Abstract
It is known that passively continuous viewing of a transparent cylinder, which rotates rightward physically, may lead to perceptual alternation between two opposite rotations: rightward (real) and leftward (virtual), as shown in Movie 1. The leftward rotation is regarded as virtual, since it does not exist physically. Once the virtual rotation is perceived, fixating any part inside of the cylinder may switch the virtual rotation immediately back to the real one. On the contrary, after passively viewing of the real rotation for a while (several minutes), the real rotation readily turns into the virtual one by fixating a nearby object outside the cylinder (a finger outside or a reference mark on the back wall, as shown in Movie 2). Fixating inside of cylinder results in the disappearance of the virtual rotation, while fixating outside of cylinder results in the appearance of virtual rotation. In other words, fixation can both facilitate and inhibit the virtual rotation. These phenomena occur both binocularly and monocularly. Fixating the top ring of the cylinder in real rotation may also leads the perceived rotation reversal of the pattern in the middle part of the cylinder.
Fixation-induced perceptual alternation is able to account for the asynchrony of perceptual alternation of multiple rotating spheres consisting of ambiguous dots. For instance, in an array of eight identical rotating spheres arranged in two rows of four, perceptual alternation may occur asynchronously for these eight spheres (http://www.uq.edu.au/nuq/jack/8spheres.html). Since it is hard (or nearly impossible) to fixate all eight spheres simultaneously, passively fixating some of these eight spheres (for instance the middle two or four) may lead to the “out-of-fixation” of the remaining spheres. Asynchrony of perceptual alternation for the whole set of eight rotating spheres occurs when fixation-induced perceptual alternation occurs for these remaining spheres.