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Brett R Fajen, Rom S David; Speed information and the visual control of braking to avoid a collision. Journal of Vision 2003;3(9):555. doi: 10.1167/3.9.555.
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Using closed-loop computer generated displays in which observers adjusted a hand brake to stop at an object in the path of motion, Yilmaz and Warren (1995) provided evidence to support Lee's (1976) hypothesis that people use the first derivative of the optical variable tau (“tau-dot”) to control braking. In addition, they found only minor differences when speed and distance cues were removed, suggesting that successful braking can be achieved on the basis of tau-dot alone. More recently, Andersen, Cisneros, Atchley, and Saidpour (1999) reported that passive judgments of upcoming collisions during constant deceleration approaches to an object were also influenced by information about speed of self-motion provided by edge rate. The purpose of this study was to further explore the role of speed information in actively controlled braking. Participants sat in front of a large projection screen and viewed computer generated displays simulating approaches to a stop sign. They used a force-feedback joystick as a hand-operated brake to stop as closely as possible to the object. Initial distance and time-to-contact were varied, and information about speed was manipulated by adjusting the simulated eye height above a textured ground surface, which alters the relation between speed of self-motion and rate of optic flow. To ensure that participants were unaware that eye height varied, the ground texture was rescaled with eye height so that texture density was the same on every trial. The results indicate that braking is influenced by the rate of optic flow. When eye height was lower than normal, observers overshot the required deceleration and stopped short of the target. When eye height was above normal, observers undershot the required deceleration and often collided with the object. Braking profiles from each individual trial were analyzed to determine the influence of rate of optic flow on both the direction and magnitude of brake adjustments.
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