EFFECT OF SPATIAL-FREQUENCY ON TRANSIENT AND STEADY-STATE VEPS - STIMULATION WITH CHECKERBOARD, SQUARE-WAVE GRATING AND SINUSOIDAL GRATING PATTERNS

We recorded VEPs to the alternation of checkerboard, square-wave grati ng and sinusoidal grating patterns to evaluate the contribution of the fundamental spatial frequency and higher harmonic components in 12 no rmal subjects. Their fundamental spatial frequencies were equated and ranged from 0.5 to 8.0 c/deg. Both the transient VEP (T-VEP) and stead y-state VEP (S-VEP) were obtained. The latency and amplitude of P100 o f T-VEPs were measured. S-VEPs were Fourier analyzed, and phase and am plitude of the second harmonic response were measured. The mean P100 l atency and the mean phase had a U-shaped function with a peak at a fun damental spatial frequency of 2.0 c/deg irrespective of the stimulus p atterns, while the mean P100 amplitude and the mean amplitude of S-VEP s did not show such spatial selectivity. At low and medium spatial fre quencies, differences in P100 latency, phase and amplitude between pat tern types were more pronounced. However, this difference became insig nificant at high spatial frequencies. These results indicate that VEP responses are predominantly determined by the fundamental spatial freq uency, and that the contribution of higher harmonics to VEP responses is not negligible. Our results are consistent with the concept that th e human visual system may use spatial frequency-domain information.