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

Abstract

Primary objective 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. Design and methods Two conditions (eyes-closed and eyes-open) were tested using four different durations: ten, twenty, forty-five, and sixty seconds. The Diopsys™ NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha-wave with its related power spectrum. 16 visually-normal, young-adult subjects (ages 22 to 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. Results Regarding the VEP parameters, only variability of the VEP amplitude changed significantly with test duration: it decreased with increasing test duration, with the 45 and 60 second 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. Conclusions The findings demonstrate that forty-five second test durations are sufficient to minimize intra-session variability of the VEP amplitude and latency measurements, whereas several 10 second 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.

Objective assessment of visual attention in mild traumatic brain injury (mTBI) using visual-evoked potentials (VEP)

“…Lastly, the mean coefficient of variation (CV) values across all alpha wave frequencies and across all subjects ranged from 0.48-0.64, which was relatively small; this suggested good repeatability of the alpha wave responses. Thus, the Willeford et al [28,29] studies demonstrated that the VEP alpha wave component provided a reliable, objective correlate of human visual attention and, furthermore, significantly correlated with the subjective VSAT percentile score.…”

“…amplitude and latency) [19,45,46] and alpha band (8-13 Hz) power [28,29,40]. This system was used to generate an alternating checkerboard stimulus pattern, record the cortical responses and analyse the data.…”

“…This is an excellent way to extract and quantify the underlying frequency and amplitude aspects of a complex signal, and then relate the response amplitude to its specific bandwidth frequency component contribution. The software has been used successfully in the laboratory to measure human visual attention via alpha power responses in the visually-normal population [28,29].…”

“…This comparison is presented in Figure 1. More recent studies have demonstrated that the level of alpha band activity was correlated with different attentional states: eyes-closed as compared to the eyes-open condition [27][28][29], eyes closed with increased attentional demand as compared to the eyes-closed condition [28,30], visual imagery [31] and visual attention during reading [32]. These studies revealed that changes in neuronal activity occurred and were related to the different attentional states, thus producing predictable changes in the relative alpha band power contributions.…”

Objective Assessment of Eye Dominance Using the VEP

“…30,31 The system consists of a 17·15 (horizontal·vertical) degree display monitor for stimulus presentation, a second monitor for use by the experimenter for data viewing, and a computer for stimulus generation, analysis, and graphical display. The Diopsys system is available commercially and is approved by the Food and Drug Administration for both research and clinical use.…”