Master Thesis

Abstract - A cochlear implant is a prosthetic device that enables individuals with sensorineural hearing loss to partially regain the ability to perceive speech. However, the improvement in speech perception is limited by the degraded speech signal that is received via the device. Degraded speech makes speech perception more difficult and effortful for cochlear implant users than normal-hearing listeners. Previous studies have shown that the timely integration of contextual and lexical information can facilitate speech perception by reducing lexical competition. Whether cochlear implant users can timely integrate contextual and lexical information and also process it in the same manner as normal-hearing listeners remains unclear. Hence, two eye-tracking experiments were conducted in this study to examine the processing of contextual and lexical information in cochlear implant users and normal-hearing listeners. The first experiment investigated the processing of contextual information in cochlear implant users by means of verb-based thematic constraints. The second experiment investigated the processing of lexical information in cochlear implant users using an auditory lexical decision task. The results of the first experiment showed that cochlear implant users and normal-hearing listeners were both able to timely integrate and benefit from contextual information. However, the time course of lexical competition was prolonged in cochlear implant users relative to normal-hearing listeners due to their difficulties with the acoustic input signal. In the second experiment, cochlear implant users had lower accuracy scores and longer reaction times than normal-hearing listeners. They also had more difficulties with perceiving nonwords than words which may have been caused by top-down restoration mechanisms. Overall, the findings demonstrate that cochlear implant users can timely integrate and benefit from contextual and lexical information, but they still have difficulties with the processing of acoustic input information which prolongs the time course of lexical competition relative to normal-hearing listeners.

Publications

• Nagels, L., Bastiaanse, R., Başkent, D., & Wagner, A. (2020). Individual differences in lexical access among cochlear implant users. Journal of Speech, Language, and Hearing Research, 63 (1). https://doi.org/10.1044/2019_JSLHR-19-00192.
• Wagner, A. E., Nagels, L., Toffanin, P., Opie, J. M., & Başkent, D. (2019). Individual Variations in Effort: Assessing Pupillometry for the Hearing Impaired. Trends in Hearing, 23, 2331216519845596. https://doi.org/10.1177/2331216519845596