Story of Psychology - Morton Hunt [294]
But psychophysics was plagued by a chronic problem: subjects were inconsistent in their responses. If given the same threshold stimulus a number of times, sometimes they would see or hear it, sometimes not. If a light at an intensity below a subject’s threshold was gradually increased, he might begin to see it at a given level, but if it was presented above that threshold and gradually decreased, he might cease to see it at a somewhat different level.15
To solve this problem, in 1961 the psychologist J. A. Swets proposed applying to psychophysics the engineering concepts of signal detectability and information theory, which psychologists had come into contact with during World War II. Swets and his collaborators even gave their approach a name betokening the impersonality and objectivity of engineering—the Theory of Signal Detection. It held, first, that there would always be some random variation in the number of neurons excited by any signal and in the amount of “noise” (extraneous or accidental excitations) entering the neural system, and it corrected for these variations by statistical theory. It held, second, that a subject’s response on any trial is partly determined by his expectations and his effort to maximize his rewards and minimize his costs; these variables could be accounted for by decision-making theory.
Although “decision making” sounds mental, the Theory of Signal Detection remains outside the mind; it predicts the likelihood of correct and incorrect responses according to purely mathematical parameters. Signal detection theory was a major advance in psychophysics and is a part of the standard repertoire of experimental methods today, but it concerns only certain objective results of perception and casts no light on how perception takes place.16
All along, however, a small number of psychologists had been exploring the internal or cognitive aspects of perception. They were mentalists, but not in the metaphysical sense; rather, in the tradition of James, Freud, and Binet, they believed that higher mental processes are the heart of psychology and can be experimentally investigated.
In 1897, even as Thorndike and others were beginning to turn toward animal experimentation and what would become behaviorist psychology, an American psychologist named George Stratton undertook a perception experiment of a human and distinctly cognitive kind. For a week, allowing himself no respite, he wore lenses that turned his view of the world upside down. At first he had so much difficulty getting about and reaching for objects that he would often close his eyes and rely on touch and memory. But by the fifth day he was automatically making the right movements and by the end of the week felt that things were where he saw them and even, at times, that they “seemed upright rather than inverted.” When at last he removed the lenses, everything was bewildering. For several hours he found that he was reaching for objects in the wrong direction; then he relearned where things were when seen normally. The experiment dramatically showed that spatial perception, at least in human beings, is in some part learned and can be relearned.17
Striking as these findings were, the outlook of most psychologists in the early decades of the century was so antimentalist that there was little follow up of Stratton’s work and almost no cognitively oriented perception research until half a century later. But by the 1940s several unrelated strains of cognitively oriented psychology—Freudian, Gestalt, personality research, and the nascent discipline of social psychology— were gaining strength, and psychologists who found any of them congenial took a wholly different approach to perception research from that of psychophysiologists and psychophysicists.
Some, in America and elsewhere, rediscovered Stratton’s work and conducted new optical-distortion experiments. In 1951, Ivo Kohler, an Austrian psychologist, persuaded volunteers to spend fifty days seeing the world through prism goggles that displaced part of their visual field 10 degrees