Recruitment (medicine)

Recruitment, in medicine, is a physical condition of the inner ear that leads to reduced tolerance of loudness. It commonly occurs in individuals who suffer hearing loss due to cochlear damage. While low-magnitude sounds cannot be heard in the affected ear(s), the perceived loudness increases over-proportionally with sound volume once the auditory threshold has been overcome. This can result in a (seemingly paradoxical) reduced tolerance to loudness, as loud sounds may be perceived louder than normal.

In those with hearing impairment, the presence of a recruitment phenomenon points towards a cochlear dysfunction, while its absence (also referred to as negative recruitment) indicates a source outside the cochlea (e.g. cochlear nerve injury, tympanic membrane rupture).

A source of frustration for people with sensorineural hearing loss (SNHL) is reduced speech intelligibility. The common lament "I can hear, but I cannot understand," underscores this point. This problem relates to abnormal frequency resolution and aberrant patterns of growth in loudness, each of which reduces speech intelligibility under challenging listening conditions, such as noisy surroundings. SNHL also imposes severe constraints on the dynamic range of perceived sound. For normal listeners, the dynamic range from sensing soft sounds to the loudest tolerable noise is more than 100 dB. Within this wide dynamic range of hearing lies an approximately 35-dB dynamic range of conversational speech.