Exchange thresholds for green tests.

Thresholds for detection of foveal pi 4-detected 522 nm, 1 deg, 200 msec test flashes rise by up to 0.4 log units just after a pi 4-equated "exchange" field has been substituted for the adaptation field, and take 60-90 sec to recover. This effect is not changed by an intense blue auxiliary field, and varies with the difference between adaptation and exchange field wavelengths as if only inputs from long-wavelength (LW) cones are involved. The effect can be virtually eliminated by adaptation to a background which alternates at 15 Hz between selected pi 4-equated long- and short-wavelength fields, which suggests that the LW cones exert their effect at a red-green opponent site.