Objective The aim of this study was to assess the benefit of having preserved acoustic hearing in the implanted ear for speech recognition in complex listening environments. Design The current study included a within subjects, repeated-measures design including 21 English speaking and 17 Polish speaking cochlear implant recipients with preserved acoustic hearing in the implanted ear. The patients were implanted with electrodes that varied in insertion depth from 10 to 31 mm. Mean preoperative low-frequency thresholds (average of 125, 250 and 500 Hz) in the implanted ear were 39.3 and 23.4 dB HL for the English- and Polish-speaking participants, respectively. In one condition, speech perception was assessed in an 8-loudspeaker environment in which the speech signals were presented from one loudspeaker and restaurant noise was presented from all loudspeakers. In another condition, the signals were presented in a simulation of a reverberant environment with a reverberation time of 0.6 sec. The response measures included speech reception thresholds (SRTs) and percent correct sentence understanding for two test conditions: cochlear implant (CI) plus low-frequency hearing in the contralateral ear (bimodal condition) and CI plus low-frequency hearing in both ears (best aided condition). A subset of 6 English-speaking listeners were also assessed on measures of interaural time difference (ITD) thresholds for a 250-Hz signal. Results Small, but significant, improvements in performance (1.7 – 2.1 dB and 6 – 10 percentage points) were found for the best-aided condition vs. the bimodal condition. Postoperative thresholds in the implanted ear were correlated with the degree of EAS benefit for speech recognition in diffuse noise. There was no reliable relationship among measures of audiometric threshold in the implanted ear nor elevation in threshold following surgery and improvement in speech understanding in reverberation. There was a significant correlation between ITD threshold at 250 Hz and EAS-related benefit for the adaptive SRT. Conclusions Our results suggest that (i) preserved low-frequency hearing improves speech understanding for CI recipients (ii) testing in complex listening environments, in which binaural timing cues differ for signal and noise, may best demonstrate the value of having two ears with low-frequency acoustic hearing and (iii) preservation of binaural timing cues, albeit poorer than observed for individuals with normal hearing, is possible following unilateral cochlear implantation with hearing preservation and is associated with EAS benefit. Our results demonstrate significant communicative benefit for hearing preservation in the implanted ear and provide support for the expansion of cochlear implant criteria to include individuals with low-frequency thresholds in even the normal to near-normal range.

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The Hearing Preservation Classification System proposed herein fulfills the following necessary criteria: 1) classification is independent from users' initial hearing, 2) it is appropriate for all cochlear implant users with measurable pre-operative residual hearing, 3) it covers the whole range of pure tone average from 0 to 120 dB; 4) it is easy to use and easy to understand.

The authors present the accepted strategy of Partial Deafness Treatment (PDT) based on long-term observation and results: 8-years long in adult patients and over 5-years long in children. In therapy, there are two fundamental modes of complementary stimulation in cases of moderate to severe hearing loss. One of them is the acoustic stimulation (AS), comprising patients who use amplification with hearing aid (HA) and/or middle ear implant (MEI). The other mode, presented by the authors in this study, is the electric stimulation using cochlear implant (PDCI). The entire material in this mode is divided into three groups: 1. Electrical Complement (EC); 2. Electric Acoustic Stimulation (EAS); and 3. Electric Stimulation (ES). Surgical approach in PDT is based on the 6-steps method, emphasizing round window approach to the scala tympani. The results obtained in the long-term follow-up shows the preservation of preoperative hearing in 97% of subjects. Overall, for all audiometric frequencies the differences in mean pre- and mean postoperative thresholds, measured before surgery and 3 months afterwards were not statistically significant (p>0.05). In all four groups we observed a significant increase in scores between pre-operative and 12 months after surgery both under quiet and noisy conditions. The presented concept, supported by the substantial material and long-term follow-up, allows the comprehensive approach to the treatment of partial deafness using different modes of stimulation.

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