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Introduction

Binaural hearing is a fundamental property of the normal auditory system. Although only one ear is necessary for speech understanding, hearing through both ears provides major benefits because the auditory system combines information arriving from the two ears and forwards it to the central auditory system for further computation. The main binaural effects include binaural summation, improved localization of the sound source, better hearing in background noise , better auditory spatial organization, greater ease of listening, and better sound quality . Bilateral hearing aid (HA) fitting has been considered the standard of care for many years for individuals with relative bilateral symmetrical hearing loss (HL) . In a survey conducted in Switzerland , on a sample of 6027 participants with symmetrical HL, the data supported superiority of bilateral over unilateral amplification. Presumably, useful synthesis of information occurs when auditory signals are presented simultaneously to the two ears, and, as a result of this binaural integration, binaural performance is superior to monaural performance in either ear.

However, under some circumstances, bilateral HAs are not necessarily better than one HA. There are situations in which binaural interference effects may cause a disturbing fusion of the signal arriving to the two ears, which leads to better performance with unilateral fitting for some individuals, especially in tasks involving speech recognition in noise , and in particular among older participants . Additional issues unrelated to hearing, sometimes prevent bilateral HA fittings, such as higher costs for two HAs compared to one, difficulties handling two HAs among elderly persons, and some individuals’ perceptions of greater handicap with two than one HA .

Furthermore, the benefit of bilateral hearing fittings may depend on the degree of HL. Boymans et al conducted a prospective study evaluating the benefits of a second HA, using functional tests as well as subjective measures (questionnaires) among participants in four subgroups based on HL level (PTA in the better ear): < 35dB, 35-45dB, 45-55dB, and > 55dB. Findings revealed that participants with more severe HLs showed a higher bilateral benefit for speech reception tests with spatially separated sources, than did participants with milder HLs. Also, satisfaction from the second HA was higher for greater HL groups. On the other hand, mean auditory functioning was significantly poorer in groups with greater HL. Finally, for the subgroups divided according to degree of asymmetry in the pure-tone audiogram, no relevant significant differences emerged between unilateral and bilateral benefit. The bilateral benefit tended to be larger for the symmetrical group than for the asymmetrical group.

Benefit of sensory aids is traditionally quantified through various speech perception tests conducted in clinical settings. These tests include various stimuli (such as words, sentences) and may be administered in quiet or in noise . Yet, they are administered in very controlled conditions, where, for example, one speaker presents either words or sentences, the noise is very specific (such as speech noise), and stimuli are presented from specific angles [e.g., ]. These controlled conditions are very different from the conditions that individuals encounter in everyday life.

In everyday listening situations, listeners should be able to follow a conversation against background noise such as in supermarkets or restaurants, with various partners – both familiar and strangers, with different speech rhythms, and so on. Furthermore, conditions in everyday situations are very dynamic, changing over the course of a single communication interaction. Speech can be presented by different speakers from various angles, in the presence of different sources of background noise such as competing speech signals from another talker or group of talkers or environmental sounds.

Previous research results demonstrated that the difficulties expected in everyday listening interactions cannot be predicted from the results of conventional speech perception tests carried out in clinical settings, calling for assessments of sensory aid benefits in dynamic extra-clinical environments. Noble and Gatehouse quoted Arlinger et al’s literature survey concluding that although laboratory conditions uphold the benefit of fitting two HAs, there is a need for a reliable clinical evaluation of functioning in everyday situations in order to support the contention that bilateral fitting reduces disability in comparison to unilateral fitting.

Self-report questionnaires on difficulties in various everyday listening situations following HA fitting may provide an important complementary source, providing real-time assessment. Two commonly used questionnaires assessing individuals’ disabilities due to HL are the Abbreviated Profile of Hearing Benefit [APHAB; ] and the Speech, Spatial, and Qualities [SSQ; ]. Both questionnaires include items related to difficult everyday listening situations. The SSQ, however, contains a wider variety of complex situations, including special attention to spatial hearing ability and listening to music and various sounds.

Gatehouse and Noble developed the self-report SSQ questionnaire to assess everyday hearing functioning in many difficult listening situations, in three main content areas: speech hearing ability, spatial ability, and quality of hearing. This questionnaire can comparatively investigate the contribution of various sensory aids including bilateral and unilateral HAs and cochlear implants (CI) . Using the SSQ, Noble and Gatehouse demonstrated that bilateral amplification surpassed unilateral amplification among individuals with mild to moderate HL regarding ease of listening, hearing from distances, and spatial fidelity (accurate identification of sounds’ or voices’ direction before seeing the source). Rogers et al reported better results in the bimodal condition (CI in one ear and a HA in the other) than in the CI-only condition for two SSQ content areas: spatial ability and quality of everyday hearing. Ching et al assessed the changes in everyday hearing functioning using the SSQ in two individuals who were using CI in one ear and HA in the other and then decided to undergo an additional implantation in the HA ear. Twelve months after the second implantation, the reports demonstrated better results only in the area of spatial abilities.

All the above research findings demonstrated the benefit from using the SSQ with participants differing in their degree of hearing loss and in the use of various sensory aids. The aim of the present study was to examine everyday hearing functioning using the SSQ questionnaire among unilateral HA users compared to bilateral HA users, extending Noble and Gatehouse’s study to participants with various degrees of HL. We hypothesized that participants within each HL severity subgroup (mild to profound) would benefit more from bilateral HAs than from unilateral HAs in different everyday listening conditions. We further hypothesized that participants with symmetric unaided HL will benefit more from bilateral HAs in comparison to those with unilateral HA while those with asymmetric unaided HL will not show the bilateral advantage.

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Method

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Method