NONLINEAR DISTORTION OF GRATINGS AT THE FOVEAL RESOLUTION LIMIT

Aliasing by the foveal cone mosaic causes high frequency interference fringes to look like bright and dark zebra stripes (primary zebra stripes) [Williams, Vision Research, 25, 195 (1985); Vision Research, 28, 433 (1988)]. Some observers report another type of zebra stripes defined by variations in chromaticity as well as brightness, which we call secondary zebra stripes. The conditions required to see the secondary zebra stripes are almost identical to those required to see the primary zebra stripes, except that they are seen at approximately half the frequency. We consider the hypothesis that the secondary zebra stripes arise from aliasing by a particular packing arrangement of the M and L cone submosaics, but present evidence favoring an alternative hypothesis based on a known local nonlinearity in the visual system.