Abstract

Steady-state VEPs were recorded and analyzed using laser interference gratings in Maxwellian view as a pattern reversal stimulus and Fourier analysis. Two groups of 51 and 36 persons served as normal subjects in this study. The object of interest was the relationship of phase to spatial frequency (2-30 cycles/deg), contrast (0.1-0.99), and pattern reversal rate (2-31 rps). The phase shows a weak increase of some 10° with decreasing contrast. It remains constant with spatial frequency until local flicker effects lead to a small increase for coarse gratings (2 cycles/deg). This phase behavior appears to be approximately constant in contrast to phase and latency results of other authors,^1,2 who obtained large variations as a function of spatial frequency and contrast with VEP stimulation involving the MTF of the eye. We find constant phase both with gratings offered in isolation and with simultaneous multifrequency stimulation using superimposed laser gratings. The reversal rate was varied from 2 to 31 rps in 0.5-rps steps. The extremely linear phase relationship enables a precise latency estimation (t = 1/360 × dϕ/df). Estimated latencies correspond well with P₂ latencies. For example, estimates were 113.6 ms for a 2-cycles/deg grating, 104.9 ms for18 cycles/deg, and a value of 105.6 ms for a 30-cycles/deg grating.

© 1987 Optical Society of America