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Junjie Liu, Brian A. Wandell; Contrast perception and discrimination of chromatic temporal modulations. Journal of Vision 2005;5(8):1024. doi: 10.1167/5.8.1024.
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© ARVO (1962-2015); The Authors (2016-present)
INTRODUCTION. Color desaturates and detection sensitivity to chromatic modulations deteriorates as temporal frequency increases (1–10 Hz, heterochromatic flicker photometry). Here we ask whether the apparent contrast and contrast discrimination of color stimuli, measured at suparthreshold contrast levels, also deteriorate over this temporal frequency range.
EXPT.1. Observers matched the perceived contrast of a chromatic flicker (S- or (L−M)−cone, 2° dot) and a spatiotemporally equivalent luminance flicker ((L+M)−cone). At 1 Hz, the detection thresholds and perceived contrast matches shared a single scaling ratio roughly as (L+M):(L−M):S = 1:0.2:3 (Switkes and Crognale, 1999). As temporal frequency increased to 8 Hz, the detection thresholds significantly changed, reaching a ratio of (L+M):(L−M):S = 1:0.5:10. The perceived contrast matches at suprathreshold contrast levels, however, remained roughly unchanged across this temporal frequency range.
EXPT.2. Contrast discrimination thresholds were measured using a forced-choice staircase design. On each trial observers compared two stimuli that differed only in contrast and decided which one had higher contrast. For all color directions tested (S-, (L−M)- and (L+M)−cone), discrimination thresholds at suprathreshold contrast levels remained roughly invariant with temporal frequency. For example, the discrimination thresholds for 25% contrast S-cone flickers were 3% at both 1 and 8 Hz. Over the same frequency range, S-cone detection thresholds changed by a factor of three (3%, 1 Hz; 10%, 8 Hz).
CONCLUSION. Unlike color saturation and chromatic detection sensitivity, contrast perception and discrimination of suprathreshold chromatic modulations do not deteriorate as temporal frequency increases (1–10 Hz). The preservation of contrast perception and discrimination for chromatic modulations in this frequency range has applications to the design of video coding algorithms as well as the interpretation of cortical neuronal responses.
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