June 1996
Roger N. Shepard was always a prankster. As a boy, he delighted in playing visual tricks -- like the time he surreptitiously moved all the furniture out of his sister's room.
He went on to a distinguished career at Bell Labs, Harvard, and Stanford, all the while continuing to play visual tricks on people. By recording and analyzing their reactions, he discovered astonishing truths about mental processes. Shepard showed, for example, that when people compare two objects rotated at different angles, they first reorient the objects in their mind's eye. The astonishing part: Everyone does this at approximately 60° per second.
In the 1950s, Shepard began to discover universal laws that govern how people and animals perceive similarities among sensory input like colors, sounds, or smells. He worked out a computer method for measuring the perceived difference between stimuli.
When Shepard applied this method to colors, the computer yielded a circle. The physical wavelengths of visible light fall along a straight line, moving from red to violet; but the circle more accurately depicts the psychological (as opposed to physical) truth. This is that people perceive red and violet as more similar to each other than either color is to an intermediate color such as green. Shepard also discovered that:
- The distance between stimuli decreases along a particular curve -- a steep drop, followed by a slow tailing off (in mathematical terms, an exponential decay curve).
- All stimuli -- simple or complex -- produce the same curve.
- So do all experimental subjects -- whether humans, monkeys, rats, or pigeons.
Until Shepard began publishing his imagery work in the 1970s, no one had objectively measured mental imagery. It was thought to be impossible. The scientific community has since taken notice.
Today, his work influences fields as diverse as psychology, philosophy, computer science, linguistics, and neuroscience. Shepard says his image orientation work has been used in a pilot aptitude test. The test accurately identifies trainees who are most likely to make pilot errors. His imaging methods were also used in the design of a computer-based diagnostic system for breast and prostate cancers. Joseph L. Young, the NSF program director who has overseen Shepard's NSF grants for more than 19 years, anticipates other practical benefits such as better organization of control rooms and cockpit displays, as well as more effective educational programs.
In 1995, Shepard was awarded the National Medal of Science. He is noteworthy for other reasons as well. In an era of specialization, Roger Shepard is not only a scientist; he is a skilled artist and writer whose publications, while challenging, have broad appeal.
Shown here are a few drawings from his bookMind Sights,subtitledOriginal Visual Illusions, Ambiguities, and Other Anomalies With a Commentary on the Play of Mind in Perception and Art(W.H. Freeman and Co., 1990). In it, Shepard explains:
"The drawings ... achieve their effects by means of various visual tricks. But to call them tricks is not to imply that they are without psychological significance. The tricks work by taking advantage of fundamental perceptual principles that have been shaped by natural selection in a three-dimensional world. Our ability to make pictures, which emerged only recently on an evolutionary time scale, enables us to present the eyes with visual patterns that systematically depart from the patterns that we and our ancestors experienced in nature. In considering the ways pictures can trick the eye, we can gain insight into the nature and ultimate source of the principles of visual perception."
"OUR PERCEEPTUAL MACHINERY...IS DEEPLY ENTRENCHED"--ROGER N. SHEPARD
"Our perceptual machinery for making use of retinally available information about the disposition of objects in three-dimensional space is deeply entrenched in our nervous system and wholly automatic in its operation. Without our bidding or even our awareness of its existence, this machinery immediately goes to work on any visual input, including the visual input provided by a two-dimensional drawing. As a result, we cannot choose to see a drawing merely as what it is -- a pattern of lines on a flat, two-dimensional surface. To the extent that the pattern of lines conforms with the rules of linear perspective, for example, that pattern automatically triggers the circuits in the brain that make the three-dimensional interpretation appropriate to such a perspective display. Any consciously adopted intentions to ignore such an interpretation are largely powerless against the swift deliverances of this underlying machinery. This should not surprise us. We have inherited this machinery from individuals who, long before the advent of picturemaking, interpreted -- by virtue of this machinery -- what was going on in the three-dimensional world around them with sufficient efficiency to survive and to continue our ancestral line."
GRAVITATIONAL BENDING