Correlated P300b and phasic pupil-dilation responses to motivationally significant stimuli

Motivationally significant events like oddball stimuli elicit both a characteristic event-related potential (ERPs) known as P300 and a set of autonomic responses including a phasic pupil dilation. Although co-occurring, P300 and pupil-dilation responses to oddball events have been repeatedly found to be uncorrelated, suggesting separate origins. We re-examined their relationship in the context of a three-stimulus version of the auditory oddball task, independently manipulating the frequency (rare vs. repeated) and motivational significance (relevance for the participant's task) of the stimuli. We used independent component analysis to derive a P300b component from EEG traces and linear modeling to separate a stimulus-related pupil-dilation response from a potentially confounding action-related response. These steps revealed that, once the complexity of ERP and pupil-dilation responses to oddball targets is accounted for, the amplitude of phasic pupil dilations and P300b are tightly and positively correlated (across participants: r = .69 p = .002), supporting their coordinated generation.Significance Statement: Motivationally significant stimuli may trigger diffuse release of norepinephrine in many cortical regions eventually leading to both a P300 ERP and pupil dilation. However, previous studies repeatedly failed to observe a correlation between these two events. Here, we isolated a component of P300 and pupil-dilation responses that were specifically related to the occurrence of task-relevant infrequent events (auditory oddball). This revealed a strong positive association between their amplitude, measured across participants, supporting the hypothesis of a common origin.