Variability of evoked-potential response to regularly repeated stimulation with checkerboard pattern-reversal and flashlight in healthy volunteers.

Pattern-reversal and flash-evoked potentials (EP) were analyzed in 20 healthy male volunteers (age 40-49 years) to investigate the response variability to monotonously repeated stimulation. The EPs were recorded over O2-T6. Each stimulus train consisted of 256 sweeps. The digitized signals were averaged in four consecutive, non-overlapping blocks, each consisting of 64 sweeps. The subjects were classified according to Q-factor analysis on the basis of five primary personality factors. Two-factorial analyses of variance (repeated measurement) were calculated on the baseline differences with the personality type as grouping factor. The amplitudes of the pattern-reversal EP were increased, those of the flash EP, with one exception, decreased as the stimuli were successively repeated. Differential effects of the personality type on the latencies of the positive components of both VEPs were observed.