Post-receptoral undersampling in normal human peripheral vision.

In human far peripheral vision, drifting stimuli of particular periodicities appear to move in the opposite direction from their true direction of motion. This "reverse motion illusion" is a consequence of spatial undersampling of the retinal image. The illusion occurs for spatial frequencies an order of magnitude lower than that expected on the basis of anatomical measurements of human photoreceptor density. We conclude that for naturally imaged stimuli the site of undersampling in far peripheral vision must be post-receptoral.