HOW BIG IS A GABOR PATCH, AND WHY SHOULD WE CARE

We propose a two-parameter model for the perceived size (spatial exten t) of a Gaussian-windowed, drifting sinusoidal luminance pattern (a Ga bor patch) based on the simple assumption that perceived size is deter mined by detection threshold for the sinusoidal carrier. Psychophysica l measures of perceived size vary with peak contrast, Gaussian standar d deviation, and carrier spatial frequency in a manner predicted by th e model. At suprathreshold peak contrasts Gabor perceived size is rela tively unaffected by systemic noise but varies in a manner that is con sistent with the influence of local contrast gain control. However, at and near threshold, systemic noise plays a major role in determining perceived size. The data and the model indicate that measures of contr ast threshold using Gaussian-windowed stimuli (or any other nonflat co ntrast window) are determined not just by contrast response of the neu rons activated by the stimulus but also by integration of that activat ion over a noisy, contrast-dependent extent of the stimulus in space a nd time. Thus, when we wish to measure precisely the influence of spat ial and temporal contrast integration on threshold, we cannot do so by combining contrast threshold measures with Gaussian-windowed stimuli. (C) 1997 Optical Society of America.