Psychophysics began with the work of which 19th-century german scientist (s)

Psycho-Physics as a discipline within the psychology began with the work Elemente de Psychophysics (Elements Of Psychophysics), written by German philosopher and physicist Gustav theodor Fechner. He actually aimed at developing a method that relates mind (psych) to matter (physics). So Psychophysics is the scientific study of the relation between stimulus and sensation.