Investigating Speech Recognition and listening effort with different device configurations in adult cochlear implant users

Abstract

Objectives: The purpose of this study was to investigate speech recognition in noise and listening effort among a group of adults with cochlear implants (CIs). Two main research questions were addressed. First, what are the effects of omni versus directional microphone configuration on speech recognition and listening effort for noisy conditions? Second, what is the effect of unilateral versus bimodal or bilateral CI listening on speech recognition and listening effort in noisy conditions?

Design: Sixteen adults (mean age 58 years) with CIs participated. Listening effort was measured using a dual-task paradigm and also using a self-reported rating of difficulty scale. In the dual-task measure, participants were asked to repeat monosyllabic words while at the same time press a button in response to a visual stimulus. Participants were tested in two baseline conditions (speech perception alone and visual task alone) and in the following experimental conditions: (1) quiet with an omnidirectional microphone, (2) noise with an omnidirectional microphone, (3) noise with a directional microphone, and (4) noise with a directional microphone and with a second sided CI or hearing aid. When present, the noise was fixed with a +5 dB signal-to-noise ratio. After each listening condition, the participants rated the degree of listening difficulty.

Results: Changing the microphone from omni to directional mode significantly enhanced speech recognition in noise performance. There were no significant changes in speech recognition between the unilateral and bimodal/bilateral CI listening conditions. Listening effort, as measured by reaction time, increased significantly between the baseline and omnidirectional quiet listening condition though did not change significantly across the remaining listening conditions. Self-perceived listening effort revealed a greater effort for the noisy conditions, and reduced effort with the move from an omni to a directional microphone.

Conclusions: Directional microphones significantly improve speech in noise recognition over omnidirectional microphones and allowed for decreased self-perceived listening effort. The dual task used in this study failed to show any differences in listening effort across the experimental conditions and may not be sensitive enough to detect changes in listening effort.

Keywords: Cochlear Implant; Directional Microphone; Listening Effort; Speech Recognition.