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Ebbinghaus–Titchener illusion
 

The Ebbinghaus illusion (sometimes called the "Titchener illusion") is an optical illusion of relative size perception. In the best-known version of the illusion, two circles of identical size are placed near to each other and one is surrounded by large circles while the other is surrounded by small circles; the first central circle then appears smaller than the second central circle.

The Ebbinghaus illusion, as well as numerous other visual and perceptual illusions, provide a valuable way to investigate how the eye and brain process visual information. Equally, they are used by artists for visual effect, entertaining and satisfying the endless fascination human beings have with novelty and creativity.

Ebbinghaus–Titchener illusion
 

Description
The classic Ebbinghaus illusion consists of a circle surrounded in one image by smaller circles, and in another by larger circles. The viewer tends to perceive the circle surrounded by smaller circles as being larger than the circle in the other image, even though both are exactly the same size.

Explanation
The difference in size perception is due to the surrounding visual cues (larger or smaller surrounding circles), and the way the brain processes these visual cues.
The Ebbinghaus illusion has played a crucial role in the debate over the existence of separate pathways in the brain for perception and action. Experiments have shown that, while adult subjects perceive the center circles as differing in size, they reach out to grasp the circle accurately. In theory, this is due to the process of perception using a different visual pathway than the process of action. While adults rarely misjudge the size of the center disk while reaching for it, experiments have found that young children do, in fact, misjudge size both perceptually and through action. Researchers have proposed that this is because young children rely on both pathways to process tasks, instead of the separate pathways that adults use.

 
 
 
 

Hermann Ebbinghaus (January 24, 1850 — February 26, 1909), German psychologist

Hermann Ebbinghaus was the founder of experimental psychology of memory. Among his most famous discoveries are the forgetting curve, the learning curve and the spacing effect. Ebbinghaus published his groundbreaking results in a monograph entitled “Uber das Gedachtnis” (1885), which was later translated into English as “Memory: A Contribution to Experimental Psychology” (1913).

 

 

Edward Bradford Titchener (11 January 1867 – 3 August 1927), British psychologist

Edward Bradford Titchener was a psychologist who studied under Wilhelm Wundt for several years. Titchener is best known for creating his version of psychology that described the structure of the mind: structuralism. He created the largest doctoral program in the United States (at the time) after becoming a professor at Cornell University, and his first graduate student, Margaret Floy Washburn, became the first woman to be granted a PhD in psychology (1894).

 
 
 
 
 
Visual Phenomena
  REFERENCES:
V. H. Franz, F. Scharnowski and K. R. Gegenfurtner (2005). "Illusion effects on grasping are temporally constant not dynamic".
J Exp Psychol Hum Percept Perform 31 (6): 1359–1378.

M. A. Goodale & Brenda Milner (January 1992). "Separate pathways for perception and action". Trends in Neuroscience 15 (1): 20–25.
 Burton, Gregory. "The Tenacity of Historical Misinformation: Titchener Did Not Invent the Titchener Illusion" The History of Psychology. American Psychological Association. 2007.
 Hanisch, C., J. Konszak, and C. Dohle. "The effect of the Ebbinghaus illusion on grasping behaviour of children" Department of Psychology. University of Dusseldorf, Germany. 2007
 
 
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