Priceless: The Myth of Fair Value (and How to Take Advantage of It) (5 page)

One name “Smitty” Stevens wasn’t so keen on being called was “psychologist.” He spent his career fretting about the unscientific bunkum, as he saw it, perpetuated under that name. A bone of contention was the popular lectures his Harvard collegues insisted on giving to enraptured undergraduates. Stevens feared that the pop psychology would attract the wrong kind of people to the field—touchy-feely do-gooders. In his ongoing quest to dissociate himself from psychology, Stevens insisted on styling himself a “psychophysicist.” By 1962 he managed to persuade Harvard to name him their first (and apparently last) professor of psychophysics.

That term had been popularized in the mid-nineteenth century by German psychologist Gustav Fechner (1801–1887). According to Fechner, “Psychophysics is an exact doctrine of the relation of function or dependence between body and soul.” Fechner, unlike Stevens, was a deeply mystical man, bridging German romanticism and German science.

The son of a rural pastor, Fechner penned satires and studied medicine
until an allowance from his mother ran out. Forced to get a steady source of income, he became a prolific author, editing
Home Encyclopedia
, a how-to compendium for Biedermeier households. Fechner wrote about a third of the encyclopedia himself, including entries like “Carving Meat and Setting the Table.”

He continued his academic studies, now in physics. In 1834 Fechner was appointed professor of physics at the University of Leipzig. “But then I ruined my eyesight by doing experiments in subjective color perception, looking often at the sun through colored glass . . . so that by Christmas 1839 I could no longer use my eyes and had to interrupt my lectures,” Fechner wrote in an autobiographical note. “When I finally could no longer bear daylight at all, I gave up my position.”

For some time, Fechner believed himself blind, and the citizenry of Leipzig believed him mad. Fortunately, both conditions improved. On October 22, 1850, Fechner woke up with the characteristically mystical insight that sensations could be measured and connected to the physics of the material world. This event is traditionally taken as the starting point for psychophysics. Its anniversary, “Fechner Day,” is still celebrated at Harvard and elsewhere.

“People called Fechner a fool and a fanatic,” German physicist Ernst Mach confided to the doyen of American psychology, William James. When not experimenting on perception, Fechner attended séances and claimed that plants have souls. Under a pen name he wrote a tome on the popular obsession of the German romantic era (every era, actually)—the
Little Book on Life After Death
.

With psychophysics, Fechner was confronting one of the oldest questions in philosophy: Can subjective experiences be compared or communicated? Colors are often held up as a convenient example: Do people experience colors the same way, or is it just barely possible that one person sees a red
STOP
sign as red and another experiences the same sign as green? Would there be any way of telling? The person who sees green would still call the sign red because he’s been taught to call the color of a
STOP
sign red.

Taken in a full-bore philosophical spirit, questions like this are unanswerable. This leaves open the question of whether the intensity of sensations can be measured. Nineteenth-century German psychologist Wilhelm Wundt offered a skeptical view:

How much stronger or weaker one sensation is than another, we are never able to say. Whether the sun is a hundred or a thousand times brighter than the moon, a cannon a hundred or a thousand times louder than a pistol, is beyond our power to estimate.

Understand what Wundt was saying. He
wasn’t
saying that a physicist couldn’t measure the objective intensity of sunlight and moonlight. That was already beginning to happen in Wundt’s time. He
wasn’t
saying that you couldn’t ask people whether the sun looks brighter than the moon and get 100 percent agreement that the sun is way, way brighter.

Wundt was saying (only) that subjective ratios are meaningless. And in this, he was staggeringly wrong. Over the next century, Wundt’s contemporaries and successors, who often went by the name “psychophysicists,” assembled compelling evidence that people are fairly good at doing just what Wundt thought to be impossible.

A down-to-earth definition of “psychophysics” would say it is the study of the relationship between physical quantities (noise, light, heat, weight) and subjective perceptions of them. Fechner was not the first to explore this, even in Leipzig. As early as 1834, Ernst Weber, a Leipzig physiologist, established what is still one of the field’s great overarching results. He blindfolded people and had them judge how heavy various combinations of weights felt. Weber carefully added tiny weights until the subject said his burden felt noticeably heavier (a “just noticeable difference”). He determined that it was the relative (percentage) change in weight that mattered—not the absolute change in grams or pounds. A fly landing on a strongman’s barbell does not make it noticeably heavier. The same fly landing on a coin held in a blindfolded person’s palm might be noticeable.

Before the age of lightbulbs and loudspeakers, psychophysics was a primitive affair. One early researcher, Julius Merkel, asked people to judge the loudness of noises made by dropping a metal sphere onto a block of ebony. When Merkel wanted to make the noise louder, he had to drop the ball from a greater height. Another pioneer, Belgian physicist Joseph-Antoine Ferdinand Plateau, asked eight artists to paint a gray that was
exactly
halfway between black and white. Just so there was no confusion
about what “black” and “white” meant, Plateau supplied swatches. The artists took the samples and went back to their studios to paint their gray. Despite the fact that the lighting must have been different in each of the studios, the resulting grays were virtually identical, Plateau reported. This was taken as proof that perceptions were not so subjective as some proposed. In an experiment oddly like Fechner’s ill-fated one, Plateau stared directly at the sun for twenty-five seconds, permanently damaging his eyesight. He died blind in Ghent, steps away from guidebook masterpieces of the van Eycks.

The growth of psychophysics in the twentieth century was largely a matter of better audio-visual equipment. Fitted out with the latest slide projectors, rheostats, and audio oscillators, the field blossomed. Its scope spanned not only the world of the senses but also that of ethical, aesthetic, and economic value judgments. College students were instructed to look at inclined lines, colors, or reproductions of modern paintings; sniff noxious oils or listen to white noise; compare atrocities, salaries, and perfumes. Then the grilling began:
How inclined is that line to the horizontal? Rate the loudness of that tone you just heard on a scale of 1 to 7. Which crime is worse? How intelligent would you say the child in this photograph is?

S. S. Stevens is renowned for establishing the shape of the curve relating physical intensity to subjective perception. It was long known that this curve is not a straight line. Imagine a completely dark room. Turn on a 60-watt lightbulb. Then turn on a second 60-watt bulb. Does the light look twice as bright? No (says almost everyone). It looks brighter, but not twice as bright. Careful experiments have shown that point sources of light have to be about four times brighter, physically, to look twice as bright, subjectively.

This is characteristic of a
power curve
. Without getting into the math, here’s one way of grasping the gist of it: You’re decorating your house with Christmas lights and want to outdo your neighbor. Specifically, you want your lights to look
twice
as bright. According to Stevens, it’s not good enough to buy twice as many lights. You’ll need something like
four
times as many strings of lights in order to
double
the perception of glittery holiday excess.

This rule holds no matter whether your neighbor has a single, environmentally sensitive string, or whether he’s one of those obsessives whose houses make the news. Doubling the subjective effect means quadrupling the wattage (and, unfortunately, your December electric bill).

Stevens noted with satisfaction that his power curve rule can be stated in seven words:
Equal stimulus ratios produce equal subjective ratios
. This is often called Stevens’s law, or
the
psychophysical law. Within a generation, Stevens and contemporaries established that the power law is a very general one, applying not just to brightness of lights but also to perceptions of warmth, cold, taste, smell, vibration, and electric shock.

The factor connecting the two ratios varies with the type of stimulus. It’s not always “four times the stimulus doubles the response.” For instance, it takes only about 1.7 times as much sugar, in a watery soft drink, to double the perception of sweetness. The ratio can also depend on how a stimulus is presented. Perceptions of heat follow different power curves depending on whether it’s a warm piece of metal touching the arm, the irradiation of a small area of skin, or sauna-like heat enveloping the whole body. But for a given experiment, the curves are remarkably consistent. By 1965, two of Stevens’s colleagues could write, “As an experimental fact, the power law is established beyond any reasonable doubt, possibly more firmly established than anything else in psychology.”

S. S. Stevens tried to explain why the senses obey a power law. He noted that most of the laws of physics (like E=mc
²
) are power laws. By adapting to the form of physical law, the senses are better able to “tell us how matters stand out there.” In his posthumously published text,
Psychophysics
, Stevens wrote,

For example, is it the differences or the proportions and ratios that need to remain constant in perception? Apparently it is the proportions—the ratios. When we walk toward a house, the relative proportions of the house appear to remain constant: the triangular gable looks triangular from any distance. A photograph portrays the same picture whether we view it under a bright or a dim light: the ratio between the light and shaded parts of the photograph seem approximately the same even though the illumination varies . . . The usefulness of perceptual proportions and relations that remain approximately constant despite wide changes in stimulus levels is immense. Think how life as we know it would be transformed if speech could be understood at only a single level of intensity, or if objects changed their apparent proportions as they receded, or if pictures became unrecognizable when a cloud dimmed the light of the sun.

Put this way, our ratio-based senses are eminently reasonable. There is an Achilles’ heel. The price of being so acutely sensitive to ratios and contrasts is a relative insensitivity to the absolute.

Stevens makes this point, too, with characteristic poetry:

The print in this book looks black, but not because there is no light coming from the black area to your eye. Actually the black gives off so much light that, if we could remove all the white paper surrounding the black, the black standing by itself would seem to glow as brightly as a neon sign at night.

The ratio-based nature of perception has many consequences. One of the more trivial ones is that it affects the design of psychophysics experiments. It was discovered that results depend a great deal on the response scale. This is the “answer sheet,” a printed form in the old days and a Web page now. There are two popular kinds of response scales: category and magnitude. You’re already familiar with both.

Category scales
are used in consumer surveys and Internet polls. How would you rate your Whirlpool dishwasher? Check one:

1–poor

2–fair