Gustav Fechner studied the quantitative relationship between stimulus and sensation.
"psycho-physics is an exact doctrine of the relation of function or dependence between body and soul" (Elemente der Psychophysik, 1860)
His law: sensation increases logarithmically with stimulus intensity.
Considered one of the founders of experimental psychology.
Merged philosophy and empirical science through measurement.
Inspired later studies of perception and thresholds.
