People with hearing impairment are known to exert more effort to understand speech, which leads to increased listening fatigue, need for recovery after work, incidence of stress-related sick leave, greater prevalence of unemployment, and social isolation. Listening effort is an issue of great importance to patients' quality of life and satisfaction with treatment. However, the gold standard of audiological outcome measures is speech intelligibility scores, which do not convey information about the effort exerted during speech perception, nor the perceptual mechanisms by which speech sounds are identified. Cochlear implants (CIs) are an increasingly common form of treatment for people with severe to profound hearing loss. Despite the increased prevalence and increased success of CIs in the past decade, there is little known about listening effort and auditory factors that elevate or reduce effort in this clinical population. One factor that is likely to be relevant is auditory spetral resolution, or signal clarity in the frequency domain, which is known to be especially poor in CIs. Poor spectral resolution also alters the way that listeners weight acoustic cues when identifying speech sounds. A chief goal in CI technology is to improve spectral resolution, which should facilitate not just better speech intelligibility, but also reduced effort. Spectral resolution inCIs can be improved by reducing the spread of excitation (SOE) in the cochlea. The partial tripolar (PTP) stimulation mode reduces SOE by using opposite-polarity flanking electrodes to focus current generated by each active electrode in a CI. PTP has been shown to yield modest improvements in speech intelligibility, pitch perception, and distinction of spectral cues in non-speech sounds for some patients. As speech intelligibility measures can remain stable in spite of changes in effort and resolution, it is not known whether reduction in SOE can lower listening effort or facilitate spectral cue perception in speech sounds. In the current project, PTP stimulation will be used to reduce SOE in CIs, which is hypothesized to lower listening effort and increase perception of spectral cues in speech. Effort will be measured using pupillometry, which is a sensitive measure of cognitive load that has been used across many domains, including speech perception. Speech cue perception will be assessed with auditory cue-weighting tasks that have previously shown to be sensitive to changes in spectral resolution. Cue-weighting patterns that are changed to resemble those used by listeners with normal hearing are expected to be associated with reductions in listening effort. The planned measures represent an effort to address the critical problem of spectral resolution in CIs, which are a common treatment for hearing impairment. Using innovative physiological and behavioral measurement techniques, it is expected that the benefits of using PTP as a means of improving spectral resolution for CI users will be borne out in measures of listening effort and phonetic cue weighting.
People with hearing impairment (including those with cochlear implants) exert extra effort to understand speech, and the resulting fatigue has dramatic negative consequences on occupational and social life. The goal of this project is to evaluate the improvement of spectral resolution (i.e. sound quality) in cochlear implants that comes as a result of using the partial tripolar stimulation mode. Improvements in spectral resolution will be measured with regard to their effects on listening effort and also the perception of acoustic cues for speech sounds.
