A correlation method for detecting the sound-evoked post-auricular muscle response (PAMR)

Area of Science:

• Auditory Neuroscience
• Bioacoustics
• Neurophysiology

Background:

• The post-auricular muscle response (PAMR) is a sound-evoked reflex.
• Understanding PAMR amplitude and detection is crucial for auditory assessments.
• Factors influencing PAMR, including voluntary muscle activity and noise, require detailed investigation.

Purpose of the Study:

• To investigate the relationship between sound level, electromyographic (EMG) activity, and the amplitude and detectability of the sound-evoked PAMR.
• To model the PAMR amplitude as a function of sound intensity and tonic EMG.
• To evaluate a correlation measure for PAMR detection and its dependence on signal-to-noise ratio (SNR) and EMG levels.

Main Methods:

• Detailed measurements of PAMR were conducted in four adults and two infants.
• PAMR amplitude was analyzed in relation to monophasic click level (dB) and tonic EMG.
• A correlation measure (C) was assessed against the signal-to-noise ratio (SNR).
• Potentiation of PAMR was studied with voluntary muscle contraction and eye rotation.

Main Results:

• PAMR amplitude showed a linear relationship with sound level (dB) and a saturating power function with tonic EMG.
• A mathematical model was proposed: PAMR = PAM(o)·SL·(EMG-EMG(noise))² / [(EMG-EMG(noise))² + β²].
• The correlation measure C followed C = SNR² / (SNR² + δ²), indicating saturation with increasing SNR.
• Correlation was non-monotonic with EMG, being optimal at moderate activation levels, effectively induced by eye rotation.

Conclusions:

• PAMR amplitude is predictable based on sound level and EMG.
• Correlation provides a robust and convenient method for PAMR detection in both adults and infants.
• Moderate EMG activation, achievable via eye rotation, optimizes PAMR detection using the correlation measure.