Thursday, 7 February 2008

Making up the Mind 8: Our Perception of the World is a Fantasy that Coincides with Reality


Chapter 5 of cognitive neuropsychologist Chris Frith's latest book Making up the Mind is concerned to answer the following two questions (p. 111):

  • How do our brains discover what is out there in the world?

  • How do our brains discover what is causing our sensations?

Questions such as these will undoubtedly suggest to philosophical critics of cognitive neuroscience - such as Peter Hacker, Hubert Dreyfus, Romme Harre, Brendan Wallace, Jeff Coulter, & Daniel N. Robinson - that even in asking such questions, and before any research gets done, Frith has been seduced by the epistemological tradition. According to that tradition we are to understand the relation between the person and their body as the person being 'inside' the body, on the passive receiving end of sensory deliverances, as an inner causal initiator of motor acts, as having an immediate access only to the putative acts and events and states and processes that occur in consciousness, and a merely mediated access to a world which - since the subject has become estranged from it, lodged in the interior of their own body - must now be thought of as 'external' - 'out there'.


Others - such as Daniel Dennett - may be more tolerant of Frith's flirtations with epistemological presentations, viewing these as a distraction from the important neuropsychological material which must not be overly philosophically interpreted by philosophical critics who can't even be bothered to get their hands dirty in the cognitive neuroscience. Who is right?


In these posts I've been suggesting that it is the philosophical critics who, on the whole, are to be trusted. Once the three (mereological, homuncular, and reifying) fallacies are expunged from Frith's text, the appearance of genuine and interesting questions to be asked and puzzles to be solved simply drops away. We have a collection of more or less interesting mischaracterised facts about visual illusions and neuropsychology, but little by way of a compelling theory to integrate the neurological and the psychological material. Chapter 5 is a perfect example to substantiate this claim: the entire chapter contains but a minimum of neuropsychological data, and much of the text is spent in elaborating epistemological and metaphysical claims (e.g. colours are not in objects but in our minds) on the basis of the interpretation of minimal data (our capacity to tell the colour of objects in different colour lighting) according to tacitly espoused, and highly optional, philosophical rubrics. Let me elaborate.


Pages 132ff consider various themes under the title 'My perception is not of the world, but of my brain's model of the world.' Our question is: Does the book show how this extraordinary conclusion is rooted in the empirical data, or is it basically presupposed in any interpretation of the data? Well, Frith starts by telling us that what we perceive are not 'the crude and ambiguous cues that impinge from the outside world onto my eyes and my ears and my fingers'. This is surely a good point: We do not perceive our 'surface irritations', as Quine called them. One might have thought that this is because what we actually see are objects in the world. But no, Frith tells us straight away: 'I perceive something much richer [than surface irritations] - a picture that combines all these crude signals with a wealth of past experience. My perception is a prediction of what ought to be out there in the world.' No argument is given for this extraordinary idea that what we actually perceive is 'a picture', nor for the further logically curious claim that my perception of this picture is 'a prediction'. But perhaps the data will come later?


What does come later is the consideration of several visual illusions and other curios (Ames room, Necker cube, Rubin vase, etc.). In the text these are just cited. Sometimes they are followed by statements such as 'The fact that our brains make this kind of [switching] response to ambiguous figures is further evidence that our brain is a Bayesian machine that discovers what is in the world by making predictions and searching for the causes of sensations.' Again, we are not shown how to understand this.


Ames RoomPerhaps however we can reconstruct. Let us imagine ab initio that our epistemic relation to the world is (indubitably) not only grounded in sensory stimulation, but that it is (contestably) actually mediated by such stimulation. That is, let us imagine ab initio that our brain itself has an epistemic job to do on our behalf. This to interpret the sensory inputs it receives, and then to create an accurate picture of the world for us - now a kind of retreating homunculus on the receiving end of neurological presentations - kindly makes predictions or constructs interpretations or puts together sensory data with mnemic data etc. - to provide a compelling end product for consciousness.


Now let's imagine that we have a case of visual illusion such as the Ames room. We find we can use our epistemic model to explain this as follows: The sensory inputs to the eye are the same in the following two cases:



  • The illusory case


  • That non-illusory case which it seems to us we see when presented by the illusor case


The reason these two cases look the same to us is therefore because the epistemic inputs are identical. And because of this, it must be apt to say that the brain has work cut out for it to do in the inference-making, prediction, and picture-generating departments.


Yet clearly this gets us nowhere. The simple truth is that the epistemic inputs are quite different. It is the sensory stimulations that are so similar. Yet it is only if we presuppose from the start that we stand in some kind of doxastic / epistemic relationship with the causal substructure of our perceptual acts that we feel the need to invoke the psychological machinery in question.


What Frith provides for us are some interesting cases of visual illusion and related cases. We have the barest bones of a neurophysiological theory of illusion developed in the text. What Frith wants the data to provide, however, is rather the basis for a comprehensive psychological theory of vision. Not only is this not provided, but outside of the epistemological paradigm which he presupposes rather than establishes, it is unclear what such a theory could possibly tell us. When I (genuinely and accurately) see a vase, what I see is simply that: the vase. Such is true 'by definition'. I don't actually see a picture of a vase. Nor do I - or my brain - make any predictions about the vase - although of course my perception of it may come along with all sorts of expectations that are manifest in my perceptuo-motor engagement with it.


A later section is called 'Color is in the brain, not in the world.' The same conflation of epistemic relations and causal grounding is immediately apparent:

We only know about the color of objects from the light that is reflected from them. The wave-length of the light is what makes the color. Long wave-lengths give red, short wave-lengths give blue... So does activity in these receptors tell us what color the tomato is? There is a problem here. The color isn't in the tomato. It's in the light reflected from it. When illuminated with white light, a tomato reflects red light. That is why we see it as red. But what if the tomato is illuminatetd with blue light? ... It can't reflect any red light, so does it now look blue? No. We still perceive it as red. From the colors of all the objects in the scene our brain decides that the scene is being illuminated by blue light and predicts what the "true" color of the various objects must be. ... Because we see the predicted and not the "real" color, we can create striking illusions in which patches which are identical in terms of the wave-length of the light seem to have quite different colors [see here].


In what sense is it true that we only know about the colour of objects from the light reflected from them? Epistemically, if you asked me how I know the colour of the tomato, I might say: 'By looking at it'. Or if pushed I might say: 'By looking at it in good light' (i.e. in normal daylight). Here no reference is apt to the wavelength of the light - I know nothing about this. But sub-personally - at the level of the physics and physiology of vision - it is simply not true to say that our colour vision is exhausted by a registering of different wavelengths. As Frith himself notes, previous exposure to these objects, the contexts in which they are seen, etc., all play a role here. The thesis that we - or our brains - need to somehow construct a picture of the world out of the chaos of sensory impingements seems to be a result of a simple conflation of the two (epistemic and subpersonal) levels of inquiry.


Frith's text may well be useful for someone who expected any simple mapping of the two levels onto one another. Cases of illusion remind us that at the subpersonal level, perceptual processes are not passive receptivity. But the idea that the personal level tags along at the end of the subpersonal - that the brain must reconstruct the visual world for the now alienated internalised subject to witnes - this is a function of Frith's own curious epistemology, and not at all of the epistemology of vision itself.