Spatial frequency and orientation tuning of spatial visual mechanisms in human albinos

A masking paradigm was used to measure the spatial frequency and orientation tuning of spatial mechanisms in the albino visual system. Threshold elevation curves obtained in this manner at test spatial frequencies of 0.25 cycles/deg (cpd), 0.50 cpd, and 1 cpd have the same shape as curves obtained from normal subjects at test frequencies two octaves higher. Additional masking studies showed that contrast processing in albinos obeys the same compressive power law as in normals. Thus, spatial mechanisms in albino central vision have normal spatial frequency and orientation bandwidths. As central cones in the albino are spaced 3-4 times further apart than in the normal fovea, these results support the hypothesis that monocular spatial vision in albinos is primarily limited by this increased receptor spacing. It is hypothesized that this, in turn, is the result of arrested development of the albino retina.