Cochlear implantation in unilateral deafness (UD): Implications for speech understanding, self-perceived hearing improvement, tinnitus suppression and spatial acuity

Background
Patients with unilateral deafness (UD) lack the benefit of binaural hearing. As a result, they experience difficulties in understanding speech in the presence of background noise, in understanding speech that comes from the side of hearing loss (HL), as well as in localising the sound source. Furthermore, a large number of these patients suffer from tinnitus that cannot be treated by conventional masking devices. In the paediatric population, UD has been linked to delayed speech and language development, and poorer academic performance.

Aims
1. To conduct a pilot study to investigate the use of cochlear implant (CI) in patients with UD with and without associated tinnitus.
2. To evaluate the results from CI on speech understanding in the most challenging scenarios, on self-perceived improvement of hearing, and on tinnitus suppression in patients with UD.
3. To investigate the localisation abilities of unilaterally deaf patients who received CI.
4. To investigate the factors that influence the outcomes of CI in UD, with particular focus on deafness duration and speech coding strategies.
5. To investigate the benefits of CI in the paediatric population with UD.

Methods
Speech perception was assessed using the Bamford-Kowal-Bench adaptive speech-in-noise (BKB-SIN) test in three spatial configurations: (1) speech and noise from the front, (2) speech from the front and noise from the hearing ear, and (3) speech from the CI side and noise from the hearing ear. Subjective benefits were assessed using the Speech, Spatial and Qualities of Hearing (SSQ) questionnaire and the Abbreviated Profile of Hearing Aid Benefit (APHAB). Localisation abilities were also evaluated using the A§E localisation setup. Tinnitus was assessed using the Tinnitus Reaction Questionnaire (TRQ). Results were evaluated pre-operatively and at 3, 6, 12 and 24 months post-surgery.

Results
Aim 1 (Chapter 3)
 CI improves speech understanding in noise significantly and as early as 3 months post-operatively.
 CI decreases tinnitus perception significantly when the speech processor is on.
 CI improves self-perceived hearing performance.
Aim 2 (Chapter 4)
 CI improves speech understanding in the most challenging scenarios and the benefits remain stable in the long-term.
 CI significantly increases self-perceived improvement of hearing and remains stable in the long-term.
 CI suppresses tinnitus significantly in the short- and long-term.
 Outcomes are not influenced by duration of deafness.
 Age at implantation does not influence the outcomes.
Aim 3 (Chapter 5)
 Localisation ability improves significantly with CI on.
 Localisation ability is not influenced by age at implantation, duration of deafness or gender.
Aim 4 (Chapters 6 and 7)
 Patients with more than 25 years duration of deafness benefit from CI use for the treatment of UD.
 The speech coding strategy FS4-p is preferred by unilaterally deaf CI users.
 FS4-p is perceived as providing the most natural and pleasant signal when compared with the normal hearing ear.
Aim 5 (Chapter 8)
 Children with post-lingual UD experienced improvement in speech understanding in noise similar to the adult group.
 Children with congenital UD did not show any sign of binaural hearing benefits when implanted post-lingually.
 Children with congenital UD show signs of binaural hearing benefits when implantation occurs at a young age.

Conclusions
Cochlear implantation is a viable treatment option for UD and provides significant improvements in terms of hearing performance, localisation ability, lowering of tinnitus perception and high subjective acceptance of the implant. Age at implantation and duration of deafness do not influence the benefits from CI in patients with UD.