On-demand surround suppression explains the spatiotemporal window of the tilt illusion
What we see at one location depends on what surrounds it. Such contextual e[ff]ects 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 e[ff]ective 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.