Abstract
The posterior auricular muscle (PAM) reflex to sounds has been used clinically to determine hearing threshold as an alternative to other audiological diagnostic measures such as the auditory brainstem response. We have shown that the PAM response is also sensitive to interaural timing differences in normally hearing adults. PAM responses were evoked by both ipsilateral/ contralateral monaural stimulation and by binaural stimulation. Introducing sound delays ipsilaterally or contralaterally decreased the PAM response amplitude and increased its latency. The PAM response in this study shows a qualitatively similar pattern to that seen by the binaural interaction component (BIC) of the auditory brainstem potential to binaural clicks described in previous studies, in that both: have their shortest latency and maximal amplitudes centred around zero interaural timing differences, have response latencies increase with increasing interaural delays up to 1.2 ms and have response amplitudes decrease with increasing interaural delays of up to 1.2 ms. Our data show that the PAM response may be useful in measuring binaural integration in humans non-invasively for diagnostic or research studies.
Highlights
Binaural hearing uses interaural timing (ITD) and intensity differences (ILD) that occur between the two ears to localise sounds in the horizontal plane [1]
In this study we investigate an alternative approach to the non-invasive study of binaural integration by recording the sensitivity of an auditory reflex; the sound-evoked posterior muscle (PAM) response [34,35,36,37,38,39] to binaural stimulus parameters
We generally found the posterior auricular muscle (PAM) response to be greatest with the subject sitting as opposed to lying and in an alert state rather the being sleepy
Summary
Binaural hearing uses interaural timing (ITD) and intensity differences (ILD) that occur between the two ears to localise sounds in the horizontal plane [1]. Streaming allows the person to focus their attention on one particular target sound amongst a cacophony of distracter sounds [2]. Fundamental to this process is the binaural integration of signals from the left and right ears which is thought to occur in the auditory brainstem nuclei [3,4]. Brainstem binaural processing can be measured physiologically using the binaural interaction component of the auditory brainstem response (ABR)[6].
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