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Modelling chromatic processes in human vision

Pinney, H. D. (1992). Modelling chromatic processes in human vision. (Unpublished Doctoral thesis, City, University of London)

Abstract

This investigation programme has concentrated on a number of topics concerning visual function in humans, with particular emphasis on the processing of chromatic information.

The programme included an investigation of colour constancy which was carried out using a computer - controlled colour display. A new dynamic colour matching method was developed and the experimental conditions arranged so as to test the constancy of colour appearance. The technigue makes possible the definition of an index of colour constancy which simplifies the interpretation of experimental results. Various spatial, temporal and chromatic parameters of the stimulus configuration were investigated and the results show the importance of the stimulus boundary and near surround in determining the magnitude of the constancy effects observed.

Pupillary function was investigated in normal and amblyopic observers. The results suggest that the pupil light reflex is essentially of normal amplitude in amblyopic eyes, although a latency anomaly does exist. Pupillary responses to achromatic, sinusoidal grating stimuli were anomalous in the affected eyes of many amblyopic subjects. Interestingly, certain response parameters were found to be anomalous in the normal eyes of amblyopic observers.

Pupillary responses in normal observers were measured following stimulation with isoluminant, red - green chromatic gratings. Responses were found to vary systematically with grating spatial frequency, and broadly reflect the way in which detection thresholds for the same stimuli vary with spatial frequency. Response latencies were approximately 80 ms longer than for equivalent responses to achromatic gratings. No responses were observed when the same experiments were carried out with a protanope.

Chromatic discrimination thresholds were measured using a spatio - temporal luminance masking technique. The technique is implemented on a carefully calibrated colour monitor and obviates the requirement of stimulus isoluminance. Preliminary experiments employing psychophysical and pupillometric procedures illustrate the use of the technique in the subjective and objective assessment of colour vision.

The rapid changes in visual sensitivity which occur following an intense flash of light were investigated by measuring increment thresholds for a small, brief test stimulus. Results are presented which show the dependence of the sensitivity changes on various spatial, temporal and chromatic parameters. An attempt is made to relate the experimental findings to the properties of retinal neurones.

Publication Type: Thesis (Doctoral)
Subjects: R Medicine > RZ Other systems of medicine
Departments: School of Health & Psychological Sciences > Optometry & Visual Sciences
School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses
Doctoral Theses
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