Outer ear prosthesis aids speech recognition

NEW YORK (Reuters Health) - A prosthetic outer ear not only improves the appearance of a damaged ear but also seems to improve hearing and speech recognition in noisy environments, according a study released today.

A person may be fitted with a prosthetic outer ear when their ear is removed during surgery for cancer or damaged by trauma, Dr. William E. Walsh, of Northwestern University Feinberg School of Medicine, Chicago, and colleagues explain in the Archives of Facial Plastic Surgery.

"Their external auditory canal is usually intact, and the remainder of their auditory system should function normally," they write. In these patients, the physician must strive not only to correct the aesthetic defect caused by the missing (outer ear) but also to correct the hearing loss caused by its absence."

In part one of a two-part study, Walsh and colleagues tested eight different silicone rubber ear prostheses using a life-sized plastic foam head with a hole drilled through the ear. A microphone placed at the entrance of the ear canal measured sound pressure levels with and without the ear prosthesis while the head was rotated 360 degrees in 30-degree increments.

The researchers found that, on average, the prosthetic ears improved the sound pickup by 8.1 decibels when the frequency of the sound was 4.6 kilohertz, and 9.7 decibels when the frequency was 11.5 kilohertz.

The benefits of this level of improvement were demonstrated in part two of their study in which 11 English-speaking young adults with normal hearing took two versions of a speech test.

The first test was unmodified but in the second, subjects plugged their left ears and sat in front of two speakers, one playing normal speech and one playing "white noise." The sound level of the speech was increased by one decibel at a time until all of the sentences in the speech test were understood. The trial was then repeated with the prosthesis over the right ear.

According to the researchers, in these "real-life" tests, the prosthesis significantly improved the average ratio of speech to noise at which all sentences were understood.

This part of the study "answers the question whether the gain measured in a model system actually improves a patient's hearing," Walsh and colleagues say.