Spatial and temporal limits of vision in the achromat.

Threshold detection for sine-wave grating stimuli of varying spatial and temporal frequency was used to investigate the nature of spatial and temporal post-receptoral sensitivity in the typical, complete achromat. Threshold spatial and temporal sensitivities under low photopic conditions show no evidence of cone function. The abrupt fall-off in sensitivity is consistent with known psychophysical and electrophysiological measures of rod saturation. Threshold spatial and temporal sensitivities under scotopic conditions are identical in form and absolute sensitivity to that of the normal scotopic system. Spatial and temporal acuity measurements substantiate the above conclusions based on contrast sensitivity. We conclude that the typical and complete achromat possesses only a normal functioning rod post-receptoral mechanism.