Subliminal

In June 1879, the American philosopher and scientist Charles Sanders Peirce was on a steamship journey from Boston to New York when his gold watch was stolen from his stateroom. Peirce reported the theft and insisted that each member of the ship’s crew line up on deck. He interviewed them all, but got nowhere. Then, after a short walk, he did something odd. He decided to guess who the perpetrator was, even though he had nothing to base his suspicions on, like a poker player going all in with a pair of deuces. As soon as Peirce made his guess, he found himself convinced that he had fingered the right man. “I made a little loop in my walk,” he would later write, “which had not taken a minute, and as I turned -toward them, all shadow of doubt had vanished.”? ?Peirce confidently approached his suspect, but the man called his bluff and denied the accusation. With no evidence or logical reason to back his claim, there was nothing Peirce could do—until the ship docked. When it did, Peirce immediately took a cab to the local Pinkerton office and hired a detective to investigate. The detective found Peirce’s watch at a pawnshop the next day. Peirce asked the proprietor to describe the man who’d pawned it. According to Peirce, the pawnbroker described the suspect “so graphically that no doubt was possible that it had been my man.” Peirce wondered how he had guessed the identity of the thief. He concluded that some kind of instinctual perception had guided him, something operating beneath the level of his conscious mind.? ?If mere speculation were the end of the story, a scientist would consider Peirce’s explanation about as convincing as someone saying, “A little birdie told me.” But five years later Peirce found a way to translate his ideas about unconscious perception into a laboratory experiment by adapting a procedure that had first been carried out by the physiologist E. H. Weber in 1834. Weber had placed small weights of varying degrees of heaviness, one at a time, at a spot on a subject’s skin, in order to determine the minimum weight difference that could be detected by the subject. In the experiment performed by Peirce and his prize student, Joseph Jastrow, the subjects of the study were given weights whose difference was just below that minimum detectable threshold (those subjects were actually Peirce and Jastrow themselves, with Jastrow experimenting on Peirce, and Peirce on Jastrow). Then, although they could not consciously discriminate between the weights, they asked each other to try to identify the heavier weight anyway, and to indicate on a scale running from 0 to 3 the degree of confidence they had in each guess. Naturally, on almost all trials both men chose 0. But despite their lack of confidence, they in fact chose the correct object on more than 60 percent of the trials, significantly more than would have been expected by chance.

Excerpted from Subliminal by Leonard Mlodinow. Copyright © 2012 by Leonard Mlodinow. Excerpted by permission of Pantheon, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.