Modeling shifts in perceived spatial frequency between the fovea and the periphery.

A quantitative multiple-channels model can account for changes in perceived spatial frequency between foveally and peripherally viewed patterns; these frequency shifts are as large as 0.47 octave (38.5%). Factors that change as a function of eccentricity and that can alter the appearance of visual patterns include (1) scaling of receptive-field sizes, (2) overall sensitivity, and (3) steepness and nonlinearity of contrast-transfer functions (CTF's). Computations based on receptive-field size scaling, combined with fixed perceptual labels, predict higher perceived spatial frequency for peripheral patterns. Computations based on reduced sensitivity, however, predict the opposite result and thus partially offset the effect of receptive-field size scaling. The predicted perceived-frequency shifts based on changes in CTF's are quite small and can be ignored. Both individual differences and visual-field-location differences in magnitudes of perceived-frequency shifts are predicted by the model. An alternative perceptual explanation based on size-distance invariance and size constancy is also evaluated.