Chapter 7 164 strategies can be used effectively to reduce the difficulties in professional functioning of employees with hearing loss. For example, the effect of the different rehabilitation components should be investigated, the effect of interventions that affect the working environment, and the optimal intensity and duration of these intervention. Therefore, there is a great need for high quality intervention studies, such as randomized controlled trials with a sufficient sample size. In particular, we recommend the investigation of interventions that focus on optimizing the use of PA and interventions that focus on work adjustments. Our results suggest that extra effort in this area may be promising. A limitation of the studies of chapter 1, 2, 3, and 4 is that some measurements were used with low measurement quality. We had to deal with the lack of valid instruments that can be used for the diagnosis and evaluation of aspects of work functioning in employees with hearing loss (Granberg & Gustafsson, 2021; Tufts et al., 2009). Psychometric research is required of questionnaires that can be used for research, the diagnosis, and evaluation of employees with hearing loss. For example, the NFR scale may be validated for the diagnosis and evaluation of work-induced fatigue in the population of employees with hearing loss. Also, the LE and auditory demands scale may be standardized and validated for the same population. Another limitation of our studies is that some potential effects of aural rehabilitation could not be investigated. The effect of speech reading training on speech perception could not be evaluated with a behavioral test, because there is no validated audiovisual speech perception test in noise available in Dutch. The effect of sensory management interventions on speech understanding could also not be evaluated with a clinical test, because speech perception tests were only sparsely used for aided measurements in a free field condition. Part III: Measuring hearing-critical job tasks For locomotive engineers, detecting acoustic warning signals is crucial for safe and effective job performance. The results of chapter 5 show that Dutch locomotive engineers need to detect these signals in a challenging acoustic environment making this task hearing-critical. Since detection of the Automatic Train Protection (ATP) signal often depends on the detection of high frequency signal peaks, especially at higher speed, at higher speed, the detection of this signal is critical for employees with a high-frequency loss.
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