Vector analysis of rotary motion perception

Abstract

Five displays with light dots at two or three rim locations on a wheel that rolled inside a hoop of twice the wheel's diameter were observed. In this arrangement the motion paths of the rim dots are straight and are apparently more readily perceived than the cycloids on which rim dots move when the wheel rolls on a plane. Circular dot motion, the apparent result of vector analysis, is, however, often perceived as an alternative to linear dot motion. New findings that had been obtained in experiments with two of Johansson's motion patterns that demonstrated vector analysis were shown to apply to this rolling wheel display. They are here presented in the context of a recent interpretation of Johansson's findings. It regards the simultaneously perceived motions that Johansson's displays yield as the direct result of two kinds of proximal stimulation, made possible by vector analysis taking place between distal and proximal stimulation. The following findings are reported. Adding a stationary dot in the periphery of the displays increased linear and decreased circular perceived motion when the displays were freely viewed. The perception of linear motion, which is given by subject-relative stimulation, and the perception of circular motion, which is given as orientation change, can combine to form perceived elliptic motion paths. This happened frequently, regardless of whether the linear motion was given by means of ocular pursuit or as retinal image path.A point on the edge of a rolling wheel moves through an arched path, called a cycloid. A cycloid is the kinematic resultant of two component motions, one circular and the other translatory. When a rolling wheel is observed under ordinary conditions, these two component motions are simultaneously perceived, and the cycloids are not seen. Only when, in the dark, a light dot is fixed to the wheel edge is its cycloid path seen. When a second light dot is added, the cycloid paths of the dots are no longer visible; rather, the two dots appear to move about each other. Experiments of this sort were first done by Duncker (1929), who credited Rubin (1927) for suggesting them. Duncker did not expose two points on the wheel edge but, in most of his experiments, a light dot at the wheel's center and another dot at a midpoint between the center and the wheel edge. Nevertheless, he often obtained reports that one dot circled about the other or that the dots revolved about a common center. Duncker thought of these motions as analogues to certain features of induced motion, to which he referred as "separation of systems."Eventually, Johansson (1950) introduced the term' 'vector analysis" to refer to the perceptual process that takes This work was supported by Grant 11089 from the National Institute of Mental Health to Swarthmore College, Hans Wallach, principal investigator. We are grateful to Martha Teghtsoonian for her help in writing this report and to Dennis R. Proffitt for his helpful criticism of our presentation.H. Wallach's mailing address is: Department of Psychology, Swar...

The rubber square illusion

“…Therefore, processes of spatial interpolation provide no basis for predicting changes in size, however slight. At the same time, however, motion signals specifying square rotation are obviously above threshold and factors that "glue" the occluded filled square to the occluding black pattern, or perhaps to a more salient lack of configural change (22) of the filled visible portion of the square, specifying rigid rotation. These factors may explain the difference with the effect of a similar manipulation on the illusion studied by Shiffrar & Pavel (14) , which contained such configural change due to relative motion between the occluding and the occluded surface.…”