Part III: Measuring hearing-critical job tasks 141 Academy of Otolaryngology, 1979). We also calculated an overall BHI combining the mean pure-tone thresholds at 2000 and 4000 Hz (the frequencies at which the DSD signal has its most prominent signal peaks) and an overall BHI combining the mean pure thresholds at 4000 and 8000 Hz (the frequencies at which the ATP signal has its most prominent signal peaks). Speech reception in noise was assessed in an unaided, free field setting (S0N0) using everyday Dutch sentences. The noise level was fixed at 65 dBA in most cases and at 70 dBA or 75 dBA in case of severe hearing loss. Two different tests were used: the one developed by Plomp andMimpen (1979) or the test developed by Versfeld et al. (2000). These sentence materials have been shown to result in similar test outcomes (Versfeld et al., 2000). The speech reception test was performed in continuous and single-speaker fluctuating noise. We calculated the speech reception threshold (SRT) for the two noise conditions separately. Subjective rating of effort and concentration All engineers were asked on a five-point Likert scale: Does detecting auditory warning signals cost you effort and concentration at your workplace? The answer options were as follows: no, a small amount, a moderate amount, and a lot. Signal detection test After completing the practice tests from experiment 1, the signal detection test was applied. Due to time constraints, not all 12 driving conditions could be assessed. Instead, the SNR50 was determined in four different driving conditions. Detection of DSD and ATP signal was assessed in the Mat64, the train with the highest ambient noise level, and in the V-IRM, the train type that is relevant for most Dutch engineers. Construct validity Construct validity was assessed by the degree to which the SNR50’s of the signal detection test were consistent with predefined hypotheses. We tested seven hypotheses (Table 3), of which four concerned the association between the signal detection test and conventional hearing tests. We expected moderate, positive correlations between the SNR50 and the pure-tone audiometry thresholds at the frequencies at which the warning signal is the most prominent (hypothesis
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