Chromatic sensitivity of ganglion cells in the peripheral primate retina

Visual abilities change over the visual field. For example, our ability to detect movement is better in peripheral vision than in foveal vision, but colour discrimination is markedly worse(1,2). The deterioration of colour vision has been attributed to reduced colour specificity in cells of the midget, parvocellular (PC) visual pathway in the peripheral retina(3-5). We have measured the colour specificity (red-green chromatic modulation sensitivity) of PC cells at eccentricities between 20 and 50 degrees in the macaque retina. Here we show that most peripheral PC cells have red-green modulation sensitivity close to that of foveal PC cells. This result is incompatible with the view that PC pathway cells in peripheral retina make indiscriminate connections ('random wiring') with retinal circuits devoted to different spectral types of cone photoreceptors(4,6,7). We show that selective cone connections can be maintained by dendritic field anisotropy, consistent with the morphology of PC cell dendritic fields in peripheral retina(8,9). Our results also imply that postretinal mechanisms contribute to the psychophysically demonstrated deterioration of colour discrimination in the peripheral visual field.