Two sinusoids: 6 - 1 perceptions

An interference of two sinusoids creates ambiguous stimulus which, when observed, can result into five alternating perceptions and another one, physically plausible, but hardly perceptible.

The motion created as multiplication of slowly moving and stationary sinusoids can evoke following perceptions:

1. leftward moving spindles – press “1D Cue” and fixate one of the blue dots;
2. rotating rigid double-helix – unselect all buttons (green ones) press “Helix Cue” and when you will have filling that the cues rotate press “Dot Curve”;
3. rigid double-helix rotating in opposite direction – as in the previous point, but after “Helix Cue” press “Switch”;
4. flexible ribbon with weaving edges – unselect all buttons but “Dot Curve” and then press “Ribbon Cue”. Try to imagine that thick line is closer to you, it is not rotating, but it is waving just as diver’s fins (up and down);
5. flexible ribbon with weaving edges 2– as in the previous point, but press “Switch” to help imagine that the other edge is closer to you;
6. bouncing dots – there is still one possible interpretation, which is hard or even impossible to perceive. Physically the dots are bouncing up and down without any change of their horizontal position. To perceive the bouncing dots is, however, unachievable without breaking the curve context. To explore this select “Bounce” and “Dot curve” button.

First five described perceptual experiences can be gained from dotted or full curve or just with beam cue as it can be explored in the Flash application. As soon as the perceptions are developed, the observer can switch among them voluntarily (eye movements can help) or the perceptions switch implicitly without an effort.

When I explored illusion literature to verify originality of my pursuance, I found that related observation was described as moving diamonds versus double helix rotation. Gilbert, S. (1991) "A New Kinetic Depth Illusion for Introductory Psychology and Sensation and Perception Courses." Teaching of Psychology 18(1): 55-56.

If motions are not smooth enough, try to decrease quality of the Flash playback. Right click on the movie and select Quality low.

Jan Kremlacek
jan.kremlacek@lfhk.cuni.cz

Charles University in Prague, Faculty of Medicine in Hradec Kralove