Influence of middle-ear muscle contraction on pure-tone suprathreshold loudness judgments.

Abstract

Some effects of middle−ear muscle (MEM) contraction on TTS and suprathreshold loudness judgments have been assessed in three experiments. Experiment I was designed to demonstrate the effect of MEM contraction on TTS while in Experiments II and III the influence of MEM contraction on the loudness of suprathreshold pure−tone stimuli was measured. In Experiment I, MEM contraction decreased the effective level of a high−intensity TTS−inducing stimulus reaching the cochlea. In Experiments II and III signal paradigms were chosen to reduce or eliminate the effects of binaural loudness summation, and contralateral remote and backward masking effects, and to maximize the influence of MEM contraction. Results of the loudness judgments indicated no effect of binaural interaction, whereas the MEM contraction affected the loudness of pure tones only when the stimuli were low frequencye (250, 500 Hz) and high intensity (≳100 dB SPL). The results further imply that at high intensity levels there was an interaction between the effects of the intensity of the loudness−judgment stimulus and the intensity of the reflex−inducing stimulus. That is, when the reflex was induced the effect on loudness increased as the intensity of the loudness−judgment stimulus was raised; likewise, when the loudness−judgment stimulus was maintained at a constant sound−pressure level but the intensity of the reflex−inducing stimulus was increased, the effect on loudness increased. Subject Classification: 65.50, 65.22, 65.24.