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Gabriel J. Diaz, Brett R. Fajen; Visual control of braking behind a moving lead vehicle. Journal of Vision 2005;5(8):317. doi: 10.1167/5.8.317.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research on visually guided braking has focused on avoiding collisions with stationary objects in the path of motion. We extended the investigation of braking to the situation of decelerating behind a lead vehicle moving at a constant speed. Our model, an extension of Fajen's (in press; VSS 04) model for braking behind a stationary obstacle, predicts that braking is controlled by keeping the perceived “ideal deceleration” between zero and maximum deceleration. For stationary objects, ideal deceleration is optically specified by optical angle, expansion rate, and global optic flow rate (GOFR). Because GOFR specifies absolute rather than relative speed, the extended model predicts a bias to brake harder than necessary when following a moving lead vehicle. The magnitude of the bias should increase at higher absolute speeds, even when relative speed is held constant. Participants performed a simulated braking task, using a joystick to slow down and maintain a short but safe headway behind a moving lead vehicle. Subject vehicle absolute speed and subject vehicle/lead vehicle relative speed were independently manipulated. Analyses focused on ideal deceleration at the onset of braking and brake adjustment magnitude. If braking behind a moving lead vehicle is biased by GOFR, then participants should brake earlier and/or harder when absolute speed is higher. To test whether participants compensated for this bias after practice braking behind a moving lead vehicle, we included a second block of trials in which the range of absolute speeds was slower, but the range of relative speeds was the same. If participants learn to compensate for the bias, then there should be an aftereffect in the opposite direction to brake too weakly behind slowly moving or stationary lead vehicles. The resulting pattern of biases is the consequence of using an identical strategy for braking behind stationary and moving lead vehicles.
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