Reception of Environmental Sounds Through Cochlear Implants

Objective: The objective of this study was to measure the performance of persons with cochlear implants on a test of environmental-sound reception. Design: The reception of environmental sounds was studied using a test employing closed sets of 10 sounds in each of four different settings (General Home, Kitchen, Office, and Outside). The participants in the study were 11 subjects with cochlear implants. Identification testing was conducted under each of the four closed sets of stimuli using a one-interval, 10-alternative, forced-choice procedure. The data were summarized in terms of overall percent correct identification scores and information transfer (IT) in bits. Confusion patterns were described using a hierarchical-clustering analysis. In addition, individual performance on the environmental-sound task was related to the ability to recognize isolated words through the cochlear implant alone. Results: Levels of performance were similar across the four stimulus sets. Mean scores across subjects ranged from 45.3% correct (and IT of 1.5 bits) to 93.8% correct (and IT of 3.1 bits). Performance on the environmental-sound identification test was roughly related to NU-6 word recognition ability. Specifically, those subjects with word scores greater than 34% correct performed at levels of 80 to 94% on environmental-sound recognition, whereas subjects with word scores less than 34% had greater difficulty on the task. Results of the hierarchical clustering analysis, conducted on two groups of subjects (a high-performing [HP] group and a low-performing [LP] group), indicated that confusions were confined to three or four specific stimuli for the HP subjects and that larger clusters of confused stimuli were observed in the data of the LP group. Signals with distinct temporal-envelope characteristics were easily perceived by all subjects, and confused items tended to share similar overall durations and temporal envelopes. Conclusions: Temporal-envelope cues appear to play a large role in the identification of environmental sounds through cochlear implants. The finer distinctions made by the HP group compared with the LP group may be related to a better ability both to resolve temporal differences and to use gross spectral cues. These findings are qualitatively consistent with patterns of confusions observed in the reception of speech segments through cochlear implants.