Abstract

At high spatial frequencies, drifting interference fringes viewed in the fovea and parafovea can appear to move opposite to their true direction. We have previously shown that aliasing by the cone mosaic is responsible for this motion reversal. We measured forced-choice psychometric functions for direction discrimination as a function of the spatial frequency of drifting vertical interference fringes. For a regular sampling lattice, the perceived direction of motion should reverse at integer multiples of the lattice Nyquist frequency. Despite disorder in the cone mosaic, the data in the fovea and parafovea agree with this prediction. At each retinal location tested, motion reversals occur at two spatial frequencies which correspond to one and two times the cone Nyquist frequency. However, in the periphery, from 10 to 25° eccentricity, the first motion reversal occurs at a lower frequency than would be predicted from cone sampling. The reason for this discrepancy is unclear, but it probably involves postreceptoral mechanisms. Nonetheless, the Nyquist frequency obtained at the second motion reversal agrees with peripheral anatomical cone spacing data.

© 1987 Optical Society of America