The sense of self-motion can be described as the awareness of motion of our head and body, be it active, as in walking, or passive, as in moving in a vehicle. It also gives us information about our orientation relative to gravity. This sense is unique among all the senses in that it does not depend on a single sensory receptor organ. Its first scientific description dates back to Ernst Mach with his publication in the year 1875 of Grundlinien der Lehre von den Bewegungsempfindungen (Fundamentals of the Theory of Motion Perception). In humans, motion sense primarily utilizes information from the labyrinths and from the visual and somesthetic systems. Other sensory organs such as the acoustic system may play a greater role in some animals (e.g., owl). The labyrinths in the inner ear detect linear and angular acceleration. This information is transformed into electrical activity by the hair cells which in turn modulate activity in the vestibular nerve. The nerve projects to the vestibular nuclei in the brain stem. At this level the labyrinthine input converges with motion-specific information from other sensory systems. For example, imagine sitting on a turntable and being rotated in the light.