tube implementations, November 1919, two groups of researchers — K.L. Schaefer and G. Gruschke, B. Griessmann and H. Schwarzkopf — demonstrated before the Berlin Oto-logical Society two instruments designed to test hearing acuity. Both were built with vacuum tubes. Their designs were characteristic of the two basic types of electronic circuits used in most electronic audio devices for the next two decades. Neither of the two devices was developed commercially for some time, although the second was to be manufactured under the name "Otaudion." The Western Electric 1A, developed by <who> was built in 1922 in the United States. It was not until 1922 that otolaryngologist Dr. Edmund P. Fowler, and physicists Dr. Harvey Fletcher and Robert Wegel of Western Electric Co. first employed frequency at octave intervals plotted along the x axis and intensity downward along the y-axis as a degree of hearing loss. Fletcher et al. also coined the term "audiogram" at that time. With further technologic advances, bone conduction testing capabilities became a standard component of all Western Electric audiometers by 1928. Electrophysiologic audiometry In 1967, Sohmer and Feinmesser were the first to publish auditory brainstem responses (ABR), recorded with surface electrodes in humans which showed that cochlear potentials could be obtained non-invasively. Otoacoustic audiometry In 1978, David Kemp reported that sound energy produced by the ear could be detected in the ear canal—otoacoustic emissions. The first commercial system for detecting and measuring otoacoustic emissions was produced in 1988. Auditory system Components The auditory system is composed of epithelial, osseous, vascular, neural and neocortical tissues. The anatomical divisions are external ear canal and tympanic membrane, middle ear, inner ear, VIII auditory nerve, and central auditory processing portions of the neocortex. Hearing process Sound waves enter the outer ear and travel through the external auditory canal until they reach the tympanic membrane, causing the membrane and the attached chain of auditory ossicles to vibrate. The motion of the stapes against the oval window sets up waves in the fluids of the cochlea, causing the basilar membrane to vibrate. This stimulates the sensory cells of the organ of Corti, atop the basilar membrane, to send nerve impulses to the central auditory processing areas of the brain, the auditory cortex, where sound is perceived and interpreted. Sensory and psychodynamics of human hearing Cocktail party effect Understanding speech Non-linearity Temporal synchronization – sound localization and echo location Parameters of human hearing