Fechner Day!

G. T. FechnerAccording to legend, on this date in 1850, Gustav Theodor Fechner arose from his sleep armed with wholly new method to attack the problem studying the mind. Rather than relying on introspective reports of what was going on in people’s minds, scientists could, instead, vary the intensity of some external physical stimulus and ask the “participant” (as we now call them) whether s/he could detect any difference perceptually. For instance: “Does this weight seem heavier than that one?” “Does this light seem brighter or greener than that one?” “Does sound seem louder or higher than that one?”

By using this method rigorously, Fechner was able (borrowing on some earlier work by Ernst Heinrich Weber) to develop a mathematical law putatively mapping changes in physical intensity on to changes in perceived intensity. Called the Weber-Fechner Law, it says that the relationship between the physical and the psychological is logarithmic (i.e., linear changes in perception require proportional changes in the physical stimulus)

The insight was developed by Fechner into the field of psychophysics, and its basic methodology spread throughout the study of mind, culminating in Wundt’s launch of the discipline of experimental psychology (or “physiological psychology,” as he called it) in the mid-1870s.

For more on Fechner, see the Wikipedia article.

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About Christopher Green

Professor of Psychology at York University (Toronto). Former editor of the Journal of the History of the Behavioral Sciences. Creator of the "Classics in the History of Psychology" website and of the "This Week in the History of Psychology" podcast series.

2 thoughts on “Fechner Day!

  1. It’s not simply a legend. Fechner cites that date in Volume II of the “Elemente der Psychophysik”. See Titchener’s “Experimental Psychology”, 1905, Volume II, Part II, p.xx.

  2. Scott, Fechner cited the date in an earlier book as well — Zend Avista. But as all historians know, fixing exact points in time for the origins of things is a difficult thing to do. Although the “eureka” moment is a popular trope in the narrative of scientific discovery, upon examination, they usually turn out to be be more complicated than that (e.g., Galileo dropping stones from the Leaning Tower of Pisa, Newton having an apple drop on his head, Kekule’s dream about snakes biting their own tails — all of which turn out to be false). Even having Fechner’s own recollection doesn’t make things much more reliable. Memories that are a decade or more old are notoriously unreliable. (Do you remember what you were doing ten years ago today?) Thus my use of the term legend. It may have happened that way, but even if it didn’t it has come down as a story that symbolizes the moment when psychophysical method was founded (just like Washington not lying about chopping down the cherry tree — which didn’t happen — has come to symbolize the putative purity of the American republic).

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