Spatial and temporal response properties of the major retino-geniculate pathways of Old and New World monkeys

Old World monkeys, apes and humans all enjoy trichromatic colour vision, an d the absorption spectra of the photopigments are very similar in all speci es and all individuals. Colour vision in New World monkeys however, is very heterogeneous. In many species, the majority of individuals is dichromatic . Recently, anatomical and electrophysiological studies revealed that the r etinal organisation in Old World monkeys and New World monkeys is very simi lar, although the cells belonging to the parvocellular pathway do not show any colour opponency and their spectral sensitivity is similar to that of t he magnocellular cells. Apparently, the magnocellular and parvocellular pat hways in the retina and the LGN have not developed as an adaptation to lumi nance and chromatic processing. It is more likely that the two pathways ori ginally evolved to cover different ranges in the spatio-temporal domain. In the present paper, several spatial and temporal properties of parvo- and m agnocellular cell s (which are identical for dichromatic and trichromatic a nimals) are compared.