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.