© 2009 Richard Russell

In the Illusion of Sex, two faces are perceived as male and female. However, both faces are actually versions of the same androgynous face. One face was created by increasing the contrast of the androgynous face, while the other face was created by decreasing the contrast. The face with more contrast is perceived as female, while the face with less contrast is perceived as male. The Illusion of Sex demonstrates that contrast is an important cue for perceiving the sex of a face, with greater contrast appearing feminine, and lesser contrast appearing masculine.

Russell, R. (2009) A sex difference in facial pigmentation and its exaggeration by cosmetics. Perception, (38)1211-1219.

© 2008 Papathomas

The well-known hollow-mask illusion: hollow masks appear as normal faces that “follow” viewers who move in front of them. Also, when a hollow mask rotates on a turntable, it appears to turn opposite to the actual direction of the turntable.
An interesting variant: If we add 3-D objects to the mask (e.g., a cigarette) or attach 3-D eyeballs on the whites of the eyes, what will the percept be when we turn the mask? Answer: The result is a compelling illusion in its own right; these objects appear to rotate in the opposite direction to that of the mask.

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Click on the big button to toggle between a blurred version of the display and an unblurred version. When the display is blurred, the motion is dramatic; when the display is not blurred, there is only minimal motion. The effect can also be seen with a defocused lens. Blur eliminates high-spatial frequencies. It does not add information to the image. Why, therefore, does the removal of high-spatial frequencies add motion to the display? The buttons and levers allow control over the many of the parameters in the display.

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Here we present a new multistable stimulus generated by continuously rotating an ellipse behind four fixed occluders. Observers can perceive one of four percepts: (1) a continuously morphing cross, (2) two independent perpendicular bars oscillating in depth, (3) a rigidly rotating ellipse observed behind the occluders, or (4) a fixed cross observed through a continuously rotating, elliptical aperture.

The bar – cross – ellipse illusion: Alternating percepts of rigid and nonrigid motion based on contour ownership and trackable feature assignment Gideon P. Caplovitz & Peter U. Tse Perception. 2006. 35:993-7

(© 2005 Dejan Todorović)

Shading is a powerful way to represent the relief of 3-dimensional objects in pictures. However, the way our vision interprets shaded images depends on the shape of their contours. Here two different contours of the same shading pattern convey two different reliefs, joined into an impossible object.

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Powerpoint Presentation