 Wundt, like most early experimental  psychologists,[22]  concentrated his investigations upon sensation and perception; of all psychic phenomena, sensation is the most obviously connected to the body and the physical world (Hearst 1979b: 33). For Wundt, sensations and our somatic sensory apparatus are especially important for the project of physiological psychology for the simple reason that sensations are the “contact points” between the physical and the psychological (PP I: 1). Sensations (Empfindungen), as the medium between the physical and psychic, are uniquely susceptible to a double-sided  inquiry,[23]  viz. from the “external” physical side of stimulus, and the “internal” psychological side of corresponding mental representation  (Vorstellung).[24]  The Wundtian psychologist therefore controls the external, physiological side experimentally, in order to generate diverse internal representations that can only “appear” to the introspective observer. According to Wundt, the representations (Vorstellungen) that constitute the contents (Inhalt) of consciousness all have their elemental basis in sensations (Empfindungen) (PP I:  281).[25]  Sensations are never given to us as elemental, however; we never apperceive them “purely”, but always already “combined” (verbunden) in the representation of a synthesized perception (PP I: 281). Yet, the manifestly composite nature of our representations forces us to abstract such elementary components (PP I: 281) (cf. PP II: 256). Pure sensations, according to Wundt, display three differentiae: quality, intensity, and “feeling-tone” (Gefühlston) (PP I:  282–3).[26]