General discussion 165 In chapter 6, the development and validation of a signal detection test for Dutch locomotive engineers is described. The test was found to have sufficient reliability and agreement in most driving conditions and hypotheses testing supported the construct validityof the test.Moderateassociationswerehypothesizedandconfirmed between the outcomes of traditional hearing tests and the signal detection test. This finding implies that ability to detect warning signals in train noise is not reflected well by traditional hearing tests. This underlines the importance of performing more advanced tests to assess auditory fitness of locomotive engineers. The signal detection test described in chapter 6 also requires further development and validation. Specifically, a cut-off for safe detection of the signals has not yet been established. Although the signal detection test is task and job specific, it does not include all work characteristics. For example, the cognitive complexity of driving is not investigated during the test. Therefore, a cut-off for safe driving would be based on a theoretical estimation and a safety margin. Also, to keep the test up-to-date, new measures are requiredwith new trains. For example, theMat64 is no longer in use. Also, there are trains with potentially higher noise levels than in the trains under study, such as in high-speed trains. Therefore, the worse-case cannot yet be investigated. Lastly, the approach and test design of the signal detection test may have the potential to be useful for the assessment of auditory fitness for job performance in other occupations. Implications for clinical practice The studies of this thesis have shown that hearing loss impacts on work functioning in different ways. Employees with hearing loss may face difficulties with fulfilling auditory job tasks or with recuperating from work-induced fatigue. The difficulties deserve to be adequately recognized, diagnosed, rehabilitated (if possible), and counselled. Also, the effects of treatment need to be evaluated. Improving the awarenessof employees ándemployers about hearing loss and its potential impact on work functioning may help for early recognition of employees with hearing loss. Hearing screening can raise awareness about hearing loss (Smits &Houtgast, 2005) and may serve for this purpose. At this moment, screening is routinely performed in employees that are exposed to excessive noise levels at their workplace (Sorgdrager et al., 2006). However, since hearing loss is not only caused by noise, employees working in workplaces without high noise exposure may also benefit from routinely screening.
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