Abstract

Masking by cosine gratings has been previously used to study spatial-frequency tuning of spatial mechanisms in human vision. Here we report on effects of masking on foveal spatial-frequency discrimination. Un-masked discrimination was first measured with vertically oriented stimuli of 50% contrast and localized in space and spatial frequency. The test stimuli were flashed for 30 ms. Then discrimination thresholds were measured in the presence of a 25% contrast cosine mask and at various stimulus onset asynchronies (SOAs). Measurements were made for each combination of test and mask at spatial frequencies of 3.0 and 8.0 cpd. Discrimination threshold elevations averaged 2.5 times at zero SOA but are virtually absent by 200 ms. We hypothesized that the discrimination-threshold elevation was the result of the increased contrast-threshold for the test patterns. Therefore, we measured the contrast threshold elevation due to masking at zero SOA. Unmasked spatial frequency discrimination was remeasured with the patterns adjusted to the appropriate multiple of threshold contrast. Under these conditions, unmasked spatial frequency-discrimination thresholds were the same as the unmasked thresholds using 50% contrast patterns. Thus, interference with spatial frequency discrimination can be accounted for by the elevation in contrast thresholds due to masking.

© 1990 Optical Society of America