Philosophical Society of Washington

Minutes of the 2034th Meeting

Speaker: Sally G. Revoile, Center for Auditory and Speech Sciences, Gallaudet University
Topic: “Speech Imperceptibility with Hearing Loss”

The President, Ms. Enig, called the 2034th meeting to order at 8:20 p.m. on November 18, 1994. Mr. Willard Grant read the minutes of the 2033rd meeting and they were with a correction. Ms. Enig then read a portion of the minutes from the 425th meeting, held on November 17, 1894.

The speaker for the 2034th meeting was Sally G. Revoile of the Center for Auditory and Speech Sciences at Gallaudet University, and the title of her talk was “Speech Imperceptibility with Hearing Loss”.

Ms. Revoile indicated that about 10% of the American population have some hearing impairment based on interviews of 90,000 households. Three quarters of the people who indicated that they had some hearing impairment were over the age of 45. Further, males were slightly more likely to have hearing impairment than females, but after the age of 18 years, the proportion of males with hearing impairment to females with hearing impairment increases.

A more detailed survey was performed of the people with some hearing impairment in order to better characterize the level of impairment. Of the hearing impaired group, 70% indicated they could understand a normal voice from across a quiet room and without seeing the speaker's face. Another quarter could understand the speaker if the speaker shouted. Those people that could understand a normal voice typically had problems with speech perception in a noisy atmosphere. Ms. Revoile demonstrated this by playing a tape of the words “choice” and “take” with no background noise and then again with background noise. Specifically, the background noise was the “cafeteria” noise, which simulates a conversational environment. The consonants tended to be more hidden in the noise than the vowel sounds. This was shown on waveforms of the words where the consonants for those words have low amplitude and are somewhat non-periodic, similar to the noise, whereas the vowel sounds have large amplitudes and are more periodic.

Ms. Revoile also simulated several mild hearing impairments upon speech perception by filtering a tape of a selection of words. The filters adjust the decibel hearing level as a function of the frequency. Three types of hearing impairments were demonstrated. A slight mild hearing loss that has a roughly constant impairment over the frequency range resulted in the words sounding muffled. The two other hearing impairments were characterized by an increasing impairment with frequency with one impairment more precipitous than the other. The more mild sloping hearing impairment attenuated the sounds more. The more precipitous hearing impairment resulted in much greater difficulty in perceiving the consonants. Waveforms and spectrograms of the words with the three filters illustrated how the words were affected by the hearing impairment. Ms. Revoile then kindly answered questions from the audience.

Ms. Revoile then kindly answered questions from the audience. The President thanked the speaker for the Society and welcomed her as a member of the Society. Mr. Willard Grant announced that nominations for Society officer positions are requested. The President then announced the next meeting, made the usual parking announcement, and adjourned the 2034th meeting to the Social Hour at 9:51 p.m.


Respectfully submitted,
Alan Russell
for the Recording Secretary

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