Universität zu Köln

Weglage, Anna ORCID: 0000-0002-4824-3293 (2025). Speech processing in cochlear implant patients across different modalities. PhD thesis, Universität zu Köln.

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Abstract

Hearing loss is one of the leading causes of chronic disability (Vos et al., 2016) and it causes major problems in interpersonal communication. Cochlear implants (CIs) are the world’s most successful neural prosthesis and they allow patients with severe to profound hearing loss to regain their hearing ability. However, hearing with a CI is very different from normal hearing (NH), as only limited auditory input is provided by the device. The capacity of the human cortex to adapt to this new auditory input, however, enables the patients to extract meaningful information within months after switch-on of the processor. During the period of deprived hearing, patients typically rely more strongly on visual cues like lip movement for communication. Hence it has been suggested that these individuals show a pronounced binding of the auditory and the visual system, allowing them to integrate auditory and visual speech information after cochlear implantation more efficiently. The included projects therefore investigate auditory, visual and audiovisual speech processing in hearing deprived individuals and different groups of CI users. They comprise three event-related potential (ERP) studies, split over four publications, each focusing on an individual perspective. The main result of the first study shows a side-of-implantation effect in the auditory cortex of SSD CI users for auditory stimulation of both the CI ear and the NH ear. This is shown by an enhanced functional asymmetry for the left-ear implanted SSD CI users when compared to right-ear implanted SSD CI users. The second study reveals multisensory integration for NH listeners, SSD CI users and CI users with bilateral hearing loss, as depicted in shorter response times for audiovisual as compared to unimodal stimuli. Nevertheless, both CI user groups show delayed auditory-cortex responses and enhanced visual-cortex responses in comparison to the NH listeners. Different processing patterns are also evident in our prospective longitudinal study. Regarding the audiovisual speech stimuli, the CI group displays a more occipitally pronounced topography, especially in a visually attended condition, as well as a reduced auditory cortex response when compared to the NH listeners. Additionally, a condition difference between visually and auditory attended stimuli is present in the beta frequency range for the NH listeners only, which indicates an enhanced allocation of attention when processing the visually attended stimuli. Regarding the visual only speech stimuli, the CI group displays a reduced visual cortex activation, but a stronger functional connectivity between the visual and auditory cortex when compared to the NH listeners. All the results of the longitudinal study seem to be deprivation induced and remain unchanged after six months of CI use. Furthermore the altered visual processing relates to the CI outcome. Taken together, the included projects contribute to a better understanding of speech processing in hearing deprived individuals and CI users in different modalities (auditory, visual and audiovisual). They reveal distinct processing strategies used to overcome the deprivation and the limited regained auditory input via a CI. The results could be used to improve the clinical rehabilitation process by including visual speech information into the currently purely auditory training and assessment. Moreover, first evidence for a relation between electrophysiological measures and the CI outcome pave the way for more precise prediction models.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Weglage, Anna anna.weglage1@uk-koeln.de orcid.org/0000-0002-4824-3293 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-752357
Date:	2025
Language:	English
Faculty:	Faculty of Medicine
Divisions:	Faculty of Medicine > Hals-Nasen-Ohrenheilkunde > Klinik und Poliklinik für Hals-, Nasen- und Ohrenheilkunde
Subjects:	Natural sciences and mathematics Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language cochlear implants English cortical plasticity English audiovisual speech English
Date of oral exam:	10 February 2025
Referee:	Name Academic Title von Kleist-Retzow, Jürgen-Christoph PD Dr. med. van Eimeren, Thilo Prof. Dr. Schroeter, Michael Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/75235