Public defence in Systems Neuroscience, M.Sc. (Tech) Sasu Mäkelä

Title of the thesis: Challenges in magnetoencephalographic studies of naturalistic reading and speech

Doctoral student: Sasu Mäkelä
Opponent: Lecturer Mathieu Bourguignon, ULB Neuroscience Institute, Belgium
Custos: Professor Riitta Salmelin, Aalto University School of Science, Department of Neuroscience and Biomedical Engineering

The aim of this thesis was to find ways to study the processes in the cerebral cortex that underlie naturalistic reading and, to some extent, naturalistic speech using magnetoencephalography, a brain imaging method with both a good temporal and spatial resolution. Knowledge on the cortical basis of reading and speech is mostly built on studies which restrict and simplify these tasks greatly even though reading and speech in everyday life are very complex functions. Consequently, obtaining data that is truly representative of the cortical mechanisms of reading and speech requires paradigms where participants can read and speak as naturally as possible. Additionally, the length of the read texts or spoken utterances should not be unrealistically short. However, the use of naturalistic language paradigms especially with magnetoencephalography sets challenges which must be met. The most significant of these are reading- and speech-induced signal artefacts that confound the measurement data. Also necessary is a novel perspective on determining cortical effects in long continuous data, such as an emphasis on cortical rhythms.

The first three studies in the thesis concentrated on reading. They compared the performance of different methodological pipelines in removing reading-induced artefacts and charted the distribution of cortical activity among different brain areas and the functional connections between them during naturalistic reading of multi-page texts. The fourth study investigated the cortical basis of naturalistic speech production and perception.

The results from these studies showed that while the classical views of the cortical basis of reading and speech largely apply to the processing of longer texts and utterances, the transition from short to long stimuli seems to also alter the brain activity associated with these tasks. Particularly, the results of the studies demonstrated consistent and abundant cortical effects in the right brain hemisphere that are in contrast with the established view of reading and speech as strongly left-hemispheric processes. The significance of this thesis lies especially in that it expands the knowledge on the cortical basis of naturalistic reading and speech towards more everyday situations of reading and speaking and provides groundwork for future studies on this topic.

Key words: magnetoencephalography, natural reading, natural speech, language, artefact

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/ 

Contact information:

Doctoral theses at the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52