The Poggendorff illusion: an explanation based on neurophysiological mechanisms



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A review of the literature concerning the Poggendorff illusion implicated four basic components effecting its magnitude: (1) the size of the angle formed by the intersection of the interrupted oblique line segments with the parallel distractor lines, (2) the orientation (vertical, horizontal, or oblique) of the interrupted illusory segment in space, (3) the amount of experienced £ has had with the illusion, and (4) the nature of 0's eye movements as he views the illusion. Earlier investigations from our own laboratory suggested a fifth factor, this being the possibility of alternate perceptual organizations of the component parts of the illusory figure. Possible explanatory mechanisms to account for these various components are suggested. These suggestions are based on recent neurophysiological findings concerning the functional nature of the visual system. Hypotheses derived from these suggestions are tested by the psychophysical method of adjustment using 15 Os practiced in reporting their perceptual experiences. The conclusion reached was that the illusion involves the interaction of multiple factors. These factors, for the most part, can be accounted for on the basis of the known neurophysiological structure and its function in the visual-perceptual system. Modifications of the illusion based on hypotheses regarding these neurophysiological mechanisms resulted in predictable phenomenal alterations with respect to the magnitude of the illusion.