Relationship between the horizontal-vertical illusions for velocity and extent

Studied the horizontal-vertical (HV) velocity illusion in which an object moving vertically seems to move faster than one moving horizontally at the same physical speed. 6 experiments were conducted with a total of 65 male and 47 female paid volunteers using a stimulus display consisting of a lighted L figure and 2 points of light moving in paths parallel to the 2 bars, in an otherwise dark field. Results indicate that (a) the direction of movement (upward, downward, rightward, leftward) in each orientation was not a significant variable; (b) there was no significant effect due to the movement orientation (horizontal, vertical) used as the standard; (c) the illusion persisted when horizontal and vertical paths were equated for apparent length; (d) different functions for the length and velocity illusions occurred as the separation and overlap of the motion paths were varied; and (e) the velocity illusion did not occur when S was recumbent. Results are interpreted as showing that the HV velocity illusion is not secondary to the HV length illusion but has independent determinants. (29 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved).