Maria de la Paz Cardin, V.; (2008) The form pathways in the visual brain. Doctoral thesis , University of London.

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Abstract

The perception of visual forms is crucial for humans for successful interactions with the environment. This process occurs automatically, and its outcome is reflected in the inferences and decisions we constantly make. The focus of this thesis is on how the brain handles different aspects of the perception of forms. To study this in normal human individuals, experiments were performed using functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and psychophysical methods. This thesis first discusses experiments designed to unravel the mechanisms of form construction, i.e. those from which all the component parts of a single form are assembled. Results suggest that the construction of very simple forms occurs in intermediate visual areas in a parallel and recursive process, with an increase in brain activity with increments in form complexity. A further experiment was performed to study how regularities or known characteristics of images, and the brain responses they elicit, will contribute to explain current percepts. Results from this experiment are consistent with a model where images with learnt attributes activate more strongly anterior visual areas and images with random patterns cause higher activations in earlier visual areas, probably due to top-down signals that reduce activity when it is possible to explain the causes of the sensory stimulation. Finally, it shows differences in the evoked neural activity when forms are either detected or classified, relating these processes to the activity generated in early visual areas. Based on the results of these experiments, a mechanism of top-down and bottom-up interactions between visual areas in the human brain is discussed in the context of the perception of forms.

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