Responses to coloured patterns in the macaque lateral geniculate nucleus: pattern processing in single neurones.

Cell responses to complex visual patterns such as compositions of broad-band (non-monochromatic) colour areas are presented. Patterns were scanned over the receptive field, and cell response at each point was recorded. "Response patterns" were constructed which display the cell transform of the stimulus pattern. Parvocellular layer (PCL) cells in the lateral geniculate nucleus, in a very sustained fashion, signal the spectral composition of areas in the pattern, cells of different classes showing different spectral responsiveness. Little or no edge enhancement was present. Magnocellular layer (MCL) cells mark luminance steps in a pattern; they are not colour-specific. Responses to monochromatic stimuli provided a reliable guide to cell responsiveness with mixed colours. However, integration by spectrally opponent mechanisms is present with broad-band colour stimulation and partly accounts for a high variability of response patterns within the same cell class. With some cells, stimulus patterns were either shown through narrow-band colour filters, or a monochromatic background was added. Response patterns to isolated wavelength components compared with those to full colour patterns revealed an almost linear additivity of individual spectral components. Adaptation to a chromatic background, on the other hand, strongly modified the effectiveness of excitatory and suppressive components in the stimulus pattern and markedly changed the structure of a response pattern compared with the non-adapted situation.