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Anurag Shrivastava, Mary M. Hayhoe, Jeffrey B. Pelz, Ryan Mruczek; Influence of optic flow field restrictions and fog on perception of speed in a virtual driving environment. Journal of Vision 2005;5(8):139. doi: 10.1167/5.8.139.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast is known to affect perceived speed, and it has been suggested that one of the reasons for difficulty in driving in fog is impaired speed judgments resulting from the contrast reduction caused by the fog (Snowden, Stimpson, & Ruddle, 1998). However, fog also reduces the area of the field from which image motion is available, in addition to contrast reduction in the near visual field. In this study we investigated the influence of reduced spatial structure from the flow field on perceived speed in a virtual driving environment, and compared this with the effects of fog. To simulate fog we used a model that reduces contrast exponentially with distance, rather than the spatially uniform reduction in contrast used by Snowden et al. To examine the effects of reduced spatial structure we removed road texture and line markings, and changed the density of roadside objects. These manipulations substantially reduced perceived speed, but exponential mist or fog had only a small effect. This was true both in the immersive environment with a head mounted display, or when subjects viewed the scene on a monitor. Thus the reduction in area of the field from which optic flow information is available, rather than contrast reduction, is at least partially responsible for reduced ability to judge speed of self-motion in foggy conditions. In addition the data suggest a role of optic flow in judgments of speed of self-motion in natural environments, in addition to the roles previously suggested for flow, such as control of heading and control of braking.
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