NORMAL VARIABILITY OF THE AMPLITUDE AND PHASE OF STEADY-STATE VEPS

The present study quantifies the amplitude and phase variability of st eady-state VEPs (S-VEPs) and compares this variability between subject s and between individual runs. The S-VEPs were recorded repeatedly in 14 normal subjects with varying spatial and temporal frequencies of si nusoidal gratings; 6 spatial frequencies (range 0.5-8.0 c/deg) with 3 temporal frequencies (4, 6 and 8 Hz) were used. A total of 75 response s were averaged and analyzed by the Fourier method, Four recordings we re obtained in each spatio-temporal combination. In general, the phase data showed small inter- and intrasubject variability. As anticipated , the amplitude data showed a large degree of intersubject variability , although the intrasubject variability was very small. In addition, i n some stimulus conditions the inter- and intrasubject variability inc reased, which thus suggested the existence of an optimal spatio-tempor al combination. Therefore, these stimulus parameters should be taken i nto consideration when S-VEPs are applied in clinical practice.