8 #Winning Visual Illusions You'll Have To Watch Twice

Each year, a satellite organization of the Visual Sciences Society holds a contest for the best visual illusions of the year. Well this year's finalists have been announced and the 9th annual contest, on May 13, 2013, will showcase and debut each of these 10 new illusions that have been created and studied over the past year or so. Although these latest visual wonders won't be released by the judges until the winner is announced, we can still experience the winning illusion from each of the last 8 years. [thumbnail from:]

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2012 -- The Disappearing Hand Trick

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From Illusion of the Year:

This multi-sensory illusion uses vision, touch and position sense to create the illusion that the hand has disappeared. The felt positions of the hands are gradually adapted without the participant noticing so that the real locations of the hands end up further outwards than their perceived locations. When the right hand is removed from vision and the participant reaches across to touch it, all they can feel is the empty table. The combined loss of vision and touch creates a powerful illusion that the hand is missing and was designed to simulate loss of awareness in stroke patients.

2011 -- Silencing Awareness to Change By Background Motion

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From Harvard's Vision Lab:

Play the movie while looking at the small white speck in the center of the ring. At first, the ring is motionless and it’s easy to tell that the dots are changing color. When the ring begins to rotate, the dots suddenly appear to stop changing. But in reality they are changing the entire time.

2010 -- Impossible Motion

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From Illusion of the Year:

In this video, wooden balls roll up the slopes just as if they are pulled by a magnet. The behavior of the balls seems impossible, because it is against the gravity. The video is not a computer graphic, but a real scene. What is actually happening is that the orientations of the slopes are perceived oppositely, and hence the descending motion is misinterpreted as ascending motion. This illusion is remarkable in that it is generated by a three-dimensional solid object and physical motion, instead of a two-dimensional picture.

2009 -- Feature Blur and the Break of a Curveball

From Illusion Sciences:

When you look directly at this one-ring display, you can discern two sources of information (the ring will spin one way, and the motion caused by the internal lines goes the other way). But when you look at this display peripherally, it becomes difficult to separate the two sources of information, and the internal motion drives the perceived direction of the ring. (To look at the display with your peripheral vision, focus your eyes on a spot a few inches above the display.)


Now, when specifically applied to a curveball, feature blur acquires a "practical" component. Play with the interactive curveball perceptual puzzle here, which was also published as a research hypothesis here.

2008 -- Filling in the Afterimage After the Image

From Illusions of the Year:

Fixate your gaze on the center of one of the figures and stare at it for some time (20-30 seconds) while it cycles (without moving your eyes). After several iterations you’ll start noticing that the empty outlines fill in with ghostly redish or bluish colors! These illusory colors are called “afterimages”. Interestingly, the colors of the afterimages vary, which is puzzling because they come from the same original figure. Moreover, the shape of the outlines determines the filled-in color, which is complementary to the color of the same shape in the original figure.
What’s happening?
It is well known that viewing a colored surface can induce a vivid afterimage of the complementary color (for example, the color red induces a greenish/bluish afterimage). Our illusion shows that a colored image can produce different colored afterimages at the same retinal location. The perceived afterimage colors depend on the contours that are presented after the colored image. More specifically, the illusion shows that the afterimage colors spread and mix between those contours. In addition, alternating different contours after the original colored image causes rapidly switching afterimage colors.

2007 -- The Leaning Tower Illusion

From Illusion of the Year:

Here is a novel illusion that is as striking as it is simple. The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more, as if photographed from a different angle. The reason for this is because the visual system treats the two images as if part of a singlescene. Normally, if two adjacent towers rise at the same angle, their image outlines converge as they recede from view due to perspective, and this is taken into account by the visual system. So when confronted with two towers whose corresponding outlines are parallel, the visual system assumes they must be diverging as they rise from view, and this is what we see. The illusion is not restricted to towers photographed from below, but works well with other scenes, such as railway tracks receding into the distance. What this illusion reveals is less to do with perspective, but how the visual system tends to treat two side-by-side images as if part of the same scene. However hard we try to think of the two photographs of the Leaning Tower as separate, albeit identical images of the same object, our visual system regards them as the ‘Twin Towers of Pisa’, whose perspective can only be interpreted in terms of one tower leaning more than the other.

2006 -- The Freezing Rotation Illusion

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From Illusion of the Year:

An object (e.g. airplane) is turning on a surround (greenhouse), which is swaying back and forth. Observe the rotation of the object. Is it turning smoothly all the time? Or does it “freeze” from time to time? Convince yourself by covering the swaying surround that the object is really turning continuously. If the object is swaying back and forth and the surround is turning continuously we do not perceive a slow-down of the surround. Assuming a stable surround, our visual system probably uses the surround as a reference to measure motion of the included objects.

2005 -- Motion-Illusion Building Blocks

From Illusion of the Year:

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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