Thesis defense Claudia Lüttke (Donders series 350)

In a conversation we do not only effortlessly translate soundwaves into words and sentences but we also use the mouth movements of the other to understand what is being said. These mouth movements can even have a direct effect on what we hear someone say, as is famously illustrated by the McGurk illusion (spoken /ba/ sound and mouth movements of the syllable /ga/ is perceived as ‘da’). This thesis investigates these visual influences of seeing the speaker’s mouth on auditory speech perception using functional magnetic resonance imaging and behavioural experiments. Among others, it demonstrated that auditory perception can be flexible. Auditory speech perception can be affected by integrating mismatching audiovisual input. Importantly, this after-effect persists in the absence of visual stimulation.