Factors influencing post-implantation hearing ability of adult cochlear implant candidates with pre-operative acoustic hearing

© 2016 Dr. Kerrie Lynne PlantIt is becoming increasingly common for adults with significant residual acoustic hearing in one or both ears to attend cochlear implant centres for candidature assessment. The clinical decision-making and provision of recommendations regarding this candidate population is complex, because there are only limited clinical data currently available to assist with counselling of candidates regarding expected outcomes. Pre- and post-implantation (3, 6 and 12-month) measures were obtained for 65 subjects who were implanted unilaterally in the poorer ear, and who had significant pre-operative acoustic hearing in one or both ears. This research first investigated outcomes in relation to the potential risks associated with implantation of such candidates; (1) the risk to loss of acoustic hearing in the implanted ear for candidates with pre-operative bilateral acoustic hearing, (2) the potential for less post-implantation benefit in candidates with better contralateral hearing, and (3) the unknown influence of predictive factors in this expanded population. In (3) were included the influence of demographic and hearing configuration, as well as an aspect of post-operative device fitting relating to the degree of match between the assigned acoustic input frequency in the sound processor and the electrical pitch percept. Finally, the factors that influenced the electrical pitch percept were examined. Significant group mean post-implantation improvement was observed on a sentence-in-coincident babble test and for spatial release from masking advantage when the noise location favoured the implanted side. Self-reported group ratings of functional benefit were improved post-implantation for all questionnaires administered. Objective assessment revealed poorer group mean localisation ability post-operatively for subjects with pre-operative bilateral acoustic hearing, however subjective ratings in real-world environments were more variable. Degree of post-implantation SRT benefit on the coincident babble test and on self-reported ratings of perception of soft speech and sounds in the environment was greater for subjects with less contralateral hearing. Factors that predicted better unilateral word scores in quiet (and accounted for 34.1% of the variance) were a shorter duration of severe-to-profound hearing loss in the implanted ear and poorer pure-tone-averaged thresholds in the contralateral ear. A shorter duration of severe-to-profound hearing loss in the implanted ear, a lower age at the time of implantation, and better contralateral hearing thresholds were associated with higher bilateral word recognition in quiet and SRT in noise (and accounted for 36.0% and 30.9% of the variance respectively). Degree of match between the initial (pre-activation) pitch percept elicited from stimulation on the most apical channel and the assigned frequency affected rate of post-operative improvement in the unilateral but not bimodal device configuration. Post-experience measures revealed higher unilateral word in quiet and sentence in babble scores for those subjects with closer match between the assigned acoustic input frequency and electrical pitch percept. No significant correlation was observed between degree of match and bilateral speech recognition ability. Subjects with poorer hearing in the implanted ear tended to have a lower pitch and a shallow electrical pitch function than predicted by the spiral ganglion frequency-position model. There was no significant group effect of listening experience