noun plural but singular in construction\ˌsī-kō-ˈfiz-iks\(Medical Dictionary)
Medical Definition of PSYCHOPHYSICS
: a branch of psychology concerned with the effect of physical processes (as intensity of stimulation) on the mental processes and especially sensations of an organism
Branch of psychology concerned with the effect of physical stimuli (such as sound waves) on mental processes. Psychophysics was established by Gustav Theodor Fechner in the mid-19th century, and since then its central inquiry has remained the quantitative relation between stimulus and sensation. A key tenet has been Weber's law. Psychophysical methods are used today in vision research and audiology, psychological testing, and commercial product comparisons (e.g., tobacco, perfume, and liquor).