Temporal properties of visual channels measured by masking.

Threshold elevations for spatially localized test stimuli were measured as a function of the temporal frequency of a sinusoidal mask grating. Ten of these temporal-masking curves were determined, each using a test stimulus of different temporal frequency. It was found that these data could be accounted for by four temporal-tuning curves: one low-pass curve with a corner frequency of 8.0 Hz and three bandpass curves with bandwidths of 2.0-2.5 octaves and peaks all within the region 4.0-8.0 Hz. In another set of experiments, a series of 1 spatial-masking curves was determined, each using a test stimulus of different spatial frequency. Measurement of the entire series was repeated using 1.0- and 8.0-Hz mask temporal modulations. Spatial-masking data collected under the two temporal conditions could both be accounted for by a single set of seven spatial-tuning curves, without changing the shape of any of these curves. The data are therefore compatible with spatiotemporal separability. Finally, a large set of contrast-response curves (threshold elevation as a function of mask contrast) was collected. These curves were found to follow a power law whose exponent varied with the spatiotemporal conditions of the experiment.