Effect of the acoustic reflex on the spondee threshold.

To determine the effects of the intra-aural muscle reflex on the spondee threshold, 12 normal-hearing adults were tested monaurally with two contralaterally presented stimuli, a 2000 Hz pure tone and a broad-band noise, at two presentation levels: -10 dB and +10 dB re each subject's acoustic reflex threshold for each stimulus. The mean spondee threshold in the +10 dB condition was significantly higher than the mean spondee threshold in the -10 dB condition for both contralateral stimuli. Although some threshold shift in the presence of the +10 dB contralateral broad-band noise was no doubt due to overmasking, it is believed that one-half of the shift occurring with the +10 dB pure-tone stimulus were the result of the contraction of the intra-aural muscles. This presumption is supported by data collected on patients with unilateral anacusis.