Objective: Although P300 is regarded as cognitive or endogenous, studies have demonstrated that stimulus intensity influences the component. To isolate effects of hearing from cognition, two experiments were designed to compare the effects of variation in stimulus intensities with naturally occurring differences in hearing thresholds.
Methods: In experiment 1, 18 participants were tested with 5 auditory oddball event-related potential (ERP) paradigms with different intensities. In experiment 2, an auditory oddball ERP task was completed by 3 groups of participants with different hearing thresholds (n=57). P300 was then correlated with block design and matrices from Wechsler's abbreviated scale of intelligence.
Results: At Cz and Pz, manipulation of intensity had less effect on P300 than the observed differences between groups with different hearing thresholds. At Fz, however, the effect of manipulations of stimulus intensity was greater than the effect of naturally occurring differences in hearing thresholds. P300 still correlated in predicted directions with cognitive tests after correcting for the estimated effect of differences in hearing.
Conclusions: The results indicate that P300 is an index of cognitive function even when the relationship is corrected for perceptual differences, at least at posterior scalp areas.