The present study aimed to fulfill the lack of scientific evidence about listening effort in school-age children with UHL [19], and investigating the impact of a HA fitting. The single task of speech recognition in quiet and noise did not show any significant differences (Table 1). This is outcome is different from a similar test design in older children with bilateral hearing loss. Their study showed significant results when performed utilizing the HINT with adolescents with normal hearing (group 1) and with bilateral hearing loss (group 2) [18].
This study found that those with bilateral hearing loss required a better S/N ratio than those with normal hearing. This suggests that children with UHL may not experience the same difficulties as those with hearing loss in both ears. This lack of difficulty may contribute to late or no intervention, and the late fitting of hearing aids to children with UHL [8]. This is because children with UHL can present with listening abilities less noticeable than those with bilateral hearing loss.
No significant results were found in the speech recognition task, the secondary task analysis, and the response time in the single condition (Figs. 1 and 2). These results were expected as they were performed in the single task condition and were independent of listening effort [20]. The most important results were those for the dual-task analysis. The speech recognition results in the dual-task condition were not different from the results found in the single task condition (Fig. 3). Although better results with speech recognition in children fitted with the hearing aid were observed, no statistically significant results were found (p = 0.148). A possible explanation for these results is that the patient receives instructions to improve his/her performance only in the primary task for the single and dual task conditions [21, 22].
The number of correct answers in the secondary task was significantly greater after the fitting of the HA (p = 0.013) (Fig. 4). A tendency of consistency was observed between the number of correct answers in PALETA and response time of the same test also documented in a previous study [18]. The main measure of listening effort, the dual-task response time results [23, 24] showed a statistically significant decrease of response time after the HA fitting (p = 0.019). The children had more difficulties completing the secondary task without the hearing aid. This may be due to the impairment of listening to the speech signal and impacting the speed at which they could answer the secondary task (Figs. 5 and 7).
These findings are consistent with a previous study that included twenty-three adults with bilateral hearing loss. They also showed a lower response time in the secondary task after the HA fitting [25]. In addition, this study described the importance of the response time measures, because they help to observe the differences between monaural and binaural fittings. They further noted that measures of listening improvement of subjects already using hearing technology can also be used to assess the quality of the HA fitting.
Fatigue analysis may be performed to assess and the level of salivary cortisol [23]. The hypothalamus-pituitary-adrenocortical axis controls the cortisol level during the stressful situations and induces the production of corticotropin factor, hence this factor stimulates the secretion of adrenocorticotropic hormone. Thus, this hormone stimulates the adrenal gland, which induces the cortisol production [26]. Therefore, the cortisol has been used to measure the fatigue level due to the stressful listening situations such as in subjects with UHL.
The present study performed the cortisol collection before and after the HA fitting in four different moments. Only the fourth salivary tube presented statistically significant results with a greater cortisol level being observed after the HA fitting (Fig. 6). These results show the sensitivity of salivary cortisol to capture fatigue changes or stress related to the speech recognition task [23]. Another explanation for the found results could be that atypical stressful situations during the scholar period may cause changes in the cortisol levels [14]. There was a great variance of cortisol level despite attempts to control external factors. Previous studies that included children with hearing loss and those with normal hearing have cortisol levels which were higher in the morning and that was present in this study [14, 23].
While this study yielded some positive findings, there are some limitations that are important to acknowledge. First, although saliva collection was controlled in the clinic environment, this could not be standardized with home collection. It was not possible to control atypical stressful situations in the lives of our participants, and this could explain the high standard deviation in the salivary cortisol analysis (Fig. 6). Second, the small sample size is also a factor to be considered during the analysis of the present study. Children with UHL do not represent a large proportion of the clinical caseload, and recruitment for this study was difficult. Data analysis across all conditions, examining all variables should be viewed as a whole, and not evaluated in isolation.