Spatial and temporal contexts drive visual temporal integration via spatiotemporal normalisation

Abstract

The visual system is known to integrate sensory information across both space and time, but these dimensions are often studied separately. Here we provide novel behavioural evidence for an early integration over space and time, and propose a computational model of this integration that is biologically plausible. We designed a controlled task that forces human participants to integrate information over both space and time to perform well. Stimuli were temporally segmented rings of oriented elements and participants had to detect a missing element in the ring. We found that temporal integration was enhanced when successive visual events were temporally proximate, spatially aligned to form a continuous contour, but also, and more surprisingly, when they were brief. Notably, the spatial effects on integration are temporally asymmetric: integration is facilitated when more events are presented earlier in the sequence, and even more so when they form a collinear contour. These findings indicate that temporal integration is sensitive to both the spatial configuration and the number of visual events presented over time, supporting a continuous rather than discrete process at early visual stages. All of these results are well accounted for by a computational model in which temporal integration arises from the overlap of internal signals generated by individual visual events. These signals are shaped by a spatially and temporally tuned divisive normalisation mechanism and integrated via coincidence detection. Predictions from this model match human performance in seminal past work as well as novel stimulus displays, offering an account of how spatio-temporal interactions determine what we perceive and when.