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Albert Yonas, Lee Zimmerman, Heweon Seo, Amelia J. Alexander, Annie S. Olinick, Sara Z. Polley; The effect of luminance contrast and stroboscopic presentation on the threshold for the discrimination of approach from withdrawl. Journal of Vision 2005;5(8):730. doi: 10.1167/5.8.730.
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© ARVO (1962-2015); The Authors (2016-present)
In Minnesota last winter more than 70 vehicles crashed into the rear end of snowplows in daylight, while the frequency at night was lower. One explanation is that luminance contrast is lower in daylight when blowing snow matches the luminance of the snowplow. Low luminance contrast lowers motion sensitivity, which is vital because expansion of a retinal image specifies that approach is taking place and allows one to avoid collision. A second cause of collisions with snowplows is the use of bright, flashing, warning lights. While flashing lights increase the detectability of snowplows, they may reduce the ability to perceive optical expansion, increasing the likelihood of a collision. In this study we examined the effects of luminance contrast, duration of expansion or contraction patterns, and intermittent presentation of displays on the observer's ability to discriminate approach from withdrawal. The Quest procedure estimated the lower velocity threshold for the discrimination of events in which a simulated vehicle (a square against a darker background) either approached (expanded) or withdrew (contracted) on a screen. During each presentation the square also translated in a random direction so that perception of global motion rather than motion of a single contour was required. When presented with lower contrast displays, observers easily detected the square on the computer screen. In contrast, lowering the luminance contrast between the display and background more than doubled the velocity threshold. Observers required twice the velocity to detect expansion when the display flashed 5 times, over a one second period, compared to a continuous display. Performance was much better when 3 flashes were presented than 5. Duration and amount of expansion were also varied. Sensitivity increased linearly as duration increased. Snowplows should be designed so that continuous optical change provides information that collision will occur if the driver does not slow down.
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