Abstract

Photoreceptors and neurons at various levels to cortex have been counted in mouse and rat. The ratios of neuron numbers (rat/mouse) are similar to the ratio of retinal areas or the squared ratio of eye sizes; so to a first approximation the two species have linearly scaled eyes, equal photoreceptor spacings (in microns), and visual pathways scaled numerically by the number of photoreceptors. The following points can be made: Photoreceptors outnumber neurons at all subsequent levels. Cone sampling exceeds the behavioral acuity limit, the latter being largely determined at or before the ganglion cell level. There are few neurons in the LGNd, and so the corresponding eye parameter p is very large, as is appropriate for nocturnal animals. The general organization is economical, if not sparse, so undersampling occurs even for central vision when the pupils are small. However, aliasing should be slight if the retinal and geniculate sampling lattices are irregular with only a local spatial order. Cortical encoding appears less explicit than in the primate. This seems compatible with either the photon limitations of nocturnal vision or the advantages of a fast though limited range of behavior.

© 1987 Optical Society of America