The far-anchor effect: errors in the perception of motion and implications for aviation safety

The far-anchor effect is responsible for a motion-in-depth illusion that has only recently been recognized. When viewing conditions are limited, motions in depth of a farther target in a two-object display may readily be perceived as opposite motions in depth of the nearer target. The present studies determined whether this error could be avoided through controlled fixation or training with feedback. Under conditions of reduced visibility, participants (college students) viewed 64 two-target presentations varying in the position of the moving target and its direction of motion. Neither fixation instructions nor informational feedback about motion errors affected the occurrence of the basic illusion, nor did a vertical separation of the targets eliminate the main effect, indicating the robustness of the motion illusion under some relatively realistic variations. Such errors in judging motion in depth have significance for both midair collisions between aircraft and ground-incursion accidents under conditions of reduced visibility. Potential applications include the elaboration of examples used in pilot training programs or in training programs for ground personnel.