A Note on Conjuring Tricks and the Psychology of Event Perception

December, 1971

A Note on Conjuring Tricks and the Psychology of Event Perception

J. J. Gibson

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 References to these essays must cite them explicitly as unpublished manuscripts.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 may be circulated if this statement is included on each copy.

In the long history of magic and conjuring thousands of feats have been devised, and new tricks and illusions are still being invented. There have been attempts to classify this vast repertory of effects, however, and they fall into a relatively few types. These are very interesting for the psychologist who is interested in the general laws of event perception. The following basic forms of conjuring have been extracted from a book on magic by Dariel Fitzroy. Mental phenomena (clairvoyance, telepathy, and prophecy) have been omitted. We are here concerned with physical events and their laws, not mental events.

The magician is able to do the following things:

1. To make a thing appear to go out of existence in an unperceived way, i.e. to make it vanish. The “thing” may be an object, animal, or person. In all cases it actually goes out of sight, not out of existence, that is, it is hidden (covered, occluded).

2. To make a thing appear to come into existence in an unperceived way, i.e., to be created. Actually it merely comes into sight from a “hiding place.”

3. To appear to make whole something that has been cut or broken; to restore something destroyed (e.g. ribbons, ropes, rings, or a sawed-in-two woman.)

4. To make a thing appear to have been displaced from one location to another without having been moved from one to the other.

5. To make a solid material thing appear to have changed into a different thing (change of identity.)

6. To make a massive material thing appear to float in the air (levitation.)

These events would, if they occurred, violate the “laws of physics,” it is said, and the conjurer appears to “defy” these laws. But the laws referred to are not found in the textbooks; instead they are environmental regularities of the following sort, not usually stated explicitly.

1. Things go out of existence in a limited number of specific ways which can normally be observed (by fire, evaporation, solution, etc.)

2. Things come into existence in a number of quite different ways which can be observed (growth, assembly, crystallization, etc.)

3. Things and surfaces go out of sight in a few quite specific and regular way, by occlusion, by minification in the distance, and by lack of illumination (darkness.) They come into sight in precisely the opposite ways. (Nothing is here said about the rare and exceptional case of going out of sight by loss of contrast or by optical manipulation. That is a separate problem.)

4. Things that go out of sight do not go out of existence.

5. Cutting, breaking, and destroying are not reversible changes.

6. Nothing can exist in one place and then another without having been moved.

7. A solid object may undergo certain kinds of changes but it does not undergo certain other kinds of change (complete change of identity, e.g. a frog into a prince, or a billiard ball into a bouquet.)

8. A solid cannot penetrate a solid without breakage.

9. A massive object cannot come to rest except on a solid surface of support.

The above “laws”, I suggest, are actually regularities of event perception that are noticed or learned by attentive observers. Children learn them by observation. They are forms of tacit knowledge, not of explicit, formal, rational knowledge. The conjurer takes it for granted that everybody perceives events in accordance with these regularities. The audience is only mystified, surprised, and puzzled insofar as it has this tacit knowledge already.

The problem of optical information for the perception of events and the ways in which the conjurer manipulates the information so as to induce misperceptions (illusions) in the onlookers is a separate set of questions, not here considered.