The Hidden Spring: A Journey to the Source of Consciousness by Mark Solms

Author:Mark Solms [Solms, Mark]
Language: eng
Format: epub
ISBN: 9780393542028
Barnesnoble:
Published: 2020-12-31T00:00:00+00:00

Figure 18 (a) = the Rey Complex Figure as shown to Patient WB; (b) = the same figure as copied by him; (c) = the figure as drawn by him from memory. These drawings provide objective evidence of the inversion of WB’s predictive model of the world. The Rey Complex Figure is difficult to reproduce at the best of times; why would this seriously ill patient compound the difficulty by drawing it upside down?

In other words, her visual cortex receives the sort of information that we all do, but she cannot generalise from the noisy sensory signals and automatically infer the stable objects they stand for (e.g. recognise a familiar face). She has suffered these anomalies all her life, and has developed elaborate ways of compensating for them. Since her visual ‘association’ cortex does not automatically integrate the two visual fields and rotate the scene, she adjusts her representation of the world by making deliberate inferences. For example, when I asked her to identify the location of a well-known city on an unmarked map, she said: ‘Should I show you where I sense it is located or where I know it is?’ When she ‘senses’ that something is located in the west, she ‘knows’ it must be located in the east.

Rather than appealing to such rare neuropsychological disorders, however, let me illustrate the self-generated nature of perception by way of the phenomenon that is conventionally used for this purpose, namely binocular rivalry.

This phenomenon was first described in 1593; and it featured prominently in Helmholtz’s seminal work on the topic of unconscious inference.8 It involves simultaneous presentation of different pictures to each eye, using a mirror stereoscope. Let’s say the left eye is presented with a face and the right one a house. Under these artificial conditions, visual experience unfolds in a ‘bi-stable’ manner, whereby you do not see a superimposed blend of the two images but rather an alternation between them. You see a house then a face then a house then a face, rather than a combined house-face. This clearly demonstrates the distinction between the objective signal that is transmitted to the brain and the subjective percept that is generated by it. Helmholtz concluded: ‘In such cases the interpretation [of the visual signal] vacillates such that the observer has different experiences, one after another, for the unchanging retinal image.’9 As with colour vision, therefore, what you experience is an inference about the sensory input, not the input itself.

Broadly similar things happen in everyday life, such as when I ‘saw’ my British friend Teresa at Cape Town airport. All these illusions show that what you perceive is generated largely by your expectations. In Bayesian terms, binocular rivalry is taken to show that if the prior hypothesis that best fits the sensory data (the high likelihood that you are seeing a house-face) does not square with your background knowledge (the low probability that house-faces exist) then the hypothesis is rejected. The inference that you’re seeing a house trumps the one that you’re seeing a house-face; so, a house is what you experience.

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