Duration thresholds for chromatic stimuli

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Abstract
The duration necessary to detect chromatic stimuli was measured for wavelengths between 463 and 620 nm. Stimuli were presented either in hue substitution (replacement of white by a chromatic stimulus of matched luminance) or as increments. Two observers viewed a 1° 45′ homogeneous white field. A trial consisted of replacement of the central 40′ of the field by a chromatic stimulus. In substitution mode the white field was 2.4 cd/m2; the chromatic replacement was of matched luminance using heterochromatic flicker photometry (HFP). In increment mode, the white field was decreased to 1.2 cd/m2; the chromatic replacement remained at 2.4 cd/m2. In substitution mode, duration threshold varied from approximately 3–4 ms for the spectral extremes to 45–66 ms at 570 nm. Detected stimuli were always seen as a change in chromaticity. In increment mode, thresholds were in the 2–4 ms range with no dependence upon spectral composition. Detected stimuli were seen either as changes in chromaticity or brightness. A control experiment indicated that HFP did establish equivalent luminance for the hue substitution mode. We conclude that duration thresholds in substitution mode reveal chromatic processing channels; duration thresholds in increment mode are mediated by chromatic and/or achromatic processing channels.

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