Bartels, Andreas Martin Sebastian; (2001) The modularity of processing and perception in the visual brain. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Practical and theoretical approaches were applied to try to unravel the relationship of the anatomical processing sites to the relative timing of processing and perception. Psychophysical, imaging and theoretical studies led to the overall conclusion that simultaneously presented attributes that are perceived at the same time are processed at the same site, and ones that are perceived at different times are processed at different sites. This is referred to as to the theory of perceptual sites. Functional magnetic resonance imaging (fMRI) experiments charted the organisation of the human colour centre (the V4-complex), and found it to be more complex than previously believed. It has two subdivisions, V4 and V4α, of which V4 is retinotopically organised, while V4α is not. The extent and organisation of the colour centre revealed in this study may account for the variability and severity of the syndrome of achromatopsia (acquired cortical colour blindness). Application of an independent components analysis (ICA) to fMRI data showed that these two subdivisions are coactive and can be isolated together from the remaining brain activity. It was further shown that, because cortical areas enjoy substantial autonomy, they differ in their activation time courses, such that ICA can dissect the brain computationally into its functional units, creating what we call chronoarchitectonic maps. The above evidence, when viewed in context of previous experimental and clinical studies, leads us to propose the following: First, that the activity in different visual areas reaches conscious perceptual endpoints at different times; leading to the supposition that consciousness is not unitary but consists of many microconsciousnesses. Second, that since activity at each processing site can become perceptually explicit, there is no terminal perceptual stage in the visual brain; leading to the conclusion that activity at each site of the visual brain can be integrated with activity at any other site, and to the theory of multistage integration.

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