Spatial Induction of Illusory Motion

Abstract

Induced motion is not limited to continuous motions presented on a frontoparallel plane. Experiments were conducted to investigate several varieties of induced motion to which theories of induced motion must apply. The observer indicated the perceived path of motion of a vertically moving test point to which induced motion at right angles to the physical motion was added by the motion of two inducing points. In experiment 1 all motions (both apparently and physically) were in a frontoparallel plane. It was found that discrete displacement as well as continuous motion of the test and inducing points produced substantial amounts of induction. In experiment 2 the inducing points were continuously moved in stereoscopic distance rather than remaining in an apparent frontoparallel plane. A large amount of apparent motion in depth was found in the vertically moving test point and was interpreted as an induced motion in depth. In experiment 3 an alternative interpretation of the phenomenon of experiment 2, in terms of an apparent vergence for the two images of the test point, was investigated and found to be unlikely. In experiment 4, with all the points moving continuously in a frontoparallel plane, eye motions as well as induced motions were measured, with the observer fixating either the test point or an inducing point. Substantial amounts of induction were obtained under both conditions of fixation. The consequences of these findings for theories of induced motion are discussed.

Induced movement in the visual modality: An overview.

“…Induced rotation has received relatively little attention since Duncker's (1929Duncker's ( /1938 early observations (Day, 1981;Reinhardt-Rutland, 1981). Much the same is true of induced movement in depth (Fame, 1972(Fame, , 1977Gogel & Griffin, 1982;ReinhardtRutland, 1983c), and induced expansion and contraction have apparently received independent investigation in only one study (Wade & Swanston, 1984).…”

“…In some displays, particularly involving spot and frame, the inducing stimulus starts, moves steadily in one direction, and then stops (e.g., Day, Miller, & Dickinson, 1979;Duncker, 1929Duncker, /1938Rock, Auster, Schiffman, & Wheeler, 1980;Wagenaar et al, 1984;Wallach, 1959). In other displays, the inducing stimulus has oscillatory movement (e.g., Becklen & Wallach, 1985;Carr & Hardy, 1920;Gogel, 1979;Gogel & Griffin, 1982;Wallach & Becklen, 1983). Such differences raise the question of whether acceleration of the inducing stimulus may have an effect: It seems likely that induced movement from oscillatory motion can be stronger than induced movement from steady motion (Speed Effects section).…”

“…The induced stimulus is often a spot in studies of linear induced movement (e.g., Brosgole, 1966;Duncker, 1929Duncker, /1938Gogel & Griffin, 1982;Wallach, 1959;Wallach & Becklen, 1983) and occasionally in studies of induced movement in depth (Gogel & Griffin, 1982). Other induced stimuli include pairs of lines surrounded by the inducing stimulus (Fame, 1970;Nakayama & Tyler, 1978) and areas of pattern, such as gratings (e.g., Levi & Schor, 1984;Over & Lovegrove, 1973).…”

“…Suppose the physical movement is vertical and the putative induced movement is horizontal. Vector addition of the two will give a path of the induced movement at some angle to the vertical (e.g., Gogel, 1979;Gogel & Griffin, 1982;Wallach, Bacon, & Schulman, 1978). A variant of this may yield an elliptical path, the width of which is to be judged (e.g., Becklen & Wallach, 1985;Wallach & Becklen, 1983).…”

“…For induced rotation, the inducing stimulus has often been a patterned annulus surrounding and concentric with the induced stimulus (Day, 1981;Reinhardt-Rutland, 1981). For induced movement in depth, the inducing stimulation has included a surface oscillating in depth (Fame, 1970(Fame, , 1972, binocularly generated oscillation in depth of dots (Gogel & Griffin, 1982), and a rotating spiral (Reinhardt-Rutland, 1983c. Induced expansion and contraction arose from a grating "zooming in" and "zooming out" within a fixed window (Wade & Swanston, 1984).…”