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.