Gradient-Offset Induced Motion

Po-Jang Hsieh

Dartmouth College, USA

When a gradient stimulus, whose luminance contrast ranges gradually from white on one side to black on the other, is made to disappear all at once so that only the uniform white background remains visible, illusory motion is perceived. This motion lasts ~700ms, as if the stimulus moves from the low to the high luminance contrast side. This gradient-offset induced motion does not occur for equiluminant color-defined gradient offsets, suggesting that it relies mainly on the magnocellular pathway. We hypothesize that this illusion is caused by the difference of decay rates within the gradient afterimage.

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Illusory motion induced by the offset of stationary luminance-defined gradients Po-Jang Hsieh, Gideon P. Caplovitz & Peter U. Tse Vision Research. 2006. 46:970-8

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The Occlusion Velocity Illusion

Evan Palmer & Phillip Kellman

Harvard Medical School & UCLA, USA
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The Occlusion Velocity Illusion shown in the video demonstrates that when one part of a moving object goes out of view before another part, the two pieces appear misaligned, even though they are not (top row). This illusion can be counteracted by misaligning one portion of the rod in the direction opposite to the perceived misalignment (middle row). If observers are instructed to attend to the rod’s shape only within the blue box, they are still subject to the illusion (bottom row). This final observation indicates that the illusion is obligatory and not under volitional control.

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Motion-Illusion Building Blocks

2005 First prize
Arthur Shapiro & Justin Charles

Bucknell University, USA
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A number of well-known motion illusions arise when luminance modulates next to a stationary edge (e.g., Anstis and Rogers, 1975; Gregory and Heard, 1983). Here, we reduce these phenomena to four novel elemental conditions and show how these conditions can be combined (like building blocks) to generate an infinite number of new illusory configurations.
Click on the “Elemental Conditions” button in the accompanying movie . In the top two panels, the luminance of the edge modulates next to stationary black or white center fields; in the bottom two panels , the luminance of the center modulates next to black or white stationary edges (Figure 1A shows one frame of the movie). In all four conditions, the fields appear to move even though they maintain a fixed spatial position. The apparent direction of motion may seem counter-intuitive: when the luminance of a modulating edge is similar to the luminance of the center, the motion is outward, whereas when the luminance of a modulating center is similar to the luminance of the edge, the motion is inward.

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Visual illusions based on single-field contrast asynchronies Arthur G. Shapiro, Justin P. Charles & Mallory Shear-Heyman Journal of Vision. 2005. 5:764-82

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Two-Stroke Apparent Motion

2005 Second prize
George Mather

Sussex University, UK

The illusion contains two pattern frames depicting a moving image (hence two-stroke) which are displayed using a technique that creates an impression of continuous forward movement.

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Two-stroke: a new illusion of visual motion based on the time course of neural responses in the human visual system George Mather Vision Research. 2006. 46:2015-8

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Backscroll Illusion

Kiyoshi Fujimoto

Kwansei Gakuin University, Japan
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Backscroll illusion is the apparent motion perceived in backgrounds of movie images that present locomotive objects such as people, animals and vehicles. In the attached movie, a human figure presents a walking gait against a counterphase grating. Although the grating has physical motion energies equally in the left and right directions, it appears to drift in a direction opposite to that of the gait.

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Backscroll illusion in far peripheral vision Kiyoshi Fujimoto & Akihiro Yagi Journal of Vision. 2007. 7(8):16, 1–7

Backscroll illusion: apparent motion in the background of locomotive objects Kiyoshi Fujimoto & Takao Sato Vision Research. 2006. 46:14-25

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ECVP Waves

Akiyoshi Kitaoka

Ritsumeikan University, Japan

This stationary image appears to wave without effort. The elemental illusion is our revised version of the peripheral drift illusion, in which the direction of illusory motion is black-to-dark-gray and white-to-light-gray (Kitaoka and Ashida, 2003). In this image, blue and yellow correspond to dark gray and light gray, respectively.

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