I've experienced the Ames Window optical illusion many times, including in physical forms, but the video clip below from an early 1970s episode of Australia's long-running Curiosity Show is my all-time favorite. The combination of the illusion, the pulsing analog synth sounds, and the contrast between the green background and Deane Hutton's orange sweater vest absolutely melted my brain.
From Wikipedia:
During the 1960s, the concept of "transactional ambiguity" was studied and promulgated by some psychologists based on the use of the Ames Window. This hypothesis held that a viewer's mental expectation or "set" could affect the actual perception of ambiguous stimuli, extending the long-held belief that mental set could affect one's feelings and conclusions about stimuli to the actual visual perception of the stimuli itself.
The Ames Window was used in experiments to test this hypothesis by having subjects look through a pinhole to view the rotating window with a grey wooden rod placed through one pane at an oblique angle. Subjects were divided into two experimental groups; one told that the rod was rubber and the other that it was steel. The hypothesis held that there should be a statistically significant difference between these two groups; the steel group more often seeing the rod cutting through the pane while the rubber group more often saw it as wrapping around it. These experiments were popular in university experimental psychology courses, with results sometimes supporting the hypothesis while other times not.
Although literature describing "transactional ambiguity" and the hypothesis of the perceptual effect of mental set has largely disappeared from the scene, it remains an interesting and provocative use of the visually ambiguous demonstrations for which Ames was well known, and if true provides additional scientific foundation for the "eye witness" phenomenon well known in law enforcement and research circles.
