Offset characteristic of transient and steady‐state flash visual evoked potentials

Abstract

PurposeIn ISCEV flash stimulations, the brief stimuli onset time results in an overlap of the onset and offset response in the recorded visual evoked potential (VEP). However, the influence of a prolonged onset time in flash stimulation has not been studied yet. The aim of our study was to investigate the effect of the onset time on the transient and steady‐state VEP.MethodsWe studied 8 healthy subjects (3 m, 26 ± 3.6 years) using flash stimuli (d = 10°, luminance = 350 cd/m2, contrast = 99%). For transient stimulations, stimuli were presented with an onset time of 16 ms, 34 ms, 67 ms, and 200 ms at 1Hz for 180 sweeps. The amplitudes and latencies of P2 and P3 peaks were used for analysis. For steady‐state stimulations, stimuli were presented with an onset time of 16 ms, 33 ms, and 67 ms at 7.5 Hz for 5 sweeps with 30 cycles each. The amplitudes at 7.5Hz and the ratio of the amplitudes at 7.5 Hz and 15 Hz were evaluated. VEPs were recorded using electrodes at Oz (active), FCz (reference) and FPz (ground). For statistical analysis, Friedman's test and Wilcoxon Post‐Hoc tests (α = 0.05) were used.ResultsFor transient stimulations, significant differences (p = 0.000*) were found for latencies of the P3 peaks (median: 201 ms, 216 ms, 230 ms, 319 ms; p*16/67 = 0.0078, p*16/200 = 0.0078, p*33/200 = 0.0078, p*67/200 = 0.0078). The P2 peak amplitude (17.6 µV, 18.1 µV, 16.6 µV, 16.2 µV; p = 0.3476), P3 peak amplitude (5.1 µV, 3.4 µV, 5.3 µV, 8.0 µV; p = 0.0917) and P2 peak latency (103 ms, 105 ms, 106 ms, 104 ms; p = 0.2453) showed no significant differences. For steady‐state stimulations, no significant differences were found for amplitudes at stimulation frequency (2.0 µV/Hz, 1.5 µV/Hz, 1.1 µV/Hz; p = 0.197) and amplitude ratio (0.5, 0.6, 0.3; p = 0.093).ConclusionsA prolonged onset time leads to a significant increase of the P3 peak latency in transient VEP. No significant influence of the onset time was found for steady‐state VEP. Thus, the steady‐state VEP seems to be dominated by the onset response of the flash stimulation.