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MIND Guest Blog

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The Limits of Psychophysics, and Physics

Psychophysics secretly dominates our social sciences. Such physics-ing often improves experimental practice, but its mathematical methods face new challenges. As every infant knows, but too many scientists ignore, people aren't biological billiard balls. The founders of psychophysics were the first to treat psychology as an experimental and quantifiable science. They studied the effects of physical stimuli on mental states as physicists would. Gustav Fechner popularized the term in 1860 along with his theory that the intensity of sensations varied geometrically with stimulus. The metaphors and methods of physics were already being tried on people. John Locke, the "Newton of the mind," described the pull of pleasure as "gravitational." And Jeremy Bentham believed: "Nature has placed mankind under...two sovereign masters, pain and pleasure...[they]...alone...determine what we shall do...The principle of utility recognizes this." Utility became the keyword, used to lock away libraries of literature on the complexities of human motivation. There were dissenters--Darwin wrote "The common assumption that men must be impelled to every action by experiencing some pleasure or pain may be erroneous...[we often act]...independently of any pleasure or pain felt at the moment." But utility's simplicity still attracts. Daniel Kahneman's 2002 Nobel Prize was awarded for using the psychophysics of utility--nonlinear psychological responses to money--to challenge rational-agent economics. Clearly, people are subject to the laws of physics. But nothing in physics chooses. Physics needs no strategies or game theory. Its main business is mechanical causation. Physics has no future. Like the best Buddhists, it feels only the forces of the present. Human psychology is different from physics precisely because it evolved to weigh and choose between forces from different possible futures. Physics developed in situations like this: Everything of type X always does Y under conditions Z, where X, Y and Z are mathematically related. And simple scenarios such as: Every action has an equal and opposite reaction. Some people behaviors are like that. But many are not. Consider Darwin's observation that "many a Hindoo...has been stirred to the bottom of his soul by having partaken of unclean food." The same food eaten unknowingly, or by an unbeliever (even an identical twin), wouldn't cause the same reaction. The story of the food, not the food itself, causes the "soul shaking." In psychology, the same stimulus often doesn't cause the same reaction. Unmathematical narrative-like patterns of contingency influence our reactions and decisions. Their flexible, if-then, weakly causal, multifactor kind of logic is different from that typical of the number-struck sciences. Babies use "contingency patterns" to distinguish objects that behave with physics-like regularities from objects with agency. Free will, real or not, changes practical predictability. Too many scientists aren't as practical as babies. Illustration by Julia Suits, The New Yorker Cartoonist & author of The Extraordinary Catalog of Peculiar Inventions. Previously in this series: Kahneman and Bentham's Bucket of Happiness Kahneman's Clarity: Using Mysterious Coinage in Science What Rational Really Means The Cognitive Science of Star Trek Colonoscopies Clarify Inner Workings of Minds Happiness Should Be A Verb Better Behaved Behavioral Models Rationality In Markets Is Cognitively Unnatural

The views expressed are those of the author and are not necessarily those of Scientific American.

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