Signals leaving the retina must transfer information about the luminance and chromatic dimensions of the natural world. It has been suggested that, to optimize information transmission, these signals should be strictly segregated in different pathways, such as the parvocellular and magnocellular systems. Another suggestion is that signals about luminance and colour may be combined in the parvocellular pathway. We compared physiological and psychophysical responses to gratings that compound both luminance and colour to responses with pure luminance colour and gratings. The results strongly support the idea of strict segregation of luminance and chromatic signals in the afferent visual pathway.
Segregation of chromatic and luminance signals in afferent pathways are investigated with a grating stimulus containing luminance and chromatic components of different spatial frequencies. Ganglion cell recordings were obtained from the retinae of macaques (Macaca fascicularis). Cell responses to the ‘compound’ gratings were compared to responses to standard chromatic and luminance gratings. Parvocellular (PC) pathway cell responses to compound and chromatic gratings were very similar, as were magnocellular (MC) cell responses to compound and luminance gratings. This was the case over a broad range of spatial and temporal frequencies and contrasts. In psychophysical experiments with human observers, discrimination between grating types was possible close to detection threshold. These results are consistent with chromatic and luminance structure in complex patterns being strictly localized in different afferent pathways. This novel stimulus may prove useful in identifying afferent inputs to cortical neurons.