Development of VEP Vernier acuity and grating acuity in human infants

To compare the developmental sequences of two basic measures of pattern vision, Vernier acuity and grating acuity, using steady state visual-evoked potentials (VEPs) and an analysis designed to isolate pattern-specific responses from those due to motion in the Vernier stimulus.

The authors recorded VEPs from 57 healthy full-term infants and 4 adults. The grating acuity stimulus was a sinusoidal grating, temporally modulated (appearance-disappearance) at a rate of 3 Hz, with spatial frequency decreasing in linear steps during each 10-second trial. The Vernier acuity stimulus was a vertical square-wave grating with portions of each bar temporally modulated to make offsets appear and disappear at a rate of 3 Hz. Vernier offset size changed in log steps from small to large offsets. The authors recorded each observer's electroencephalogram (EEG) during multiple presentations of each stimulus type, and the EEG was digitized and filtered to obtain the amplitude and phase of the response at the first two harmonics of the stimulus temporal frequency. Thresholds were estimated with an extrapolation technique that took into account the signal-to-noise ratio and phase of the response.

VEP Vernier acuity and grating acuity develop at different rates, with grating acuity approaching adult levels earlier than Vernier acuity. The within-subject relationship between VEP Vernier acuity and grating acuity follows the same developmental trajectory established by previous psychophysical studies of humans and monkeys.

This VEP technique provides a rapid estimate of Vernier acuity in infants. VEP Vernier acuity remains strikingly immature throughout the first year of life, similar to behavioral Vernier acuity. Because Vernier acuity is a sensitive measure of amblyopia, this VEP test may be useful in the future to identify amblyopia and to follow its treatment progress in pediatric patients.