Abstract
Understanding of the visual system can be informed by examining errors in perception. We present a novel illusion—Wandering Circles—in which stationary circles undergoing contrast-polarity reversals (i.e., flicker), when viewed peripherally, appear to move about in a random fashion. In two psychophysical experiments, participants rated the strength of perceived illusory motion under varying stimulus conditions. The illusory motion percept was strongest when the circle’s edge was defined by a light/dark alternation and when the edge faded smoothly to the background gray (i.e., a circular arrangement of the Craik-O’Brien-Cornsweet illusion). In addition, the percept of illusory motion is flicker rate dependent, appearing strongest when the circles reversed polarity 9.44 times per second and weakest at 1.98 times per second. The Wandering Circles differ from many other classic motion illusions as the light/dark alternation is perfectly balanced in time and position around the edges of the circle, and thus, there is no net directional local or global motion energy in the stimulus. The perceived motion may instead rely on factors internal to the viewer such as top-down influences, asymmetries in luminance and motion perception across the retina, adaptation combined with positional uncertainty due to peripheral viewing, eye movements, or low contrast edges.
Highlights
Understanding of the visual system can be informed by examining errors in perception
As will be discussed further in the general discussion, in spite of these similarities, the specific combination of features and resulting percept of the Wandering Circles is unique when compared with other motion illusions such as apparent motion, reversed-phi motion, and drifting-Gabors (Anstis & Ramachandran, 1986; Anstis & Rogers, 1975, 1986; De Valois & De Valois, 1991; Mather, 2017)
Before attempting to assess what the Wandering Circles may clarify about the functioning of motion perception, it is necessary to first determine the stimulus conditions under which the Wandering Circles are most readily observed
Summary
Understanding of the visual system can be informed by examining errors in perception. When an observer maintains fixation near the center of this display, after a brief period of time, the circles will appear to randomly move around (i.e., wander) Viewers differ in their perceived strength of the illusion, as well as in how long it takes for the illusion to manifest. The illusion often emerges over time, and the viewer should give themselves a few seconds of relaxed peripheral viewing before the illusion may manifest At times, these illusory motions can be quite striking, with the circles appearing to follow remarkably long trajectories. We describe the results of two experiments that probe two such factors: flicker rate and type of circle-defining contour that, in our initial observations, appear to be critically important for the manifestation of the illusion
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