Separating colour and luminance information in the visual system

In our visual world we can distinguish with ease between chromatic and luminance contrasts. However, in our retinae most neurones are responsive to both chromatic and luminance changes and therefore send ambiguous or 'multiplexed' information to the higher visual centres. Psychophysical evidence suggests that some cortical process must subsequently separate out this information into its chromatic and luminance components. The purpose of this communication is to review and critically evaluate the different existing schemes for doing this. To assist in this evaluation a linear systems analysis is employed in which model cortical neurones are imputed with the property of providing information about either colour or luminance. It is concluded that there is currently no unified scheme available to explain a separation of colour and luminance information in the visual system. Some theoretical considerations and most promising approaches to solving the problem are noted, but it is suggested that there may be definite limits to the ability of the visual system to achieve complete separation of colour and luminance from the retinal signal.