Spatial frequency effects in masking by light.

Observers detected briefly pulsed sine-wave gratings presented with various asynchronies before, during or after a 700 msec conditioning flash. Although the conditioning flash raised increment thresholds for detection of both low and high spatial frequency gratings, shapes of the masking curves differed. Curves for low spatial frequency gratings exhibited peaks at the conditioning field on and offset, resembling data reported by Crawford (1947). However, when a high spatial frequency grating was detected, no on or offset peaks were found. These results are consistent with a model of the human visual system postulating the existence of separate sustained and transient mechanisms.