In the Eye of the Beholder: Medical Museum: University of Iowa Health Care: Sight, Illusion, and Disorder

In the Eye of the Beholder: Sight, Illusion, and Disorder

Optical Illusions

Much of what we think we see is a product of our minds. Indeed, while the eyes are the means by which we look, it is in the brain that we see -- our perception of the world is created, not simply presented. The eyes detect information about size, color, pattern and proportion but the mind adds the sensations of distance and depth according to previous visual experience. In many ways, seeing is a subjective process and is vulnerable to what we call optical illusion.

Scientists have devised numerous examples of optical illusions, which museum visitors can experience first-hand. Observers may succumb to James Fraser's illusive spiral or set onto motion a spiral of their own choice from one of Marcel Duchamp's Rotoreliefs. Comic book illustrations come to life with the help of "3-D" glasses, and photographs and drawings take on depth and dimension when observed through a stereoscope. The ultimate in illusion is revealed in photographs of everyday optical phenomena.

37. Although this photograph is actually a composition of black shapes on a white surface, the mind organizes the elements, based on past experience, into the image of a Dalmatian dog, Ronald C. James, photographer, from J. Thurston and R. G. Carraher, Optical Illusions and the Visual Arts.

38. Lateral inhibition is induced by the Hermann-Hering grid. The drawing induces the appearance of illusory gray spots at the intersections of the white lines. From Lael Wertenbaker, The Eye: Window to the World, New York: Torstar Books, 1984.

39. Stereoscope photographs, circa 1920.

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