of listening to the same sound through both ears, or to two discrete sounds, one through each ear. It was not until 1916 that Carl Stumpf (1848–1936), a German philosopher and psychologist, distinguished between dichotic listening, which refers to the stimulation of each ear with a different stimulus, and diotic listening, the simultaneous stimulation of both ears with the same stimulus. Later, it would become apparent that binaural hearing, whether dichotic or diotic, is the means by which sound localization occurs. Scientific consideration of binaural hearing began before the phenomenon was so named, with speculations published in 1792 by William Charles Wells (1757–1817) based on his research into binocular vision. Giovanni Battista Venturi (1746–1822) conducted and described experiments in which people tried to localize a sound using both ears, or one ear blocked with a finger. This work was not followed up on, and was only recovered after others had worked out how human sound localization works. Lord Rayleigh (1842–1919) would do these same experiments and come to the results, without knowing Venturi had first done them, almost seventy-five years later. Charles Wheatstone (1802–1875) did work on optics and color mixing, and also explored hearing. He invented a device he called a "microphone" that involved a metal plate over each ear, each connected to metal rods; he used this device to amplify sound. He also did experiments holding tuning forks to both ears at the same time, or separately, trying to work out how sense of hearing works, that he published in 1827. Ernst Heinrich Weber (1795–1878) and August Seebeck (1805–1849) and William Charles Wells also attempted to compare and contrast what would become known as binaural hearing with the principles of binocular integration generally. Understanding how the differences in sound signals between two ears contributes to auditory processing in such a way as to enable sound localization and direction was considerably advanced after the invention of the stethophone by Somerville Scott Alison in 1859, who coined the term 'binaural'. Alison based the stethophone on the stethoscope, which had been invented by René Théophile Hyacinthe Laennec (1781–1826); the stethophone had two separate "pickups", allowing the user to hear and compare sounds derived from two discrete locations. See also Acoustic location Animal echolocation Binaural fusion Coincidence detection in neurobiology Human echolocation Perceptual-based 3D sound localization Psychoacoustics Spatial hearing loss References External links auditoryneuroscience.com: Collection of multimedia files and flash demonstrations related