Common electrophysiological signatures of relative magnitude in both space and time.

Duration processing can be indexed by the amplitude of two electrophysiological potentials, the contingent negative variation (CNV) and the late positive component (LPC). When a currently elapsing event becomes longer than that of a memorized standard, CNV amplitude begins to resolve back to baseline even if the event is not yet over, and LPC amplitude, evoked by event offset, is reduced. Using electroencephalography in 30 human participants, we examined whether these patterns were unique to explicit duration judgements or might also be observed during spatial judgements. Two dynamic visual stimuli were presented consecutively on each trial. The relative duration (temporal task) or distance (spatial task) of the second stimulus was compared to the first. Confirming prior findings, CNV dynamics and LPC amplitude reflected the relative duration of the two stimuli. However, this occurred only when duration was task-relevant during the temporal task, not when it was irrelevant during the spatial task. Moreover, CNV and LPC activity indexed relative distance only when distance was task-relevant in the spatial (not temporal) task. Together these results suggest that CNV and LPC dynamics reflect domain-general mechanisms for processing the magnitude of task-relevant stimulus features, whether in the temporal (duration) or spatial (distance) dimension.