POST-RECEPTORAL MECHANISMS OF COLOR-VISION IN NEW-WORLD PRIMATES

Diurnal platyrrhines, both di- and trichromats, have magnocellular (M- ) and parvocellular (P-) retinal ganglion cells which are morphologica lly very similar to those found in catarrhines. Catarrhine central P g anglion cells contact single midget bipolar cells, which contact singl e cones. Physiological recordings of retinal ganglion cells of dichrom atic Cebus monkeys showed very similar cell properties to the catarrhi ne macaque, except that P ganglion cells lacked colour-opponency. We d escribe the presence of single-headed midget bipolar cells in the Cebu s retina. These midget bipolar cells have axon terminal sizes in the s ame range as the dendritic tree sizes of P ganglion cells as far as 2 mm of retinal eccentricity. This result supports the view that, as in catarrhines, central P ganglion cells of platyrrhines receive input fr om single midget bipolar cells which in turn, receive input from singl e cones. This finding is consistent with the idea that. a P pathway wi th one-to-one connectivity was present in the anthropoid ancestor befo re the divergence between catarrhines and platyrrhines. (C) 1998 Elsev ier Science Ltd. All rights reserved.