Effects of Reverberation on Acceptable Noise Level in Adults Elizabeth M. Adams, Susan Gordon-Hickey, Robert E. Moore, H

1. Effects of Reverberation on Acceptable Noise Level in Adults Elizabeth M. Adams, Susan Gordon-Hickey, Robert E. Moore, Holly Morlas University of South Alabama INTRODUCTION METHODS RESULTS • Participants • 30 participants • 7 males, 23 females • 2 groups • Young adults – 22 to 39 years of age (M = 26.7 years) • Older adults – 43 to 69 years of age (M = 54.9 years) • Mean hearing threshold levels • Young adults – Normal hearing thresholds 250 to 8000 Hz • Older adults – Normal hearing 250 to 2000 Hz, sloping to mild sensorineural hearing loss at 4000 & 8000 Hz • Less than 10 dB interaural difference at all frequencies tested • All participants met the following criteria: • Native speakers of American English • Negative history of tinnitus, middle ear pathology, speech and language disorders, & neurologic disorder • Not being treated with centrally acting medications at the time of testing • Stimuli • Commercially available recording of ANL test materials (Cosmos, Inc.) • 5 experimental conditions with varying amounts of reverberation • Non-reverberant condition – 0 second (sec) reverberation time (RT) • Mild reverberation – 0.4 sec RT • Moderate reverberation – 0.7 sec RT • High reverberation – 1.2 sec RT • Very high reverberation – 2.0 sec RT • Reverberation added to primary discourse (Arizona Travelogue) & multi-talker background noise (R-SPIN) • Procedures • Participant seated in a sound-treated booth • Experimental stimuli were delivered through a single loudspeaker mounted 1.5 meters from the participant at 0 degrees azimuth • Stimuli were presented through a Sony compact disc player, and routed through a GSI-16 audiometer • MCL for primary discourse • Determined for each reverberant condition separately • Intensity level deemed most comfortable for each listener in each reverberant condition • BNL • Presentation level of primary talker set at participant’s MCL for the specific reverberation condition being tested • Intensity of background noise varied to find the level considered by the participant as the “most noise you are willing to put up with for a long period of time, still following the story, without getting tense or tired” • Procedure repeated three times for each of the 5 reverberant conditions • Average BNL was calculated for each reverberation condition • ANL • Calculated as the difference between the MCL and BNL for each condition • To determine whether a significant effect of age was present, 3 omnibus ANOVAs were conducted for ANL, MCL, and BNL. The results were the following: • No significant age effect for • ANL (p > .05), MCL (p > .05), or BNL (p > .05) • No significant effect of reverberation for • ANL (p > .05) • Significant effect of reverberation for • MCL, F(4, 112) = 2.58, p < .05, and BNL [F(4, 112) = 2.97, p < .05] • No significant interaction of age and reverberation for • ANL (p > .05), MCL (p > .05), or BNL (p > .05) • Because age was not a significant factor in determining the effects of reverberation on ANL, MCL, and BNL, results were collapsed across age group. Three one way ANOVAs were conducted and the results were the following: • No significant main effect of reverberation for ANL, (p > .05) • Significant main effect of reverberation for • MCL, F(4, 116) = 2.66, p < .05, and BNL, F(4, 116) = 2.99, p < .05 • Post hoc testing revealed no significant pairwise comparisons for either MCL or BNL when the alpha level was set with Holm‘s sequential Bonferroni procedure. The effect of reverberation on most comfortable listening level (MCL) and an individual’s acceptance of background noise was examined through the acceptable noise level (ANL) procedure. Previous research has not specifically examined the effect of reverberation on MCL, but has concentrated on performance in reverberation and/or listening difficulty ratings at varying intensity levels in reverberation. Additionally, the effect of reverberation on ANL has not been previously evaluated. Because listening situations are frequently degraded by both noise and reverberation, and because these degradations have a considerable effect on speech intelligibility, it is important to evaluate the effect of reverberation on preferred listening level and acceptance of noise, particularly with older adults. The ANL measurement was developed to quantify the amount of background noise an individual would accept while listening to continuous discourse (Nabelek et al, 1991). Research has suggested ANL as a valuable tool in predicting success with hearing aid amplification (Nabelek et al, 1991; Nabelek et al, 2004; Nabelek et al, 2006). ANL has not been shown to be related to subject age, gender, or hearing threshold status (Nabelek et al, 1991; Rogers et al, 2003; Crowley & Nabelek, 1996; Nabelek et al, 2006). Previous research has not examined the effect of reverberation on an individual’s willingness to accept background noise. The purpose of the present research was to examine how different amounts of reverberation affect the level of speech chosen as the most comfortable listening level by listeners, and to examine how the addition of reverberation changes an individual’s willingness to accept noise while listening to continuous discourse. RESEARCH QUESTIONS Figure 1. Mean ANL, MCL, & BNL in dB HL for each reverberant condition by age. • The following research questions were asked: • Is there an age effect for ANL, MCL, or background noise level (BNL) in the presence of reverberation? • Is there an effect of reverberation on ANL, MCL, or BNL? • Is there an interaction between age and reverberant condition for ANL, MCL, or BNL? DISCUSSION • Lack of significant ANL findings across reverberant condition indicates that reverberation does not affect the amount of background noise adults are willing to accept while listening to continuous discourse. • Additionally, there were no differences between the groups, indicating that the amount of background noise younger and older adults are willing to accept in reverberant conditions does not differ. Previous research has suggested no difference in the ANLs of younger and older adults, and the results of this project support this finding in the presence of reverberation. This finding is shown in Figure 1. • The significant differences found for MCL and BNL were not present during post hoc analyses; therefore, it was concluded that while there is statistical significance for these measures, these findings hold limited practical significance. This suggests that the differences in MCL and BNL in reverberant conditions are negligible, and do not represent a relevant change in real-world situations with reverberation. AUTHOR CONTACT INFORMATION Elizabeth M. Adams, Ph.D., CCC-A University of South Alabama 251.380.2771 eadams@usouthal.edu