Bergson, Time and Free Will, Chapter 1, §41 "Fechner's Psychophysics. Weber's Law."

by Corry Shores
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Bergson, Time and Free Will

Chapter I, "The Intensity of Psychic States"

Part XIV: Psychophysics

§41 "Fechner's Psychophysics. Weber's Law."

Fechner builds from Weber's Law. Weber first had someone hold a weight. Then he gradually increased the mass very slowly until the person first felt a change in weight-sensation. Then Weber had the person begin with another quantity of weight, and also found the least sensible difference. What he discovered was that no matter what weight we begin with, the smallest perceptible difference will be 1/52 of that initial weight. In all other sensation types, there was also a constant, yet of a different numerical value.

Bergson gives the formula for Weber's Law. By E we mean the amount of initial stimulus, and by S we mean the sensation corresponding to that stimulus. Now we will increase the original stimulus just only by the minimal amount needed for the subject to feel a difference of sensation. We will denote this least change in stimulus as delta-E or ΔE. We find that for each type of sensation, there is a consistent ratio no matter what quantity of stimulus we start with. So by const. we mean this constant ratio value (which in the case of sensing weight is 1/51):

We see that we have not yet given a value for the whole sensation of the weight ('S'). Rather, we only determine the precise moment when an increase in the stimulus produces a change in the sensation. (61bc)

Bergson questions how we may pass from a stimulus' extensive magnitude to a sensation's intensive magnitude. But this is precisely what psychophysicists aim to do. Bergson will now further examine this questionable transition. (61c)

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Images from the pages summarized above, in the English Translation [click on the image for an enlargement]:

Images from the pages summarized above, in the original French [click on the image for an enlargement]:

Bergson, Henri. Time and Free Will: An Essay on the Immediate Data of Consciousness, Transl. F. L. Pogson, (New York: Dover Publications, Inc., 2001).

Available online at:

http://www.archive.org/details/timeandfreewill00pogsgoog

French text from:

Bergson, Henri. Essai sur les données immédiates de la conscience. Originally published Paris: Les Presses universitaires de France, 1888.

http://www.archive.org/details/essaisurlesdonn00berguoft

Formula Image from:

Bergson, Henri. Essai sur les données immédiates de la conscience. Originally published Paris: Les Presses universitaires de France, 1888.

Available online at:

http://classiques.uqac.ca/classiques/bergson_henri/essai_conscience_immediate/essai_conscience.pdf