Amplitude variability of the steady-state visual evoked response (VER)

The reliability of steady-state visual evoked responses (VER's) was determined for nine normal subjects using Fourier analyses with 1.0 and 0.25 Hz bin resolutions. No correlations were found between VER amplitudes and subjects' reports of attention, accommodation, fixation, or perceived organization of the stimulus. Across subjects, there was also no sustained amplitude modulation of the VER by any frequency (including alpha), and frequency drift of the VER did not contribute significantly to its amplitude variability. Modeling, using mixed sine waves to simulate different signal/noise (S/N) ratios, established that a significant portion of VER amplitude variability can be accounted for by noise which occurs at the same frequency as the VER and which is not removed by ensemble averaging.