Spectral sensitivity of dichromats: role of postreceptoral processes.

Increment spectral sensitivity functions were determined for dichromatic subjects; these functions were interpreted in the context of parvo and magno pathways. Increments of either 200 or 10 msec in duration were presented on a spatially coincident, 1000 td white background. When compared to the control trichromatic data, the 200 msec functions of dichromats manifest a reduction in sensitivity at middle and long wavelengths. These data are consistent with the notion that 200 msec threshold increments reveal the sensitivity of the parvo pathway; the sensitivity of this pathway is reduced in dichromacy due to pigment replacement with a resultant loss of spectral opponency. The 10 msec functions of dichromats do not show a comparable reduction in sensitivity. Therefore, it is concluded that 10 msec increments reveal the sensitivity of a pathway whose spectral-opponent status is not substantially altered in dichromacy, presumably the magno pathway.