154th ASA Meeting, New Orleans, LA

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Perception and Performance of Hearing-Impaired versus Normal-Hearing Persons under Noise

Lauren M. Ronsse - lronsse@mail.unomaha.edu and
Lily M. Wang - lwang4@unl.edu
Architectural Engr. Prog.,
Univ. of Nebraska – Lincoln Peter Kiewit Institute
1110 S. 67th St.
Omaha, NE 68182-0681

Popular version of paper 4aAA3 Presented 9:00 a.m. Friday morning, November 30, 2007
ASA 2007 Meeting, New Orleans, LA

Examining the effects of mechanical system noise on worker performance and perception for normal-hearing persons has been an area of previous research; this study extended this research area to include hearing-impaired subjects.  The goal was to determine if persons with hearing impairments respond similarly to seven different mechanical system background noise conditions as persons with normal hearing.  The seven noise signals varied in terms of level and spectral quality, but were all within the range of background noise conditions found in commercial offices.

Fifteen normal-hearing subjects and thirteen hearing-impaired subjects participated in the study.  The hearing-impaired subjects were fit with a standard set of hearing aids to produce similar hearing thresholds for all subjects.  The study was conducted in an office-like testing chamber, where the noise signals, lighting level, and temperature range were carefully controlled for each session.

Performance was gauged on three types of tests (math, verbal and typing), while subjective perception was measured via a questionnaire.  The subjects completed the tasks over a period of one hour for each background noise condition.  The background noise conditions included two different loudness levels (RC-40 and RC-50), with rumbly, neutral, and hissy spectrums presented at each level.  A fluctuating noise condition, similar to heat pump noise, was also used.

The results show that, in general, both the normal-hearing and the hearing-impaired subjects rated the background noise to be increasingly more annoying and distracting as the noise level spectrum changed from neutral to rumbly to hissy.  Their perception of annoyance and distraction caused by noise also heightened as the background noise increased from the lower level (RC-40) to the higher level (RC-50).  However, a notable difference in perception between the two subject groups was found to occur.  The normal-hearing group rated the fluctuating noise condition to be the most annoying and distracting, whereas the hearing-impaired group rated the loudest (RC-50) noise conditions to be the most annoying and distracting.

The results from the productivity data collected are not as clear as the perception results.  While the normal-hearing group tended to perform better on the typing and math tasks, the hearing-impaired group typically performed better on the verbal task.  However, the data do not indicate that the background noise condition significantly affected the productivity scores.  Statistical significance tests are in progress to further quantify these relationships.  The following graph depicts the average math productivity scores for the two subject groups under the different background noise conditions.

The results of this investigation have shown consistent relationships between the subjects’ perceptions of the noise and the background noise condition.  Further research is needed to fully describe the effects of background noise on productivity.  If significant differences are found to be present between the two groups, they may lead to the development of different standards for noise criteria levels in spaces designed for the hearing-impaired. [Work supported by a Univ. of Nebraska Layman Award and an ASHRAE Graduate Student Grant-in-Aid]

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