Estimates for the temporal response characteristics of chromatic pathways.

When equiluminous red and green fields are temporally alternated, it is generally accepted that the hue of the field fuses to yellow at a slower flicker rate than the critical flicker frequency (cff). However, when sufficient precautions are taken to avoid optically created achromatic artifacts and the illumination of the test field is kept fairly low (70 trolands), the modulation threshold for color fusion and that for flicker fusion are equivalent. The purely chromatic, artifact-free stimulus shows a much lower cff than has been reported in the literature under comparable conditions. It seems likely that many studies of the chromatic pathways have overestimated the ability of these pathways to follow rapid temporal alternation, presumably because the more sensitive achromatic pathways were detecting achromatic artifacts. A simple means for detecting achromatic artifacts in a temporal alternation will be demonstrated by the finding that an equiluminous surrounding field enhances modulation sensitivity only for achromatic flicker and not for chromatic flicker.