Effect of test duration on the visual-evoked potential (VEP) and alpha-wave responses

The purpose of this study was to assess the effect of test duration on the visual-evoked potential (VEP) and related alpha power spectrum measures. Two conditions (eyes-closed and eyes-open) were tested using four different durations: 10, 20, 45, and 60 s. The Diopsys (TM) NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha wave with its related power spectrum. Sixteen visually normal, young-adult subjects (aged 22-25 years) participated in the experiment. The stimulus for the eyes-open condition consisted of a black-and-white, alternating checkerboard pattern with a small central fixation target. All trials were performed during one session. Regarding the VEP parameters, only variability of the VEP amplitude changed significantly with test duration. Sentence should end with a period, not a colon. It decreased with increasing test duration, with the 45- and 60-s trials showing similarly low variability. Regarding the alpha-wave parameters, test duration did not have a significant effect on either the mean alpha power or its variability across trials. The findings demonstrate that forty-five-second test durations are sufficient to minimize intra-session variability of the VEP amplitude and latency measurements, whereas 10-s test durations may be sufficient for accurate measurement of the alpha wave. Optimization of test duration allows for repeatable measures with less total test time. This is especially important for special clinical populations.