Evaluation of Central Auditory Processing in Individuals with Occupational Noise exposure

Abstract

oise-induced hearing loss (NIHL) is a significant public health problem in industrialized nations across the world. In the United States, the Occupational Safety and Health Administration (OSHA) provides workplace guidelines for noise exposure limits whereas the National Institute for Occupational Safety and Health (NIOSH) provides more conservative recommendations on exposure limits. Although there are differences between these organizations with respect to recommended exposure limits, both OSHA and NIOSH monitor noise-induced damage to the inner ear using audiometric permanent changes in hearing thresholds. Exposures that damage hearing are not necessarily painful or even annoying. After overexposure, NIHL recovers with an exponential time course for 2–3 weeks, depending on initial severity. Thresholds may fully recover defined as “temporary” threshold shift or stabilize at an elevated value which is called “permanent” threshold shift. Permanent NIHL is due to destruction of cochlear hair cells or damage to their mechano-sensory hair bundles. Recent studies in animal models suggest interruption of synaptic communication between sensory inner hair cells and subsets of cochlear nerve fibers. This occurs early before the onset