Abstract
It is a common conviction among philosophers who hold that phenomenal properties, qualia, are distinct from any cognitive, intentional, or functional properties, that it is possible to trace the neural correlates of these properties. The main purpose of this paper is to present a challenge to this view, and to show that if “non-cognitive” phenomenal properties exist at all, they lie beyond the reach of neuroscience. In the final section it will be suggested that they also lie beyond the reach of psychology, so that they may be said to lie beyond the reach of science.
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Notes
The expression “the neural correlate of consciousness” (often abbreviated as “NCC”) might sound as if it presupposes dualism, for correlation is only possible between distinct entities, but most of the philosophers and researchers writing on the issue of NCC are physicalists. For this reason, perhaps the expression “the neural realizer of consciousness” would be more appropriate. Nevertheless, I follow the literature in using the “correlate” terminology.
Chalmers (2004) now endorses a version of representationalism of phenomenal consciousness, but this is a non-reductive form of representationalism which in essence should be classified within the category of non-cognitive views of phenomenal consciousness.
Crick and Koch (1990) claim that one of the functions of consciousness is to present the result of various underlying computations, and thus seem to presuppose the non-cognitivist (or the Cartesian) conception of consciousness as a show presented to a spectator in a theater. Commenting on this claim of Crick and Koch, Dennett asks (1991, p. 255): “... but to whom [is consciousness supposed to present this result]? The Queen?..”
Among the scientists who maintain that only the neural correlate of a cognitive form of consciousness (what they call “access to consciousness”) can be found are Dehaene and Changeux (2004).
The very notion of the neural correlate of consciousness is not free of difficulties (see, e.g., Noe and Thompson 2004), but I will not pursue this topic here.
I am concerned in this paper with the positions of Dennett and his critics only insofar as they may serve to highlight the issue of the neural traceability of phenomenal consciousness, and so I will ignore various aspects and subtleties of their works which are irrelevant to this issue.
Though I share their rejection of the notion of (non-cognitive) phenomenal consciousness, I disagree with current cognitivists about which cognitive characteristics should figure in an account of phenomenal consciousness. The resources they appeal to are too meager. See Jacobson-Horowitz 2003.
Dennett (1991, p. 123) also claims that “the experience would ‘feel the same’ on either account”, and Block (1993, p. 189) denies this. Clearly, Dennett cannot take it for granted that the two cases feel the same, in the phenomenal sense of “feel” (exactly as Block cannot take it for granted that the cases do not feel the same), on pain of begging the question. But in his argument to the effect that there is no fact of the matter regarding the occurrence of “brief flickers of consciousness” Dennett uses “feel the same” as more or less synonymous with “is indistinguishable by the subject”. In this sense, his claim that “the experience would ‘feel the same’ on either account” should not be controversial.
Rejecting this kind of verificationism, Dennett (1991, p. 461) adds, leads to “nonsense” like epiphenomenalism, zombies, indistinguishable inverted spectra, and others.
Dennett’s verificationist reasoning certainly raises questions and deserves a wider discussion (for example, the role that is played in this reasoning by the claim that no third-person evidence is available should be elucidated). But examining the validity of this reasoning is not important for the epistemological and methodological issues with which this paper is concerned.
According to Dennett, when the question of whether contents are conscious concerns cases like metacontrast, in which—due to the short period of time in which the content is accessible to the subject’s cognitive system—it cannot leave cognitive traces, the question presupposes more fine-grained temporal boundaries than the phenomena admit (see Dennett and Kinsbourne 1992, pp. 235–36). This emphasis on the temporal element should not induce us to overlook the general lesson: the principal reason for Dennett’s taking the question to be unanswerable concerns the fact that the stimulus does not influence the subject’s cognitive life. (We shall later encounter cases which exemplify similar inaccessibility of perceptual contents to subjects’ cognitive systems but in which no temporal constraints are in effect.) It has been argued by some commentators that Dennett’s rejection of the notion of such (non-cognitive) brief flickers of consciousness in fact positions him as Stalinesque. Again, assessing this claim is not essential for the epistemological issues with which this paper is concerned.
Block’s notion of access consciousness is a dispositional notion. A subject who is access conscious of a certain content in his sense need not actually use the content in the ways described above; it suffices that the content be freely available for reasoning and poised for rational control of action or speech. But I speak of actual uses of contents in those ways, since, of course, if we are interested in identifying phenomenally conscious states, we need to identify actualizations of such dispositions. In spite of this difference, and in spite of the (related) fact that Block’s purpose in introducing this notion is to characterize a non-phenomenal type of consciousness whereas my purpose is to suggest an epistemic linkage between phenomenal consciousness and cognitive attitudes and processes of certain sorts, I will use Block’s term—“access consciousness” to refer to these cognitive processes and the attitudes they involve. It should also be emphasized that my arguments do not depend on whether the cognitive patterns I speak of exactly match Block’s characterizations. In the next section I will further clarify the evidential linkage between phenomenal consciousness and the various kinds of cognitive consciousness. I will only add here that a content’s being freely available for the cognitive usages in questions in the sense explained above is an important evidential factor. Block correctly points out, with respect to blind sight subjects—who need to be prompted by the experimenter’s request in order to guess which stimuli are present in their “blind” visual field—that the contents representing these stimuli are not freely available to them. This illustrates that behavioral data can tell us whether certain contents are freely available for cognitive usages or not. (I will discuss the phenomenon of blind sight below.)
In his later work Block (1998) expresses awareness to the fact that various hypotheses may account for the phenomenon in question.
Another example that Block (1995, pp. 239–41) takes to involve phenomenal but no (or very deficient) cognitive consciousness is the example of epileptic patients performing some activity (walking home or playing the piano) during seizures. Block accuses Penefield (1975), Searle (1992) and van Gulick (1989) of taking these patients to lack phenomenal consciousness, while actually the evidence shows only that they lack access consciousness (or that their access consciousness is very deficient). There is no reason to doubt, he says, that these subjects are phenomenally conscious: “they do show every sign of normal sensation” (Block 1995, p. 239) Again, according to the reasoning I am suggesting, the controversy over this phenomenon is not accidental: in the absence of access consciousness we cannot be in a position to know that the patients are phenomenally conscious.
Block also raises in the same context several objections to the idea that the only possible evidence for phenomenal consciousness is introspective evidence or introspective reports. But I by no means assume that this is the only possible evidence for phenomenal consciousness. (On this issue, see also the discussion of SDI in the next section.)
Such a subtraction—referred to in cognitive neuroscience as “cognitive subtraction”—is not free of difficulties. As pointed out by Poeppel (1996), it is threatened by various findings that suggest that neural processing stages may be sensitive to adding or deleting other processing stage. (The discussion of metacontrast below has some affinity to this issue.) Whether or not there are conditions under which cognitive subtraction can nevertheless be justified is a matter of dispute. Poeppel himself answer this question positively; for a negative reply to this question see, e.g., Sartori and Umilta 2000.
Blindsight was discovered by Lawrence Weiskrants (1986).
Can the occurrence of this belief be prevented? Plausibly it can (see the discussion of SDI in the next section). But what cannot be prevented is the occurrence of the phenomenal apprehension of the disc with no accompanying cognitive attitudes whatsoever.
Examples of negatively testifying cognitive evidence are a negative reflective belief, and the (“free”) use of a content that clashes with the content of the alleged phenomenal state.
In fact, the argument advanced here does not depend on the assumption that cognitive attitudes of no other kind may serve as evidence for phenomenal consciousness (and as I said (see note 14 above), nothing hinges on whether the cognitive patterns I speak of exactly match Block’s characterizations). The suggestion that cognitive attitudes of these two kinds are the required ones might seem more plausible when we bear in mind that “access consciousness” covers several sub-kinds of cognitive attitudes.
I write “neural stages” in the plural, since a process which involves a digitalization of analogue-perceptual information would most plausibly not be a simple one-stage process. (This fact makes the indeterminacy problem even more severe.)
This is true, at any rate, with respect to the phenomenal states of others. But this is the important thing as far as scientific findings regarding consciousness are concerned.
For convenience, I speak of prediction and explanation of behavior, but the points argued for here equally apply to the prediction and explanation of various mental states that ensue from the “mediating” cognitive attitudes (and indirectly from the phenomenal states).
In his debate with Shoemaker about absent qualia, Block (1980) argues that the possibility of functionally identical states only one of which is qualitative does not imply that qualia are epiphenomenal, since the causal efficacy of a qualitative character is compatible with the possibility that a state with a qualitative character and a state which lacks a qualitative character play the same causal role. The epistemic linkage I highlight is compatible with this view and it does not depend on qualia being epiphenomenal. For the very possibility that Block mentions prevents us from taking evidence for the obtaining of a state with the causal profile characteristic of a certain qualitative state to indicate that it is the qualitative state, rather than causally identical non-qualitative state, that obtains.
A related issue which I can only briefly mention is the following. One might argue for the existence of non-cognitive phenomenal properties on the grounds that postulating them best explains our reflective beliefs concerning our phenomenal states. Indeed, it seems plausible to claim that introspective beliefs are ultimately causally anchored in, and hence explainable by the postulation of, some “intrinsic” features of brain events which correlate with phenomenally conscious events. But this claim falls short of vindicating the existence of non-cognitive phenomenal properties, since it is significantly weaker than the claim that those intrinsic features are identical with phenomenal properties. (Further, one can deny the latter claim while still accepting that phenomenal properties are causally relevant for the existence of those reflective beliefs. For example, it is arguable that if phenomenal properties are identified with (segments of) the functional profiles of those brain events, they are causally relevant for the existence of reflective beliefs.) The same rationale would undermine the objection that postulating non-cognitive phenomenal properties best explains various other cognitive processes (other than those which involve reflective beliefs). A mistaken line of reasoning similar to the one which moves from the first (and weaker) of those claims to the second is exemplified by Flanagan’s argument to the effect that propositional attitudes have characteristic qualitative feels. According to Flanagan, the fact that there is almost never any doubt that a person who takes herself to be in a state of belief is indeed in a state of belief rather than in a state of desire, is best explained by the assumption “that there really is a certain way it feels to be believing something and that way of feeling is different from the way it feels to be desiring something” (Flanagan 1992, p. 68). But it isn’t clear why this explanation is the best one. What advantage does it have over the explanation according to which it is simply part of the causal role of beliefs and desires to produce characteristic second-order beliefs? What explanatory insight is gained by identifying the internal features in virtue of which beliefs and desires cause characteristic second-order beliefs with qualitative feels?
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Jacobson-Horowitz, H. The Scientific Untraceability of Phenomenal Consciousness. Philosophia 36, 509–529 (2008). https://doi.org/10.1007/s11406-008-9126-8
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DOI: https://doi.org/10.1007/s11406-008-9126-8