Effects of input processing and type of personal frequency modulation system on speech-recognition performance of adults with cochlear implants.

OBJECTIVES

The objective of this study was to compare speech recognition in quiet and in noise for cochlear implant recipients using two different types of personal frequency modulation (FM) systems (directly coupled [direct auditory input] versus induction neckloop) with each of two sound processors (Cochlear Nucleus Freedom versus Cochlear Nucleus 5). Two different experiments were conducted within this study. In both these experiments, mixing of the FM signal within the Freedom processor was implemented via the same scheme used clinically for the Freedom sound processor. In Experiment 1, the aforementioned comparisons were conducted with the Nucleus 5 programmed so that the microphone and FM signals were mixed and then the mixed signals were subjected to autosensitivity control (ASC). In Experiment 2, comparisons between the two FM systems and processors were conducted again with the Nucleus 5 programmed to provide a more complex multistage implementation of ASC during the preprocessing stage.

DESIGN

This study was a within-subject, repeated-measures design. Subjects were recruited from the patient population at the Hearts for Hearing Foundation in Oklahoma City, OK. Fifteen subjects participated in Experiment 1, and 16 subjects participated in Experiment 2. Subjects were adults who had used either unilateral or bilateral cochlear implants for at least 1 year.

RESULTS

In this experiment, no differences were found in speech recognition in quiet obtained with the two different FM systems or the various sound-processor conditions. With each sound processor, speech recognition in noise was better with the directly coupled direct auditory input system relative to the neckloop system. The multistage ASC processing of the Nucleus 5 sound processor provided better performance than the single-stage approach for the Nucleus 5 and the Nucleus Freedom sound processor.

CONCLUSIONS

Speech recognition in noise is substantially affected by the type of sound processor, FM system, and implementation of ASC used by a Cochlear implant recipient.