Clinical Outcomes for Adult Cochlear Implant Recipients Experiencing Loss of Usable Acoustic Hearing in the Implanted Ear

Objectives: The first aim of the study was to quantify the change in clinical performance after cochlear implantation for adults who had pre-operative levels of acoustic hearing in each ear of greater than or equal to 46% phoneme score on an open-set monosyllabic word test, and who subsequently experienced loss of useable acoustic hearing in the implanted ear. Pre- and postoperative spatial hearing abilities were assessed, because a clinical consideration for candidates with bilateral acoustic hearing is the potential for post-operative reduction in spatial hearing ability. Second, it was of interest to examine whether preoperative localization ability, as an indicator of access to interaural timing and level cues preoperatively, might be correlated with post-operative change in spatial hearing abilities. Design: Clinical performance measures in the binaural condition were obtained preoperatively and at 12 months postoperatively in 19 post-linguistically hearing-impaired adult subjects. Preoperative localization ability was investigated as a potential correlate with post-operative change in spatial hearing abilities. Results: Significant postoperative group mean improvement in speech perception was observed on measures of open-set monosyllabic word perception in quiet and on an adaptive sentence test presented in coincident 4-talker babble. Observed benefit was greater for a lower presentation level of 55 dB SPL as compared with a conversational speech level of 65 dB SPL. Self-reported ratings of benefit also improved for all questionnaires administered. Objective assessment of localization ability revealed poorer localization postoperatively, although subjective ratings of post-operative change in localization ability in real-world environments were more variable. Postoperative spatial release from masking was not different to that measured preoperatively for the configuration where the side of the head with the hearing aid was advantaged, but improved postoperatively for the configuration that advantaged the implanted side. Preoperative binaural localization ability was not correlated with postoperative spatial hearing abilities. Conclusions: The findings from this study support cochlear implantation for candidates with pre-operative levels of binaural acoustic hearing within the range examined within the present study. This includes subjects with preoperative open-set monosyllabic word scores ranging from 11 to 62% in the implanted ear, and from 16 to 75% on the contralateral side. Post-operative improvement would be expected for those subjects on a range of clinical measures, even when acoustic hearing was lost in the implanted ear after implantation.