The classic P300 encodes a build‐to‐threshold decision variable

Abstract

The P300 component of the human event-related potential has been the subject of intensive experimental investigation across a five-decade period, owing to its apparent relevance to a wide range of cognitive functions and its sensitivity to numerous brain disorders, yet its exact contribution to cognition remains unresolved. Here, we carry out key analyses of the P300 elicited by transient auditory and visual targets to examine its potential role as a 'decision variable' signal that accumulates evidence to a decision bound. Consistent with the latter, we find that the P300 reaches a stereotyped amplitude immediately prior to response execution and that its rate of rise scales with target detection difficulty and accounts for trial-to-trial variance in RT. Computational simulations of an accumulation-to-bound decision process faithfully captured P300 dynamics when its parameters were set by model fits to the RT distributions. Thus, where the dominant explanatory accounts have conceived of the P300 as a unitary neural event, our data reveal it to be a dynamically evolving neural signature of decision formation. These findings place the P300 at the heart of a mechanistically principled framework for understanding decision-making in both the typical and atypical human brain.

When three is greater than five: EEG and fMRI signatures of errors in numerical and physical comparisons

“…The centro-parietal component (Fig. 4a) with the source estimated in the bilateral inferior parietal cortices showed pronounced P3b/CPP potential (Polich 2007;Twomey et al 2015). A significant interaction effect was found on the amplitudes within both stimulus-locked and responselocked ERPs (around 300 ms post stimuli and around -110 and -18 ms prior to response; see Table 5 for details; Fig.…”

“…4a). However, in light of the aforementioned methodological aspects, P3b/CPP amplitude decreases for more difficult conditions due to the temporal variability of the peak onset (Twomey et al 2015). Thus, analysing the response-locked CPP is more accurate and informative approach.…”

“…4a). In light of the interpretation of Twomey et al (2015), this slope represents the build-up rate of accumulating evidence in favour of a particular outcome. To strengthen this association, we measured the build-up rate by fitting a straight line to the signal before the response onset separately for each condition .…”

“…Several recent findings speak in favour of the latter perspective. First, Twomey et al (2015) indicated that the DV signal is supramodal as it was detected during auditory and visual oddball tasks. Second, an fMRI study implementing a saccadic task revealed that, as opposed to regions involved in conflict resolution, IPS exhibits strong trial-by-trial variations with RTs (Domagalik et al 2014;Beldzik et al 2015b).…”

“…It increases steadily with incoming evidence, peaks at the time of response execution, scales with target detection difficulty, and accounts for trial-to-trial variance in RT. Recently, Twomey et al (2015) indicated that the commonly observed centro-parietal P3b potential exhibits the same accumulation characteristics as CPP, thus it encodes the DV signal. The authors pointed out that these effects observed at the slope of response-aligned P3b have been overlooked in previous EEG studies, possibly due to the spatiotemporal overlap with distinct frontal potentials.…”