Applying Bayes’ concepts to the understanding of consciousness – Some errors

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Leandro Castelluccio

Image – Thomas Bayes. n.d. In Wikipedia. Retrieved October 26, 2017.

Lately there seems to be a boom in the application of mathematical-statistical concepts of Bayes in different disciplines, including Neuroscience. And in this field there are increasingly applications of these concepts to explain things like consciousness. Consider the following articles as an example: Link 1, Link 2, Link 3.

There are many cases of visual optical illusions that could give us the idea that the conscious aspect of our experience is a process of brain inference from what is outside of it, in the environment, and not an exact reflection of reality. Take, for example, the illusion of the rotating mask: link.

This is a classic illusion that has been studied in neurosciences and refers to the processing of the human face. The theme here has nothing to do with the sense of turning but with the inability to perceive hollow faces. The effect of the hollow face (the brain seems to be conditioned to see normal faces), is very interesting, because it is an illusion, among others, that could be considered as an argument of consciousness as a product of Bayesian type: what we consciously perceive are not perceptions to put it one way, what the person sees, but brain predictions of what one should be seeing. In the illusion, when the face is turned and exposed the hollow part, at that moment, the brain does not seem to process the hollow face and reverses the image of it to see it in a normal way. We could argue, as I indicated, that the brain is conditioned to see normal faces, and so with many other things.

But the interesting aspect about these illusions is that they have a visual component, and this has been overlooked in relation to consciousness as a product of inference. And I want to focus on this. That is, the error of applying baynes to the understanding of consciousness as something predictive, taking into account that if such visual illusions speak of a predictive character of the brain, is to ignore other types of perceptions: why are there no such diversified illusions in sensory modalities as touch or sense of smell? Is it not possible that there is a misinterpretation of these illusions as to what they imply?

Consider the example of when we travel on a bus or train next to another one, and while being stopped the other begins to move but it seems to be oneself that does, the crucial question here is: is the brain conditioned or predisposed to see oneself moving instead of other things? The truth is that sometimes it is one possibility and sometimes the other. The answer is no, the brain does not expect oneself to be the one that moves, in fact it contemplates both possibilities, and yet that illusion exists and the brain does not expect that it is oneself that moves, there is not that “a priori”. In that way, the illusion would imply some perceptual issues that go beyond a predictive functioning of the brain. And again, if it were Bayes in absolute terms for the brain, why cannot we correct prediction errors in visual illusions by incorporating new perceptual information? Would not this be more adaptive in evolutionary terms? One could argue that there is no such possibility of new information to re-adjust the predictions, and thus perceive things differently, in such case I would say that we enter into a tough terrain where we run the risk of not being able to falsify the theory of the predictive brain, taking into account its own postulates of what should happen. If indeed the brain cannot adjust its “a priori” by some perceptual impossibility of a biological character, would we be talking about a genetic unmodifiable “a priori” for example? Or are there simply things that the brain can perceive and things that cannot?

I would be cautious in the conclusions we can draw from this type of optical illusions. We could even say that what the brain does is not to predict, but rather we confuse the prediction with the simple activation of certain neural patterns, that is, in front of certain things there will be certain activated patterns with higher probability, these refer to the conscious experience, and the previous activation of certain patterns will cause them to be activated in turn more likely, that does not imply a constant predictive act based on what is perceived moment by moment, but rather there is a perception that conditions perception, but prediction would be something different, one step or process further. The fact that one would be constantly making predictions based on what is perceived would be inefficient as well, because with the previous case it would be enough. In addition, there are things that we are not able to perceive, and if this were the case for hollow faces, that isolated fact would explain the illusion and not the concepts of Bayes.

And let us not forget the practical absence of other illusions of different sensory modalities, which I would say such existence of other examples would be expected and would generate greater support to the notion of the brain and consciousness as something predictive.