Development of the spatio-chromatic visual evoked potential (VEP): a longitudinal study.

Most prior visual evoked potential (VEP) research on the development of color vision has employed pattern-reversing stimuli that are not optimal for producing chromatic responses. We measured infant VEPs using low spatial frequency, onset-offset stimuli, modulated along the three axes of a cone-based color space (Derrington et al. [J. Physiol 1984;357, 241-265.]). Three color-normal infants were tested in a longitudinal design over the first postnatal year. One red/green color-deficient infant was also tested at 197 days. We found that VEP responses to S-axis (tritan) stimuli have their initial onset later than responses to red/green (L-M) or achromatic stimuli, and that developmental changes in VEP waveforms are more complex and longer lasting for chromatic than for achromatic stimuli. Possible mechanisms underlying these changes are discussed.