Perceptual and Motor Skills, 1975, 40, 29-30. @ Perceptual and Motor Skills 1975
A NOTE O N ILLUSIONS S. HOWARD BARTLEY
Memphis State Universiiy
St~rn.mary.-The crucial factor in illusion is not in perception but rather assumption that all two-dimensional drawings represent two-dimensional reality. This leads in some cases to making unwarranted comparisons between parts of the figures. in the
A number of workers have studied visual illusions such as the Miiller-Lyer figure by noting changes in the amount of the illusory effect as a function of repetition in viewing and as a function of the subject's age. There seems to be little than can be derived from a repetitious kind of extension of this work. The questions asked do not seem to flow from a clear conception of the nature of perception. Illusion is a concept found both in everyday thinking and in technical circles such as psychology. An illusion is defined as a mistaken perception. From this it is easy to infer that perception is sometimes unlawful-that cause-and-effect sometimes go awry. Any intimation that this can be the case would conflict with what we know about the character of Natural Law and is not to be tolerated. Line drawings on two-dimensional surfaces which give rise to illusion often can also be seen in a non-illusory way. The problem then is "what happens to produce this change?" There are several theories of illusion, most of which do not satisfy. One of these is the perspective theory. The central idea of this theory is that illusory figures "suggest depth by perspective" and the changes in size are a result of this. Some say that the predictions of this theory are opposite to those that actually occur. It ought to be recognized that the implication of perspective involves seeing certain parts of the figures as viewed obliquely. If so, i t is not fair to use the same metric to such parts (lines, etc.) as for those which are seen to lie in the plane of che drawing; hence, where is the illusion? It occurs only i f one makes this inappropriate comparison. Actually, what seems to be the case when an illusory figure seen as a rwodimensional construction loses its illusory character is that it turns to being seen as a three-dimensional representation. There is also the class of figures that are abszbrd or nonse?uical. As total figures they lack internal consistency. If one isolates part of such a figure, it makes sense as a three-dimensional represencation. As rhe remaining part, or parts, are viewed separately they, too, are consiscent and non-illusory. Thus it must be realized that line drawings can be constructed which cannot represent any consistent set of three dimensions. To require the totality to make sense is unrealistic.
Not all natural situations are fully unambiguous. Take for example, a haze, and what is seen as we look at something through the rapidly revolving blades of a fan. In both situations the area looks "blurry," but in one case this appearance is produced by suspended water particles and in the other case rapidly moving fan blades. In case the individual is about to reach out for something in front of him, he can successfully do it in the one case and not the other. But direct perception may not predict which will result. This is a demonstration of the probabilistic character of response situations. If the logic of the conventional notion of illusions was to be consistently applied to all pictorial representations, it would have to be said that illusion is the rule rather than the exception, since very often what is seen does not fully tally with some standard of expectation. Whether the discrepancies have been called illusions has been simply a matter of convention or tradition. Different rules have been applied to line drawings and productions when color and shading are involved. Ambiguities occur very often in dealing with color, wherein the seen color of an object is erroneously attributed to be intrinsic to the object rather than in any degree to the illumination. But seldom is this called illusory. If the conventional illusions involve inappropriate usage of geometric principles in the ways suggested, it is not apparent why studies of illusion by the method of repetitive presentation are so often undertaken. It does not seem that such studies have disclosed much, if anything, of value in understanding perception. Certain understandings, if present to begin with, would have precluded such experiments. Accepted
Novernbez 22, 1974.
A NOTE O N ILLUSIONS S. HOWARD BARTLEY
Memphis State Universiiy
St~rn.mary.-The crucial factor in illusion is not in perception but rather assumption that all two-dimensional drawings represent two-dimensional reality. This leads in some cases to making unwarranted comparisons between parts of the figures. in the
A number of workers have studied visual illusions such as the Miiller-Lyer figure by noting changes in the amount of the illusory effect as a function of repetition in viewing and as a function of the subject's age. There seems to be little than can be derived from a repetitious kind of extension of this work. The questions asked do not seem to flow from a clear conception of the nature of perception. Illusion is a concept found both in everyday thinking and in technical circles such as psychology. An illusion is defined as a mistaken perception. From this it is easy to infer that perception is sometimes unlawful-that cause-and-effect sometimes go awry. Any intimation that this can be the case would conflict with what we know about the character of Natural Law and is not to be tolerated. Line drawings on two-dimensional surfaces which give rise to illusion often can also be seen in a non-illusory way. The problem then is "what happens to produce this change?" There are several theories of illusion, most of which do not satisfy. One of these is the perspective theory. The central idea of this theory is that illusory figures "suggest depth by perspective" and the changes in size are a result of this. Some say that the predictions of this theory are opposite to those that actually occur. It ought to be recognized that the implication of perspective involves seeing certain parts of the figures as viewed obliquely. If so, i t is not fair to use the same metric to such parts (lines, etc.) as for those which are seen to lie in the plane of che drawing; hence, where is the illusion? It occurs only i f one makes this inappropriate comparison. Actually, what seems to be the case when an illusory figure seen as a rwodimensional construction loses its illusory character is that it turns to being seen as a three-dimensional representation. There is also the class of figures that are abszbrd or nonse?uical. As total figures they lack internal consistency. If one isolates part of such a figure, it makes sense as a three-dimensional represencation. As rhe remaining part, or parts, are viewed separately they, too, are consiscent and non-illusory. Thus it must be realized that line drawings can be constructed which cannot represent any consistent set of three dimensions. To require the totality to make sense is unrealistic.
Not all natural situations are fully unambiguous. Take for example, a haze, and what is seen as we look at something through the rapidly revolving blades of a fan. In both situations the area looks "blurry," but in one case this appearance is produced by suspended water particles and in the other case rapidly moving fan blades. In case the individual is about to reach out for something in front of him, he can successfully do it in the one case and not the other. But direct perception may not predict which will result. This is a demonstration of the probabilistic character of response situations. If the logic of the conventional notion of illusions was to be consistently applied to all pictorial representations, it would have to be said that illusion is the rule rather than the exception, since very often what is seen does not fully tally with some standard of expectation. Whether the discrepancies have been called illusions has been simply a matter of convention or tradition. Different rules have been applied to line drawings and productions when color and shading are involved. Ambiguities occur very often in dealing with color, wherein the seen color of an object is erroneously attributed to be intrinsic to the object rather than in any degree to the illumination. But seldom is this called illusory. If the conventional illusions involve inappropriate usage of geometric principles in the ways suggested, it is not apparent why studies of illusion by the method of repetitive presentation are so often undertaken. It does not seem that such studies have disclosed much, if anything, of value in understanding perception. Certain understandings, if present to begin with, would have precluded such experiments. Accepted
Novernbez 22, 1974.
