RECEPTIVE-FIELDS OF PRIMATE RETINAL GANGLION-CELLS STUDIED WITH A NOVEL TECHNIQUE

We have reinvestigated receptive-field structure of ganglion cells of the macaque parafovea using counterphase modulation of a bipartite fie ld. Receptive fields were mapped with luminance, chromatic, and cone-i solating stimuli. Center sizes of middle (M) and long (L) wavelength c one opponent cells of the parvocellular (PC) pathway were consistent w ith previous estimates (Gaussian radii of 2-4 min of are, correspondin g to center diameters of 6-12 min of are). We calculate that a large f actor of the enlargement relative to cone radius could be blur due to the eye's natural optics. Maps were consistent with cone selectivity i n surround mechanisms, which had radii of 5-8 min of are. For magnocel lular (MC) cells, center size estimates were also consistent with grat ing measurements from the literature (also Gaussian radii of 2-4 min o f are). The surround mechanism contributing the MC-cell frequency-doub led response to chromatic modulation appears to possess a subunit stru cture, and we speculate it derives from nonlinear summation of signals from M,L-cone opponent subunits, such as midget bipolar cells.