HUMAN PERCEPTION

Effects of perceptual assumptions

According to one version of the enrichment thesis, exposure to recurrent regularities among stimuli prompts one to assume specific relationships between the environment and his sensory experience. For example, one learns that a continuous sequence of projective transformation (e.g., the circular profile of a dinner plate seems to become elliptical) is associated with changing positions of the object in view, or that continuous symmetrical expansion of the retinal image is associated with approach. In addition, one presumably learns to make assumptions about what is called reality; e.g., despite alterations in retinal image, one perceives the plate to stay the same size. Psychologists Adelbert Ames, Jr., and Egon Brunswik proposed that one perceives under the strong influence of his learned assumptions and inferences, these providing a context for evaluating sensory data (inputs). In keeping with enrichment theory, Brunswik and Ames contended that sensory stimuli alone inherently lack some of the information needed for mature, adaptive perceiving; enrichment was held necessary to reduce ambiguity.

Much of the evidence for the contention that all perceiving is modified by one's assumptions comes from investigations in which most of the visual, everyday stimuli are eliminated. Often, the subject may view an isolated target in total darkness or look at a motionless display while keeping his head steady. To show that learned assumptions about physical size affect perceived distance, the observer may be asked to judge how far he is from a rectangle of light displayed against total darkness. He is told at one time that the rectangle is a calling card; at another it is called a business envelope. His assumptions about these objects in relation to the size of his retinal image are invoked as prompting him to say that the "envelope" looks more distant than does the "calling card." Dramatic examples of this effect were invented by Ames, including his famous distorted room (see Figure 1).

Figure 1: Perception modified by learned assumptions in a distorted room.
The same men change...

Ames held that perceiving under unusual conditions (e.g., in a dark room) follows the same principles that govern more ordinary experience. The special conditions are said to permit experimental scrutiny of the same processes that are so difficult to examine under ordinary, uncontrolled conditions.

An opposing view is that such perceptual assumptions and inferences operate only under specific experimental conditions. It is asserted that only when commonly available sources of information are eliminated is the subject forced to rely on assumptions.

In the tradition of Helmholtz, Ames and Brunswik seemed to liken perceiving to reasoning, although not as a conscious process. They held that perceptual assumptions, once established, are influenced only slightly by logic. Although the floor and ceiling of the distorted room are sloped and all windows are of different size, it projects the same retinal pattern as a normal room; and a naive subject will report that he sees an ordinary room. But even after he explores the room he remains likely to say it looks rectangular as before, despite his new informaton. Comparable observations have been reported for a variety of situations. Familiarization or instruction seems to have little effect on long-established perceptual assumptions.

William Epstein. Professor of Psychology, University of Wisconsin, Madison.
Author of "Varieties of Perceptual Learning".

Psychoanalytic theory explicitly calls for motivational influences on such functions as memory, thinking, and perceiving. In particular, the theory is concerned with unconscious motives and conflicts and with unconscious defenses (such as repression) used to control them. According to the psychoanalytic hypothesis, there should be wide perceptual variation among individuals in response to stimuli that have motivational significance. At any rate, a host of experiments have been designed to show that perceiving is indeed subject to unconscious influences.

In some studies, for example, it seemed that so-called obscene words flashed on a screen had to be exposed longer than apparently neutral (control) words before their meaning could be perceived. In the other studies, children of poor families have been found to overestimate the size of coins as compared with the judgments of children of richer families. One major problem with such research lies in finding or creating appropriate experimental and control stimuli. Considering differences in the use of language, for example, it is most unlikely that what once were widely called obscene words would currently evoke the conflicts and defenses of more than a few subjects.

Assuming suitable stimuli can be found, an even more serious problem arises around the interpretation of the subjects' behaviour; for example, do people really find it more difficult to recognize obscene words or are they simply reluctant to admit recognition? Problems of this sort have plagued researchers, and unambiguously interpretable experiments in this field are most difficult to produce. The hypothesis of such individual influences as motivation on perception remains appealing and viable, but unproved.

William N. Dember. Professor of Psychology, University of Cincinnati, Ohio.
Author of "The Psychology of Perception".