Effects of isolated and combined exposures to whole-body vibration and noise on auditory-event related brain potentials and psychophysical assessment

Effect of Combined Exposure to Noise and Vibration on Hearing

Aim:

This study was conducted to examine the effect(s) of combined exposure to whole-body vibration (WBV) and noise in railway workers.

Methods:

In this historical cohort study, train drivers with combined exposure to WBV and impermissible noise as the case group (n = 85) and shunters with just exposure to impermissible noise as the control group (n = 30) were recruited. The hearing threshold at the conventional audiometric frequencies was measured in both the groups, and the standard threshold shift (STS) and hearing threshold shift at higher frequencies were calculated. Data were analyzed by SPSS version 20 using t-test, Chi-square, and paired t-test.

Results:

There was no significant difference between the groups for age of participants as well as work duration and body mass index. Increased hearing threshold was most frequently observed at 3000, 4000, and 6000 Hz. STS and hearing threshold shift at high frequencies were observed at 6.0% and 3.3%, and 8.2% and 26.7% in train drivers and shunters in the left ear, respectively, but these were not statistically significant.

Conclusion:

Despite the unauthorized exposure to noise and WBV of train drivers, the STS and hearing threshold shift at higher frequencies were not more prevalent compared with the shunters who were exposed only to impermissible noise levels; hence, no association was found between noise and vibration in this study.

Effects of age, age-related hearing loss, and contralateral cafeteria noise on the discrimination of small frequency changes: psychoacoustic and electrophysiological measures

The aim of the study was to examine central auditory processes compromised by age, age-related hearing loss, and the presentation of a distracting cafeteria noise using auditory event-related potentials (ERPs). In addition, the relation of ERPs to behavioral measures of discrimination was investigated. Three groups of subjects participated: young normal hearing, elderly subjects with normal hearing for their age, and elderly hearing-impaired subjects. Psychoacoustic frequency discrimination thresholds for a 1000-Hz pure tone were determined in quiet and in the presence of a contralateral cafeteria noise. To elicit ERPs, small frequency contrasts were presented with and without noise under unattended and attended conditions. In the attended condition, behavioral measures of d' detectability and reaction times were also obtained. Noise affected all measures of behavioral frequency discrimination significantly. Except N1, all ERP components in the standard and difference waveforms decreased significantly in amplitude and increased in latency to the same degree in all three subject groups, arguing against a specific age-related sensitivity to the effects of contralateral background noise. For N1 amplitude, the effect of noise was different in the three subject groups, with a complex interaction of age, hearing loss, and attention. Behavioral frequency discrimination was not affected by age but deteriorated significantly in the elderly subjects with hearing loss. In the electrophysiological test, age-related changes occurred at various levels. The most prominent finding in the response to the standard stimuli was a sustained negativity (N2) following P2 in the young subjects that was absent in the elderly, possibly indicating a deficit in the inhibition of irrelevant information processing. In the attended difference waveform, significantly larger N2b and smaller P3b amplitudes and longer N2b and P3b latencies were observed in the elderly indicating different processing strategies. The pronounced age-related changes in the later cognitive components suggest that the discrimination of difficult contrasts, although behaviorally maintained, becomes more effortful in the elderly.