Date of Defense


Date of Graduation



Speech Pathology and Audiology

First Advisor

Stephen Tasko

Second Advisor

Gregory Flamme

Third Advisor

Kristy Deiters


Purpose: Damage risk criteria for impulsive noise currently consider only acoustic stimuli as elicitors of middle ear muscle contractions (MEMC). Previous literature suggests non-acoustic events and stimuli can elicit MEMC. The purpose of this study was to explore the role of masseter muscle activity as a potential elicitor of MEMC.

Method: Data from 74 participants of normal hearing and neurological health were used. Masseter muscle activity associated with mastication, or chewing, was measured using electromyography (EMG). Masseter EMG measurements were obtained as participants chewed and swallowed three candies successively. Changes in sound energy reflectance relative to baseline were simultaneously taken using a distortion-product otoacoustic emissions (DPOAE) probe system.

Results: Acoustic data consistently demonstrated a change in reflectance concurrent with the onset of masseter muscle activity. The group median of 25th percentile intra-subject data showed a maximum sound energy reflectance of 14.9 dB for bite gestures and 27.6 dB for chew gestures. Parameters of masseteric electromyograms are described.

Conclusions: Mastication may contribute to the magnitude of a middle ear response in the presence or absence of an external acoustic stimuli. Potential sources of change in sound energy reflectance during masticatory gestures include MEMCs and acoustic disturbances through bone conduction. Further research is needed to determine the source of change in sound energy reflectance. If not controlled for adequately, masseteric activity may complicate interpretations of studies of MEMC elicited by acoustic stimuli.

Access Setting

Honors Thesis-Restricted