Measuring the average evoked response to light flashes: The contribution of eye-blink artifact to augmenting-reducing

There have been numerous reports relating individual differences in stimulus intensity control to psychopathology and personality. Most of these studies record the averaged evoked response (AER) to light flashes of different brightness and assess the relationship between response amplitude and stimulus intensity. The present investigation used procedures commonly employed in these studies to examine the effects of eye blinks on the AER. Twenty normal subjects were tested twice over a 1-week interval while the AER and electroocculographic (EOG) response generated by a blink were recorded. The averaged EOG was digitally subtracted from the AER to yield a blink-corrected AER. Various comparisons of amplitude measures derived from corrected and uncorrected AERs and the averaged EOG revealed that blinking contributed a pronounced artifact that tended to reduce the magnitude of AER amplitude, especially to the more intense stimuli. These findings raise questions about the validity of interpretations drawn from studies of AER augmenting-reducing, very few of which control for eye-blink artifact. The linearity of the amplitude-intensity relationship for each subject was also assessed. This analysis revealed that the data points were poorly described by a straight line and therefore that the use of linear slope to characterize the amplitude-intensity relationship is unwarranted.