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Marina Danilova, John Mollon; Chromatic discrimination at phenomenological category boundaries: The case of unique red. Journal of Vision 2013;13(15):P10. doi: 10.1167/13.15.45.
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© ARVO (1962-2015); The Authors (2016-present)
Is it a general principle that discrimination is enhanced at the boundaries of perceptual categories? We recently found that forced-choice chromatic discrimination is optimal near the locus of unique blue, the subjective category boundary between reddish and greenish hues (Danilova and Mollon, 2012, Vision Research, 62, 162–172). We now ask whether an analogous enhancement of discrimination is found near the locus of unique red.
In interleaved experimental runs, we estimated the phenomenological locus of unique red (i.e. a set of chromaticities that are neither bluish nor yellowish) and we obtained forced-choice performance measures of discrimination along lines that intersected this locus. The eye was adapted throughout to a 10 cd/m2 field that was metameric to Illuminant D65. For the phenomenological judgements, the targets were 150 ms, 2° uniform disks. For discrimination, the targets were 150 ms, 2° disks divided into four quadrants; the observer was asked to indicate which quadrant differed in chromaticity from the other three. To ensure that only chromaticity could be used to solve the task, the luminance of each quadrant was independently jittered in luminance by ±1% (around an average value of 13 cd/m2). Auditory feedback was given only in the performance task. Results were expressed in the terms of the changes of cone ratios in the MacLeod-Boynton diagram.
All observers show a locus of minimal thresholds that lies just below, or coincides with, the phenomenological boundary between yellowish and bluish hues, i.e. the locus of unique red.
Support: Russian Foundation for Basic Research Grant 12-04-01797, Royal Society International Exchanges Grant IE110252
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