The auditory system is remarkable in the range of sound frequencies and intensities it can detect and in the small differences in these parameters it can discriminate. A young listener can hear sounds ranging in frequency from 20 Hz (cycles per second) to 20,000 Hz (20kHz). Within this range, as little as a 0.1% change in frequency is detectable. In the intensity domain, the same listener detects displacements of the ear drum two orders of magnitude smaller than the diameter of a hydrogen atom. At the same time, hearing is quite clear when the amplitude of the sound is raised by a factor of 106, which gives good listeners a dynamic range of more than 100 decibels (dB) on the scale of acoustic energy. Within this dynamic range, a change of 1 or 2 dB is easily detected. Our listener may detect with uncanny accuracy the location of a sound in space and will discriminate between two speakers located within a few degrees of each other on the horizontal plane. This ability to both detect and discriminate sounds is achieved by mechanisms operating at the levels of the external ear, middle ear, and inner ear (Fig. 1) and in the central auditory pathways of the brain (Fig. 2).
KeywordsHair Cell Tympanic Membrane Auditory Cortex Auditory Nerve Basilar Membrane
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