Consciousness Explained Daniel Dennett Penguin ISBN 0-14-012867-0
This has been possibly the most influential book on consciousness since discussion of the subject revived about 20 years ago. Apart from the fact that Dennett is undoubtedly a better writer than many of his peers, the main reason for his success appears to be that he offers an explanation for consciousness that does not require any adjustment of an essentially 19th century scientific paradigm. Critics of this paradigm have nicknamed Dennett’s book ‘Consciousness Explained Away’.
The Multiple Drafts Model
The Multiple Drafts model (MDM) is the core of the Dennett thesis about consciousness. The model assumes parallel processing and continuous editorial revision of data in the brain. For instance, the five-a-second saccades of the eyes are edited out in our conscious perception of the scene. The editorial processes extend over large fractions of a second, during which amendments can be made.
The MDM argument claims that there is only one discrimination in the brain, and the initial discrimination is not passed on to some notional discriminator or Cartesian theatre. Dennett thinks that the discriminations are precisely located in time and space, but they do not coincide with the onset of consciousness of their content.
Most modern students of consciousness would probably agree that the Cartesian theatre is a delusion. However, Dennett builds on this to suggest that anyone who thinks that consciousness emerges at a particular time must believe it emerges spatially within the Cartesian theatre. He never discusses the possibility of emergence spread out across the whole or across large areas of the brain. The reader is however pressured into thinking that this must be the case.
At one stage, Dennett discusses the Kolers version of the Phi experiment. This is seen as central to Dennett’s theory of consciousness. In the first phase of the experiment, it is shown that if two small spots are lit in quick succession, only a single spot will be seen to move back and forth. The next stage was to ask what would happen if the two spots were of different colours, say red and green. It was found, when this was tested that the red spot started to move, and then turned green in mid-journey.
In attempting to explain this result, Dennett produces an analogy based on his MDM. He points out that in modern academia articles are often circulated to the more important members of their audience in various slightly different drafts. Later on, the article will be officially published in some learned journal, but by then most of the key members of the intended audience will have read it in one or other of the earlier draft versions. So the official recorded date of publication is some while after it was read by most of the intended audience. Dennett contends that there wasn’t a date of publication but that publication is spread out over the various drafts. He sees this as analogous to consciousness, with consciousness of an event is spread out over the multiple versions of the event existing in the mind.
But is this really true? Even at the level of the publication of an article the analogy does not really hold. We happen to live in a culture where publication of a book or an article by a mainstream publishing house or a learned journal is important in terms of career, status and self-esteem. But this is a cultural feature and as such ephemeral. Through much of human history this would have been a meaningless or incomprehensible process. It is perhaps necessary to go back to the original meaning of publishing i.e. to make public, which ultimately means to transfer the article from the private domain of the writers mind to the public domain of another mind or minds. Even this is a big step in gauging the quality and appropriateness of a work. So in the strict sense of the word publication is the first time the work is shown to another mind. The same could probably be said of consciousness, the final ‘official’ version of event which might be consigned to long term memory may be preceded by other versions, but in the publishing analogy, consciousness would happen with the very first version.
Dennett v. the Evidence
The whole direction of Dennett’s thesis is to some extent at variance with brain scanning studies in the 1990’s. These indicated that specific areas of the brain such as the dorsolateral prefrontal were particularly active during conscious choice (Passingham 1993 & 1997), (1&2) (Goldman-Rakic 1992), (3) while the same area is less active during routine tasks (Ingvar & Philipson 1977) (4). Studies in the nineties also suggest that the dorsolateral may be involved in active suppression or inhibition of impulses coming from the parietal and other areas of the brain. (Goldman-Rakic, 1997) (5), (Fuster, 1989 & 1995) (6&7), (Frith, 1991 & 1992), (8&9) (Posner & Raichle, 1994) (10) (Feinberg et al, 1992) (11). These studies could be said to go against the spirit of the Dennett thesis in highlighting areas of the brain involved with conscious choice or suppression of unwanted unconscious impulses, while other area produce such impulses or carry out habitual tasks without much conscious involvement.
Chapter Eight of Dennett’s book launches into a lengthy and inconclusive debate about the production of spoken words and sentences. However the purpose of this is not to discuss linguistics as such, but to look at the origins of all intentional actions, of which speech is only an example. This isn’t really a discussion on a level playing field, because Dennett, burdened by his anti-Cartesian luggage, can’t allow for any conscious direction of actions. He makes a reasonable case for the idea that elements of trivial or spontaneous speech or actions might be self organised by widespread groups of neurons. He does, however, admit that sometimes we are conscious of a complicated process of reasoning leading to a decision. However, he decides that this process is so rare that he will apparently leave it out of account. Many might disagree as to reasoning being as rare as he makes out, but this is not the main point. It is apparent that for human culture these periods of more complex reasoning are disproportionately important, and are also brain activity most definitely involving consciousness. This makes it difficult to take seriously a theory of consciousness that leaves these key processes out of account, as being inconvenient irrelevances.
In many ways the weakest part of the book is the section that looks to be meant to be the culmination of Dennett’s thesis. This is the section at the end of Part 2. This follows a lengthy piece on various theories concerning the functioning of the brain. The processes of the brain are variously described by Dennett as virtual or Joycean machines, the former being an analogy to the virtual worlds found in computer systems. This discussion contains barely any direct reference to consciousness. At the end of this, Dennett himself entitles the final section of Part 2, ‘But is this a theory of consciousness?’ Dennett does not in fact answer this question. He simply declares the brain systems as he has described them to be conscious by fiat, saying:
“Anyone or anything that has such a virtual machine as its control system is conscious in the fullest sense, and is conscious because it such a virtual machine.”
He does not advance any reasoning for why these systems could not function very well without consciousness, but resorts to intimidating and ridiculing the dissenting reader rather than any process of argument, comparing objections to ‘A Tibetan prayerwheel’ simply because they have been repeated so often, and saying:
“Oh can you? (imagine a non-conscious version of this machine)”
Well, a moment thought, if the reader isn’t too intimidated, would produce the answer, yes I can. Most people in the modern world are familiar with apparently non-conscious machines that perform impressive feats that would have required human mental activity until the middle of the last century.
Having ridiculed the reader Dennett then takes refuge in the classical materialist fall back position of ‘oh, it’s so complex, there’s bound to be something in there that proves the materialist theory, saying
‘how do you know you imagined ‘all that’ in sufficient detail, and with sufficient attention to all the implications.’
This appears to be sleight of hand. The preceding section was all discussed in terms of our existing knowledge of neuroscience and computers. The implication of the passage was that this was exposition of everything that was known and relevant, and that the Dennett theory of consciousness was based on that. But the quote here suggests that he is holding back on some level of detail and knowledge not known to the reader. Of course, we don’t actually know everything about the brain, but there is no guarantee that what we don’t know will turn out to support the Multiple Drafts Model, and no guarantee that it will not support an alternative theory of consciousness.
Dennett uses the same sleight of hand elsewhere in his discussion of zombies. In order to focus on consciousness, philosophers sometimes look at what it would be like if there existed zombies that were in every way identical to humans, except that they were not conscious. In respect of this Dennett is logically correct in stating that if a zombie were exactly the same as a human it would have to be conscious, because it would contain the physical basis of consciousness. However, this is really a way of deflecting people from the main point of the argument, which is that everything done by the brain as described by contemporary neuroscience could be done by a zombie. The card trick is to make us forget the difference between what we now know about the brain, and what we might know about it in the future.
Towards the back of his book Dennett tucks away his commentary on the phenomena of blindsight. This subject looks at first glance like a peripheral curiosity, but in fact it is potentially fatal to the entire Dennett argument that consciousness is nothing different from the brain as described in neuroscience text books.
Blindsight occurs in patients who have a scotoma, a blind area in a part of the field of vision. These patients have no conscious awareness of sight in this area. However, tests show that they do have a degree of unconscious perception of objects and movement in this area. It is surmised that there are separate conscious and unconscious routes to the visual cortex. What it demonstrates, however, is that conscious and unconscious processes are essentially different, something which Dennett’s Multiple Drafts theory denies.