Innate versus learned perception
The organization apparent in percepts has been attributed by some to learning, as being built up through arbitrary associations of elements that have repeatedly occurred together in the person’s experience. Other theorists (particularly Gestaltists) stress the view that perceptual organization is physiologically inborn, being inherent in innate aspects of brain functioning rather than depending on a synthesizing process of learning to combine simpler elements into more complex, integrated wholes. One way of resolving such theoretical disputes would be to deprive people from birth of all visual sensory experience and, hence, of all opportunity for visual perceptual learning. Then at the time normal sensory function was restored, they would need to be tested to determine what perceptual functions, if any, were intact. Such a strategy was proposed in a letter to the British philosopher John Locke by a fellow philosopher William Molyneux in 1690. Molyneux’s suggestion waited until the 20th century to be taken seriously, after surgical methods had been found to restore the sight of people born blind because of cataract (clouded lens within the eye).
After removal of their cataracts, such newly sighted people are found to be normally sensitive to changes in intensity of illumination and to colour. Though they are able initially to tell when a figure is present, they cannot at first discriminate one simple shape from another, nor can they readily remember the shape of a just-exposed object. This deficiency extends to such socially important visual stimuli as people’s faces. Only after a long and painstaking period of experience—perhaps of several months duration—do such seemingly primitive visual performances as discriminating a square from a triangle come easily. Until then, the person must count corners, for example, to achieve accurate discrimination.
Findings derived from cataract surgery have provided a rich source of hypotheses for further research, including posited neurophysiological mechanisms (e.g., assemblies of brain cells) that might serve as the medium for the structural changes presumed to accompany perceptual learning. This situation led to experimental attempts to show how, through repeated stimulation, the perceptual system could progress from performance of only very primitive functions to the highly complex operations (such as form identification and discrimination) that are characteristic of the mature organism.
A host of experiments using laboratory animals as subjects (e.g., pigeons, rats, cats, dogs, monkeys, and chimpanzees) have been conducted to determine, under rigorous experimental control, the extent to which learning early in life contributes to later perceptual functioning. By analogy with humans born with cataract, such animals were deprived of visual experience from as close to birth (or hatching) as possible; e.g., chimpanzees were reared in darkness. In another type of experiment, animals were reared in environments that provided more than the normal amount and variety of stimulation or were exposed to specific stimuli they might not ordinarily encounter. These research strategies are said to provide impoverished or enriched environments. Experiments of both sorts have consistently provided verification of the general hypothesis that early perceptual experience plays an important role in later perceptual (as well as intellectual and emotional) development, even producing changes in brain weight and biochemistry. This research also offers a strong scientific rationale for efforts to enrich the environments of so-called disadvantaged or culturally deprived children.
Studies of human infants indicate that their early perceptual experiences are not the “blooming, buzzing confusion” postulated by the U.S. psychologist William James late in the 19th and early in the 20th century. Rather, even infants one or two days old are capable of refined visual discriminations. Recording of the infants’ visual fixations as their eyes move indicates them to have reliable preference for one paired stimulus over another, giving evidence of visual discrimination. Research employing this technique shows that preferences among various visual patterns or shapes generally are related to the complexity and novelty of the stimuli, for infants and for older human subjects as well. Evidence of this sort seems out of keeping with the findings of cataract surgery, which suggest that figural discrimination is not innate for the visually naïve. It may be, however, that adults who were blind with cataracts at birth suffer more than mere lack of normal visual experience; they are not quite comparable to visually naïve, but otherwise intact, infants. It may be that visual experience is necessary, not to generate pattern perception but to maintain it; that is, the infant’s built-in (innate) perceptual abilities may somehow deteriorate through disuse.
Similar research has dealt with visual depth perception in laboratory animals and human babies. One technique (the visual cliff) depends on the evident reluctance of young animals to step off the edge of what seems to be a steep cliff. The so-called visual cliff apparatus in one of its versions consists of a narrow platform on which the subject is placed and two wide platforms on either side of it. Although both flanking platforms are equally and only slightly lower than the central platform, the subject sees visual patterns designed so that one looks much deeper than the other. Typically, the subject explores the central platform and then investigates the flanks, finally stepping down onto the shallow-appearing side. By this response, the subject indicates sensitivity to visual depth cues. To discover if prior visual experience is necessary for the typical avoidance of the flanking platform that looks deepest requires subjects able to locomote well from the start (e.g., chicks) or those deprived of visual experience (e.g., rats) until their locomotor ability has developed. Research with the visual cliff clearly demonstrates the presence of depth perception in visually naıve subjects.
In summary, there is evidence among cataract sufferers of the necessity of early visual experience in human visual pattern discrimination; laboratory animals reared in impoverished or enriched environments demonstrate the importance (if not necessity) of early visual stimulation for perceptual development; human infants and other visually naïve animals behave as if they are innately capable of pattern and depth perception (e.g., without the need for learning). These data together suggest that some basic visual functions, including pattern perception, are built in but that visual experience serves to maintain and elaborate them.