A Distinction Between
By BRENT SILBY
Copyright (c) Brent Silby 1998
In his paper "On A Confusion about a Function of Consciousness", Ned Block claims that the concept of consciousness is best described as a mongrel concept.1
For Block, the word "consciousness" refers to many different concepts and phenomena that have been bundled together under the one concept. Block suggests that we run into problems when we analyse certain aspects of consciousness using premises that cannot be applied to other aspects of consciousness. In an effort to clear up the confusion associated with reasoning about consciousness, Block breaks consciousness down into several different concepts. In this paper I will be concerned only with what Block calls access consciousness and phenomenal consciousness. These two concepts appear to constitute his primary distinction and deserve attention. I will consider David Chalmers' contribution to the issue and will then outline an alternative view offered by Daniel Dennett.
Block's Primary Distinction
Ned Block draws a distinction between two different types of consciousness - phenomenal and access. This distinction arises from the thought that the phenomenal properties of consciousness are of a different character to the cognitive, intentional or functional properties of consciousness. For Block, the phenomenal properties of consciousness are experiential properties. These properties are categorized as being properties of phenomenal consciousness (P-conscious properties). P-conscious states include the experiential states we have when we see, hear and have pains.
On the other side of the coin, we have what Block refers to as access consciousness (A-consciousness). This non-phenomenal category of consciousness encapsulates the tasks involved in cognition, representation and the control of behavior. A state is A-conscious if it is poised to be used for the direct rational control of thought and action. The important point to note here is that for a state to be A-conscious, it is not enough for that state to be available for use. It must be poised and ready to go. Block suggests that we may have many representations of facts that are available for use if somehow re-activated, but their mere availability does not make them A-conscious. For example, we may have once learned that the Earth is 93 million miles away from the sun and this fact is available for use whenever needed. However, this information is not A-conscious because it is not yet poised for the control of behavior.2
Block believes that A-Consciousness and P-Consciousness usually occur together but in some cases they may not.
In order to help us acquire a full understanding of the difference between P-consciousness and A-consciousness, Block provides some examples of A-consciousness without P-consciousness and of P-consciousness without A-consciousness. These examples are intended to clear up any confusion we may have between these two distinct categories of consciousness.
'A' without 'P' and 'P' without 'A'
Blindsight is a well documented phenomenon that occurs in people who have suffered damage to certain areas of their visual cortex. These people have a blind region in their visual field, and though they are aware of their blind spot, they cannot see anything that is presented to them in that area of space. The important feature of blindsight is that although subjects are unaware of stimuli in their blind spots, they have an uncanny ability to `guess' as to the location, motion and direction of such stimuli. In these cases their appears to be some visual awareness without the phenomenal properties that normally occur with visual awareness. For Blokc, cases of blindsight point to instances of absent P-consciousness. Block cannot say, however, that these people have A-consciousness of the stimuli in their blind region, because the content of the blind region is not available for the rational control of action. Blindsight patients must be prompted by an experimenter before they will `take a guess'. It is unlikely that a hungry blindsight patient would spontaneously reach for a chocolate in his blind region. But, says Block, imagine a super-blindsighter who had acquired the ability to guess when to guess about the content of her blind field. Even though she doesn't see the objects in her blind field, she can spontaneously offer verbal reports about those objects. Information about her blind field just spring into her thoughts. A super-blindsighter would be A-conscious but not P-conscious. Whether there are any super-blindsighters is an empirical question that has not been answered yet, but this does not affect Block's point. It is enough for Block that they are conceptually possible. To emphasize this conceptual possibility, Block points to evidence that the human visual system is divided into two separate subsystems - the ventral and dorsal subsystems. In blindsight there seems to be damage to the ventral system, which Block claims is closely connected to P-Consciousness.3
The ventral system is responsible for object recognition and classification, while the dorsal system is involved in computing spatial features such as location and motion. Block believes that because the visual system is comprised of these two visual subsystems, it would also be conceptually possible to find cases of P-Consciousness without A-Consciousness. This might occur if someone incurred damage to their dorsal system, while their ventral system remained intact. Of course, if Block's distinction is accurate, we would probably not know if someone was P-Conscious of events in their visual field without being A-Conscious of those events because a lack of A-Consciousness implies that content is not poised for the control of behavior. This includes behavior such as making the statement: "I see a red object."
There are other possibilities of P-Consciousness without A-Consciousness because, obviously, the P-Conscious / A-Conscious distinction does not only apply to visual events. The distinction applies to all events involved in behavior and awareness. As an example of P-Consciousness without A-Consciousness, Block asks us to imagine a situation that involves the auditory system. Suppose that you are involved in a conversation with someone when suddenly you notice the existence of a constant noise that has been occurring throughout the entire conversation. Perhaps you suddenly notice the steady ticking of a clock. The sound has been there all along and you were aware of it all along but you were not consciously aware of it. According to Block, you were P-Conscious of the noise, but you were not A-Conscious of it. In other words, even though you were P-Conscious of the sound of the clock, that information was not poised for the direct rational control of action until you noticed it. It was at that point that the noise of the clock had an influence on your behavior and thoughts. I think that if, at this point in time, you thought back over the past few minutes, you might realize that you were aware of the ticking sound all along. The important point is that it took A-Conscious awareness of the sound to shift your attention to the sound of the clock and to enable you to even consider that it had been there all along.
Assessing Block's Distinction
On the surface, Block's distinction between access and phenomenal consciousness looks like a useful way of explaining the problem of consciousness. It allows us to seek cognitivist explanations for behavior without having to find a way of including the phenomenal properties of experience in those explanations. Perhaps once we have gained a complete understanding of how access consciousness works, we could turn our attention to phenomenal consciousness. I think, however, that in making the distinction between A-Consciousness and P-Consciousness, Block has left us with a more difficult problem. What purpose does P-Consciousness actually serve? In providing us with the conceptual possibility of A-Consciousness without P-Consciousness (the super-blindsight patient), Block has eliminated the need for P-Consciousness. The reason for this will become clear in a moment when I look at David Chalmers view of the distinction.
Chalmers believes that Block's distinction is a very useful tool.4
Chalmers claims that a clear conceptual distinction can be made between access and phenomenal consciousness when one considers the fact that we can imagine P-Consciousness without A-Consciousness and A-Consciousness without P-Consciousness, and the fact that A-Consciousness can be accounted for by cognitivist explanations while P-Consciousness is resistant to such explanations. Unlike Block, however, Chalmers believes that A-Consciousness and P-Consciousness always occur together. Chalmers also offers an alternative way of describing A-Consciousness by playing down the role of rationality. Block had defined content as being A-Conscious if it was poised for the direct rational control of action. For Chalmers, it is enough to say that content is A-Consciousness if it is directly available for use in directing behaviors. On Chalmers account, the case of the background sound of a ticking clock can be described in a slightly different way. We could say that the information was available all along but it was not accessed. If we accept this view, it would seem that there was P-Consciousness and A-Consciousness of the clock noise throughout the entire event. The phenomenal aspect of the noise was always present, and at the same time the information was available for the direction of behavior; it was just not accessed.
Chalmers points out that the problem with making the distinction between A-Consciousness and P-Consciousness (his modified distinction) is that we are left with the question as to why the two always seem occur together. It would seem that there is no role for P-Consciousness to play in the collective cognitive economy. If Chalmers is right, A-Consciousness is all that is required for the control of behavior in an organism. This leaves open the conceptual possibility of zombies and other functional isomorphs who are identical to us in all respects except that they lack P-Consciousness. Chalmers concludes that P-Consciousness has no role in cognitive functioning and that A-Consciousness does all the work. It is interesting to note that while Chalmers has pointed to this problem, it does not seem to bother him much. In fact, he seems to embrace it.
"I think it best to accept ... that phenomenal consciousness is distinct from any physical or functional property, and that it does not need to have a function to be central to our mental lives." 5
The problem with this statement is that it implies that the phenomenal aspects of our experience cannot be accounted for by physicalist explanations of the mind. Pursuing this line of thought would lead us to an epiphenomenalist position and would leave the question of phenomenal consciousness largely unanswered. Phenomenal consciousness would be described as having no causal function on our mental lives and would seem to be nothing more than a `bonus' feature of experience. Before we accept this view of phenomenal consciousness, I think we should explore other options.
In response to Block's paper, Dennett offers a different solution to the confusion about the role of consciousness. In his paper "The Path Not Taken", Dennett agrees that Block is right to locate the source of the confusion in the apparent difference between phenomenal and access consciousness. However, Dennett believes that Block runs into trouble when he attempts to defend his views.
Dennett proposes a different approach to the problem. He admits that his approach may be counterintuitive, but he believes that his account is a more direct option. For Dennett, the range of conscious events that Block categorizes as being P-Conscious and A-Conscious can more accurately be described under the general headings richness of content and degree of influence.6
Dennett suggests that while some episodes of mental life have impoverished contents, others are very rich and are full of content and information. Block would characterize the rich episodes of mental life as being instances of P-Consciousness and in cases where Dennett would suggest that content is impoverished, Block would claim that P-Consciousness is missing altogether. For example; in the case of blindsight, Block claims that the subject would have A-Consciousness of information in their blind region (though this information is limited), but have no P-Consciousness of objects in that region. This is because information present in the blind region seems to be poised for the direct control of action even though there is no accompanying phenomenal event. On Dennett's account, however, the blindsighter may simply have a very limited amount of content in the visual field. Because of this limited content, there is virtually no influence on the subjects behavior. When subjects are forced to make a guess about the location of a stimuli, they normally guess correctly. Presumably this is because the content exists but is very limited. The content of the blind region is not full enough to act as a cue and spontaneously give rise to behavior, but the content is rich enough to have a small influence on behavior if the subject is cued or prompted from an external source. I think that Block could reply to Dennett by pointing to the existence of two separate visual subsystems.7
As I described above, there is evidence to show that the dorsal subsystem is responsible for computing basic features of objects, while the ventral system is involved in higher level activities such as object recognition. Block believes that the ventral system is closely connected to P-Consciousness, while the dorsal system is related to A-Consciousness. In blindsight there has been damage to the ventral system. Thus there is A-Consciousness without P-Consciousness. This is a worthwhile observation, and the accumulating evidence of these two subsystems must be taken into account. However, the existence of two distinct visual subsystems does not necessarily refute Dennett's position. Dennett might argue that these two subsystems offer nothing more than evidence of modularity in a unified visual system. Damage to the ventral system merely reduces content and thus reduces the degree of influence on behavior. If the patient had instead only suffered damage to the dorsal system, other behavioral effects might occur. Content would be impoverished and so the degree of influence on behavior would also be reduced. Perhaps the patient may be able to describe the shape of an object but not be able to offer any report on the object's motion.
Although he does not discuss it specifically, I think that Dennett could also use his account to explain the case of P-Consciousness without A-Consciousness. Block described this possibility by using the example of a person who suddenly became aware of the fact that she had been hearing the sound of a clock ticking for some length of time. For Block, this person was P-Conscious of the clock but was not A-Conscious of the clock. This is because the sound of the clock ticking was not poised for the control of action (until she became aware of it), but it was present in P-Consciousness because she realized that the sound had been there all along. I think that Dennett could explain this event by claiming that the sound of the clock was present and that it could be characterized as being rich in content. It was not noticed until a specific time because the person was simply not attending to that content. Perhaps while engaging in serious conversation, the mental content given rise to from that conversation was stronger and was influencing her behavior, while the weaker influences (the clock sound) could not get a chance to influence her behavior until her attention shifted. In other words, the conversation had a stronger degree of influence on behavior than the ticking of the clock. The sound of the clock was not important enough. Moreover, Jennifer Church suggests that it is not entirely clear that the sound of the clock had no influence on behaviour. Perhaps while engaged in conversation the person was speaking louder than she would have if the noise was not present (perhaps it was a very loud clock).8
If this was the case then we would have to say that the sound of the clock was guiding behavior.
The main reason for avoiding the distinction that Block makes between access consciousness and phenomenal consciousness is that it only gives us the scope to explain how access consciousness works. This is because access consciousness can be isolated as being a cognitive, or computational type of system. Phenomenal consciousness, on the other hand, seems to be resistant to our explanatory techniques. If Chalmers is correct, then phenomenal consciousness may have no causal role to play in the cognitivist's story. I think that before we simply accept that conclusion, we must consider other possibilities. Dennett's alternate view seems to me to be a good candidate. As we have seen, we can explain blindsight and other phenomena in a direct way without appealing to different types of consciousness. If we can avoid making the distinction between access and phenomenal consciousness, we may be able to eventually come up with a complete account of consciousness that does not leave the apparent existence of phenomenal experience unexplained.
1 Block. N., "On a Confusion about a Function of Consciousness" in The Nature of Consciousness, Edited by Block. N., Flanagan. O., and Guzeldere. G., MIT Press, 1997, Page 376.