Temporal tuning of repetition suppression across the visual cortex.

The visual system adapts to its recent history. A phenomenon related to this is repetition suppression (RS) - a reduction in neural responses to repeated compared to non-repeated visual input. An intriguing hypothesis is that the timescale over which RS occurs across the visual hierarchy is tuned to the temporal statistics of visual input features, which change rapidly in low-level areas but are more stable in higher-level areas. Here, we tested this hypothesis by studying the influence of the temporal lag between successive visual stimuli on RS throughout the visual system using fMRI. Twelve human volunteers engaged in four fMRI sessions in which we characterized the BOLD response to pairs of repeated and non-repeated natural images with inter-stimulus intervals (ISI) ranging from 50 to 1000 milliseconds to quantify the temporal tuning of RS along the posterior-anterior axis of the visual system. As expected, RS was maximal for short ISIs and decayed with increasing ISI. Crucially, however, and against our hypothesis, RS decayed at a similar rate in early and late visual areas. This finding challenges the prevailing view that the timescale of RS increases along the posterior-anterior axis of the visual system and suggests that RS is not tuned to temporal input regularities.