Story of Psychology - Morton Hunt [69]
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:
The immediate objects of the perception of our senses are merely particular states induced in the nerves and felt as sensations either by the nerves themselves or by the parts of the brain concerned with sensation. The nerves make known to the brain, by virtue of the changes produced in them by external causes, the changes of condition of external bodies.21
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.
Just Noticeable Differences: Weber
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.23 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.24He 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