Second Thoughts: Multiple P300s Elicited by a Single Stimulus

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Event‐related potentials, P300, Feedback, Decision making

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In a previous report (Johnson & Donchin, 1978), we manipulated the discriminability of tone pairs that delivered feedback information in a time‐estimation paradigm. As in other experiments using feedback stimuli, the event‐related potentials elicited by these stimuli did not return to baseline in the 800‐ms poststimulus interval. Since we were interested in this “Slow Wave'’activity, the poststimulus interval was lengthened to 1500 ms. Averages revealed that a second positive peak was present for some of the individual subjects. To investigate this activity further, the filtered singletrial waveforms were inspected visually. These data were characterized by the presence of one, and occasionally two, positive peaks, with highly variable latencies, following the P300. These peaks were indistinguishable in frequency and general appearance from the P300s elicited by the feedback stimuli. After latency adjusting the waveforms on the peak of the second positive wave, amplitude and latency were quantified. Whereas P300 amplitude was directly related to stimulus discriminability and positive feedback elicited larger P300s than negative feedback, the amplitude of the second positive wave was constant across levels of discriminability and the same for both types of feedback. In contrast, the latencies of both waves were inversely related to stimulus discriminability and shorter following positive feedback than negative feedback. Evidence is presented to support our contention that these additional positive peaks represent P300 activity. The data are discussed in terms of what these multiple P300s reveal about human information processing.

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Citation / Publisher Attribution

Psychophysiology, v. 22, issue 2, p. 182-194