Summary 186 employees was too small to run statistical analyses. Most employees used more adequate communication strategies after the group-training, but there seems to be a difference between the improvements in personal adjustments between the centers. No trends towards a decrease in NFR was observed. It was concluded that it is still challenging to reduce the work difficulties of employees with hearing loss. Part III: Measuring hearing-critical job tasks To perform their job safely and effectively, locomotive need to detect two auditory warning signals in a train cabin, respectively a bell-like signal (the automatic train protection system) and a buzzer-type signal (the driver’s safety device). Depending on the acoustic characteristics of the warning signals and the noise in train cabins, detection of warning signals can be a hearing-critical job tasks. Therefore, in chapter 5 we specified the acoustic characteristics of the warning signals and the noise present in Dutch train cabins. The effectiveness of the warning signals was evaluated when presented to normally-hearing locomotive engineers. It was concluded that the acoustical requirements for signal detectability were not met in all driving conditions. Therefore, difficulties with detecting the signals can be expected, especially in unfavorable driving conditions or in employees with hearing loss, especially in the high frequencies. In chapter 6, the development and validation of a task and job specific signal detection test for Dutch locomotive engineers is described. This test can be performed in twelve driving conditions, respectively with two warning signals and six noise environments. In an experiment with twelve normally-hearing individuals, the reliability and agreement of the test was found to be sufficient in most driving conditions. To assess the construct validity of the test, seven a priori formulated hypotheses were tested with a retrospective analysis of 83 locomotive engineers who were suspected of having hearing loss. They completed the signal detection test, pure-tone audiometry, and two speech perception tests in noise, and rated the effort and concentration it takes to detect the auditory signals at work. Six of the seven hypotheses were confirmed. The results of the signal detection test correlated moderately with the pure-tone thresholds and the speech reception threshold in fluctuating noise, but not with the speech reception threshold in continuous noise. Also, poorer test scores were obtained by hearing aid users compared with non-hearing aid users. It was concluded that evidence was provided supporting the
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