Moutoussis, Konstantinos Nikolaou; (1996) Brain strategies of colour perception. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis deals with the problem of colour vision. Part I addresses the problem of specialisation for colour, with specific reference to area V2, interposed between V1, where cells selective for the wavelength of the stimulus are found, and V4, where cells selective for the colour of the stimulus are present. The responses of cells in V2 were studied for their selectivity to the wavelength, orientation, and direction of motion of the stimulus. Cells with particular selectivities were found in clusters which were directly related to the metabolic (cytochrome oxidase, CO) architecture of V2. Orientation selective cells were mostly found in the inter and thick stripes, direction selective cells (although generally rare) in the thick stripes, and wavelength selective cells in the thin stripes. Only very few cells were selective for more than one attribute. By studying the distribution of the receptive fields of the cells in the three different stripe compartments, it became clear that the visual field is independently mapped in each set of CO stripes. The visual field is thus separately mapped for each of the different attributes of vision in V2. Wavelength selective cells in V2 were tested for colour constancy. None was found to exhibit this property, but some were selective not only to the wavelength composition of the stimulus but also to the change in the relative amount of a particular wavelength. Part II addresses the general problem of how the brain binds the different visual attributes which are processed separately, and investigates the possibility that colour, motion, form, and stereoscopic depth are not perceived in precise temporal registration with one another. It describes the use of a psychophysical method to investigate the differences in time required to perceive colour and motion. By using a stimulus which rapidly and continuously changes in colour and direction of motion, it shows that subjects bind colour and motion incorrectly because colour is perceived before motion. The idea of functional segregation not only at the level of processing but also at the level of perception is introduced.

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