It is important to keep in mind that the purpose of this study has not been to investigate the effect of acoustic shocks, but rather to assess potential auditory fatigue due to the long duration of exposure.
Occupational hearing loss is defined as a hearing deficit caused by work-related irreversible cochlear dysfunction whereas auditory fatigue is a more subtle concept.
For this reason, we also used an objective test for measuring auditory fatigue. In this test, acoustic stimulation of the efferent reflexes (ER) is used alongside measurement of the distortion product otoacoustic emissions.
Call center operators often complain about auditory fatigue at the end of their work shift, and that was the case too during this study, but the factors contributing to this fatigue have yet to be objectively studied.
This study examined peripheral and central auditory fatigue based on 2 complementary hearing tests (PTA and EchoScan).
In our investigation, the plasticity of the central auditory system could also have masked some degree of cochlear defects due to peripheral auditory fatigue, making them undetectable by PTA.
EchoScan measurements may therefore detect peripheral auditory fatigue with a high sensitivity  but nevertheless only small and insignificant variations in ER thresholds were measured in the cohort tested here.
Based on these results, we are confident in asserting that our cohort of operators from 3 different call centers have not experienced either central or peripheral auditory fatigue. These findings are not all that surprising since the mean 8-h noise equivalent exposure received through the headset (65.7 dBA) was considerably lower than the noise levels commonly recorded in factories.
Despite these findings, the population of dispatchers reported a sensation of fatigue, and a number of operators suffered from a feeling of auditory fatigue. In the occupational conditions of a call center, this perceived fatigue could be related to cognitive fatigue or emotional exhaustion, due to the heavy mental workload, and to call center specific stressors [19,20].
In such conditions, the noise level under the headset, which is a characteristic of this type of work may be experienced as the main source of strain at the work station, leading to significant levels of perceived auditory fatigue for operators.