Reaction time to square-wave gratings as a function of spatial frequency, complexity and contrast.

Visuomotor reaction time (RT) of normal human subjects to briefly presented square-wave bar patterns were measured. The pattern varied with respect to magnitude and number of spatial frequencies (one cycle/degree of visual angle, 3 cycles/degree, and both combined) with each spatial frequency stimulus presented at 3 levels of contrast. Space-average luminance was held constant. RT increased with the higher spatial frequency and was intermediate in value for the combination stimulus at each level of contrast. RT increased with decreasing contrast levels for each spatial frequency stimulus. There was no interaction between the two parameters. The findings indicate that a behavioral response measure can be employed to study the multiple channel hypothesis of human vision. The results were compared with those of other investigators employing sine-wave gratings, perceptual response measures and the evoked potentials technique.