Spatial-frequency tuning as a function of temporal frequency and stimulus motion.

Spatial-frequency tuning at two different spatial frequencies was determined by measuring the detectability of a signal grating that was made difficult to see by low- or high-pass visual noise. The signals were vertical sinusoidal gratings of different spatial frequencies. The detectability of the signal was measured in two-alternative forced-choice tasks with different temporal envelopes: (1) a slowly changing raised-cosine (Hanning) window, (2) a rectangularly gated 2-Hz counterphase flickering envelope, and (3) a rectangularly gated 10-Hz counterphase flickering envelope. Additional measurements were made using drifting stimuli with the signal and noise drifting in the same or in opposite directions. The temporal envelopes were chosen because they have different effects on the contrast-sensitivity function and it was desired to know how temporal factors affect the spatial-frequency tuning of the relatively narrowly tuned channels thought to underlie contrast sensitivity. The results show that, for counterphase flickering stimuli, spatial-frequency tuning does not depend on temporal envelopes applied identically to the signal and to the masking noise. A similar picture emerges at slow (2.7-deg/sec) but not at fast (10.9-deg/sec) drift rates.