What can blindsight tell us about the nature of consciousness?

Unless you are a Zombie, you are probably familiar with the concept of Qualia, although perhaps not the word. Qualia is a abstract noun given to things like the ‘redness of red’, the smell of freshly baked bread, the feelings of sunshine on our back, etc. Qualia is plural for the different ‘quales’ that are generally considered to be the mark of consciousness. Such ‘phenomenal feels’ are distinct from the physical correlates. In the case of the colour red, the redness of red is distinct from light at a red wavelength, in the case of baked bread, the chemical composition of the odour given off is distinct from the smell and in the case of the sun on our backs, our skin being heated by radiation is distinct from the feeling of warmth. The distinction between such phenomenal feels and the machinery of our brain, and the physical correlates of what these ‘qualia’ pick out have long been the source of problems for any theory which attempts to understand consciousness in terms of the physical processes in the human brain.

The ability hypothesis is one answer to help in explaining how it is conceivable that such phenomenal feels or qualia could be reduced to a physical explanation of processes in the human brain. The ability hypothesis is the hypothesis that phenomenal feels are what give us the ability to distinguish the concepts of heat, red, and other natural classes. This would suggest then that concepts such as ‘heat’ are just more abstract and general versions of ‘the feelings of sunshine on the back’. The ability hypothesis is the hypothesis that all that conscious qualia are, is the ability to distinguish certain properties in nature. So the qualia “redness of red” is according to the ability hypothesis just the same as the ability to pick out red from say a brown or a green.

This hypothesis is quite influential. It is easy to see why. The ability hypothesis explains consciousness without the need to elicit a ‘soul’ or stuff that have plagued philosophers since Descartes in attempting to explain the mind-body problem. The ability hypothesis fits neatly with a contemporary naturalistic view of the world as completely constituted by physical stuff.

I contend that the phenomenon of blindsight rules out the ability hypothesis as a way of explaining phenomenal feels or qualia. Blindsight is a case that points against the possibility of explaining consciousness as mere ability, and suggests that if we are to look for a physical explanation of consciousness there is something more to it than explaining it as an ability.

In these notes, I will take you through some long standing arguments for consciousness being in principle unexplainable in physical terms, and then show how the ability hypothesis answers such arguments in order to get a better view of the requirements of a physical explanation of consciousness. I will then show how the ability hypothesis falls short as a possible conceptual starting point for a science of consciousness.

The Knowledge Argument and The Ability Hypothesis

The Knowledge Argument originally put by Frank Jackson in his 1982 paper “Epiphenomenal Qualia” is one of the longest lasting objections to Physicalism (as defined by Supervenience, see Stanford Encyclopedia of Philosophy for the definition). The Knowledge argument freed advocates of the thesis of non-physical subjective information from a lot of messy philosophical work having to define the class of physical properties in order to first register their objections. Jackson’s Knowledge Argument assumes any theory of class of physical objects as a premise to the situation in the Knowledge Argument he creates with Mary.

“Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal chords and expulsion of air from the lungs that results in the uttering of the sentence ‘The sky is blue’. (…) What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then is it inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false.

(Jackson, 1982)

In premise form:

P1: Mary has complete knowledge about the physical world.

P2: When seeing colour for the first time she learns a new fact about the world: “The Redness of Red”

Therefore, there are non-physical facts about the world. Physicalism is false.

We can either accept or reject the intuition that Mary gains new knowledge. People such as Dennett (Dennett, 1991) have argued given that so many of the results in the physical sciences have been counter intuitive, we should reject this intuition. I don’t find this convincing. Given a lack of explanation surrounding consciousness we have to work with what we have got. We should grant the intuition as an easily describable problem of consciousness. Rather than explaining away we should accept what we have and attempt to explain this intuition within current knowledge of physical nature. I see the knowledge argument as a benchmark to meet for acceptance of a physical theory of the mind and consciousness.

Looking at responses to the knowledge argument we see several types of replies in an attempt to motivate a physical theory of the mind. One range of replies denies that Mary gains any new knowledge on seeing red for the first time and postulates that if she knew all physical facts, she could come to know what red is like (Churchland, 1985) (Hardin, 1988). The problem with this reply is it maintains in principle that this is possible without giving any good examples of how we can come to, on the basis of physical knowledge alone, get new qualia.

Another response “The Acquaintance Hypothesis” also denies the intuition of mary recieving new knowledge by stating that Mary comes to know old facts in a new way (Tye, 1986) (Chuchland, 2004). This explanation fall short, because it seems to me in a perfectly intuitive and sensible use of the word “knowledge”, Mary does come to ‘know’ something new.

On the basis that we should accept the intuition of Mary gaining new knowledge, the only serious response in favor of a naturalistic physical explanation in the literature is the ability hypothesis outlined in (Nemirow 1990, Lewis 1983, Lewis 1988, Petit 2004).

For physicalists to refute the Knowledge Argument they must either a) provide some justification for why the sort of knowledge we gain from experience is exclusively propositional in relation to world or b) deny the intuition of new knowledge. It must claim that this is the only sort of information about the world is physical fact. If there is an element of information that is gained about a subjective, super-physical type, physicalism must necessarily be false. (Since no amount of physical information will lead us to give an account for these facts)

The Ability Hypothesis denies that Mary makes any new discovery of information about our world. Mary, before leaving the black and white room, knows all there is to know about the physical world. She has all the “facts”. Upon leaving the room, Mary changes in some way but she gains no additional information about the world. “The Ability Hypothesis says that knowing what an experience is like just is the possession of these abilities to remember, imagine, and recognise. It isn’t the possession of any information ordinary or peculiar. It isn’t knowing that certain properties arn’t actualized. It isn’t Knowing-That. It’s Knowing-How.” (Lewis 1988)

David Lewis contrasts the Ability Hypothesis with the hypothesis of Jackson (pre-1998), what Lewis calls “The Hypothesis of Phenomenal Information”. Under this latter hypothesis, seeing red for the first time as Mary does, constitutes a new fact about the world, one that inevitably has to come from the internal workings of mind, since no amount of physical explanation can get to “what it is like” for Mary to see red. The Hypothesis of Phenomenal Information postulates that there is a phenomenal type of information gained only through experience and separate to the physical world. Lewis concludes we cannot accept the ability hypothesis and the hypothesis of phenomenal information.

According another advocate of the Ability Hypothesis, (Nemirow, 1990) Jackson (pre-1998) makes 3 mistakes “to confound distinct types of knowledge by treating ability as propositional knowledge… to confuse grammar and logic by assuming that a grammatical singular term must function as a referring term… (and) to mischaracterise imagining, by equating the act of imaging the experience of a quality with the act of intellectually apprehending the quality itself.” I accept Nemirow’s Analysis of the ability hypothesis, it appeals only to good philosophical practice without having to invoke intuitions of the kind (Jackson, 1982) does in order to make the knowledge argument. Indeed, Jackson post-1998 agrees with the above analysis (Jackson, 2004). However, I will argue that the ability hypothesis leaves something out.

What is Ability Hypothesis is committed to? For the Ability Hypothesis to hold, it must prevent or block any future “Knowledge Arguments” analogous to the one drawn in (Jackson, 1982) about Mary the genius Neuroscientist. The Ability Hypothesis must be able to explain that there is no knowledge-like experience that escapes the terms of the Ability Hypothesis. This is only usual, for as the Ability Hypothesis to be complete and true we must be able to find phenomena for which it purports to explain falling within its conclusions and the axioms of the Hypothesis. In the following section I will demonstrate a case where it seems all the minimal conditions imposed by the Ability Hypothesis apply but we would be inclined to say that the account of the Ability Hypothesis has missed something out

The Objection From Blindsight: “Blindsighted Frank”

I will now turn to what I call the objection to the Ability Hypothesis from Blindsight. Blindsight is the clinically discovered phenomenon of patients reporting to be blind in all or some of their visual field, but still being able to respond to stimulus when being compelled to make a choice or decision about the stimulus in front of them. (Weiskrantz, 1990) Anecdotally, a particularly brilliant patient being asked what object was in their blind field could respond with large amounts of accuracy whether it was a pen, orange or any one of a large pool other everyday household objects. Statistically, the patients’ ability to “guess” what was in their blind field was significant enough to conclude that they were “seeing” the objects but without any of the phenomenal vision usually associated with sight in normal healthy patients. Yet all of this behaviour goes on without a conscious visual analogue of the scene occurring directly infront of them. A type of visual analogue is created of the scene in front of them, through extrastirate areas, rather than the striate cortex or “V1″ (the usual site of visual processing). The damage to V1 curiously leads to a lack of conscious visual recognition, but evidence suggests vision analogues are created in the areas around V1. But this is not a conscious visual analogue.

Recall the Ability Hypothesis. In the following example I will argue it is possible for a blindsight patient to have all of the aspects required to satisfy The Ability Hypothesis, yet something in the account of the ability hypothesis is missing. Blindsight is best thought of as the sort of visual analogue a complex pattern recognising computer, or fruitfly would create when responding to visual stimulus infront of them. In Blindsight patients, we have the curious result a vision analogue is created by a complicated network of neurons, and has its own logic, but fails to feed into the parts of the brain responsible for conscious recognition. Now for an example:

Imagine Frank a blindsight patient whose unconscious vision analogue is as behaviourally sound as a person with a fully functional V1. Perhaps Franks blindsight has been caused by precise neurosurgery to V1 that disconnects all conscious analogues of vision from V1. Frank can call whatever he is seeing in front of him by being forced to make intuitions about the scene. More than that, he can give quite complete descriptions of the scene before him, they don’t have to be Proustian, but perhaps, he could draw the scene like a child could from intuition about where the lines should go. It is quite clear to us that Frank has an ability to respond to his environment quite similar to any normal person. He can talk about what is infront of him, paint it, reflex to objects coming at him, can cross the road etc. All faculties of his brain can access the incoming visual information except the one that produces the “what it is like” aspect. It seems, his ability is astounding, and if it weren’t for Franks own verbal reporting no one but his Neurosurgeon would be able to tell he was blindsighted.

Franks case is both logically and physically conceivable. It seems Frank has the ability of a person with sight, yet lacks Qualia. If a case amazing as Franks’ were to occur, the only way for us to know apart from a brain scan, would be by them to report that they had no conscious experience. By isolating all possible modes of detecting this lack of ability, the information would have to come from one place. Frank, in other words, would have to invoke the thesis of Phenomenal Information in order to convince sceptical doctors to give him a brainscan to convince them that he had anything than fully normal ability. Therefore the Ability Hypothesis is incomplete.

By the argument above if we accept David Lewis argument about the mutual exclusiveness of the Phenomenal Information Hypothesis and the Ability Hypothesis, then the Ability Hypothesis is not just incomplete, but false.

“A Way To Miss The Point”

Let me air one obvious objection from the Ability Hypothesis. Frank is simply reporting the lack of this ability of conscious ability to process the representation information not a lack of phenomenal information! It is true that the mere fact they are reporting internally present information does not in itself refute blind sight, indeed there are cases which are only determined by the reporting of the patient that they literally “see nothing” (Weiskrantz, 1990). The conclusion of the ability hypothesis holds.

The problem arises however, that if the patient can lack conscious ability, what is the aspect of this ability they are lacking? It is not representation, since representation can be abstract as a pattern making machine. Let me quote (Lewis, 1983) on this point

“Imagine a smart data bank. It can be told things, it can store the information it is given, it can reason with it, it can answer questions on the basis of its stored information. Now imagine a pattern-recognizing device that works as follows. When exposed to a pattern it makes a sort of template, which it then applied to patterns presented to it in future. Now imagine one device with both faculties, rather like a clock radio. There is no reason to think that any such device must have a third faculty: a faculty of making templates for patterns it has never been exposed to, using its stored information about these patterns. If it has a full description about a pattern, but no template for it, it lacks an ability but it doesn’t lack information. (Rather, it lacks information in usable form.) When it is show the pattern it makes a template and gains abilities, but it gains no information. We might be rather like that.”

What does this mean for Frank? What is left out by the ability hypothesis is an explanation of why Conscious representation must necessarily be ability to recognize and process information. It is entirely possible that the sort of template creation and making in unconscious parts of the brain that enable blindsight, fits exactly the sort of ability outlined above by Lewis and satisfies what we could call Consciousness (A computer-like structure of neurons in the brain perhaps) as an external observer but fails to have conscious information. Whilst I believe the thesis of property dualism or “Phenomenal Information” must be false, David Lewis and other Ability Hypothesists do not offer an explanation that satisfies an account of lacking conscious ability, and allows future knowledge arguments to be waged analogous to the Mary one. It seems the only way out is to invoke the piece of information, the lack of “something that it is like” that enables Frank to report that they experience nothing.

The Identity Hypothesis

David Lewis’ Argument for ability hypothesis as only alternative to hypothesis of “Phenomenal Information” is not convincing and doesn’t rid it of an objection that Phenomenal Information could determine ability. We are left with two options if we are to grant the intuition of Mary gaining new knowledge and accept the Ability Hypothesis as an explanation of it. We must either accept what Lewis calls the Hypothesis of Phenomenal Information in addition to the minimal requirements of the Ability Hypothesis, or else accept a thesis that experience and “what it is like” is nothing but subjective physical facts. My response favours the latter.

We know that Frank has blindsight because we are told by him “what it is like” for him to see, despite his abilities. It is only through this information that Neuroscientists could form a theory of the neural co-relates of this experience if a case as amazing as Franks were to ever exist. An explanation along the lines of “Neuron X fires to Neuron B” would become a physical theory of this experience, that explains the phenomenon without invoking “spooky qualia” in the same way the observation that the Sun rises every morning is explained by a primitive scientific picture of the solar system, rather than having to invoke a “Sun God”. Phenomenal Facts are Physical Facts about Frank, not the world. For those phenomenal experiences that do relate to the world can be explained by the Ability Hypothesis.

What then does this mean for Mary?

The Ability Hypothesis response holds, but only if we grant that there are physical subjective facts by the Identity Hypothesis. As (Van Gulick, 2004) suggests, concluding that there are physical subjective facts denies the first premise of the knowledge argument, “Mary knows all there is to know about the physical world” (Jackson,. 1982). What the knowledge argument excludes is that within physicalism there might be physical reasons a mind cannot comprehend itself, and thus Mary didn’t know all there is to know about the physical world. This seems only possible if we are to grant physicalism as true.


Chalmers, D. (1996), The Conscious Mind, New York: Oxford University Press. (see pp 144-146 for discussion of the ability hypothesis)

Chuchland, P. M. (2004). Knowing Qualia: A Reply to Jackson (with Postscript: 1997). In N. S. Ludlow, There’s Something About Mary (pp. 163-178). Cambridge, MA: MIT Press.

Churchland, P. (1985). Reduction, Qualia, and the direct introspection of brain states. Journal of Philosophy 82 , 2-28.

Cowey, A. a. (1995). Blindsight in monkeys. Nature 373 , 247 – 249.

Dennett, D. (1991). Consciousness Explained. Boston: Little Brown and Company.

Hardin, C. (1988). Color for Philosophers. Indianpolis: Hackett.

Hofstadter, D. R. (1979). Godel, Escher, Bach: An Eternal Golden Braid. Penguin Group.

Jackson, F. (1982), “Epiphenomenal Qualia” Philosophical Quarterly 32, Rpt. in Ludlow, P., Nagasawa, Y., Stoljar, D., ed., (2004) There’s Something About Mary, MIT University Press.

Jackson, F. (2004) & (1998), “Postscript on Qualia” Mind, Method, and Conditionals (London: Routledge) Rpt. in Ludlow, P., Nagasawa, Y., Stoljar, D., ed., (2004) There’s Something About Mary, MIT University Press.

Lewis, D. (1983). “Postscript to Mad Pain and Martian Pain”. In Philosophical Papers Vol.1 (pp. 131-132). New York: Oxford University Press.

Lewis, D. (1988), “What Experience Teaches” In Proceedings of the Russellian Society. Sydney: University of Sydney. Rpt. in Ludlow, P., Nagasawa, Y., Stoljar, D., ed., (2004) There’s Something About Mary, MIT University Press.

Nemirow, L. (1990), “Physicalism and the Cognitive Role of Aquaintance” in Mind and Cognition, Lycan, W., ed., Oxford:Blackwell

Petit, P. (2004). “Motion Blindness and the Knowledge Argument”. In N. S. Ludlow, There’s Something About Mary (pp. 106-142). Cambridge, MA: MIT Press.

Ramachandran (2003) – Ramachandran, V.S. and Edward M. Hubbard. “More Common Questions about Synesthesia”. Scientific American online. (http://www.scientificamerican.com) April 14, 2003. URL accessed 26-04-2008

Tye, M. (1986). “The Subjective Qualities of Experience.” Mind 95 , 1-17.

Van Gulick, R., (2004), “So Many Ways of Saying No to Mary” in Ludlow, P.,

Tye, M., (2000), “Knowing What It Is Like: The Ability Hypothesis and the Knowledge Argument,” in Consciousness, Color and Content. Cambridge, Mass.: The MIT Press. Rpt. in Ludlow, P., Nagasawa, Y., Stoljar, D., ed., (2004) There’s Something About Mary, MIT University Press.

Nagasawa, Y., Stoljar, D., ed.,There’s Something About Mary, MIT University Press.

Weiskrantz, L. (1990). Blindsight: A Case Study and Its Implications. USA: Oxford University Press.

Bibliography (Stuff I am aware exists but I can’t get access to).

(Articles in this area I am aware talk about the issues discussed in this essay, but for some reason or another cannot access to, if you have a copy, please send me one 🙂

Blindsight and The Ability Hypothesis

Bigelow, J. and Pargetter, R. (1990), “Acquaintance with Qualia”, Theoria 61

Seager, W. (1991), Metaphysics of Consciousness. New York: Routledge.

A Defence of the Ability Hypothesis to the Blind Sight Objection

Raymont, P. (1999), “The Know-How Response to Jackson’s Knowledge Argument”, Journal of Philosophical Research 24

The entries on blindsight above were pointed out to me by Torin Alter’s Bibliography on the Knowledge Argument at http://host.uniroma3.it/progetti/kant/field/kabiblio.htm accessed 27/4/2008