Behavioral and objective measures of auditory stream segregation in cochlear implant users

Cochlear implants (CIs) are a neural prosthesis that allows severely hearing-impaired listeners to achieve high levels of speech understanding in quiet environments. However, listening to a single person’s voice among many, or to a melody in a complex musical arrangement, can be challenging for most CI listeners.

In such scenarios, the listener needs to parse the sounds in the complex auditory scene, group them into meaningful auditory objects, or streams, and selectively attend to the stream of interest. Many studies have investigated the principles or cues that allow the healthy auditory system to perceptually group sounds into streams and selectively attend to one of them.

However, the number of studies investigating these processes in CI listeners is limited and their findings are contradictory. The studies presented in this thesis aimed at improving our understanding of the perceptual organization of sounds by CI listeners. Behavioral and electrophysiological measures were combined to address the fundamental questions of whether CI listeners can perceptually segregate sequentially presented sounds and whether they can selectively attend to the stream of interest.

The results showed that perceptual differences elicited by varying either the place or the pulse rate of the electrical stimulation allowed the listeners to perceptually group the sounds into auditory streams. The listeners were able to selectively attend to a target stream, and the effects of selective attention could be assessed using electroencephalography.

However, the results also suggested that CI listeners might not be able to effectively suppress a competing stream and to initially select the stream of interest, which could contribute to the challenges experienced by CI listeners in complex listening scenarios. The findings from this thesis represent a valuable basis for future studies investigating the perceptual organization of sounds in CI listeners.

In addition, these findings are relevant for the design of future devices, since they suggest that it may be possible to use brain signals to decode selective attention. This information could potentially be used to enhance the perceptual differences between the attended stream and the background sounds, aiding the listeners in complex auditory scenes.