TEMPORAL PROPERTIES OF THE RED-GREEN CHROMATIC MECHANISM

The temporal properties of the red-green chromatic mechanism were stud ied with red and green equiluminant flashes of 1 deg diameter presente d in the center of a bright (800-3000 td) yellow adapting field. A sub threshold 200 msec red or green flash makes an immediately subsequent, suprathreshold yellow luminance flash appear tinged with the compleme ntary color. The chromatic flash also makes a subsequent chromatic fla sh of the same hue harder to detect and identify, and makes a flash of the opposite hue easier to detect and identify. These results indicat e that the response of the red-green mechanism changes polarity during its time-course, suggesting that the chromatic temporal impulse-respo nse function has a negative lobe. Pairs of chromatic pulses were used to estimate the shape of the chromatic impulse-response. The estimated impulse-response function has a zero crossing near 90 msec, followed by a long, shallow negative lobe. We also measured threshold-duration functions; the critical duration for the chromatic and luminance flash es is about 95 and 45 msec, respectively. Chromatic sensitivity (measu red in cone contrast units) is 10 times greater than luminance sensiti vity for long durations, and is 3 times greater for all durations less than 45 msec.