In noisy environments, prosthetic ears may improve hearing and speech recognition, according to an article released on September 15, 2008 in the Archives of Facial Plastic Surgery, one of the JAMA/Archives journals.

When the outer ear, also called the pinna, is removed surgically or significantly damaged by trauma, patients may require prosthetic ears, according to the article. The authors describe the situation faced by these patients: “Their external auditory canal is usually intact, and the remainder of their auditory system should function normally,” they say. “In these patients, the physician must strive not only to correct the aesthetic defect caused by the missing pinna but also to correct the hearing loss caused by its absence.”

To investigate the potential effects of a prosthetic ear on the patient, William E. Walsh, M.D., C.M.I., of Northwestern University Feinberg School of Medicine, Chicago, and colleagues examined eight different silicone rubber prostheses in a two part study. First, the researchers experimented using a life-sized head made of foam, with a 12-millimeter hole drilled at the location of the external auditory canal. Placing a microphone at the entrance of the ear canal, the sound pressure with and without the prosthesis as the head rotated.

The prosthesis improved the sound volume acquired by 8.1 decibels when the frequency of the sound was 4.6 kilohertz. This increase was 9.7 decibels when the frequency was 11.5 kilohertz.

In the second part of the study, the researchers examined whether this improvement would actually benefit patients. A total 11 English-speaking young adults with normal hearing took a speech test in two different forms. The first was unmodified, ,while the second allowed the acoustic effects caused by the absense of a pinna were stimulated, based on the data from the study made with the foam head. Participants sat in front of two speakers,  one playing normal speech and one playing white noise. The participants then plugged their left ears and tried to understand the sentences. The sound level of the speech was gradually increased, one decibel at a time, until the participant could understand all of the sentences. This was repeated with the prosthesis over the opposite ear.

The prosthesis used in this tests improved the average ratio of speech to noise at which the subject was able to understand all of the sentences heard. The authors of the study claim this “answers the question whether the gain measured in a model system actually improves a patient’s hearing,”

The continue, discussing prosthetic ears in the context of improved acoustics. “Auricular prostheses provide an acoustic gain at certain head positions and frequencies, and this acoustic gain is clinically relevant because it benefits speech recognition in noise.” They continue: “In some individuals, auricular prostheses not only effectively restore aesthetics but also may improve hearing. To verify the results of the present experiments, the main outcome measures described in this study will be used to obtain future measurements from individuals who wear auricular prostheses.”

The Importance of Auricular Prostheses for Speech Recognition
William E. Walsh, MD, CMI; Brian Dougherty, BS; David J. Reisberg, DDS; Edward L. Applebaum, MD; Chirag Shah, BS; Patrick O’Donnell, MD; Claus-Peter Richter, MD, PhD
Arch Facial Plast Surg. 2008;10(5):321-328.
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Written by Anna Sophia McKenney