Abstract
This paper deals with the visual response characteristics of a single male subject. Although members of his maternal family were found to be red-green defective, the subject's responses are not consistent with those of the recognized classes of colour vision defect. Thus his foveal colour matching is dichromatic: his foveal threshold spectral sensitivity is between 2.5 and 5.0 log units less than that of normal observers and his critical fusion frequency saturates at 15–18 Hz. Increment threshold measurements reveal the activity of only two spectral mechanisms and for long wavelength stimuli, the increment threshold level falls sharply as the illumination level of a superimposed background field is increased beyond a critical level. This last observation correlates with the observer's subjective report that objects which appear red to normal observers appear to him as “grey” or “black”, with no well-defined form. Experiments with stimuli located up to 11° off-axis on the temporal retina showed that the subject's visual responses are essentially invariant with respect to the stimulus location and that characteristic rod responses are entirely absent. We have proposed a functional model for the interpretation of the experimental data in which deuteranomalous colour vision is combined with malfunction of some of the central visual mechanisms.
Published Version
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