Vocoders are also currently used in developing psychophysics, linguistics, computational neuroscience and cochlear implant research. Stevens' experimental and theoretical work lay primarily in the fields of psychophysics and psychoacoustics. The perception of graphs is studied in psychophysics, cognitive psychology, and computational visions. Psychoacoustics is a branch of psychophysics. Most of his research has been in the fields of behavioral neurology and visual psychophysics. The math in German psychology is mainly applied in sensory and psychophysics. The origin of psychometrics also has connections to the related field of psychophysics. Among these, evaluated the axiom to the psychophysics of binaural loudness. This type of research is closely tied to that in cognitive psychology and psychophysics. The work attempted to link Gestalt theory and psychophysics (i.e., independent linear filters). But in psychophysics and experimental psychology the adjective "apparent" refers to a person's subjective experience. Helmholtz made a similar analogy during the dawn of psychophysics. Freud's most immediate predecessor and guide however was Gustav Theodor Fechner and his psychophysics. Ernst Mach was inspired by his work on psychophysics. He was influenced by the Fechner's work on perception and from the Elements of Psychophysics.