Acoustic trauma: Single neuron basis for the ’’half-octave shift’’

Abstract

Exposure to an intense pure tone can induce a loss of hearing sensitivity. If this loss recovers, then the desensitization is regarded as a temporary threshold shift (TTS). At the single auditory neuron level this TTS was monitored as a loss of sensitivity at the neuron’s most sensitive or characteristic frequency (CF). When pure‐tone exposures were presented at frequency intervals measured from the neuron CF, then a frequency half an octave below the CF was the most effective for inducing a CF TTS. All exposure frequencies higher than half an octave below the CF produce a marked reduction in TTS growth with intensity, when compared to lower exposure frequencies. This behavior is such that, with increasing exposure frequency higher than the −1/2‐octave point, the intensity needed to produce a given TTS grew faster than the neuron sensitivity. However, below the −1/2‐octave point all exposure frequencies were similarly behaved. Strong similarities exist between the frequency‐specific requirements for TTS and the mechanical and neural nonlinearities found in other studies. This suggests that the half‐octave shift may well be a direct result of basilar membrane nonlinearities.