Clinical Evaluation of Expanded Input Dynamic Range in Nucleus Cochlear Implants

In Brief Objective: The aim of this study was to investigate whether expanded instantaneous input dynamic ranges (IIDRs) in the Nucleus cochlear implant system benefit speech perception in the laboratory and listening in the real world. Design: Until recently, Nucleus cochlear implants have used an IIDR of approximately 30 dB. In this study, an IIDR of 31 dB was compared with 46 dB and 56 dB in the SPEAR3 research processor with nine adult implant recipients. Subjects were given two, 2-wk blocks of take-home experience with each of the three IIDRs. A single IIDR setting was used in each trial period. During the take-home experience with the expanded IIDRs, subjects used two programs: a standard program (with clinically measured electrode dynamic ranges) and a program with adjusted thresholds (decreased T levels). After each block of take-home experience, speech perception testing was conducted for CNC words in quiet (at 45 dB and 55 dB SPL) and for CUNY sentences in the presence of multi-taker babble. Results: On average, CNC word recognition at low presentation levels was significantly better with the 46 dB and 56 dB IIDRs, compared with the 31 dB IIDR; however, there was no significant difference between the 46 dB and 56 dB IIDR conditions. These benefits were greater for standard programs than for reduced T level programs. For CUNY sentences in babble, group results indicated no significant difference in performance across IIDR. The three IIDRs were rated similarly in real-life listening situations, and two of the subjects expressed tolerance problems with the expanded standard IIDRs. Conclusions: IIDRs of 46 and 56 dB provided benefit in accessing low-level speech without a decrement in sentence perception in babble. Most subjects accepted the standard, wider IIDR programs in everyday life. No significant differences were found between the 46 dB and 56 dB IIDR programs. It is possible that an expanded instantaneous input dynamic range (IIDR) in the Nucleus cochlear implant will benefit speech perception, providing greater access to lower level inputs. This study compared an IIDR of 31 (until recently the default IIDR), with expanded IIDRs of 46 dB and 56 dB in the SPEAR3 research processor with nine adult recipients. Four weeks of take-home experience was provided with each IIDR setting. The issue of whether lower level background noise would become intolerable with expanded IIDRs was addressed by comparing expanded IIDRs with and without threshold adjustment (decreased T levels). The expanded IIDRs improved word perception at low presentation levels without a decrement in sentence perception in babble. However, the 56 dB IIDR offered no advantage over the 46 dB IIDR. Most recipients preferred the expanded IIDRs in everyday listening without a reduction in T levels.