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Books

The Conscious Brain by Jesse J. Prinz

Sam Clarke ponders The Conscious Brain.

Consciousness is hard to understand. It is difficult to see how any physical mechanism, no matter how complex it might be, could give rise to conscious experience. And yet the brain (which is, after all, just a bag of gooey mechanisms) somehow manages to achieve this. This emergence of consciousness should strike the contemporary cognitive scientist as completely incredible. Although it is within the realms of current understanding to explain, for example, how a machine could discriminate between red and green, explaining whether a machine could experience the quality of redness or greenness as we do is not at all clear to anyone. Indeed, many have claimed that the answer lies systematically beyond the remit of the physical sciences; it is a truly hard problem.

I must admit that I have a rather dogmatic aversion to this pessimism. I am committed to thinking that a complete scientific understanding of the brain will shed light on the questions of how and why consciousness arises. Consequently, titles such as The Conscious Brain by Jesse Prinz sound like music to my ears. By synthesising formidable amounts of research taken from neuroscience, psychology and philosophy, The Conscious Brain exemplifies the inroads that scientific enquiry is making to this most intractable of problem areas. If not always convincing in its details, I think Prinz’s scientifically-grounded approach to consciousness is right in spirit.

Of course, Prinz doesn’t claim to have all the answers. His primary concern, at present, is with identifying the neural and psychological correlates of human experience. With this in mind, Prinz devotes his book to proposing and defending his ‘AIR’ (‘Attended Intermediate-level Representation’) theory of consciousness. According to this theory, consciousness arises when intermediate-level perceptual representations (representations of the world at a certain stage in the brain’s processing) undergo changes that allow them to become available to working memory.

In arguing for AIR, Prinz begins by considering a challenge that the human visual system faces. It must somehow turn the disunified patterns of light hitting the retina into meaningful pieces of information capable of guiding intelligent action. Mainstream cognitive scientists suppose that this transformation of information comes about through a hierarchical, step-by-step procedure. If we accept this (as Prinz does) then we should hope to identify the levels in the hierarchy at which conscious visual experience arises: some, none, or all? Prinz argues that we are not conscious of the lowest levels in the hierarchy: we are simply not aware of the disunified features of visual stimuli as they are splattered onto the retina. Equally, he argues that we do not experience the highest levels in the perceptual process. When we look at a chair, we recognise it as having a three-dimensional form, but we do not see its entire three-dimensional form all at once. Otherwise, our visual experience of a chair would be invariant, regardless of the angle the chair was perceived from. Therefore, while higher-level processing may be required for recognizing and acting upon the same object as seen from many different points of view, Prinz contends that we cannot experience such processing. Prinz thereby claims that we are only conscious of representations at the intermediate-levels in the processing hierarchy – areas of brain processing where the disunified blobs and edges of the lower levels have been unified to produce coherent perspective-specific representations of objects’ boundaries and depth-relations.

The proposal that consciousness is limited to these intermediate levels is highly controversial. An old issue in the philosophy of perception considers whether a penny viewed at a slight angle shows up in visual experience as round or elliptical. On this point, Prinz’s intermediate-level hypothesis seems committed to holding that the experience of the penny is exhausted by the ellipticality of its appearance. However, some commentators propose that there is a sense in which the penny looks elliptical and a sense in which it looks round, with such roundness being a higher-level feature of the coin not represented at the intermediate-level. Prinz thinks these commentators are simply mistaking their knowledge of the penny’s form for their visual experience of it; but this is not convincing since it is plausible to think that an accurate two-dimensional drawing of a tilted coin can continue to look both elliptical in some sense, and round in some sense, even when the observer knows that it is neither; when they know that it’s a mere line drawing, say.

This is not to say that Prinz’s arguments are not impressive: Prinz takes his intermediate-level hypothesis and effectively shows how it is consistent with current state of the art neuroscience; he posits a role in action for conscious experience; he synthesises the functionalist and identity theories of mind; and he argues that AIR’s grounding in intermediate-level perception is sufficiently rich to capture conscious experience in its entirety. It is this uncanny ability to unify these separate debates that makes The Conscious Brain a standard-setting contribution to the literature. For anyone interested in consciousness, this book cannot be ignored, despite some problems in its details.

While Prinz proposes that intermediate-level representations are necessary for conscious experience, he stops short of saying that they’re sufficient for conscious experience. This brings us to the second half of Prinz’s AIR theory, which argues that intermediate-level representations become conscious if and only if they’re ‘attended’ to – where attention is defined as availability to working memory.

In many ways this appeal to ‘availability’ seems an odd move for Prinz to make. As Prinz reminds us several times, consciousness is no longer just a subject of metaphysical enquiry. There are now many empirical topics open to the interested philosopher of mind. Indeed, in many ways, The Conscious Brain is a celebration of just how far the science of consciousness has come in the last twenty years. However, by identifying experience with the representations available to attention rather than those which are actually attended to, Prinz seems to garner more harm than good for a science of mind, because it is hard to see what criteria a scientist could possibly use to verify this claim. Moreover, this position seems to allow that I could be conscious of a red blob even if I had absolutely no awareness of being so, and therefore no means of reporting an experience of it!

While I have focused on potential problems that I anticipate for Prinz’s AIR theory, those points did not detract from my enjoyment of the book. The Conscious Brain is highly readable throughout and offers a detailed and balanced overview of the relevant scientific literature. The arguments it presents are sophisticated, subtle and engaging, and interrelated in such a way that it gives us a glimmer of hope that one day we will discover a complete theory of consciousness. So while I might not agree with its main thesis, I do think that The Conscious Brain has a lot to add to the debate. Now go buy a copy and give your brain a treat!

Sam Clarke is an MPhil/PhD student in Philosophy at the University of Warwick.

• The Conscious Brain: How Attention Engenders Experience, by Jesse Prinz, Oxford University Press, 2012, 397pp, $26.95 (pb), ISBN 978-0195314595