# Abstract

 

## OBJECTIVE: The aim of this study was to determine the effects of occupational noise on sound localization in different spatial planes and frequencies among normal hearing firefighters. 

## METHOD: A total of 29 adults with pure-tone hearing thresholds below 25 dB took part in the study. The participants were divided into a group of 19 firefighters exposed to occupational noise and a control group of 10 adults who were not exposed to such noise. All subjects were assigned a sound localization task involving 117 stimuli from 13 sound sources that were spatially distributed in horizontal, vertical, midsagittal and transverse planes. The three stimuli, which were square waves with fundamental frequencies of 500, 2,000 and 4,000 Hz, were presented at a sound level of 70 dB and were randomly repeated three times from each sound source. The angle between the speaker's axis in the same plane was 45°, and the distance to the subject was 1 m. 

## RESULT: The results demonstrate that the sound localization ability of the firefighters was significantly lower (*p*\<0.01) than that of the control group. 

## CONCLUSION: Exposure to occupational noise, even when not resulting in hearing loss, may lead to a diminished ability to locate a sound source. # RESULTS The results were obtained from a cohort of fifteen men and four women (n = 19). The test subjects' ages ranged from 23 to 41 years (mean = 31.4 with a standard deviation of 5.5 years, and the 10^th^ and 90^th^ percentiles were 23 and 40 years, respectively). The control group ages ranged between 20 and 45 years (mean = 29.6 with a standard deviation of 6.2 years). Correct sound source localization by the normal hearing firefighters is depicted in [Figure 1](#). A higher percentage of correct responses was observed in the horizontal plane, followed by the frontal and vertical planes, where the numbers of correct answers were equal. Utilization of the ANOVA and Tukey's tests, however, demonstrated that the percentage of correct sound localization responses was statistically significant in the horizontal plane (*p* = 0.01). Conversely, those in the frontal plane were not statistically identical to the vertical plane (*p* = 0.03). The responses between the frontal and vertical planes were only equal with regards to the mean. [Figure 2](#) presents the firefighters responses in relation to the frequencies used. Very similar values were observed, and the mean percentages of correct answer for the 500, 2,000 and 4,000 Hz frequencies were 31.9%, 30.4% and 28.07%, respectively. Differences between the frequencies, as determined by the ANOVA and Tukey tests, were not statistically significant ([Table 1](#)). A comparison between the results obtained from the firefighter group and the control group is illustrated in [Figure 3](#). The numbers of correct responses, by spatial plane, between the control and test groups were significantly different (with *p*-values less than 0.01, after applying the Student's t-test). [Figure 4](#) compares the mean correct responses between the control and test groups according to the stimulus frequency. The control group obtained means that were 24%, 21% and 25% higher than those of the test group for the 500, 2,000 and 4,000 Hz frequencies, respectively. A comparison of the responses between the groups revealed that the number of correct responses was greater in the control group at all frequencies (*p*-values were less than 0.01 using the Student's t-test). <figure> <p><img src="" /></p> <figcaption>A comparison of the average percentage of correct sound localization responses for each plane.</figcaption> </figure> <figure> <p><img src="" /></p> <figcaption>A comparison of the average percentage of success (correct responses) among the frequencies.</figcaption> </figure> <figure> <p><img src="" /></p> <figcaption>A comparison of the average percentage of success between the groups according to plane.</figcaption> </figure> <figure> <p><img src="" /></p> <figcaption>A comparison of the average percentage of success between the groups according to frequency.</figcaption> </figure> ::::table-wrap

::: caption
Firefighters responses in relation to the frequencies used (500, 2,200
and 4,000) ([Figure 2](#)).
:::

Frequencies *p*-values

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500--2,000 Hz 0.829
500--4,000 Hz 0.276
2,000--4,000 Hz 0.606::::


Extracted trial result:
Outcome: Correct response rate for 500 Hz frequency (continuous)
Intervention: Occupational noise
Comparator: Control
Intervention group size: 19
Comparator group size: 10
Notes: Mean were in a figure and SD was not given anywhere.