Abstract
High-speed trains are operated in increasingly complex railway networks and continual improvement of driver assistance systems is necessary to maintain safety. Speech offers the opportunity to provide information to the driver without disrupting visual attention. However, it is not known whether the transient pressure changes inside trains passing through tunnels interfere with speech intelligibility. Our primary goal was to test whether the most severe pressure variations occurring in high-speed trains (25 hPa in 2 s) affect speech intelligibility in individuals with normal hearing ability and secondly whether a potential effect would depend on the direction of the pressure change. A cross-over design was used to compare speech intelligibility, measured with the monosyllable word test by Wallenberg and Kollmeier, in steady ambient pressure versus subsequent to pressure events, both realised in a pressure chamber. Since data for a power calculation did not exist, we conducted a pilot study with 20 participants to estimate variance of intra-individual differences. The upper 80% confidence limit guided sample size of the main campaign, which was performed with 72 participants to identify a 10% difference while limiting alpha (5%) and beta error (10%). On average, a participant understood 0.7 fewer words following a pressure change event compared to listening in steady ambient pressure. However, this intra-individual differences varied strongly between participants, standard deviation (SD) ± 4.5 words, resulting in a negligible effect size of 0.1 and the Wilcoxon signed rank test (Z = -1.26; p = 0.21) did not distinguish it from chance. When comparing decreasing and increasing pressure events an average of 0.2 fewer words were understood (± 3.9 SD). The most severe pressure changes expected to occur in high-speed trains passing through tunnels do not interfere with speech intelligibility and are in itself not a risk factor for loss of verbal information transmission.
Highlights
Modern societies are characterised by a growing demand for mobility of individuals and highspeed trains are increasingly becoming a backbone of the transportation infrastructure in many countries [1]
The results of this study indicate that speech intelligibility is not impaired by transient pressure changes in the order of magnitude expected during train travel
High-speed train drivers are operating their vehicles in ever more complex railway infrastructures, but they are subject to a multitude of factors, such as monotonous operating cycles and shift work, known to increase the likelihood of fatigue and human error [27], consequences of which may be catastrophic
Summary
Modern societies are characterised by a growing demand for mobility of individuals and highspeed trains are increasingly becoming a backbone of the transportation infrastructure in many countries [1]. To facilitate safe operation of these fast trains in increasingly complex railway networks a multitude of driver assistance systems are currently under development [2]. In human-machine interfaces the auditory channel can be used to provide information to the user, without disrupting visual attention [3]. This is advantageous when operating heavy mobile machinery, such as trains. Speech has hereby an advantage over other acoustic stimuli; it does alert the operator but it carries the relevant information itself. If speech is considered for transmission of essential information in an operational environment it must be ensured that the acoustical transmission path is interruption-free. It is necessary to assess the train environment for interference with speech intelligibility
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