title: Foggy perception slows us down.
abstract: Visual speed is believed to be underestimated at low contrast, which has been proposed as an explanation of excessive driving speed in fog. Combining psychophysics measurements and driving simulation, we confirm that speed is underestimated when contrast is reduced uniformly for all objects of the visual scene independently of their distance from the viewer. However, we show that when contrast is reduced more for distant objects, as is the case in real fog, visual speed is actually overestimated, prompting drivers to decelerate. Using an artificial anti-fog-that is, fog characterized by better visibility for distant than for close objects, we demonstrate for the first time that perceived speed depends on the spatial distribution of contrast over the visual scene rather than the global level of contrast per se. Our results cast new light on how reduced visibility conditions affect perceived speed, providing important insight into the human visual system.DOI:http://dx.doi.org/10.7554/eLife.00031.001.
authors.affiliation: Department of Human Perception, Cognition and Action ,  Max Planck Institute for Biological Cybernetics ,  Tübingen ,  Germany.
authors.forename: Paolo
authors.initials: P
authors.lastname: Pretto
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bresciani
authors.forename: Gregor
authors.initials: G
authors.lastname: Rainer
authors.forename: Heinrich H
authors.initials: HH
authors.lastname: Bülthoff
mesh_terms: D000063:Accidents, Traffic / Q000523:psychology*; D000328:Adult; D001334:Automobile Driving / Q000523:psychology*; D003198:Computer Simulation; D003654:Deceleration; D005260:Female; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D011601:Psychophysics; D013028:Space Perception / Q000502:physiology*; D013647:Task Performance and Analysis; D014796:Visual Perception / Q000502:physiology*; D014887:Weather
keywords: Human; driving simulation; human psychophysics; motion perception; virtual reality