Crick & Koch (1990) argued in favour of the possibility that at any moment some active neural processes in the brain correlate with consciousness (Crick & Koch, 1998). They stated that all the different features of consciousness (e.g. visual awareness, pain) engage one or more fundamental common mechanisms (Crick & Koch, 1998). They selected visual awareness as the aspect of consciousness which would give and explanation to the problem of consciousness at the neural level. They searched for the features which might be typical of the activity of neurons in the cerebral cortex involved with vision when we are conscious of observing something (Young & Block, 1996). They argued that some philosophers (e.g. Chalmers, 1995) have created a creature called a “zombie” who is identical to normal people, but does not have consciousness, but this does not need to be a “fictional” idea, because there is suggestive evidence that a part of the brain does act like a zombie. (Crick & Koch, 1998). There are cases when a person produces a relevant motor output by using the present visual input, although unable to state what was seen. For example, in tennis a ball that is served at a speed of over one hundred miles per hour can be returned (by the opponent) with impressive accuracy, even though there is no sufficient time for a visual signal to “enter consciousness”, experience it and produce a conscious response (Blackmore, 2003). Possibly, the conscious visual representation is allocated in more than one area of the cerebral cortex and perhaps over certain sub-cortical structures, but not in cortical area V1 (Crick & Koch, 1998). This is to say that the neural activity in the visual area V1 is not directly correlated with what is visually perceived (Crick & Koch, 1998).
Initially, (Crick & Koch, 1990) suggested that “consciousness depends crucially on some form of rather short-term memory and also on some form of serial attentional mechanism” (in Blackmore, 2003, p 246). If we do not pay attention to some segment of the visual scene, our memory of it would last for a very short time or could be “covered” (masked) by the next visual stimulus (Blackmore, 2003). The argument goes further by stating that “the thalamus controls attention by selecting the features to be bound together by synchronization of firing” (Crick & Koch, 1990 in Blackmore, 2003, p 246).
What is happening in the visual system when I toss a coin? I watch it to fly in the air and land in my hand. I see it as a whole picture; a coin does not seem as falling apart into pieces, the shape of the coin stays the same and the colour of the coin does not leave the coin (Blackmore, 2003). Information taken out from a changing image takes different routes in the brain in order to be processed. Also, different processes differ in the length of time taken for the dropping coin to be consciously perceived as a whole picture (Blackmore, 2003). Hence, the problem of consciousness is linked to dynamic biding that occurs in actual time. What keeps all attributes of the flipped coin together is directly linked with memory and attention. If I try to remember if a locked my front door this morning when I left my house, in order to do it successfully, I have to imagine lots of features together: the colour of my front door, the key in my hand, the postman that was passing by at the moment when I was locking the door. Thus, the result of my remembering is the various attributes that are bound together (Blackmore, 2003). According to Treisman (2003) biding is fundamental to conscious experience (Blackmore, 2003).
The cat’s visual cortex study in the 1980s has showed neural firing oscillations in the range of 35 to 75 Hertz (times per seconds) in which a synchronized firing of a large number of neurons occurs (Blackmore, 2003). Crick & Koch, (1990) proposed that the biding occurs when “the neurons in different parts or cortex responding to the currently perceived object fire action potentials at about the same time” (in Young & Block, 1996, p 152). Thus, the brain by some mean co-ordinates activity between and within different regions responsible for visual perception in order to attain a joined percept (Young & Block, 1996). As Crick & Koch, (1990) put it: while “paying attention to friend discussing some points with you, neurons in area MT (respond to the motion of his face), neurons in area V4 (respond to its hue), neurons in auditory cortex (respond to the words he is saying) and perhaps memory traces involved in face recognition”, all bind together in order to “produce” the perception of your friend’s face. (in Young & Block, 1996, p 152). Biding is caused by neural firings in the cerebral cortex which come to be synchronized at 40 to 75 Hertz. ( Crick and Koch, 1990 in Young & Block, 1996). Young and Block (1996) make an objection that the account is only partial, because”binding through synchronized activity is already being incorporated into some computer simulations”, but this is not a proof that computers are conscious (p 153).
Because the most what goes on in the nervous system is unconscious, they reasoned that must be a special place in the brain where conscious experience takes place (Crick & Koch, 1990 in Blackmore, 2003).
The assumption that consciousness requires a unitary explanation and that there is a single phenomenon indicated by “consciousness” is considered unwise (Allport, 1988 in Young & Block, 1996). According to Young & Block, 1996, there are different aspects which are involved in consciousness and they require different answers. Therefore, one should not reach for the answer to the problem of consciousness, but as an alternative to look at which aspect of consciousness is meant to cover each assumed solution (Young & Block, 1996). They explain different categories of consciousness as follows: Phenomenal consciousness (P) is the conscious experience of “what it is like” (Nagel, 1974) to see, hear or smell something (Block, 1995). Therefore, P-consciousness has experiental properties and experiental states (Block, 1995). When I smell a fresh coffee in the morning I have some information about that smell, but my experience of that smell refers to experiental state. To smell freshly prepared mint tea or a fresh coffee gives not just different information about the two olfactory experiences, but there is difference that depends upon the qualitative nature of the conscious experience (Block, 1995). My experience of a smell of fresh coffee is my private conscious experience and has its own quality. Philosophers refer to this private experience as qualia (Blackmore, 2003).
As previously mentioned, Crick & Koch, (1990) offered neurophysiological theory of P-consciousness referring to it as a “product” of a synchronized 35 to 75 Hertz neural oscillation in the sensory area of the cortex (Block, 1995). But the theory does not give the answer why these occurrences are the neural basis of P-consciousness. Also, the oscillation hypothesis does not explain what it is like to smell a fresh coffee.
Access consciousness (A) is informational concept; “a representation is access-conscious if it is actively collected for direct control of reasoning, reporting and action” (Block, 1998, p 2). He argues that the way to distinguish these two concepts is to look at the possibility of one lacking the other. Block (1998) gives an illustration of access without P-consciousness as follows: Anton’s Syndrome blind patient does not understand that he is not really blind. He experiences himself as blind, so when asked if a room is lighted or dark he relies on guessing. The small part of V1 area is undamaged, therefore he can read single words and identify faces and facial expressions which are presented to the upper right part of his visual field. He denies a visual perception of the stimuli and says that it “just clicks”, so that it is how he reads a word or recognises the face. He does not have P-consciousness, but has A-consciousness; therefore A without P is possible.
Another illustration defines P-consciousness without access (Block, 1998). For example, consider the wall clock in my room (which ticks very loud) that has been ticking all along. I might have had the felling that the click have been ticking, but I did not notice it until it actually stopped, thus before the clock stop I had the experience of the ticking noise (P-consciousness), but because I did not pay attention towards it I did not have A-consciousness of it.
Furthermore, Block (1998) points at Crick & Koch’s (1990) argument that because V1 does not project to frontal cortex, V1 is not part of neural correlate of consciousness. Visual consciousness is used to control and make use of information “for directly guiding reasoning and decision making” (Block, 1998, p 2). What is required for this to occur is a direct projection to frontal cortex (Block, 1998). He points at the weakness of this argument if they referred to P-consciousness, but if they referred to A-consciousness the argument is insignificant. Even if V1 does not project directly to frontal cortex there is no reason to reject the supposition that there might be some other mechanism of control of reasoning and decision making which would allow projection in indirect manner. If Crick & Koch refer to P-consciousness, their argument is unsound.
Furthermore, Block (1998) argues that if they referred to A-consciousness their statement “that the neural machinery of A-consciousness is used to control and make use of visual information for direct control” is trivially true, because A-consciousness is direct control (Block, 1998, p 4). If a have A-consciousness, the perceived information is available for me to think about, to control it or to act on it. The argument goes further by stating: “if V1 does not project directly to the frontal cortex (areas that control action), then V1 is not part of the neural correlate of A-consciousness” (Block, 1998, p 4). This seems quite obvious, if there is no an access-conscious representation, or better if there is no “happening” of A-consciousness in that area, then that area cannot be the part if the neural correlate of A-consciousness. This is as to say, if I receive anaesthetic I would be anesthetized.
Block (1998) is not claiming that the statement that there is no direct connection in V1 areas to frontal areas is trivial, just comments on triviality of their argument’s set up. He presented a danger of treating consciousness as unified phenomena. He points out that when talking about consciousness, one has to bear in mind that there are two different concepts of the phenomena and the claim that it is not can be misleading.
One of the most exciting attempts to explore consciousness is the one of the changing perception independently of the stimulus, i.e. binocular rivalry (Block, forthcoming). Logothesis (1998) trained macaque monkeys to report which of two pictures they are presented with are seeing, buy pressing a lever. They were shown horizontal grinding to one eye and vertical grinding to another eye. When stimuli is presented in this way, one does not see it as a “mixture” of grindings, but the perception shifts from one picture to another (the same for humans as for the monkeys). Although the sensory input stayed the same, monkeys switched continuously from one lever to another. The neural firings in the monkeys’ visual system were documented. The findings indicate that 80% of the neurons in the lower visual areas did not change when the percept changed, while down the occipital-temporal pathway (“the ventral stream”) 90% changed when the percept changed (Block, forthcoming). Logothesis (1998) was looking for the areas where the neural activity corresponds to the shifting perceptions reported by the monkeys’ pressing of a lever. It seems that the neural basis of visual consciousness is identified in the ventral stream (Block, forthcoming). But, “paradoxically, what has also become commonplace is activation of the very same ventral stream pathways without ‘awareness’” (e.g. neglect patients) (Block, forthcoming, p6).
The phenomenal consciousness is considered to be a problem and it seems that neural correlates of consciousness did not solve this problem. It gave us an informational picture of what is going on in the brain when we visually perceive something but the mystery of qualia still needs the answer. “Consciousness is indeed a deep mystery…The reason for this mystery, I maintain, is that our intelligence is wrongly designed for understanding consciousness” (McGinn, 1999 in Blackmore, 2003, p33). Obviously, the solution is not to dismiss a possibility of ever finding the answer, our intelligence is designed to solve or better said to put together the pieces of the puzzle to read how the brain works. Once again, the question is when and what route we should take to achieve that quest.
References:
Block, N. (1995) Concepts of consciousness. In Block, N., Flanagan, O. & Guzeldere, G. (1997). The nature of Consciousness: Philosophical Debates. Cambridge, Mass: MIT Press.
Block, N. (1998). How Not To Find the Neural Correlate of Consciousness. .
Block, N. (forthcoming). Consciousness, Philosophical issues about. To appear in The Encyclopaedia of Cognitive Science.
Crick, F. & Koch, C. (1998). Consciousness and Neuroscience. In Bechtel et al. (2001) Philosophy and the Neurosciences: A Reader. Oxford: Blackwell.
Crick, F. & Koch, C. (2003). A framework for consciousness. Nature Neuroscience, 6, p119-126.
Kalat, J.W. (2001). Biological Psychology. London: Wadsworth Thomson Learning.
Young, A. & Block, N. (1996). Consciousness. In Bruce, V. (Ed.) Unsolved Mysteries of the Mind: Tutorial Essays in Cognition. Hove, East Sussex: Erlbaum: (UK) Taylor & Francis.
