Amplitude and Latency Changes in the Visual Evoked Potential to Different Stimulus Intensities Journal Articles uri icon

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abstract

  • ABSTRACTVisual evoked potentials (VEPs) were recorded from five sites (T3, T4, Cz, O1, O2) to six intensities of light flashes. Peak‐to‐trough amplitudes were measured for the P100‐N120 and N120‐P200 waveforms as well as baseline (prestimulus)‐to‐peak amplitudes for each component (i.e. P100, N120, and P200). Different methods of defining augmenting/reducing were compared. These included subtracting the VEP epoch mean level from mean levels within a timeband corresponding to P100 and calculating slopes both for these values and for the P100‐N120 amplitudes across intensities. The technique of using slopes to describe amplitude‐intensity functions was found to be unjustified and misleading. The Augmenting/Reducing groups defined by the slopes of peak‐to‐trough amplitudes or slopes of the timeband “amplitudes” proved to be almost mutually exclusive. Results also showed that the frequency with which actual VEP peaks occur within the appropriate timeband is very low and differs topographically. Augmenting/Reducing was then defined by monotonic increases in the P100‐N120 peak‐to‐trough amplitudes. Augmenters and Reducers differed from each other not only for amplitude‐intensity patterns but on a number of latency measures. Hemisphere differences were also found between groups. An inverse relationship was found between occipital and vertex amplitude‐intensity patterns such that vertex augmenting was accompanied by occipital reducing and vice versa. Temporal and vertex amplitude‐intensity patterns were similar.

publication date

  • November 1982