Introduction
A hearing aid is one of the most effective methods for alleviating the hearing difficulty of individuals with moderate-to-severe sensorineural and conductive hearing loss. Various technologies have been adopted to maximize the auditory benefit of hearing aids. The use of nonlinear amplification, which modifies the acoustic signal and provides the appropriate gain, is the most fundamental technique in hearing aids. This method enhances performance in terms of audibility, comfort, and speech recognition [
1]. In addition to nonlinear amplification of sound, noise reduction, directional microphones [
2], and automatic acoustic-based program classifiers [
3] are widely adopted and demonstrated as beneficial technologies to improve the audibility of hearing aids.
Wireless streaming technology (WT), which transmits sounds from a sound source directly to hearing aids, has been an important feature in hearing aids for decades [
4]. From the wellknown telecoil solution to more recent 2.4 GHz technologies, WT is an integrated part of hearing aid usage and has been widely adopted in recent hearing aids with increased battery lifespan. It thus fulfills the sound quality expectation of the user in various listening conditions. For example, phone conversations can be difficult for hearing aid users due to feedback and a low signal-to-noise ratio. WT provides increased signal-to-noise ratio sound, and the wireless streamed sound without background noise can be clear and comfortable for hearing-impaired individuals [
5].
However, it has been shown that the sound qualities of hearing aids using the same baseline streaming technologies can be significantly different between hearing aids. Moreover, previous studies have demonstrated that cognitive function may be relevant to hearing aid benefit, especially in the early adoption of hearing aids [
6,
7]. Considering that many hearing aid users are older, and that cognitive function may be compromised in this population, it is important to understand the role of cognitive function and its relationship to the benefit of various hearing aid technologies.
Hearing aid benefit can be assessed by various methods, including subjective and objective evaluations. Subjective benefit can be assessed using structured questionnaires, while objective measurement of hearing aid effectiveness can be achieved through real-ear insertion gain or real-ear aided response [
8]. Several recent studies have demonstrated the benefit of hearing aids by assessing changes in listening effort and mental fatigue [
9,
10]. In addition to objective measurement, a self-report for listening effort measurement also has provided a suitable result for testing audiologic outcomes [
11].
This study aimed to 1) investigate the benefit, assessed by the sentence/word recognition test and self-reporting listening effort, of bilateral wireless streaming in a noisy background for hearing aid users, and 2) analyze the associated factors for predicting the change in self-reported listening effort.
Results
The median age of participants was 62.5 years and ranged from 27 to 70 years. Eleven patients were previous hearing aid users and 7 patients had no prior experience with hearing aids (one unknown). The median duration of hearing aid use was 60 months, ranging from 4 to 96 months. The mean MoCA score of the study population was 27.0 (23–30). The correlation between age and MoCA was not significant (
p=0.30, Spearman’s correlation analysis); however, except for one outlier, a negative association between age and MoCA was demonstrated (
Fig. 2). Baseline characteristics of the participants are given in
Table 1.
The correct answer rate of the target sentence according to test condition is shown in
Fig. 3. Mean sentence answer score in WT-OFF was 6.6±2.5 and in WT-ON was 9.3±0.5, a significant difference (
p=0.001). The correct answer rate for the target word according to test condition is shown in
Fig. 4. The mean word answer score in WT-OFF was 30.0±10.1 and in WT-ON was 39.1±0.7, a significant difference (
p=0.001). Listening effort in background noise was significantly reduced with WT in hearing aids. The mean WT-OFF score was 85.5 (60–100), and the WT-ON score was 72.5 (20–95), a significant difference (
p=0.02) (
Fig. 5). Age did not show a significant correlation with benefit of WT (
p=0.38). No significant differences in hearing performance were observed according to MoCA scores in the three states of unaided, WT-OFF, and WT-ON. History of hearing aid use did not show a difference in benefit of WT (
p=0.84, Mann–Whitney test). MoCA score showed a significant positive correlation with benefit of WT (ρ=0.59,
p=0.01) (
Fig. 6).
Discussion
This study was designed to investigate whether WT affects sentence/word recognition ability and listening effort and if cognitive function subtests can predict performance between WT-OFF and WT-ON. First, the researchers described the results of change in sentence/word recognition ability and self-rated listening effort depending on use of WT. During the WT-ON condition, participants reported better sentence/word recognition ability and less listening effort to conduct the task. The result indicates that WT has a significant effect on audibility and alleviates self-rated listening effort in noisy background conditions.
One large-scale survey reported that 31% of hearing aid users were not satisfied with the sound during phone conversations on a mobile phone. Moreover, hearing aid users were not satisfied with the hearing aid in noisy situations (39%) or in windy conditions (42%).
Classic hearing aids can offer satisfactory sound perception in relatively quiet environments. In noisy environments, however, they provide less than adequate performance because they also amplify environmental noise, and it is difficult to pick up clear target sounds in common real-world environments. In addition, people with hearing loss usually require a much higher signal-to-noise ratio than normal-hearing people for adequate speech recognition.
Using wireless connectivity, hearing aids can minimize the interference of noise during amplification of the target sound. This can be beneficial for increasing the signal-to-noise ratio in noisy situations and challenging listening environments, such as phone conversations. In addition, wireless streaming offers bilateral sound presentation, which can provide true binaural hearing, including loudness summation. This can be beneficial in improving the satisfaction of hearing aid users. Of note is that the benefit of WT (the change of self-rated listening effort) differed among study participants. This suggests that unknown participant factors may have a role in the degree of benefit for hearing aid functions.
Several hearing aid technologies, such as noise reduction, directional microphones, automatic acoustic-based program classifiers, and wireless streaming are widely adopted and have been assessed with regard to the audibility of hearing aids. However, many studies have reported large interindividual variation in the benefit of each technology [
13,
14]. Although it is expected that a hearing aid’s various functions will be beneficial, the results are not consistent; one possible explanation is that a hearing aid wearer is usually an elderly person. It is well-documented that, as people age, they experience some decrease in cognitive abilities, and this cognitive deterioration is associated with age-related neural changes [
15,
16]. In addition, the degree of cognitive deterioration has large interindividual variation [
17]. Various genetic and lifestyle factors support brain maintenance in aging, and interventions can be designed to promote maintenance of brain structure and function in later life [
18]. Therefore, these interindividual variations may be associated with adaptation in newly-developed hearing aid technologies. The researchers hypothesized that cognitive function might affect adaptation to various hearing aid technologies and be a predictor of benefit.
In elderly patients with impaired cognitive function, there may be difficulties in operating a mobile phone, limiting the full utilization of the advantages of wireless connectivity. Nevertheless,
Figs. 3 and
4 indicate that there are substantial benefits from using WT, regardless of the degree of cognitive function. These findings suggest that if the features of hearing aids are utilized effectively, most patients with hearing impairment can potentially benefit from the useful features of hearing aids.
The present study demonstrated that cognitive function, assessed by MoCA, showed a positive correlation with benefit of wireless connectivity in hearing aid users. However, regarding the MoCA score, no significant difference was observed in hearing aid performance between WT-OFF and WT-ON conditions. Higher MoCA scores indicated higher cognitive function, and higher WT-OFF and WT-ON scores indicate greater benefit of WT. This positive correlation suggests that cognitive function may be a useful predictor of the benefit of wireless streaming in hearing aid users. Study results support previous findings that cognitive function predicts listening effort performance during complex tasks in normally aging adults. Harvey, et al. [
19] stated that cognitive function measured by the subtest of the Woodcock-Johnson III (Memory for Words, Auditory Working Memory, Visual Matching and Decision Speed) assessment predicts listening-effort performance during tasks. In this study, discrepancies in accuracy and reaction time performance were quantified as indicators of listening effort. Meanwhile, Zekveld, et al. [
20] demonstrated that better performances on the text reception threshold, used as a cognitive test, were associated with higher listening effort in the hearing impairment group. In this research, higher listening effort was measured through larger peak dilation amplitudes and extended pupil response durations during pupillometry.
This study had some limitations. First, the number of study participants was small and therefore limited the analysis of other confounding factors that may have affected study results. Second, some participants did not have enough time to adapt to unfamiliar hearing aid types, and real-ear measurements to confirm the best fitting status were not performed. Adaptation to hearing aids is an important process for maximizing their benefits, and real-ear measurement is helpful in achieving more accurate fittings [
21]; these should be considered when results are interpreted. Third, results were limited to WT with bilateral RIC hearing aids. Fourth, the WT-OFF condition does not represent the bilateral hearing in real world. To simulate the environment in which hearing aid users use mobile phones in their daily lives, we positioned a mobile phone close to one ear, allowing the participant to hear the sound. Although the sound transmission differs from bilateral hearing, where sound is transmitted via wireless streaming, it is crucial to note that the research aims to assess the benefits of wireless streaming in comparison to daily usage scenarios. Therefore, the advantages of bilateral hearing are expected to be clearly reflected in the overall effects observed.
However, the study had sufficient strength to suggest a number of results. It was the first study to analyze the association between cognitive function and wireless streaming in hearing aids. In addition, the results demonstrated the benefit of wireless streaming using sentence/word recognition tests and listening effort even though participants were not fully adapted to the new hearing aids. Therefore, future studies are needed to demonstrate the benefit of wireless connectivity in long-term hearing aid users.
In conclusion, the study demonstrated that bilateral wireless streaming could enhance sentence/word recognition and decrease listening effort during phone use for hearing aid users, and the benefit was related to cognitive function. Thus, cognitive function may be a useful predictor of benefit of wireless streaming in hearing aid users, and this finding could be incorporated into patient counseling and prescription of hearing aids.