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02/15/94

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Visualization is the secret key to scientific progress

STANFORD -- Remember learning about the scientific method in high school?

The way it's supposed to work, scientists make new discoveries by performing experiments and then come up with a theory to explain the results. But the greatest advances in scientific understanding - including those made by Galileo, Newton, Maxwell and Einstein - weren't made in this fashion, says Stanford University psychologist Roger N. Shepard.

Instead, Shepard proposes that the most revolutionary scientific insights arose from experiments that were performed only in the scientist's imagination in advance of collecting any actual data. Speaking on Monday, Feb. 21, at the annual meeting of the American Association for the Advancement of Science in San Francisco, Shepard used a set of humorous cartoons to help describe the thought experiments that he imagines may have led these famous scientists to formulate their most influential theories.

These thought experiments share two basic characteristics, the psychologist said. They appear to have been driven by a search for consistency among even the most diverse conditions imaginable. And they appear to have been guided by an innate but unconscious "wisdom" about the fundamental nature of the physical world that has been built up through eons of natural selection.

Take the example of Isaac Newton. Almost everyone has heard the story of the young Newton sitting under an apple tree, gazing at the moon on a mild autumn evening and being struck by a falling apple.

"Whether or not this story is historically accurate, it is surely possible that at some time before writing Principia, Newton performed the thought experiment of throwing a terrestrial object (such as an apple) with greater and greater force," Shepard said.

Newton already knew that the path of such an object always curves downward to return to Earth, but at greater distances for more forceful throws. He also knew that the Earth is a sphere of limited size. So, he could well have imagined that with a throw of sufficient force, the object in its downward curve would miss the spherical surface of Earth, but might instead fall forever around it. Then he could easily have realized that, in just such a way, the moon might be falling around the Earth and the Earth falling around the sun, Shepard envisions.

That is just one example of how "scientific advances arise from a painstaking process of converting implicit, internalized knowledge into an explicit, externalizable form," he said.

Psychological research by Shepard and his students supports the idea that the types of mental operations involved in performing such thought experiments arose to help our ancestors survive various evolutionary challenges.

The phenomenon known as "mental rotation" serves as a good illustration, he said. Mental rotation of objects is the type of operation that a scientist carries out in his or her imagination as part of a thought experiment.

In 1968, Shepard and student Jacqueline Metzler performed an experiment that indicated that the time it took a person to determine whether two images portrayed the same three-dimensional shape increased with the angle between the two views, requiring about three seconds longer for objects that differed by 180 degrees than for objects that were in the same orientation.

In follow-up studies, Shepard and his co-researchers determined that people don't move objects mentally in some arbitrary fashion, but along set paths that are dictated by deeply internalized principles of kinematic geometry that were not described mathematically until the 19th century.

Humans may not be the only ones who have the ability to perform thought experiments. To support his suspicion that many animals also can, Shepard relates a personal observation of a German shepherd heading for a narrow vertical opening in a fence with a long stick in his mouth: "The dog plunged toward the narrow opening with the long stick horizontally clamped in its teeth. Just as catastrophe appeared certain, the dog stopped short, paused for a brief (and perhaps thoughtful) moment and, rotating its head through 90 degrees, proceeded through the opening without mishap."

Shepard also cites neuroelectric recordings from the brains of monkeys that have been made by A.P. Georgopoulos (now at the Veterans Affairs Medical Center in Minneapolis) and his co-workers that have indicated that before rotating its arm, the monkey's brain cycles through representations of its arm in successively more rotated positions.

These are examples of how implicit wisdom about the world is present, to some degree, in all animals whose survival and reproduction depends on effective prediction and action. Such knowledge, however, is so deeply internalized, efficient and automatic that it is largely inaccessible to conscious control. Scientists are those as yet rare individuals who have the ability to access and manipulate this knowledge consciously, Shepard said.

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