A new psychophysical technique to measure chromatic afterimages W Bi, J L Barbur |
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Applied Vision Research Centre, City University London, United Kingdom
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| The purpose of this study was to measure the strength and duration of chromatic afterimages in normal trichromats and in subjects with congenital colour deficiency. A new, test was developed to measure the strength and duration of perceived chromatic afterimages in normal trichromats and in subjects with red-green deficiency. A typical chromatic afterimage experiment involves two stages: a rapid, four-alternative, forced-choice stage followed by a staircase test. The rapid phase yields a good approximation to the true threshold. This stage improves the efficiency and accuracy of the subsequent staircase procedure. The measured afterimage strength in normal subjects follows an exponential decrease to the subject’s normal colour detection threshold; colour deficients, on the other hand, exhibit a very large initial threshold followed by rapid decrease to a constant threshold that is generally much larger than in normal trichromats. A model will be presented to account for the difference in results measured in subjects with congenital colour deficiency. The results suggest that in addition to the two chromatic mechanisms involved in normal trichromats, the perception of afterimages in subjects with congenital colour deficiency is also affected by achromatic mechanisms. |
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