Among different methodologies that can quantify listening effort, the dual-task paradigm is one of the most widely-used behavioral measures [18].

Dawes et al. [19] constructed a listening effort subscale from the effort-related questions in the Speech, Spatial and Qualities of Hearing Scale (SSQ) questionnaire in order to examine changes in listening effort subsequent to acclimatization to hearing aids.

In our study, the SSQ questionnaire results showed highly significantly lower scores for subjects with hearing loss (with and without HAs) than normal hearing subjects in all sections of the questionnaire. Our results agreed with Bess and Hornsby [20], who stated that patients with hearing loss reported increased effort when listening in difficult situations. The hearing-impaired listener might not be able to hear every single word in a sentence. Consequently, more mental effort may be required to identify the relationship between the different items in the sentence, guess misheard words, and the meaning of the sentence. In the current study, all subjects with hearing loss showed significantly higher scores of FAS than normal hearing subjects which agreed with Bess and Hornsby [20] and Hornsby and Kipp [21] who found that through the use of subjective measures of fatigue, individuals with hearing loss experience decrements in their vitality as well as increase in fatigue, likely due to the increased listening effort experienced.

Bentler et al. [22] found no significant difference between unaided and aided conditions in subjective testing which agreed with our results. They also found no significant difference between basic and advanced signal processing features of hearing aids. This could be because benefits from directional and digital noise reduction (DNR) processing in real-world settings are often more subtle than those observed in laboratories.

In the dual task paradigm, our results showed that the SNHL patients without and with hearing aids showed more SNR loss than normal subjects. This can be explained as if the incoming signal is compromised (due to masking noise, or hearing loss for example), the phonological elements may fail to match existing representations [23]. This mismatch will trigger a loop of explicit processing to either restore missing information and retry matching to representations in long-term memory, or if no match can be found, to guess the meaning [24].

Our results also agreed with Picou et al. [25] who reported longer RTs in patients with hearing loss (aided and unaided) than normal hearing subjects. This can be explained by the increased processing required by patients with hearing loss to not only hear the word amidst background noise, recognize and repeat it, but also to comprehend the meaning and the linguistic category it belongs to. This required processing is more increased when speech information input is degraded consuming much of the cognitive capacity and more listening effort needed for the secondary task leading to longer RTs. There was no significant difference between the unaided and aided group which disagreed with Down [26] who found shorter RTs in patients using hearing aids than patients with hearing loss. In the current study, although there was no significant difference between two study subgroups, the reaction times at higher SNR (+25, +20, +15) were shorter in the hearing aid group than in the hearing loss group. However, in more challenging situations with lower SNR (+10, +5, 0), there was no difference between the two groups indicating that RT is better for those wearing HA in higher SNR. So much cognitive capacity and more listening effort is needed for speech processing in challenging situations. High-level background noise may not be sensitive to changes in listening effort with hearing aids [27].

The Stroop test comparison as a measure of listening effort showed no significant difference between the groups. This non-significance could be explained that the Stroop test in our study was at the end of the sentences, so it was easy for subjects to answer it. Our results agreed with Wu YH et al. [28] who found that SNR did not have an effect on the number of correct answers of the Stroop test, suggesting that results did not vary with speech intelligibility.

There was no significant difference in listening effort between patients with unilateral and bilateral hearing aids. Our results disagreed with Schoonhoven et al. [29] who reported that bilateral HAs can provide more reduction in listening effort, better speech reception in noise, and localization than unilateral HAs.

Digital signal processing algorithms in hearing aids enables noise reduction, feedback cancelation, and various dynamic compression settings. However, the benefit of hearing aids varies between individuals, which might partly be explained by individual differences in cognitive capacity. Also, speech reception in noise performance is related to cognitive abilities in individuals using hearing aids [30,31,32].

Although several studies have shown that hearing aids decrease listening effort [11, 26, 33], others have not demonstrated this benefit [34, 35]. There are many possible reasons for these conflicting findings. It is possible that tests conducted in conditions that are too easy, e.g., quiet, low-level background noise or too difficult, e.g., high-level background noise may not be sensitive to changes in listening effort with hearing aids. Under certain conditions, hearing aids may generate artifacts or distortions or amplify inaudible background noise. These alterations to the target signal may require additional cognitive resources for successful perception [27, 36].

One of the limitations of our study is the small numbers of the group using hearing aids (unilateral and bilateral) and the use of the basic signal processing HAs.

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