Keele Research Repository

A psychophysical study was made of post-receptoral processing In the human visual system. The first series of experiments investigated normal red-green opponent-colour function by Means of a paradigm in which a white auxiliary field was made spatially coincident with the test field. This auxiliary field produced a deep trough in the test spectral sensitivity curve at around S80 nm, characteristic of opponent-colour processes. The efficacy of the paradigm was verified operationally by comparing thresholds for simple detection with those for colour discrimination. The paradigm was also used in measurements of field spectral sensitivity, and the upper envelope of the resulting spectrally sharpened field curves was shown to correspond in shape to the test spectral sensitivity curve. This correspondence was thought to be evidence of unitary opponent-colour processes underlying direct and adaptational measures of sensitivity, a notion which was supported by further experiments in which the test and field-envelope curves were affected similarly by the introduction of chromatic adaptation.
The paradigm was exploited in a study of chromatic and luminance function In patients with multiple sclerosis or optic neuritis. Equal losses in chromatic and luminance sensitivity were revealed, in contrast to previous studies. As a control on the procedure, two subjects with Inherited red-green deficiencies were also investigated.
The response to time-varying luminance and chromatic stimuli was studied using square-wave flicker stimuli in normal subjects and patients with multiple sclerosis or optic neuritis. There was a greater reduction in luminance CFF than in chromatic CFF, but it was argued that this was a result of a general impairment in the ability of demyelinated nerve fibres to transmit high-frequency impulses.