Multiplexing of EEG signatures for temporal and spatial distance estimates

The perception and measurement of spatial and temporal dimensions have been widely studied. However, whether these two dimensions are processed independently is still being debated. Additionally, whether EEG components are uniquely associated with time or space, or whether they reflects a more general measure of magnitude remains unknown. While undergoing EEG, subjects traveled a randomly predetermined spatial or temporal interval and were then instructed to reproduce the interval traveled. In the task, the subjects travel speed varied for the estimation and reproduction phases of each trial, so that one dimension could not inform the other. Behaviorally, subject performance was more variable when reproducing time than space, but overall, just as accurate; notably, behavior was not correlated between tasks. EEG data revealed during estimation the contingent negative variation (CNV) tracked the probability of the upcoming interval, regardless of dimension. However, during reproduction, the CNV exclusively oriented to the upcoming temporal interval at the start of reproduction. Further, a dissociation between relatively early frontal beta and late posterior alpha oscillations was observed for time and space reproduction, respectively. Our findings indicate that time and space are neurally separable dimensions, yet are hierarchically organized across task contexts within the CNV signal.