REFERENCE REPULSION WHEN JUDGING THE DIRECTION OF VISUAL-MOTION

While humans are very reliable (ie give highly reproducible answers) w hen repeatedly judging the direction of a moving random-dot pattern (R DP) we find that their accuracy (ie the direction they so reliably rep ort) shows systematic errors, To quantify these errors, we presented a complete set of closely spaced directions and mapped the directional misjudgments by asking subjects to compare the perceived direction of a moving RDP with the direction of a test line. The results show misju dgments of up to 9 degrees, which are best accounted for by a tendency of the subjects to overestimate the angle between the observed motion and an internal reference direction. A control experiment in which su bjects had to judge the spatial distance between a point and a line de monstrates that these misjudgments are not confined to motion stimuli but rather seem to reflect a general tendency to overestimate the dist ance between a stimulus and a reference when they are close to each ot her.