The development of the chromatic visual evoked potential

Abstract

Evidence exists to suggest that visual function of very young infants is not cortically controlled and may in fact be mediated by a more primitive subcortical system. Visual evoked potentials (VEP) are used widely as a clinical and research tool and in this study the development of the chromatic VEP was investigated. Chromatic vision is a cortical function, hence the presence of a chromatic VEP may suggest the presence of a functioning cortical pathway.Using pattern reversal stimuli of red and green checks, the presence and morphology of the transient chromatic VEP were assessed. The checkerboards reversed in chromaticity and control of the relative brightness (luminance) of the checks allowed the production of a range of stimuli of different red/green luminance ratios. A black/white stimulus was included in all trails for comparison. VEPs to these stimuli were recorded from 36 infants aged between 1 and 14 weeks post‐term. Fourteen of these infants were then assessed on two further occasions to monitor the longitudinal development of the chromatic VEP. All infants tested demonstrated clear VEPs to achromatic stimuli and to those red/green stimuli that contained luminance information. As the luminance information within the stimuli decreased, the morphology of the wave changed with the major component (P1) becoming diminished and delayed. No VEP could be recorded from any infant less than 7 weeks post‐term at time of testing when using an isoluminant stimulus. In the longitudinal study, all of the infants, who initially demonstrated no response to isoluminant stimuli, did so on reaching their eighth post‐term week.These results would suggest that those channels responsible for the processing of chromatic information do not function until the eighth post‐term week. During the period prior to this, visual processing takes place via a colour‐insensitive pathway, probably subcortical.