Ivo Kohler

Ivo Kohler (1915-1985) provided painstaking evidence that the internal models of the environment (of the type proposed by Craik) could be modified by experience. He wore a variety of distorting optical devices for long periods and found that both perception and action adapted to the new spatial relations. In one study he wore binocular mirror device (which inverted the image on both eyes) Continually for almost four months. Initially everything appeared inverted and all actions based on visual input were misguided. After a period of days and weeks his behavior was no longer disrupted by the inverting mirrors: he was able to reach for objects appropriately and even carry out complex skills such as skiing. Through the weeks of adaptation he kept detailed protocols and records of his performance on perceptual-motor tasks. When the mirrors were removed, long-lasting aftereffects were reported: the world was transformed once more, but recovery was quicker than adaptation had been. "This experiment, the first of such long duration, was significant.... In the first place, the aftereffects obtained were of optimal strength. In the second place, it gave rise to a number of peculiar aftereffects which I have already referred to as "situational." Not only curvatures, distortions, deviations, apparent movements etc., were found to leave traces in the sensorium, but also the variations in intensity of these disturbances." Kohler was extending experiments that had been initiated by Helmholtz who examined the effects of prism distortion on reaching for a visible target -- initial errors were corrected with practice and aftereffects occurred in subsequent undistorted vision. Gibson also measured the aftereffects of curvature and tilt following adaptation to prisms. At the end of the nineteenth century George Malcolm Stratton (1865-1957) wore an inverting lens in front of one eye and noted the adaptation over eight days and the afteraffects thereafter. Kohler's experiments reawakened interest in visual adaptation and added many new phenomena to its study, particularly gaze-contingent color afteraffects. His observations led to the study of color-contingent afteraffects generally.

Kohler's methods were in the phenomenological tradition of Gestalt psychology, "although my attitude toward this is somewhat ambivalent. I do not deny what is called 'organization' in perception, but I believe we have found a way to change this organization by prolonged exposure to certain kinds of stimulation". This ambiguity is expressed in the portrait of Kohler: while all the parts of the portrait are inverted its organization as a Gestalt is of a normally upright face. It also reflects an unresolved riddle associated with phenomenological reports of vision during inversion -- whether the visual world appears normal after perceptual-motor adaptation. ~ Page 199