DIFFERENT SYSTEMS FOR THE VISUAL DETECTION OF HIGH AND LOW SPATIAL FREQUENCIES.

In a detection task low and high spatial frequencies are processed in a characteristically different manner by the human visual system. This conclusion is drawn from reaction time experiments in a simple detection task using supra- and subthreshold sinusoidal gratings exposed with various onset asynchronies. The main properties of the mechanism which principally processes lower spatial frequencies are: a short delay time, a transient step response (temporal band pass filter), and a nonlinearity even near threshold, while the properties of the mechanism which processes higher spatial frequencies ( greater than 3 c/deg) is characterized by a long delay time, a sustained step response (temporal low pass filter), and linear behavior near threshold.