Abstract

We examined the acuity of the human rod system pyschophysically to establish whether the parvocellar P or magnocellular M pathway carries high-frequency spatial information in scotopic vision. We measured visual acuity for smalt patches of sinusoidal grating at a range of eccentricities in temporal retina. When the targets were detected via rods, visual acuity ranged from 5.3 cycles/deg at an eccentricity of 5-2.9 cycles/deg at an eccentricity of 30°. We also calculated the highest spatial frequency that could be reliably resolved by the mosaics of Pand M cells and found that visual acuity of the rod system is too high to be supported by the M-ganglion cells. The psychophysical acuity is also lower than the Nyquist limit for P-ganglion cells. This implies that the high-frequency information for scotopic vision is carried in the P-cell pathway and that visual acuity is limited by the sizes of the receptive fields of individual cells, not by their separation. This conclusion is corroborated by our failure to find aliasing in scotopic vision, despite our finding clear aliases when corresponding measurements of acuity were made in photopic conditions.

© 1988 Optical Society of America