Decoding time-resolved neural representations of orientation ensemble perception

Abstract

The visual system is capable of computing summary statistics of multiple visual elements at a glance. While numerous studies have demonstrated ensemble perception across different visual features, the timing at which the visual system forms an ensemble representation remains unclear. This is mainly because most previous studies did not uncover time-resolved neural representations during ensemble perception. Here we used orientation ensemble discrimination tasks along with EEG recordings to decode orientation representations over time while human observers discriminated an average of multiple orientations. We observed alternation in orientation representations over time, with stronger neural representations of the individual elements in a set of orientations, but we did not observe significantly strong representations of the average orientation at any time points. We also found that a cumulative average of the orientation representations over approximately 500 ms converged toward the average orientation. More importantly, this cumulative orientation representation significantly correlated with the individual difference in the perceived average orientation. These findings suggest that the visual system gradually extracts an orientation ensemble, which may be represented as a cumulative average of transient orientation signals, through selective processing of a subset of multiple orientations that occurs over several hundred milliseconds.