Psychophysics is a branch of experimental psychology often described as being concerned with "the measurement of sensation". Some of the field's most important figures, like Gustav Fechner and S.S. Stevens, have viewed phenomenology - in the sense of the examination of the first-person experience of sensations and percepts - as playing a crucial role in psychophysics. But other practitioners and philosophers have been critical of this assumption. Some have held that what psychophysics really measures are functionally-characterized discriminative capacities. Others have taken the even more radical view that psychophysics does not really measure any inner variables, whether phenomenological or neural.