Why fog increases the perceived speed

Abstract In the first experiment we investigated the effect of reduced visibility on the produced speed in a driving simulation. Participants were required to drive at a target speed of 90 km/h in different visibility conditions. We found that when realistic fog was simulated, the driving speed was reduced accordingly to the fog density. When a uniform reduction of the image contrast was implemented, no effects were observed on the produced speed. We speculated that fog reduces selectively the visibility of the distant region of the scene and leaves visible only the proximal area that contains high angular velocities. We hypothesized that the perceived speed is then biased by the available raw velocity signals from the visual field. In the second experiment we addressed the question whether the observed behavioral effect has indeed a perceptual origin. In a psychophysical task we asked the participants to estimate the speed of moving scenes when the sight was limited either to the periphery (high angular velocities) or to the center (low angular velocities) of the field of view. According to our hypothesis, we found that when the central region was occluded, the speed at the periphery was perceived as being higher, and conversely, when the peripheral region was missing the speed at the center was perceived as being lower. We conclude that the speed reduction while driving in fog is due to a non-optimal perceptual compensation for the hidden central region with low angular velocities, which causes an overestimation of the driving speed.

[1]  Karl R. Gegenfurtner,et al.  Contrast dependence of colour and luminance motion mechanisms in human vision , 1994, Nature.

[2]  Astros Chatziastros,et al.  Changes in optic flow and scene contrast affect the driving speed , 2006 .

[3]  J. Dichgans,et al.  Differential effects of central versus peripheral vision on egocentric and exocentric motion perception , 1973, Experimental Brain Research.

[4]  N Osaka,et al.  Speed estimation through restricted visual field during driving in day and night: naso temporal hemfield differences , 1988 .

[5]  K R Gegenfurtner,et al.  Seeing movement in the dark , 1999, Nature.

[6]  Heinrich H. Bülthoff,et al.  Velocity Perception in 3-D Environments , 1996 .

[7]  Astros Chatziastros,et al.  The role of scene contrast and optic flow on driving speed , 2006 .

[8]  B. Moulden,et al.  The Standard Deviation of Luminance as a Metric for Contrast in Random-Dot Images , 1990, Perception.

[9]  G G Denton.  The Influence of Visual Pattern on Perceived Speed , 1980, Perception.

[10]  S Anstis,et al.  Footsteps and Inchworms: Illusions Show That Contrast Affects Apparent Speed , 2001, Perception.

[11]  C. Tyler,et al.  Bayesian adaptive estimation of psychometric slope and threshold , 1999, Vision Research.

[12]  R. Snowden,et al.  Speed perception fogs up as visibility drops , 1998, Nature.

[13]  Robert J. Snowden,et al.  Textured backgrounds alter perceived speed , 2000, Vision Research.

[14]  J. Gibson.  The perception of the visual world , 1951 .

[15]  P. Thompson,et al.  Human speed perception is contrast dependent , 1992, Vision Research.

[16]  Marc Green,et al.  Contrast detection and direction discrimination of drifting gratings , 1983, Vision Research.

[17]  M. A. Recarte,et al.  Perception of speed in an automobile: Estimation and production , 1996 .

[18]  Stuart Anstis,et al.  Moving objects appear to slow down at low contrasts , 2003, Neural Networks.

[19]  Tatsuto Takeuchi,et al.  Velocity discrimination in scotopic vision , 2000, Vision Research.

[20]  William A. Schaudt,et al.  Contrast gradients increase apparent egospeed while moving through simulated fog , 2010 .

[21]  A. Kemeny,et al.  Evaluating perception in driving simulation experiments , 2003, Trends in Cognitive Sciences.

[22]  P. Thompson.  Perceived rate of movement depends on contrast , 1982, Vision Research.

[23]  Leonard Evans,et al.  Traffic Safety and the Driver , 1991 .