On-demand surround suppression explains the spatiotemporal window of the tilt illusion

Abstract

What we see at one location depends on what surrounds it. Such contextual effects are thought to arise from neural signals that travel across the retinotopic representations. Because these signals need more time to travel longer distances, a more distant surround should influence perception most strongly when presented earlier, compensating for its delay. We tested this prediction in human observers using a visual illusion in which a central target appears tilted away from the orientation of its surround (tilt illusion). Measuring the temporal window of this illusion using psychophysical reverse correlation revealed the opposite: the most effective surround occurred progressively later as distance increased. Computational modelling demonstrated that this reversal is explained if the visual system sends out a query that recruits contextual information on demand. Perceptual appearance may thus be constructed through temporally unfolding interactions in which context is actively gathered, not passively received.