ABSTRACT
When a wheel rolls along a flat surface, a point on the wheel’s perimeter follows a cycloid trajectory. Subjects, however draw the curtate cycloid, characterized by bottom loops, rather than the cycloid to depict the path that a point on a static wheel’s perimeter would trace if the wheel were rolling. This is the curtate cycloid illusion. In Experiment 1, we show that animating the wheel does not dispel the illusion and that subjects high in spatial ability are less susceptible to the illusion than are low-spatials. Experiments 2, 3a, and 3b supported the hypothesis that the illusion occurs when subjects reallocate cognitive resources from processing a rolling wheel’s translation to computing its instant centers, the point about which the wheel is rotating at a given instant in time. This reallocation occurs only when a reference point on the wheel’s perimeter contacts and leaves the surface. We conclude that the illusion does not reflect fundamental perceptual biases, but rather stems from transient shortages of cognitive resources during the higher-level processing of the wheel’s translation and rotation.
