Perceived bending and stretching motions from a line of points

Abstract.— The aim of this investigation was to study to what extent bending and stretching motions can be accurately perceived. The (imaginary) “distal” stimuli were lines of points, either in bending motion with constant distances between adjacent points or in stretching motion with the same distances equal at each moment (thus making the relations between the distances constant). The proximal stimuli were produced by a computer, and the subject indicated the slant and curvature of the turning positions of the perceived motion. The result for the stimuli with motion towards the subject was that a majority of the percepts were rather close to the accurate value. That was not true, however, for the stimuli with motion away from the subject. All stimuli were ambiguous demonstrating that more information must be added to get unambiguity.