An electrophysiological technique for assessment of the development of spatial vision

An objective visual evoked potential (VEP) technique was developed to evaluate spatial processing in humans over a wide range of ages. The constellation of stimulus conditions and analysis methods constitute a novel tool for the assessment of neural development. The key points that delineate this VEP technique are: (1) A brief, 6-s, swept-parameter stimulus with spatial frequency of square-wave grating patterns varied in octave steps, which facilitates correct accommodation and increases the likelihood of collecting uninterrupted, useable data; (2) data collection synchronous with stimulus presentation, which prevents contamination of the relevant frequency component from other frequency components in the response, thereby increasing the signal-to-noise ratio; (3) noise estimation at the response frequency of interest (second harmonic), based on a multivariate statistic (Tcirc2), which yields a realistic measure of signal-to-noise; (4) estimation of grating acuity from linear interpolation of the signal-to-noise measure; (5) monocular testing followed by multivariate statistical comparison of fellow eye data for each spatial frequency condition, which enables the determination of asymmetries within monocular neural pathways; (6) evaluation of maturation of the visual system based on vector-averaged amplitude and phase measures. Preliminary results indicate that reliable response functions are obtained from infants, children, and adults. Acuity estimates increased as a function of age. Phase values decreased consistently with increases in spatial frequency greater than 4 c/deg. Infants produced larger peak amplitude responses than did older observers, consistent with known developmental changes in cortical synaptic density. Phase data for the 2 c/deg condition provided additional evidence for the lack of maturity in the infant visual system as compared with that of older observers.