The Story of Psychology (21 page)

Müller, born in Coblenz of middle-class parents, was extremely gifted, energetic, and driven by a compulsion to excel. He was also endowed with Byronic looks—tousled hair, a sensitive mouth, and piercing blue eyes. Having earned his medical degree in Berlin when he was twenty-one, he set aside his youthful fascination with the quasi-mystical nature-philosophy of Schelling and did such dazzling work in physiology and anatomy that the University of Bonn made him Professor Extraordinarius
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at twenty-four and full professor at twenty-nine.

Müller labored so prodigiously at vivisection and animal experimentation in his early twenties that by the time he was twenty-five he had completed two fat books on the physiology of vision. But he was prey to a manic-depressive tendency, and at twenty-six, soon after becoming a professor and marrying his longtime fiancée, he fell into a severe depression and could neither work nor teach for five months. At thirty-nine, when others forged ahead of him in physiological research, he had a second attack of depression; at forty-seven, when he was at odds with the ideals of the Revolution of 1848, a third attack; and at fifty-seven, in 1858, a fourth attack that ended in his suicide.

Nearly all of Müller’s significant achievements in physiological psychology were made in his early years; by thirty-two, when he moved to the University of Berlin, he was losing interest in what he called “knife-happy” experimentation and turning instead toward zoology and comparative anatomy. He no longer believed that experimentation could solve the ultimate questions of life; his monumental
Handbook of Physiology
,
though filled with his and others’ experimental findings, contained a philosophic discussion of the soul that could have been written a century earlier. In it, he waffled about whether the soul was simply the brain and nervous system in action or was a separate “vital force” that temporarily inhabits the body.

Of Müller’s vast number of discoveries about the nervous system, many of which helped establish physiological psychology, one had an especially profound influence. The early physiological psychologists thought that any sensory nerve could convey any kind of sensory data to the brain, much as a tube will carry whatever substance is pumped through it, but they could not explain why, for example, the optic nerve conveyed only visual images to the brain, and the aural nerves only sounds. Müller offered a persuasive theory. The nerves of each sensory system convey only one kind of data or, as he put it, a “specific energy or quality”: the optic nerves always and only sensations of light, the aural nerves always and only sensations of sound, other sense nerves always and only their sensations.

Müller had reached this conclusion through a series of anatomical studies of animals—plus a tiny and seemingly clinching experiment that he performed on himself. When he pressed his own closed eye, the pressure created not sound, smell, or taste but flashes of light. He stated his doctrine in these terms:

As William James would say more dramatically, “If we could splice the outer extremity of our optic nerves to our ears, and that of our auditory nerves to our eyes, we should hear the lightning and see the thunder.”
¹⁸

As positive as Müller sounded about this, he debated with himself whether the specificity of the sensory systems resulted from the special
quality of each set of nerves or of the region of the brain to which that set traveled. Possibly the area to which optic impulses were delivered interpreted them visually, the area to which aural nerves went as sound. “It is not known,” he wrote in the
Handbook
, “whether the essential cause of the peculiar ‘energy’ of each nerve of sense is seated in the nerve itself, or in the parts of the brain or spinal cord with which it is connected.”
¹⁹
But Flourens’s view that the brain was completely generalized still dominated physiological thinking, and Müller opted for the theory of “specific nervous energies.”

Some of his own students, however, later in the century followed the lead of his honest confession of uncertainty and showed that all nerve transmissions possess the same characteristics and that it is indeed the end-location in the brain that determines the kind of experience created by the transmissions.
²⁰

Nevertheless, Müller’s physiology began to answer one of the great questions that had puzzled philosophers and protopsychologists: How do the realities of the world around us become perceptions in our minds? A detailed picture of how perception works was beginning to emerge. The process starts with the optical properties of the eyeball or the auditory machinery of the ear (both of which Müller investigated in detail), continues with the nerves that convey the stimulation coming from the sensory organs, and concludes with the brain areas that receive and interpret those nerve impulses. As opposed to the ancients’ supposition that a tiny replica of whatever is perceived passes through the air and nerves to the brain, Müller showed that what is transmitted to the brain are nerve impulses; our perceptions are not replicas of, but analogues or isomorphs of, the objects around us. As he put it:

But how do we know that what our brains make of the incoming excitations corresponds to reality? This issue, which had so plagued earlier philosophers and psychologists, seemed to him to be readily answerable. The state of our nerves corresponds to that of objects in suitable and regular ways; the image on the retina, for instance, is a reasonably faithful
portrayal of what is outside, and that is the stimulus the optic nerves carry to the brain. So, too, with the responses of the other sense organs and the messages they transmit.
²²
Müller thus answered the epistemological conundrum posed by Berkeley and Hume and transformed the untestable Kantian categories into testable and observable realities. Wrong in its details, his doctrine of specific energies was right in its most profound implications.

At the University of Leipzig, in the early 1830s, a bearded young professor of physiology was conducting perception research totally unlike Müller’s. No scalpel and no laid-open frogs’ legs or rabbit skulls for Ernst Heinrich Weber; he chose to work with healthy, intact human volunteers—students, townspeople, friends—and to use such prosaic instruments as little apothecary’s weights, lamps, pen and paper, and thick knitting needles.

Knitting needles?

Let us look in on Weber on a typical day. He blackens the tip of a needle with carbon powder and gently lowers it perpendicularly onto the shirtless back of a young man lying prone on a table.
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It leaves a tiny black dot on the young man’s back. Now Weber asks him to try to touch that place with a similarly blackened little pointer. The young man, trying, touches a place a couple of inches away, and Weber carefully measures the distance between the two dots and records it in a workbook.
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He does this again and again on different parts of the man’s back, then his chest, arms, and face.

A year or so later, carrying on this line of inquiry, he opens a drafts-man’s compass and touches both ends to different places on the body of a blindfolded man. When the legs of the compass are far apart, the volunteer knows he is being touched by two points, but as Weber brings the legs closer together, the subject finds it ever harder to say whether there were two points or one until, at a critical distance, he perceives the two as one. The critical distance, Weber discovers, varies according to the part of the body. On the tip of the tongue, it is less than a twentieth of an inch; on the cheeks, half an inch; and along the backbone, anywhere up to two and a half inches—a more than fifty-fold range of sensitivities and a dramatic indication of the relative number of nerve endings in each area.

All of Weber’s many experiments on the sensitivity of the sensory systems
were similarly simple—and important in the history of psychology. At a time when most other mechanists were working only with reflexes and nerve transmission, Weber was looking at the entire sensory system: not just organs and the consequent nerve responses but the mind’s interpretation of them. Moreover, his were among psychology’s first true experiments; that is, he altered one variable at a time—in the two-point threshold test, the area of the body being tested—and observed how much change that caused in a second variable—the critical distance between the two compass points.

To recognize how remarkable it was of Weber to conduct such experiments in the early 1830s, consider the period. James Mill, without budging from his desk, was espousing simplistic associationism; Johann Friedrich Herbart, occupying Kant’s chair at Göttingen, was maintaining, as Kant had, that psychology could never be an experimental science; Johann Christoph Spurzheim, at the peak of his popularity, was assuring crowds of enthusiasts that phrenologists could read a person’s character from the shape of his skull.

Weber (1795–1878), born in Wittenberg in Saxony, was one of three brothers, all of whom became scientists of distinction and, at times, worked together. Wilhelm, a physicist, aided Weber in his research on touch; Eduard, a physiologist, discovered along with him the paradoxical effect of the vagus nerve, which, when stimulated, slows the heartbeat.
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Like many another psychological mechanist, Weber had had medical training and specialized in physiological and anatomical research. Early in his career, he became interested in determining the minimum tactile stimulation necessary to produce a sensation of touch in different parts of the body, but soon moved on to a more complicated and interesting question about perceptual sensitivity. Many years earlier, the Swiss mathematician Daniel Bernoulli had made a psychologically shrewd observation: a poor man who gains a franc feels far more enriched by it than does a wealthy man; the perception of gain produced by any given sum of money depends on one’s economic status. This led Weber to formulate an analogous hypothesis: The smallest difference we can perceive between two stimuli—two weights, for instance—is not an objective, fixed amount but is subjective and varies with the weights of the objects.

To test the hypothesis, Weber asked volunteers to heft first one small weight and then a second, and say which was heavier. Using a graduated series of weights, he was able to ascertain the smallest difference—the “just noticeable difference” (j.n.d.)—that his subjects could perceive. As he had correctly surmised, the j.n.d. was not a specific unvarying weight.
The heavier the first weight, the greater the difference had to be before his subjects could perceive it, and the lighter the first weight, the greater their perceptual sensitivity. “The smallest perceptible difference,” he later reported, was “that between two weights standing approximately in the relation of 39 to 40: that is, one of which is about a fortieth heavier than the other.”
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If the first weight was an ounce, the j.n.d. of a second weight was a fortieth of an ounce; if ten ounces, a quarter of an ounce.

Weber went on to conduct similar experiments on other sensory systems, determining the j.n.d. between, among other things, the length of two lines, the temperatures of two objects, the brightness of two lights, the pitch of two tones. In every case he found that the magnitude of the j.n.d. varied with the magnitude of the standard stimulus (the one with which a second was being compared) and that the ratio between the two stimuli was constant. Interestingly, the ratio of the j.n.d. to the standard varied widely among the different sensory systems. Vision was the most sensitive, detecting differences as small as a sixtieth in the intensity of light. In the case of pain, the minimum perceivable difference was a thirtieth; of pitch perception, a tenth; of smell, a quarter; and of taste, a third.
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Weber summed up the rule in a simple formula:

which says that the ratio between the just noticeable stimulus, δ (R), and the magnitude of the standard stimulus, R, is a constant, k, for any sensory system. Known as Weber’s Law, it is the first statement of its kind—a quantitatively precise relationship between the physical and psychological worlds. It was the prototype of the kind of generalization that experimental psychologists would be looking for from then on.