Abstract
The apparent contrast of a plaid is a reflection of the neural relationship between the responses to its two orthogonal component gratings. To investigate the perceived contrast summation of the responses to component gratings in plaids, we compared the apparent contrasts of monocular plaids to a component grating presented alone across chromaticity and spatial frequency. Observers performed a contrast-matching task for red–green color and luminance stimuli at low- and medium-spatial frequencies. Using the measured points of subjective equality between plaids and gratings, we evaluate perceived contrast summation across conditions, which may vary between 1 (no summation) and 2 (full summation). We show that achromatic plaids have higher perceived contrast summation than chromatic plaids. The greatest difference occurs at the medium-spatial frequency, with summation highest for achromatic plaids (1.87) and lowest for chromatic plaids (1.49), while at low-spatial frequencies, there is a smaller summation difference between achromatic (1.72) and chromatic (1.65) plaids. These results are consistent with recent theories of distinct cross-orientation suppression and summation mechanisms in color and luminance vision. Two control experiments for binocular versus monocular viewing, and the overall size of the stimulus patches did not reveal any differences from our main results.
Highlights
IntroductionDifferences in the apparent contrast between color or achromatic plaids and a component grating presented alone may reflect characteristic summation and suppression processes
The lower perceived contrast summation for chromatic compared with achromatic plaids that we find complements these previous findings of increased cross-orientation suppression with both monocular and binocular stimuli
We find that the color plaids have lower overall perceived contrast summation than achromatic plaids, summation is noticeably higher for the low compared with the mediumspatial frequency chromatic plaids
Summary
Differences in the apparent contrast between color or achromatic plaids and a component grating presented alone may reflect characteristic summation and suppression processes. To evaluate perceived plaid and grating contrasts, we employed a contrastmatching paradigm in which the observer compares the contrast of a plaid to a single component grating. From these measurements, we describe the summation of responses to component gratings in the perceived contrast of plaids for different spatial frequency and chromaticity conditions. We evaluate the perceived contrast summation of suprathreshold orthogonal plaid components with respect to recent theories of distinct cross-orientation suppression and summation mechanisms in color and luminance vision
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