Chapter 6 138 Test procedure The detection test was performed in a sound-isolated booth in a free-field setting.The participant was sitting in a chair in the middle of the booth and was surrounded by six speakers located at azimuths of 0°, 45°, 80°, 180°, 280°, and 315°, and a subwoofer. The distance between the chair and the speakers varied from 55 to 140 cm. We used uncorrelated noise signals, and the speaker-system was calibrated such that the sound at the location of the participant (without the participant in place) matched the sound spectrum that was recorded in the train. All subjects were instructed to push a button when a signal was heard, even if the signal was very soft. To get familiar with the test procedure, the test started with a practice round using one signal in one driving condition. Afterwards, the detectability of the DSD and ATP signals was assessed for the different driving conditions. Experiment 1 The purpose of experiment 1 was to obtain reference values for the signal detection test and to examine the test-retest reliability and measurement error of the test. Participants Twelve normally-hearing adults were recruited between November and December 2019. Only subjects with pure-tone thresholds of 20 dB HL or better at the octave frequencies between 250 and 8000 Hz, at both ears, were included. All subjects provided written informed consent. The Ethics Committee of the Academic Medical Center declared that no formal approval of thedetailedprotocolwas requiredaccording to the Dutch Medical Research Involving Human Subjects Act (No. Xt4-148). Thirteen subjects were recruited through an online advertisement to participate in the study. One subject was excluded because the criterion of hearing thresholds at or below 20 dBHL was not met.This resulted in a study population of twelve normallyhearing subjects, including seven females and five males with a mean age of 29.5 (range 25–36). Procedure After completing pure-tone audiometric screening, the signal detection test was applied. The detectability of the DSD and ATP signal were both assessed in the
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