Dependence of apparent contrast for a sinusoidal grating on stimulus size

A contrast-matching technique was used to measure the apparent contrast of sinusoidal gratings, varying in contrast and spatial frequency, as a function of grating size. In the contrast range of 0.01–0.1, it was found that apparent contrast increases with increased grating width or length, showing a dependence on the number of cycles presented similar to that shown by detection threshold. On the other hand, apparent contrast is insensitive to grating size in the contrast range of 0.1–0.54. This difference between low- and high-contrast gratings suggests that two separate spatial-integration processes underlie suprathreshold-contrast processing.