis, to certain aspects of focal-attentive processing. In
principle, these conditions can also be specified in neurophysiological terms (see Eccles, 1980, 1987; John,
1976; Pribram, 1971,1982; Dimond, 1980; Uttal, 1978; O'Keefe, 1985; for some initial speculations). If
consciousness is not a genuine phenomenon, then what is the subject matter of these enquiries?
9.3 Complementary first-person and third-person perspectives.
Even if one accepts that consciousness is central to an understanding of the mind (Searle, 1990; Velmans,
1990a,1990b) its causal status remains a puzzle. According to the above, consciousness is a form of output
(associated with focal-attentive processing) that does not enter into cerebral processing. This appears to
support epiphenomenalism (the view that brain events have causal effects both on other brain events and
conscious experiences, but conscious experiences have no causal effects on the brain—see Huxley, 1898).
It must be emphasised, however, that the above analysis reviews the evidence only as it appears from a
third-person, external observer's perspective. While from a third-person perspective consciousness appears
to have no causal influence on human brain activity and overt behaviour, from a first-person perspective,
things look very different.
From a first-person perspective consciousness appears to exert a central influence on human affairs, and
scientists have a first-person perspective as much as their subjects. It is not surprising, therefore, that
consciousness has been thought to enter into every major phase of information processing, ranging from the
analysis, selection and storage of input to the organization, planning and execution of response. Experiences
also appear central to human motivation—ranging from the wish to engage in pleasant experiences and to
VELMANS
33
avoid painful ones, to engaging in activity simply to extend the breadth and depth of one's experience.
Experiences of the world are also thought to influence human development. Traumatic experiences, for
example, may have unwanted psychosomatic effects. Such examples of apparent causal efficacy are
innumerable. From a first person perspective, therefore, epiphenomenalism appears false.
Traditionally, science has adopted the third-person, external observer's perspective, and, as the review
above demonstrates, it is possible, in principle, to translate first-person accounts of mental activity into thirdperson accounts (for example, into information processing models which make no appeal to consciousness
entering into cerebral activity). But the fact that first-person accounts can be translated into third-person
accounts does not alter the fact that subjects have a first-person perspective from which to view the world,
including their own activity (Harnad, 1991; Nagel, 1974, 1986).
Moreover, the fact that a third-person account is possible in principle does not guarantee that it is preferable.
While brain functioning may need to be understood from the perspective of an external observer, for most
everyday purposes a first-person account of the determinants of action (in terms of what is perceived,
thought, felt, believed, desired, and so forth) may be more informative. In short, while explanations in terms
of brain states, information processing, and the like are preferable for some purposes, explanations in terms
of what is perceived, felt, and so forth are more useful for others.
Of course, the question of whether it is actually a given brain state or a given experience that determines a
particular behaviour remains—and, on this point, I suggest, no choice is necessary. These are events viewed
from different perspectives. Events viewed from an external observer's perspective (via exteroceptors)
appear different from the same events experienced by the subject (via interoceptors) because the methods
of observation are different. However, each perspective is legitimate.
Information processing models and other third-person perspective models are incomplete in so far as they
do not encompass the subject's first-person perspective. Conversely, a subject's first person account of his
actions (based on what he experiences) is incomplete in so far as it does not encompass information
available to an external observer. In this sense, first-person and third person perspectives are
complementary and mutually irreducible. A complete psychology requires both (Velmans, 1990b).
How first-person and third-person accounts relate requires detailed examination (and this cannot be done in
the space available). Once one accepts this psychological "complementarity" principle18, however, it is clear
why consciousness does not enter into human information processing—for information processing models
systematize what can be observed only from a third-person, external observer's perspective. The objection
to theories that attempt to insert consciousness into such (third-person) models is not that consciousness is
18
It is tempting to relate "psychological complementarity" to complementarity in physics. One must treat such analogies with
caution, however, as there are both similarities and differences. According to quantum mechanics, wave and particle descriptions of
light are complementary and mutually irreducible. For completeness, both descriptions are required. Its appearance as waves on
some occasions and particles on others depends entirely on the conditions of observation (which makes the conditions of
observation integral to what is observed). In this sense, physical complementarity and psychological complementarity appear
similar. Wave and particle descriptions, however, both derive from the third-person perspective, and the relation of first-person to
third-person accounts in psychology is far more complex (e.g. see Ericsson & Simon, 1984, for an initial attempt to relate first-person
introspective reports to a third-person information processing model of the brain).
VELMANS
34
causally ineffective. Viewed from a first-person perspective, consciousness is central to the determination of
human action. Rather, information processing models that attempt to incorporate consciousness within
their workings collapse the subject's first-person perspective into the external observer's third-person
perspective, a collapse of one perspective into the other which a "complementarity" principle would not
allow.
10. Summary
1. Human information processing may be "conscious" in so far as some of its aspects are available to
introspection. It may also be accompanied by consciousness of its results.
2. Introspective access, or consciousness of the results of cerebral processing must not be confused with
the operation of that processing. What enters awareness follows the processing to which that
awareness relates and cannot therefore enter into it. This applies to all stages of information
processing, whether the information is simple or complex, familiar or novel, whether the processing
is involuntary or voluntary, and whether the processing is data driven, cognitively driven or a
combination of the two.
3. Processes that are accompanied by consciousness are at the focus of attention. It appears that
consciousness is closely linked to that aspect of focal-attentive processing which makes information
generally available throughout the processing system.
4. Processes at the focus of attention function differently from those which are not. For example, focalattentive analysis of input appears to activate relevant information and to inhibit irrelevant
information; stimuli given focal-attentive processing appear to be potentially available for
subsequent recognition and recall; information given focal-attentive processing may also be generally
available to other parts of the system. Consequently, focal-attentive processing may be required in
various situations—for the identification of novel stimuli, for learning and memory, for the control of
complex, novel responses involving planning and creativity, and so on.
5. When consciousness is absent, focal-attentive processing is usually absent—which explains why
consciousness seems necessary for the completion of such tasks.
6. If consciousness does not enter into cerebral functioning then human information processing models
which restrict themselves to an account of that functioning remain seriously incomplete, in so far as
they do not contain consciousness within their workings.
7. Consciousness is, nevertheless, amenable to scientific investigation. Accounts of functioning
therefore need to be supplemented by accounts of sentience within the human brain. A complete
psychology requires both.
8. The dissociation of consciousness from cerebral functioning also poses problems for philosophy of
mind. Consciousness neither interacts with the brain, nor can it be reduced to a state or function of
the brain.
9. At the same time, the existence of consciousness—of a "first-person" perspective, cannot be
dismissed. Nor can one dismiss the everyday usefulness of "first-person" psychological accounts.
10. Information processing models view the brain from an external observer's "third-person" perspective,
which cannot encompass the subject's "first-person" perspective. These two perspectives appear to
be complementary, and mutually irreducible.
VELMANS
35
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