April 1967<\/p>\n
J. J. Gibson, Cornell University<\/p>\n
The evolution of the senses (perceptual systems) must have been a continuous process of eliminating<\/strong> misperceptions. If, in general, “things were not what they seemed” to animals, they could not be coped with<\/strong>. Hence the class of illusions that (1) mislead the observer<\/strong> so as to arouse inappropriate behavior and that (2) occurs<\/strong> regularly in Nature<\/strong> should not <\/strong>be manifested in the perception of animals. April 1967 Do animals have illusions? (Illusions caused by useless dimensions of sensitivity) J. J. Gibson, Cornell University The World Wide Web distribution of James Gibson’s “Purple Perils” is for scholarly use with the understanding that Gibson did not intend them for publication. References to these essays must cite them explicitly as unpublished manuscripts. Copies … Continue reading “Do animals have illusions? (Illusions caused by useless dimensions of sensitivity)”<\/span><\/a><\/p>\n","protected":false},"author":1001,"featured_media":0,"parent":17,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/pages\/125"}],"collection":[{"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/users\/1001"}],"replies":[{"embeddable":true,"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/comments?post=125"}],"version-history":[{"count":1,"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/pages\/125\/revisions"}],"predecessor-version":[{"id":131,"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/pages\/125\/revisions\/131"}],"up":[{"embeddable":true,"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/pages\/17"}],"wp:attachment":[{"href":"http:\/\/commons.trincoll.edu\/purpleperils\/wp-json\/wp\/v2\/media?parent=125"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nThere is, of course, a class of experiences that does not elicit overt behavior. Afterimages are an example. They are “subjective” experiences or so called “private” experiences, and are therefore notperceptions<\/strong> in the common use of that term. It would be very difficult to determine whether animals have afterimages. If they do, it is likely that they would pay no attention to them.
\nThere is another class of experiences which are not subjective or private, are similar to perceptions, but are nevertheless false. Images (virtual objects) in still water or in a mirror are examples. Such virtual objects are presumably falsely perceived by all seeing observers, animal or human. It may be that inappropriate behavior has to be unlearned (extinguished) in such cases. (Rainbows do not elicit<\/strong>behavior.)Pictures<\/strong> are another example.
\nThe straight stick which appears bent when partially immersed in water is similar to cases of the latter class. The “percept” is simply the result of the fact that the visual perception of objects depends on the optic array entering the eye. There is information in the light for a bent stick, and it can only be disallowed by what is rightly called inferential knowledge<\/strong> (i.e., knowledge about <\/strong>refraction). But this is true only so long as the stick is not moved<\/strong>.
\nWhen the stick is moved, and especially when it is rotated (as we have shown) there exists a different level of information in light: the invariants of changing perspectives over time<\/strong>. One of these invariants (information for straightness) as we have shown can be noticed by young children, who cannot possibly “know” about the laws of refraction.
\nThe moral of all this is that invariant detection over time<\/strong> is a useful<\/strong> dimension of sensitivity and that the perceptual system will tend to develop such kinds of sensitivity. But, along with these, there will inevitably be useless dimensions of sensitivity that are merely incidental to the useful ones. Animals could not evolve the ability to detect solid tridimensional shapes without incidentally having the ability to detect flat bidimensional forms (frozen pictorial forms). But this so called “form sense” never did animals any good until man began to exploit it, quite recently, by making pictures on flat surfaces. Euclidean and Platonic forms are wonderful inventions for teaching mathematics but they have caused hopeless confusion in the problem of understanding visual perception. We have taken for granted that visual forms, perspectives, were the basic elements of object-perception \u00ad the sensory basis of object perception.<\/p>\n","protected":false},"excerpt":{"rendered":"