Recruitment

Recruitment is a phenomenon of abnormal growth of loudness.

The ear which does not hear low intensity sound begins to
hear greater intensity sounds as loud or even louder than
normal hearing ear. Thus, a loud sound which is tolerable
in normal ear may grow to abnormal levels of loudness in
the recruiting ear and thus becomes intolerable. The
patients with recruitment are poor candidates for hearing
aids. Recruitment is typically seen in lesions of the
cochlea (e.g. Meniere's disease, presbycusis) and thus
helps to differentiate a cochlear from a retrocochlear
sensorineural hearing loss.
Alternate binaural loudness balance test is used to detect
recruitment in unilateral cases. A tone, say of 1000 Hz, is
played alternately to the normal and the affected ear and
the intensity in the affected ear is adjusted to match the
loudness in normal ear. The test is started at 20 dB above
the threshold of deaf ear and then repeated at every
20 dB rise until the loudness is matched or the limits of
audiometer reached. In conductive and neural deafness,
the initial difference is maintained throughout while in
cochlear lesions, partial, complete or over-recruitment
may be seen