The Poggendorff Illusion: A Neurophysiologically Based Hypothesis

Abstract

Recent neurophysiological findings on the organization of the visual perceptual systems and psychophysical evidence on the mechanisms of visual information processing combine to form the basis of a variety of hypotheses about the Poggendorff illusion. These hypotheses were systematically explored by psychophysical and phenomenological techniques. The illusion is shown to result from multiple factors that are separately manipulatable by alterations in the distal stimulus-alterations which sum to produce the final visual percept. Late in the nineteenth century, several leading German physicists became intrigued by the variance between the perceptual experience and the actual properties of stimuli yielding opticogeometric illusions, and studied that variance in the hope of gaining a better understanding of the operation of the visual system. The methods developed by these pioneers involved both introspective phenomenological reports and psychophysical judgments, and they remain standard techniques today. Due to the virtual absence of neurophysiological information at that time, it became traditional to use the results obtained with these methods in hypothesizing about the neurophysiological mechanisms supposedly producing the observed phenomenon. After the discovery of the illusions and with the onset of behaviorism in psychology, interest in the illusory phenomena waned. Two recent developments, however, have reopened their study as a profitable endeavor: the rapid development of a body of neurophysiological information, and the discovery of a number of cognitive-perceptual mechanisms involved in the processing of visual information.