Distance, duration and blur effects on the perception of pseudoisochromatic stimuli

Two experiments are reported that examine the effects of viewing distance, viewing duration, and stimulus clarity on performance with three popular versions of the pseudoisochromatic tests of colour deficiency. With a large sample of colour-normal observers, highly significant effects of these viewing conditions are found. In addition, large differences in sensitivity to these conditions are obtained among the three tests employed (The American Optical Corporation test, the Dvorine test, and the Ishihara test). Results are discussed in terms of practical implications for test administration and in terms of likely processes, in addition to colour discrimination, assessed by these tests.