IDENTIFYING THE ACCELERATION OF VISUAL TARGETS

Subjects were required to distinguish between accelerated and constant‐velocity motion of targets. For different viewing times, ‘group thresholds’ were more nearly the same when relative acceleration was expressed in terms of total change of velocity during the viewing interval (v̇v/v̈) than when in terms of change per unit time (δv/v̈). This suggests that accelerated motion is identified by comparison of early and late velocities rather than by direct sensing. Also it was shown, through reference to other studies, that it is more difficult to identify gradual change of velocity than to identify instantaneous change or to discriminate between two ongoing motions of different constant velocities.