Effect of the Contraction of the Middle Ear Muscles on Suprathreshold Loudness Judgments

Abstract

Changes in the threshold of hearing and suprathreshold loudness judgments have been reported under conditions in which the contraction of the middle ear muscles (MEM) has been induced. These psychophysical changes have been accounted for variously on the bases of contributions of contralateral direct masking, contralateral remote masking (CRM), binaural loudness summation (LS), and the effects of changes in transmission caused by MEM contraction. Experimental conditions were devised to determine the influence of the contraction of the MEM on suprathreshold loudness judgments at 250, 500, and 1500 Hz by controlling the possible influences of CRM and LS. The relative loudness of two sequentially presented 50-msec pulses (identical frequency) was judged by subjects with normal sensitivity (hearing and MEM) using the method of constants during three basic experimental conditions. In Condition A (reference condition), the test stimuli were presented monaurally separated by a 1400-msec interstimulus interval. Condition B was identical to Condition A except that a 1250-msec narrow-band noise (2900–5000 Hz) was presented contralaterally with an onset delayed 200 msec relative to the first test pulse. In Condition C an identical contralateral noise was used but with the onset of the first test pulse simultaneous with the onset of the noise. For each of these three conditions two reference tone intensities (60 and 100 dB SPL) and two narrow-band noise stimulus intensities (70 and 105 dB SPL) were employed. Essentially no suprathreshold loudness changes were observed between the two pulses among the various. conditions. We conclude that MEM contractions did not effect the suprathreshold loudness judgment.