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Time-to-collision is one of the possible sources of visual information participating in the control of deceleration when breaking a vehicle. Lee’s (1976) theory suggested that the inverse rate of expansion in the retina of an approaching obstacle, the optic variable tau (τ), and its first derivative in time, tau-dot (τ& ), provide information for, respectively, braking initiation and its intensity regulation. The purpose of this study was to test Lee’s hypotheses at the situation where a bicycle in linear trajectory is approaching a stationary obstacle. As relative quantities, τm and τ& should not be affected by the initial velocity. In three velocity conditions (high, medium, and low), participants had 23, 18 e 13 m to accelerate the bicycle until the final 14 m, when they were free to break at any time in order to stop at the obstacle. Peak velocities were 22.5, 19.5, and 16.6 m/s at 14.0, 12.0 and 10.2 m from the obstacle, respectively. Values of τm and τ& were not significantly affected by condition as expected. τm at braking initiation was 0.63, 0.62, and 0.62 s as τ& during the deceleration phase was -0.54, -0.54, and -0.55. These results strongly support the use of time-to-collision information contained in the optic flow to safely control braking initiation and intensity.

Visual control of breaking initiation and intensity in bikers: Velocity does not affect the use of time to collision information