Visual Factors in the Avoidance of Front-To-Rear-End Highway Collisions

Abstract

Two visual factors in the avoidance of front-to-rear-end collisions are (a) judging time to collision so as to control braking optimally on a moment-to-moment basis, and/or (b) judging one's heading relative to the lead car so as to steer appropriately. It is known that time to contact equals θ/(dθ/dt) and it is also known that the eye is sensitive to θ and, separately, (dθ/dt) (θ is the angular size and (dθ/dt) is the rate of increase of angular size). But whether the eye is sensitive to the ratio (θ/(dθ/dt) and, if so, whether drivers use this information are further questions. We report here that the human visual system does contain neurons sensitive to the ratio θ/(dθ/dt) rather independently of θ and (dθ/dt). It is important that the driver looks directly at the lead vehicle: sensitivity to (dθ/dt) falls off steeply in peripheral view. But, over a wide range, sensitivity to (dθ/dt) is independent of contrast. In addition to the classical disparity-driven system for binocular depth perception, there is a separate binocular system for motion in depth. Precise judgements (0.2 deg) of heading are supported by this stereomotion system, but on the other hand about 20% of the population have stereomotion “blind spots” (i.e. field defects). Monocularly-available informations can also support precise judgements of heading, and field defects seem to be rare. Field studies on flight simulators and telemetry-tracked jet aircraft showed that laboratory measures of sensitivity to (dθ/dt) and to the rate of expansion of the optical flow field predicted intersubject differences in performance on flying tasks that were closely related to the rear-end collision situation.