NIH Toolbox

The auditory system processes acoustic energy (sound) in order to allow us to hear. Sound enters the outer ear, travels down the ear canal to stimulate the eardrum, which transduces acoustic energy into mechanical energy. This mechanical energy is transmitted via 3 tiny bones (ossicles) to the inner ear (cochlea), which, via an intricate process, transduces the mechanical energy into electrochemical energy to activate the 8^th cranial nerve (the auditory nerve). The neural signal is then transmitted through the brainstem to the midbrain, the thalamus and the cortex where ‘perception’ occurs. The auditory system has high sensitivity, sharp frequency tuning, fast temporal resolution and a wide dynamic range.

 

Hearing function may be diminished or lost because of heredity, aging, injury, or disease. Such loss may occur at birth, or gradually over the course of a lifetime, or instantaneously due to trauma. Prevention of hearing loss and associated disabling conditions through improved disease prevention, detection, treatment, and rehabilitation methods is a public health priority.

 

Hearing can be measured and quantified using a variety of techniques, including behavioral, psychophysical and electrophysiological measures. In addition, hearing, communication function and the consequences of hearing loss can be quantified through self-reports and the reports of others, such as family members and caretakers. Measures of hearing can be conducted on the right and left ears separately, or on both ears at the same time (binaural hearing). The physical processing of sound and the psychological correlates of acoustic information coding can be measured at numerous points along the auditory pathway, from the cochlea to the auditory cortex. The range of sounds that can be heard varies along a number of physical parameters, including complexity, intensity, frequency and temporal characteristics. Hearing also includes the ability to determine where a sound is coming from (sound localization) and the direction and presence of sound movement. Hearing can be measured in response to both linguistic (e.g., speech syllables, words, sentences) and nonlinguistic (e.g., pips, tones, clicks) stimuli, and can be assessed under both optimal (quiet) and challenging (e.g., with background noise or other competing signals) listening conditions.

Sumit Dhar, PhD