We have reinvestigated receptive field structure of macaque ganglion cells using a novel stimulus—counterphase modulation of a bipartite field—with luminance, chromatic, or cone-selective stimulation. We previously used this stimulus (Kremers et al, 1995 Colour Vision Deficiencies XII 399 – 406) to show that surrounds of middle (M) and long (L) wavelength cone opponent cells of the parvocellular (PC) pathway are cone specific, measuring on a finer scale than in previous experiments [Reid and Shapley, 1992 Nature (London) 356 716 – 718]. Modelling of response amplitude and phase now confirms this conclusion. Second, centre sizes measured were consistent with those from the literature, with PC and magnocellular pathway (MC) cell centres having similar size. Modelling on the basis of single cone centres for PC-cells plus optical blur provided a partial description of the data, but some inconsistencies were present. Last, the chromatic nonlinearity of magnocellular pathway ganglion cells appears to result from a subunit structure within the receptive-field surround.
