Studies of normal and deficient colour vision with relevance to occupational environments
The studies described in this thesis aim to assess the importance of normal colour vision in visually demanding, colour-related tasks that are often safety-critical and aim to improve our understanding of how congenital deficiencies can affect the processing of colour signals and the corresponding changes in visual performance. The first study compares the colour vision requirements within different professional environments. 519 subjects were tested: 141 normal trichromats, 268 deutans and 110 protans. All subjects carried out the Ishihara 38-plate test, the CAD test and the Nagel anomaloscope, and sub-populations were examined with the AO-HRR plates, the Farnsworth D15, the City University test (2nd Ed.), the Holmes-Wright type A and B lanterns. Inconsistencies of outcome amongst the various tests and potential alternative practices are discussed. The second study focuses on understanding the discrepancies in performance observed on lantern tests when the subject’s task is to report the colour of small signal lights presented against a dark background field. These conditions were simulated using a psychophysical luminance pedestal technique. Variations in the measurement of chromatic sensitivity over the visual field, as well as the detection of targets where colours are combined with luminance contrasts, are discussed and explanations considered with regard to underlying retinal physiology. The last study investigates the use of colour signals in ATC (air traffic control) applications. The work carried out addresses current failings in acceptance criteria for applicants, and provides alternative methods of assessing suitability. The chromatic discrimination thresholds of normal trichromats and colour deficient subjects were related to performance on a set of visual search tasks selected to be more representative of typical colour usage in large field visual displays. Display parameters under which the performance of colour deficient observers could be comparable to that of normal trichromats are examined with regard to updating occupational acceptance criteria.
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