Temporary and permanent threshold shift: an overview.

Temporary threshold shift (TTS) as well as permanent threshold shift (PTS) represent the most common hearing effect of acute and chronic high level acoustic stimulation. TTS is typically related to the traumatizing stimulus spectrum and to the exposure level and duration. The stapedial acoustic reflex as well as the repetition rate of the exposure may influence TTS. PTS is related to a number of factors including exposure duration, subject's age, exposure to other ototoxic factors, presence of impulse noise components, etc. PTS is usually accompanied with alterations of several cochlear functions leading to altered speech discrimination mostly in presence of background noise. The main characteristics of both TTS and PTS are reviewed and discussed.