DEVELOPMENT OF SPATIAL-FREQUENCY TUNED COVARIANCE CHANNELS - INDIVIDUAL-DIFFERENCES IN THE ELECTROPHYSIOLOGICAL (VEP) CONTRAST SENSITIVITY FUNCTION

We investigated the spatial frequency tuned channels underlying the co ntrast sensitivity functions (CSFs) of adults and infants. CSFs were m easured in adults and in 8-, 14-, 20-, and 32-week-old infants, using the swept-contrast visual evoked potential (sweep-VEP). At each age, 8 to 21 subjects provided complete data. Subjects viewed achromatic sin e wave gratings (0.3 to 8 c/deg) on a 20 degrees field presented on a CRT. Gratings were counterphased at 12 reversals/s (6 Hz). The second harmonic response was used to interpolate thresholds. We computed stat istical ''sources'' of individual variability (or factors) underlying CSFs, then calculated the number, nature (discrete vs. continuous) and frequency tuning of ''covariance'' channels. CSFs from adults each co ntained three spatial frequency tuned covariance channels, consistent with psychophysical results spanning a similar spatial frequency range . Covariance channels in infants shifted upward in spatial frequency w ith age, with rapid shifts occurring between 8 and 14 weeks. The chang e in scale coincided with, and was probably determined by, development al cone migration into the fovea and growth in eye size.