Conference on Cognitive Computational Neuroscience

When presenting multiple visual items simultaneously in the receptive field, the neurophysiological response is surprisingly lower than presenting the identical items sequentially. However, the underlying computations of this suppression effect are not well-understood. Here, we leveraged population receptive field (pRF) models to computationally test how linear, compressive spatial, or compressive spatiotemporal summation contributes to suppression at the voxel level. We collected two fMRI experiments in 10 subjects: (i) retinotopy to estimate pRFs and (ii) an experiment with simultaneous or sequential stimuli, both varying in duration and size. In V1, there was no simultaneous suppression and responses were larger for bigger stimuli. This was well-predicted by linear pRFs. However, the linear model failed to capture larger responses in V1 for brief vs long durations. In V2 and high-level areas, responses were lower for simultaneous vs sequential stimuli, larger for brief vs long durations, and did not increase much with size. Both compressive pRF models predicted simultaneous suppression and the effect of stimulus size, but only the compressive spatiotemporal model predicted the effect of duration. Our results suggest that compressive spatiotemporal pRFs are necessary to predict responses in visual cortex to simultaneous vs sequential stimuli and underscore the power of pRF models for providing new insights into spatiotemporal computations of sensory suppression.