PSYCHOPHYSICS (from Gr. \lwxh, soul, <for, nature), a department of psychology which deals with the physiological aspects of mental phenomena, and in particular investigates the quantitative relations between stimuli and the resultant sensations. Following the introspective school of which the last leader was Alexander Bain, the tendency of psychological investigation, in the hands of Fechner, Helmholtz, Wundt, Miinsterberg, was predominantly psychophysical, and psychological study, especially in Germany, where the first fullyequipped laboratory was set up in Leipzig (1879) by Wundt, and in America became largely a matter of experiment and apparatus. Such apparatus has been devised for optical, acoustical, haptical (Gr. &vrfiv, touch), taste and smell experiments. Haptical apparatus includes the kinesimeter (for cutaneous sensation), the thermaesthesiomeler (for heat and cold sensation), the algometer or algesimeter (for pain sensations), the aeslhesiometer (e.g. those of Jastrow and Miinsterberg). Among important apparatus for measuring the time relations of mental processes are the d' Arsonval chronometer, which marks hundredths of a second, and the Hipp chronoscope l in which the stimulus and the clock are electrically connected.
For authorities see Baldwin's Diet, of Philos. and Psych, s.v. " Laboratory," and the latest psychological textbooks.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)