Abstract
P300 (or P3) is a major positive complex in the human event-related potential, occurring some 300 ms after stimulus onset, and long thought to be the cortical correlate of the Orienting Reflex, our automatic attention-grabbing response to a novel stimulus. The Novelty P3 was the third P3 subcomponent discovered (after P3a and P3b) and appeared promising in its sensitivity to stimulus novelty, the defining characteristic of the Orienting Reflex. But some 15 years later it was claimed to be indistinguishable from the previously-discovered P3a. This led to a decline in interest in the field and confused nomenclature, with some studies using “P3a” and “Novelty P3” interchangeably. However, recent similar studies have again reported three subcomponents of the P3. Further, using single-stimulus habituation paradigms, in addition to P3a and P3b, a later decrementing P3 subcomponent has been reported, and recently labelled “HabP3” to avoid contention. We report three studies to resolve this chaotic situation, arguing for identification of the late subcomponent following the P3a and P3b as the Novelty P3. Reinstatement of the Novelty P3 as the central index of the Orienting Reflex will have widespread impact in a range of theoretical, practical, and clinical areas involving novelty processing and attention.
Highlights
P300 is a major positive complex in the human event-related potential, occurring some 300 ms after stimulus onset, and long thought to be the cortical correlate of the Orienting Reflex, our automatic attention-grabbing response to a novel stimulus
Our event-related potential (ERP) peaks had shorter latencies (~25 ms) than those previously reported[21], possibly reflecting subject variability and our smaller sample size, so we carried out principal components analysis (PCA) on a slightly earlier epoch of the same duration (175 to 450 ms cf. 200–475 ms)
The temporo-spatial topographies shown on the right of panel c indicate that the spatial components T1S2 (P300) and T1S1 (P3a) appear unchanged, as does T3S1; as in Study 1, these were derived from 2- and 3-factor spatial solutions, respectively
Summary
P300 (or P3) is a major positive complex in the human event-related potential, occurring some 300 ms after stimulus onset, and long thought to be the cortical correlate of the Orienting Reflex, our automatic attention-grabbing response to a novel stimulus. While the autonomic Orienting Reflex (OR) has provided a wealth of information in regard to our understanding of basic learning mechanisms, and fostered theory development, the search for a cortical correlate of this reflex has been long and difficult. It was proposed more than a quarter of a century ago that the P300 (or P3) event-related potential (ERP) component held the most promise as a cortical index of the OR1. A third P3 subcomponent, a later (360–450 ms) frontal Novelty P3 elicited by rare nontargets interspersed randomly in an attended oddball series (the “Novelty Oddball” paradigm) was reported in the mid seventies[9]. This is a variety of factor analysis, and groups ERP activity into factors that correspond to ERP components, each reflecting topographically-similar time-locked activity
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