Chapter 6 144 Experiment 2 A normal distribution was confirmed for all BHI, SRT, and SNR50 values. The assumption of linearity was fulfilled. Table 2 shows the hearing status of the included participants, measured during their auditory fitness for job assessment. The majority of the engineers (65%) reported that detecting auditory warning signals at their workplace does not take extra effort or concentration. The other engineers reported that detecting auditory warning signals takes extra effort or concentration to some extent, specifically to a small amount (29%) or to a moderate amount (6%). Table 2. Hearing status of the included locomotive engineers that performed an auditory fitness for job assessment (N = 83) Value (SD) Min ; Max Pure-tone audiometry BHI 250 Hz 9.9 (9.24) dB HL -5.0 ; 61.7 dB HL BHI 500 Hz 13.4 (9.30) dB HL 0.0 – 57.5 dB HL BHI 1000 Hz 19.8 (10.59) dB HL -3.0 ; 53.3 dB HL BHI 2000 Hz 30.6 (11.15) dB HL 8.0 ; 70.0 dB HL BHI 4000 Hz 51.0 (12.53) dB HL 23.0 ; 78.0 dB HL BHI 8000 Hz 58.6 (20.63) dB HL 12.0 ; 105.8 dB HL BHI mean 2000 & 4000 Hz 40.3 (9.40) dB HL 20.0 ; 70.0 dB HL BHI mean 4000 & 8000 Hz 54.2 (14.93) dB HL 22.5 ; 85.0 dB HL Speech reception test in noise SRT in continuous noise -3.7 (1.7) dB SNR -8.2 ; 1.2 dB SNR SRT in fluctuating noise -7.6 (3.1) dB SNR -13.8 ; 1.4 dB SNR Signal detection test DSD signal Mat’64 -17.5 (4.46) dBA -29.2 ; -5.2 dBA V-IRM -23.7 (4.01) dBA -29.8 ; -9.8 dBA Signal detection test ATP signal Mat’64 -24.4 (8.3) dBA -46.9 ; -7.9 dBA V-IRM -30.9 (5.9) dBA -41.1 ; -15.9 dBA ATP indicates Automatic Train Protection; BHI, Binaural Hearing Impairment; DSD, Dead Man’s Switch; SNR, signal-to-noise ratio; SRT, Speech Reception Threshold. The results of the hypotheses testing are shown in Table 3. The associations between the SNR50 and the pure-tone thresholds at which the warning signal is the most prominent were moderate to strong (hypothesis 1 and 2). The correlation between the SNR50 and the speech reception in noise test was weak in continuous noise (hypothesis 3) but moderate in fluctuating noise (hypothesis 4). Moderate
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