Illusions

Visual Illusions
Brightness and Color Illusions
Illusions where color is misinterpreted, changes or appears where there isn't any. See: What is Lightness Constancy?, What is Color Constancy? , What is Spatial Filtering?

Checker Shadow Illusion

Chess Piece Illusion



Size & Depth Illusions
Illusions where the perceived size of an object is distorted or inaccurate.




Shape Illusions
Illusions where the shape of an object is distorted or misinterpreted.


Floating Cube Illusion


Motion Illusions
Illusions were a static image appears to be moving. See: Illusory Motion, 





Rotating Cubes


Direction Illusions
Illusions where the direction an object is travelling can be interpreted in more than one way. 


Is he going up or down the stairs?


Impossible Illusions
Illusions of objects, or parts of objects, which form geometric relations that physically cannot happen.

Assembly Impossible

Ascending Against Gravity: Kokichi Sugihara

Ambiguous Cylinder Illusion


Ambiguous Illusions
Ambiguous illusions are pictures or objects that can be interpreted in more than one way. Often, the viewer sees only one interpretation of the object and only realizes the second interpretation after some time or prompting. See: Multistable perception



'All is Vanity' by Charles Allen Gilbert




Perspective/Anamorphic Illusions
Illusions which require the viewer to occupy a specific vantage point to experience the illusion.
Anamorphosis is an optical illusion whereby an image appears to be totally distorted when seen from the usual vantage point, but appears normal when viewed from a specific angle (perspective anamorphosis), or indirectly in a mirror (mirror anamorphosis). 

Bernard Pras: Anamorphic Art









Hidden Image Illusions
Though I've given them a separate category, I believe these could easily be considered perspective illusions. To see the hidden image or text, you have to look at the image from a distance or squint. We saw a slew of these images in 2023-2024 as A.I. became accessible to the general public. 



Afterimage Illusions
An afterimage is a type of optical illusion in which an image continues to appear briefly even after exposure to the actual image has ended. See: Afterimage

Pretty Girl Afterimage


Motion Aftereffect (Waterfall) Illusions
Illusions were a stationary object or scene moves following prolonged fixation of a moving stimulus. The illusory movement is in the opposite direction to the movement of the stimulus that induced the effect. See: Motion Aftereffect




Thatcher Effect 
The Thatcher effect or Thatcher illusion or Eyesmouth-Wrongway is a phenomenon where it becomes more difficult to detect local feature changes in an upside-down face, despite identical changes being obvious in an upright face. It is named after the late British prime minister Margaret Thatcher, on whose photograph the effect was first demonstrated. See: Thatcher Effect

Thatcher Effect Video: Adele, Kanye West, Obama

Auditory Illusions
Shepard Tones


Multisensory Illusion
McGurk Effect

XRAYHEAD

Brainstorm/Green Needle

Bodiject Fingers

Rubber hand Illusion

Weight Illusion


Notes
Ambiguous Image
Multistable perception (or bistable perception)

Note: There doesn't seem to be a generally acknowledged way of organizing illusions, so I pieced together the categories above. It's a blend of somewhat common illusion categories along with groupings which describe the thing distorted by the illusion. 

While some illusions fit nicely into a single category, often this isn't the case. For instance, with the Ames room illusion, two people of equal height standing at opposite corners of the room will appear to be of differing height. As such this illusion would fit in the size illusion category. The room itself appears to be an ordinary cubic shaped room but in reality is a trapezoidal room and the walls and ceiling are at an incline. Therefore it could fit in the shape illusion category. Finally, to see the illusion you must look through a peephole at a particular vantage point. Thus it could be considered a perspective/anamorphic illusion. 

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