Drawing on work in psychophysics, psychometrics, and sensory neurophysiology, Clark analyzes the character and defends the integrity of psychophysical explanations of qualitative facts, arguing that the structure of such explanations is sound and potentially successful.
This paper contrasts three different schemes of reference relevant to understanding systems of perceptual representation: a location-based system dubbed "feature-placing", a system of "visual indices" referring to things called "proto-objects", and the full sortal-based individuation allowed by a natural language. The first three sections summarize some of the key arguments (in Clark, 2000) to the effect that the early, parallel, and pre-attentive registration of sensory features itself constitutes a simple system of nonconceptual mental representation. In particular, feature integration--perceiving something as (...) being both F and G, where F and G are sensible properties registered in distinct parallel streams--requires a referential apparatus. Section V. reviews some grounds for thinking that at these earliest levels this apparatus is location-based: that it has a direct and nonconceptual means of picking out places. Feature-placing is contrasted with a somewhat more sophisticated system that can identify and track four or five "perceptual objects" or "proto-objects", independently of their location, for as long as they remain perceptible. Such a system is found in Zenon Pylyshyn's fascinating work on "visual indices", in Dana Ballard's notion of deictic codes, and in Kahneman, Treisman, and Wolfe's accounts of systems of evanescent representations they call "object files". Perceptual representation is a layered affair, and I argue that it probably includes both feature-placing and proto-objects. Finally, both nonconceptual systems are contrasted with the full-blooded individuation allowed in a natural language. (shrink)
We assemble here in this time and place to discuss the thesis that conscious attention can provide knowledge of reference of perceptual demonstratives. I shall focus my commentary on what this claim means, and on the main argument for it found in the first five chapters of "Reference and Consciousness". The middle term of that argument is an account of what attention does: what its job or function is. There is much that is admirable in this account, and I am (...) confident that it will be the foundation, the launching-pad, for much future work on the subject. But in the end I will argue that Campbell's picture makes the mechanisms of attention too smart: smarter than they are, smarter than they could be. If we come to a more realistic appraisal of the skills and capacities of our sub-personal minions, the "knowledge of reference" which they yield will have to be taken down a notch or two. (shrink)
Although the capacity to discriminate between different qualia is typically admitted to have a definition in terms of functional role, the qualia thereby related are thought to elude functional definition. In this paper I argue that these views are inconsistent. Given a functional model of discrimination, one can construct from it a definition of qualia. The problem is similar in many ways to Goodman's definition of qualia in terms of 'matching', and I argue that many of his findings survive reinterpretation (...) into a physicalistic basis which employs 'indiscriminability' as its primitive term. I show how one can identify the critical properties to which discrimination capacities are sensitive, and then identify their order. A problem arises concerning the different ways in which qualitatively distinct experiences can differ (hue, shape, and so on). Physicalist accounts have often been accused of relying in a circular fashion on some antecedent understanding of phenomenal properties in order to specify those differences. This account avoids such an accusation: ordering of critical properties is determined by the dimensionality of discriminations, and the latter is given by the structure of the discrimination pair lists. Once a topology of quality is constructed, qualia names can be defined by their relative location within the order. In the conclusion I argue that psychophysics employs physicalist techniques to define a topology of quality, and that it can provide what Thomas Nagel calls an "objective phenomenology.". (shrink)
the philosophical regions. I will identify three: three obvious zones of The first and third of these kinds of problem are studied almost tectonic conflict within contemporary cognitive approaches to exclusively within departments of philosophy. Applied to perception.
Suppose we admit for the sake of argument that "folk" explanations of human behavior--explanations in terms of beliefs and desires--sometimes succeed. They sometimes enable us to understand and predict patterns of motion that otherwise would remain unintelligible and unanticipated. Is the only explanation for such success that folk psychology is a viable proto-scientific theory of human psychology? I shall describe an analysis which yields a negative answer to that question. It was suggested by an observation and an analogy, both of (...) which may initially seem remote from the topic at hand. (shrink)
Many philosophers doubt that one can provide any successful explanation of sensory qualities - of how things look, feel, or seem to a perceiving subject. To provide such an explanation, one would need to explain qualitative facts in non-qualitative terms. Attempts to construct such explanations have seemed, in principle, doomed. Austen Clark examines the strategy used in psychophysics, psychometrics, and sensory neurophysiology to explain qualitative facts. He argues that this strategy could succeed: its structure is sound, and it can answer (...) the various philosophical objections lodged against it. On this basis Professor Clark presents an analysis of senosry qualities that offers the possibility of explaining at least some qualia, and he sketches how this scheme might eventually reduce to neurophysiology. If he is correct, we are not doomed to an eternity of mere acquaintance with our qualia. (shrink)
The goal of this paper is to challenge the rather insouciant attitude that many investigators seem to adopt when they go about describing the items and events in their " visual fields". There are at least three distinct categories of interpretation of what these reports might mean, and only under one of those categories do those reports have anything resembling an observational character. The others demand substantive revisions in one's beliefs about what one sees. The ur-concept of a " visual (...) field" is that of the "sum of things seen", but one can interpret the latter in very different ways. The first is the "field of view", or the sum of physical things seen. The second is an array of visual impressions, whose spatial relations are distinct from those of physical phenomena in front of the eyes. The third is an intentional object: the world as it is represented visually. These three categories are described, and various locutions of vision science--such as "optic array", "retinocentric space", " visual geometry", "virtual object" and others--are analyzed and variously located within them. Finally, a recent argument purporting to necessitate the existence of a version two visual field is examined and shown wanting. (shrink)
A neighbor who strikes it rich evokes both admiration and envy, and a similar mix of emotions must be aroused in many neighborhoods of cognitive science when the residents look at the results of research in color perception. It provides what is probably the most widely acknowledged success story of any domain of scientific psychology: the success, against all expectation, of the opponent process theory of color perception. Initially proposed by a Ewald Hering, a nineteenth century physiologist, it drew its (...) inspiration from the existence of opposing muscle groups. Hering thought that analogous opposing processes could explain some aspects of color perception, but the resulting theory was more complicated and less intuitive than that proposed by the great Hermann von Helmholtz. Helmholtz carried his day, but in the long run Hering turned out to be right. (shrink)
When you suffer a pain are you suffering a sensation? An emotion? An aversion? Pain typically has all three components, and others too. There is indeed a distinct sensory system devoted to pain, with its own nociceptors and pathways. As a species of somesthesis, pain has a distinctive sensory organization and its own special sensory qualities. I think it is fair to call it a distinct sensory modality, devoted to nociceptive somesthetic discrimination. But the typical pain kicks off other processes (...) too. For one it can grab your attention in a distinctive way, alerting you to its presence and sometimes obliging you to focus attention on the damaged member. Intense pain can eliminate your ability to think about anything else. Pain typically has direct and immediate motivational consequences: one wants it to stop, has an incentive to do whatever one can to reduce it, and is gratified by its termination. As these desires and motives collide with neural reality, emotional components of mental anguish, anxiety, and dread arise. The suffering involved in suffering from pain has multiple strands: it is not just the painfulness of the sensation, or the frustration of the desire that it end, but also the anguish over the possibility that it will never end, and the impossibility, if the pain is sufficiently intense, of focusing one’s attention on anything else. (shrink)
I am very grateful to my commentators for their interest and their careful attention to A Theory of Sentience. It is particularly gratifying to find other philosophers attracted to the murky domain of pre-attentive sensory processing, an obscure place where exciting stuff happens. I can by no means answer all of their objections or counter-arguments, and some of the problems noted derive from failures in my original exposition. But a theory is a success if it helps spur the creation of (...) better successors. By those lights this one seems to be succeeding admirably. Would that every author could receive such commentaries! (shrink)
If one examines the sky at sunset on a clear night, one seems to see a continuum of colors from reds, oranges and yellows to a deep blue-black. Between any two colored points in the sky there seem to be other colored points. Furthermore, the changes in color across the sky appear to be continuous. Although the colors at the zenith and the horizon are obviously distinct, nowhere in the sky can one see any color borders, and every sufficiently small (...) region of the sky is made up of regions that all seem to be of the same color. (shrink)
We assemble here in this time and place to discuss the thesis that conscious attention can provide knowledge of reference of perceptual demonstratives. I shall focus my commentary on what this claim means, and on the main argument for it found in the first five chapters of Reference and Consciousness. The middle term of that argument is an account of what attention does: what its job or function is. There is much that is admirable in this account, and I am (...) confident that it will be the foundation, the launching-pad, for much future work on the subject. But in the end I will argue that Campbell's picture makes the mechanisms of attention too smart: smarter than they are, smarter than they could be. If we come to a more realistic appraisal of the skills and capacities of our subpersonal minions, the "knowledge of reference" which they yield will have to be taken down a notch or two. But first let us clarify what the argument is. (shrink)
The possibility that what looks red to me may look green to you has traditionally been known as "spectrum inversion." This possibility is thought to create difficulties for any attempt to define mental states in terms of behavioral dispositions or functional roles. If spectrum inversion is possible, then it seems that two perceptual states may have identical functional antecedents and effects yet differ in their qualitative content. In that case the qualitative character of the states could not be functionally defined.
Can psychology explain the qualitative content of experience? A persistent philosophical objection to that discipline is that it cannot. Qualitative states or " qualia " are argued to have characteristics which cannot be explained in terms of their relationships to other psychological states, stimuli, and behavior. Since psychology is confined to descriptions of such relationships, it seems that psychology cannot explain qualia.
"Consciousness" is a multiply ambiguous word, and if our goal is to explain perceptual consciousness we had better be clear about which of the many senses of the word we are endorsing when we sign on to the project. I describe some of the relatively standard distinctions made in the philosophical literature about different meanings of the word "conscious". Then I consider some of the arguments of David Chalmers and of Ned Block that states of "phenomenal consciousness" pose special and (...) intractable problems for the scientific understanding of perception. I argue that many of these problems are introduced by obscurities in the term itself, and propose a distinction between epistemic and non-epistemic senses of the term "phenomenal consciousness". That distinction helps explain why phenomenal consciousness seems so mysterious to so many people. States of "phenomenal consciousness" are not states of one, elemental kind; they are a ragtag lot, of differing levels of complexity, corralled under one heading by a regrettable ambiguity in our terminology. (shrink)
The papers by Macpherson, O'Callaghan, and Batty reveal some startling differences in the objects and properties represented by different modalities. They also reveal some tensions between different ways of understanding what it is for any one modality to represent objects and properties.
University of Connecticut Storrs, CT 06279-2054. Recent versions of objectivism can reply to the argument from metamers. The deeper rift between subjectivists and objectivists lies in the question of how to explain the structure of qualitative similarities among the colors. Subjectivism grounded in this fashion can answer the circularity objection raised by Dedrick. It endorses skepticism about the claim that there is some one property of objects that it is the function of color vision to detect. Color vision may enable (...) us to detect differences in spectral composition without granting us the capacity to detect identities. (shrink)
Asked on the Dick Cavett show about her former Stalinist comrade Lillian Hellman, Mary McCarthy replied, "Every word she says is a lie, including 'and' and 'the'." The language used to describe sensory and perceptual consciousness is worthy of about the same level of trust. One must adapt oneself to the fact that every ordinary word used to describe this domain is ambiguous; that different theoreticians use the same words in very different ways; and that every speaker naturally thinks that (...) his or her usage is, of course, the correct one. Notice that we have already partially vindicated Mary McCarthy: even the word "the" cannot always be trusted. (shrink)
One of the biggest challenges in understanding perception is to understand how the nervous system manages to integrate the multiple codes it uses to represent features in multiple sensory modalities. From different cortical areas, which might separately register the sight of something red and the touch of something smooth, one effortlessly generates the perception of one thing that is both red and smooth. This process has been variously called "feature integration", "binding", or "synthesis". Citing some current models and some historical (...) precursors, this paper makes some simple observations about the logic of feature integration. I suggest that "feature conjunction" is not strictly speaking conjunction at all, but rather joint predication; and that the critical task in "binding" is not simply grouping scattered representations together, or providing them a common label, but rather identifying those that have a common subject matter-those that are. (shrink)
Sensory classification is a central theme of Mohan Matthen's wonderful book, Seeing, Doing, and Knowing. ( All page references are to Matthen 2005 unless otherwise indicated.) My plan for this commentary is simple: I shall list a series of claims that Matthen makes about the classes involved in sensory classification. Each member of the series is admirable, and seems credible on its own. The question at the end is whether we can hold them all, together.
_tableau_ can be given a full and satisfying explanation, while others cannot. We can explain in a full and satisfying way why the water in the mug is identical with H2O, why its liquidity is identical with a state of its molecular bonds, and why its heat is identical with its molecules being in motion. But we cannot explain in the same way why the neural processes which Joe undergoes when he looks at the mug are such as to make (...) the mug look green, and not red. The latter explanations have gaps. (shrink)
Imagine, if you will, that the entire community of investigators interested in the problems of perception all lived together in the same town. Some continual shuffling of neighbors would be inevitable, and there might be occasional episodes of mass relocation and energetic bulldozing, but after a while the residents would probably settle down and find themselves living in districts defined roughly by disciplinary boundaries. The experimental psychologists would occupy the newer part of town, laced with superhighways, workshops and factories, machines (...) and measuring instruments, computers and overhead display units. But the town also has an Old City, marked by the complete absence of highways and factories, where the streets are lined with ancient hovels. There are, to be sure, some colossal palaces and museums in this part of town, breathtaking monuments to the grandeur of past centuries, but the current residents lack the inclination to construct such buildings, and many of the old palaces have been boarded up and condemned as unfit for human habitation. The somewhat scraggly and irascible inhabitants of this district have few viable economic enterprises, and no free markets, but rather organize themselves in units resembling nothing so much as medieval guilds. Congratulations. You have stumbled into the neighborhood where the philosophers live. (shrink)
What are the relations between preattentive feature-placing and states of perceptual awareness? For the purposes of this paper, states of "perceptual awareness" are confined to the simplest possible exemplars: states in which one is aware of some aspect of the appearance of something one perceives. Subjective contours are used as an example. Early visual processing seems to employ independent, high-bandwidth, preattentive feature "channels", followed by a selective process that directs selective attention. The mechanisms that yield subjective contours are found very (...) early in this processing. An experiment by Greg Davis and Jon Driver is described; it seems to show that multiple subjective figures can be coded in these preattentive, parallel stages of visual processing. I propose that some of these preattentive states might register the very same differences that, were one aware of them, would be phenomenal differences. Some arguments pro and con on this possibility are assessed. (shrink)
I address this talk to anyone who believes in the possibility of an informative empirical science about sensory qualities. Potentially this is a large audience. By "sensory quality" I mean those qualities manifest in various sensory experiences: color, taste, smell, touch, pain, and so on. We should include sensory modalities humans do not share, such as electro-reception in fish, echolocation in bats, or the skylight compass in birds. Those pursuing empirical science about this large domain might pursue it in the (...) halls of experimental psychology, psycho-physics, psychometrics, psycho-physiology, sensory physiology, neuroscience, neuro-biology, comparative psychology, neuro-anatomy, and so on and on. These days even molecular genetics has kicked in with some notable recent contributions to the sequencing of genes for photopigments and for olfactory receptors. But to all those investigators in all those halls I bring bad news. Your discipline is _a priori_ impossible. Philosophers whom you do not know have uncovered _a priori_ proofs that empirical investigation which proceeds along the lines currently underway, or which will proceed along lines that are currently _imaginable_, does not, will not, and cannot explain the sensory qualities of experience. Or at least so they say. You might as well give up now. (shrink)
Recent work in experimental psychology and neuroscience has revealed a rather surprising architecture for early (or preattentive) perceptual processes. This paper will describe some of the surprising features of that architecture, and how they bear on recent philosophical debates about the notion of phenomenal consciousness. I will argue that the common sense idea that states of phenomenal consciousness are states of a unitary kind cannot survive confrontation with the details of how our early perceptual processing works. In particular, that architecture (...) forces us to contemplate the prospect of phenomenal consciousness being sundered in two, with states that have phenomenal character making an appearance far before the arrival of anything one could call consciousness or awareness. (shrink)
A standard view in philosophy of mind is that qualia and phenomenal character require consciousness. This paper argues that various experimental and clinical phenomena can be better explained if we reject this assumption. States found in early visual processing can possess qualitative character even though they are not in any sense conscious mental states. This non-standard interpretation bears the burden of explaining what must be added to states that have qualitative character in order to yield states of sensory awareness or (...) sensory experience. I argue that the study of selective attention reveals resources that can be useful in that project. Two traditional objects are briefly considered. (shrink)
The psychofunctionalist claim that psychological terms can be defined through the use of an experimental theory has been criticized on the grounds that it is "chauvinistic": that it denies mentality to any creature of which the selected theory is false. I analyze the "argument from science fiction" that is thought to establish this conclusion, and show that its plausibility rests on a scope ambiguity in formulations of functional definitions. One formulation is indeed chauvinistic, but an alternative rendering is not, and (...) is perfectly consistent with ascribing mentality to creatures of which the selected psychological theory is false. This alternative interpretation of psychofunctionalism is set out in detail, defended from several objections, and finally tied to the semantics of ordinary language psychological terms. (shrink)
The perception of the lightness of surfaces has been shown to be affected by information about the spatial configuration of those surfaces and their illuminants. For example, two surfaces of equal luminance can appear to be of very different lightness if one of the two appears to lie in a shadow. How are we to understand the character of the processes that integrate such spatial configuration information so as to yield the eventual appearance of lightness? This paper makes some simple (...) observations about the vocabulary of appearance used in these contexts, and proposes that the end results can be called "phenomenal" in a traditional sense of that word. Processes whose products are phenomenal are next distinguished from processes characterized in other terms: (a) processes of perceptual grouping; (b) processes of perceptual organization; and (c) attentional (as opposed to preattentive) processes. These four categories are conceptually and empirically distinct. In particular, the paper reviews some evidence that appearances as of contours, occlusion, and amodally completed shapes can occur preattentively. Some implications for understanding gestalt grouping processes are briefly discussed. (shrink)
Three different ways to understand the representational content of the feature maps employed in early vision are compared. First is Stephen Kosslyn's claim, entered as part of the debate over mental imagery, that such areas support "depictive" representation, and that visual perception uses them as depictive representations. Reasons are given to doubt this view. Second, an improved version of what I call "feature-placing" is described and advanced. Third, feature-placing is contrasted with the notion that the representational content of those feature (...) maps could be conveyed in a list of sentences about visual objects. Some problems with this last alternative are described. (shrink)
Can psychology explain the qualitative content of experience? A persistent philosophical objection to that discipline is that it cannot. Qualitative states or 'qualia' are argued to have characteristics which cannot be explained in terms of their relationships to other psychological states, stimuli, and behavior. Since psychology is confined to descriptions of such relationships, it seems that psychology cannot explain qualia. A paradigm case of qualia is provided by simultaneous color contrast effects, in which a neutral grey patch is made to (...) look reddish by being enclosed in a green surround. If the qualia based objections are sound, psychology ought not to be able to explain simultaneous color contrast; but psychology at least seems to be able quite successfully to explain those effects. This paper analyzes the logic of psychological explanations of simultaneous color contrast effects, and the import of various qualia based objections to those explanations. I argue that the qualia objections do not demonstrate any explanatory inadequacy in existing psychological explanations of 'looks'. Psychology succeeds in explaining at least some qualia. In a more positive vein, I argue that once the structure of such explanations is sufficiently understood, a place can be found for qualia within the emerging scientific account of color perception. The resulting account can deal with many of the traditional perplexities over qualia. (shrink)
If, as Ned Block has argued, consciousness is a mongrel concept, then this collection resembles nothing so much as a visit to a dog pound, where one can hear all the varieties baying, at full volume. The experience is one of immersion in a voluminous excited cacophony, with much yipping and barking, some deep-throated growling, and other voices that can only be characterized as howling at the moon. What a time to be conscious! What a time to be conscious of (...) being conscious! (shrink)
I'm very happy here to be sandwiched between Lycan and Millikan, two of the living philosophers from whom I've probably learned the most, and to whom I am the most grateful. Plus the intermediary position is appropriate for someone commenting on intermediary representations in vision. There's much to like in Bill 's account of "layering" in visual representation. For one, it makes explicit and publicizes the notion that there are multiple layers of representation involved even in the seemingly simple achievement (...) of. (shrink)
Common sense says that visual agnosia is impossible. It ought not exist. If an object like a safety pin or a bar of white soap is in full view, you see it, and you know what a "safety pin" or a "bar of soap" is, then you cannot fail to recognize what you see. If you identify the safety pin as "something silver and shiny like a watch or a nail clipper," or you identify the bar of white soap as (...) "a piece of paper," then common sense would dictate that either you fail to see the object, or your knowledge is somehow deficient. But visual agnosics, who make such responses, clearly do--in some sense--"see" the objects in question. Often they can, for example, make accurate and recognizable drawings of what they see. Some lack measurable visual field defects; they have a full visual field. And they clearly know what a "safety pin" or a "bar of soap" is: if allowed to touch the object, or its use is pantomimed, correct identification is immediate. "I see it now," they may say. We get a failure specifically in visual recognition, even though sufficient sensory functions and cognitive functions are demonstrably intact. Such is the mystery of visual agnosia. (shrink)
As a reductionist and a subjectivist I find little to dispute, and much to cheer, in the use of the comparative argument against objectivism. The best available form of objectivism is anthropocentric realism, and at the very least the comparative argument dispels much of the..
When I was revising _Sensory Qualities_ there was a period of about a year when I set the manuscript aside and did other things. When I returned to it I found that certain portions of the argument had collapsed of their own weight, like an old New England barn, and could be carted off the premises without compunction. Other parts were wobbling on their foundation, while some had weathered well and seemed nice and solid. My revision strategy was simple: I (...) kept just the nice solid bits, thinking that I could go back and work on the wobbly portions later. (shrink)
Marr's computational theory of stereopsis is shown to imply that human vision employs a system of representation which has all the properties of a number system. Claims for an internal number system and for neural computation should be taken literally. I show how these ideas withstand various skeptical attacks, and analyze the requirements for describing neural operations as computations. Neural encoding of numerals is shown to be distinct from our ability to measure visual physiology. The constructs in Marr's theory are (...) neither propositional nor pictorial, and provide a counter example to many commonly held dichotomies concerning mental representation. (shrink)