Impulse noise and continuous noise of equivalent frequency spectrum and total sound energy.

It has been proposed that impulse noise and continuous noise affect the inner ear differently and investigations have found impulse noise to be harmful to both the inner hair cells and the outer hair cells. Scanning electron microscopy and non-standard methods for statistical analysis have facilitated the evaluation of different types of morphological changes after exposure to various kinds of noise. Morphological differences were compared in groups of guinea pigs exposed to either impulse noise or continuous noise of equivalent duration, spectral content and energy. Functionally, the groups also showed similar threshold elevations. In order to separate the two groups, subtle hair cell changes were recorded and evaluated either alone, in combination with each other or with hair cell loss. It was found that both the inner hair cells and the outer hair cells were affected differently by impulse noise than by continuous noise even though the auditory thresholds were similar.