Aitken

In homage to Robert Grant Aitken astronomer, director of the Lick observatory, president of the University of California. Minor planet (3070) Aitken is named in his honor as well as a Moon crater 2 on the far side.

From another Aitken: Concentrating on the wheel center for a few minutes will make the wheel spin.

Somers and Adelson.

The diamonds are the same shade of gray and they are seen against light or dark backgrounds. Sets of half-ellipses have been added along the horizontal contours. The X-junctions aligned with the contour are consistent with transparency, and they establish atmospheric boundaries between strips.

Orbison

When we add oblique lines to a circle, the circle crooks and looks an ellipse, maybe...

You may understand the tendency, comparing appearances of the little circle and large circle...

The small circle is perfectly round, but seems bent because of the lines in the background.

Edward H. Adelson

Optical illusion using X-junctions to make atmospheres perceptible as such. The centers of the two diamond shaped regions are physically the same shade of light gray.

Edward H. Adelson

One can intentionally combine statistical and configural cues to produce large contrast illusions. In the ñcriss-crossî illusion, the small tilted rectangles in the middle are all the same shade of gray. The multiple psi-junctions along the vertical edges establish strong atmospheric boundaries.

Ponzo

First noticed by Mario Ponzo in 1913, size perception depends on the eye's interpretation of depth clues. The upper horizontal line segment appears to be longer.

Wertheimer-Koffka

Compare the two halves of the annulus. The left half looks subtly darker than the right one. In the presence of the bar, the brightness difference without luminance difference is a standard case of simultaneous contrast. This is probably due to retinal mechanisms.

You may need to change your observation distance to see a sizable effect.

Hermann

Dark patches appear in the street crossings, except for the ones which you are directly looking at.

If you look around in the neighboring figure you will notice the appearance and disappearance of black dots at the crossings.

(Invoked to explain FloridaÕs election problems in 2001:Ê ÒCount the black dots, recount to confirmÉÓ)

Sanders

The parallelogram illusion: Diagonals a and b are of equal length.

The researchers hypothesized that people living in highly carpentered environments would learn to interpret oblique and acute angles as displaced right angles and to perceive two-dimensional drawings in terms of depth.

Blommer

The center square at the top left looks smaller than the center square at the bottom left. Variation on the Delbeuf /Tichener observation: Identical objects are perceived as unequal in size because they are surrounded by objects of a different size.

Hering

Discovered in the 19th century by German physiologist Ewald Hering.

In this illusion, two straight lines appear curved or bowed in the context of intersecting lines with orientations that change progressively. Hiding the oblique lines from the view will reveal the fact that the horizontal bars are equally straight.

Wundt

 

Considered the founder of experimental psychology, Wilhelm Wundt introduced cognitive principles to the psychology community in the late 1880s. The overestimation of the sub tense of acute angles and the underestimation of obtuse ones was reported first by Wundt and has been confirmed repeatedly by modern studies

Delbeuf/Tichener

The center circle at the bottom right looks smaller than the center circle at the top left. Variation on the Delbeuf/Tichener observation: Identical objects are perceived as unequal in size because they are surrounded by objects of a different size.

Wertheimer-Koffka

Variation on the Wertheimer-KoffkaÊ illusion Compare the two halves of the annulus. The left half looks subtly darker than the right one. In the presence of the bar, the brightness difference without luminance difference is a standard case of simultaneous contrast.

Ehrenfels

A combination of HeringÕs and ZšllnerÕs illusions. The background of concentric circles makes the squares appear distorted. Again, judge the straightness of the lines, by hiding the background

Edward H. Adelson

Optical illusion using X-junctions to make atmospheres perceptible as such. The centers of the two diamond shaped regions are physically the same shade of light gray.

Aitken

In homage to Robert Grant Aitken astronomer, director of the Lick observatory, president of the University of California. Minor planet (3070) Aitken is named in his honor as well as a Moon crater 2 on the far side.

From another Aitken: Concentrating on the wheel center for a few minutes will make the wheel spin.