Pattern detection and the two-dimensional Fourier transform: Flickering checkerboards and chromatic mechanisms

Abstract Fourier effects are obtained from simple detection thresholds for checkerboard and striped gratings, without using complex waveforms, masking or pattern adaptation. Spatial contrast predicts that the checkerboard thresholds should be lower than the bar-grating thresholds, but this never occurs. The opposite result, predicted by magnitude detection in the two-dimensional Fourier domain, occurs in a variety of flicker experiments, with red or green homochromatic fields, and under selective chromatic adaptation. It persists at spatial frequencies as low as 1.4 c/deg. and cannot be attributed to stray light, image blur, or orientational selectivity. Even with opponent-color patterns of unvarying luminance, the bar-check sensitivity ratio is still π/2 (as predicted by the Fourier magnitudes) over a broad frequency range. This Fourier mechanism seems to affect both achromatic and opponent-color pathways equally; therefore, we cannot infer that its location is post-retinal.