Fechner and the Development of Psychophysics

Fechner is considered by many to be the first experimental psychologist. It is more accurate to say that he was likely the first well-known and modern experimental psychologist. In any case, he was the first to publish a widely-read experimental psychology textbook. He was more than a writer though. He conducted a series of experiments investigating the nature of human sensation and perception. He even partially blinded himself by staring too much at the sun during studies about visual afterimages. His various studies solidified him as the premiere psychophysicist of the day.

Fechner was greatly interested in applying mathematics to various bodily sensations and perceptions. He believed that he could accurately measure the workings of the brain by measuring the perceptions of the body. Fechner built a lot on the work of Weber, who formulated Weber’s law (jnd/S = k), a law that calculated the difference in the mass of weights required for a person to sense a difference. Fechner expanded on this by recalculating Weber’s law as S = k log R. Briefly the equation represented the relationship between sensation (S) and the size or mass of a stimulus. Like Weber, he believed that there was a threshold that had to be crossed in order to perceive a difference in sensations. Fechner was the first psychophysicist to talk about an absolute threshold, where a stimulus was first noticed. Once a stimulus was noticed, each “just noticeable difference” of the stimulus (i.e., each time, with increasing size or mass of stimuli, that a person can perceive a difference) was termed a difference threshold by Fechner. He also came up with experimental methods for establishing thresholds in laboratory settings. The method of limits is a method in which a stimulus is presented either above or below threshold and then decreased or increased, respectively, systematically to a point where it crosses the absolute threshold. So, Fechner is usually regarded as the first modern experimental psychologist (some of his methods are still employed today). He not only built on Weber’s law but also greatly expanded the field of psychophysics.

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