Why there is less peri-saccadic compression in the dark E Brenner1, R J van Beers1, F Maij2, J B Smeets1 |
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1Faculty of Human Movement Sciences, VU University Amsterdam, Netherlands |
| Flashes presented near the time of a saccade are judged to be nearer the saccade endpoint than they really are. This peri-saccadic compression of perceived positions might result from a foveal bias that influences localisation whenever there is uncertainty about when a flash occurred relative to the saccade. Such a bias probably reflects prior expectations: people are most likely to see something if their gaze is directed at it, so if they saw it they are likely to have been looking at it. If so, why is there less peri-saccadic compression when flashes are presented in the dark than in the light? To examine whether a larger range of flash positions should be considered likely in the dark, we determined how the light level influences the likelihood of detecting flashes at different retinal locations in the presence of moving distracters. We compared a photopic and a scotopic condition. The relative likelihood of detecting flashes at higher eccentricities was higher in the dark than in the light, presumably because rods are more uniformly distributed across the retina than cones. This result supports the idea that the difference in peri-saccadic compression results from context-dependent prior expectations about perceived objects’ retinal locations. |
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