Vincent, C; (2004) The contribution of colour to visual processing. Doctoral thesis , University of Nottingham.

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Abstract

The contribution that colour provides in visual object recognition was assessed in a variety of human and non-human primate species. A stimulus was designed to assess the degree to which removal of stimulus chromaticity affected object recognition ability. Stimuli were designed so that all chromatic modulation, all red-green chromatic modulation, all blue-yellow chromatic modulation or all achromatic modulation was removed. The stimuli were used in tests of object recognition to assess the functional advantage that stimulus colour or stimulus colour mediated by one of the chromatically opponent pathways provided towards object discrimination. Tests were carried out on normal human observers, macaque monkeys (Macca mulatta) and dichromatic marmoset monkeys (Callithrix jacchus). Experiments were conducted to examine the underlying neuronal processing of feature-like stimuli in visual area 1 (V1) of the anesthetised marmoset. Stimuli contained both chromatic and achromatic modulation or only achromatic modulation. Results showed that for all species, removal of stimulus chromaticity affected object recognition ability. For human observers and the macaque monkeys, the removal of red-green chromatic modulation impaired ability, the removal of blue-yellow chromatic information did not. Although cells were found in marmoset V1 that displayed selectivity for the feature-like elements used to construct the objects used in behavioural tests, they were rare. Few cells showed a significant response when stimuli contained chromaticity. It was concluded that stimulus chromaticity provides a functional advantage towards the sensory aspects of object recognition in humans, macaques and marmosets. For trichromatic species, there was a bias towards the red-green chromaticity providing a functional advantage. Although few cells were found to link the neural processes in V1 to these findings, V1 remains a candidate in the distributed map of neuro-anatomical areas that have been implicated in combining chromatic and achromatic cues to represent the visual world.

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