Children typically learn language not just by hearing speech but also by seeing visual cues during face-to-face interactions with caregivers. These cues include eye gaze, which helps children focus on important aspects of their environment, and lip movements, which aid in processing speech. This thesis explores the role of visual cues in early language development, focusing on neural mechanisms in the infant brain. In a series of experiments, I examined 10-month-old infants’ speech and word processing using EEG. First, I presented infants with continuous speech including repeated words, and tested their recognition of these words to understand how they learn to identify individual words within fluent speech. I found that that infants were able to pick up new words from continuous speech, with neural processing of repeated words differing when the speaker’s gaze was directed at them. Additionally, I investigated neural tracking of speech rhythms to understand speech processing. Infants tracked speech rhythms equally well, regardless of the speaker’s gaze direction or visibility of the speaker’s lip movements. Furthermore, successful neural tracking of speech was associated with a larger vocabulary size at 18 months, indicating that it predicts language development. These findings shed light on the role of visual cues in speech processing and the importance of neural synchronisation with speech rhythms for language development.
Melis Çetinçelik completed her bachelor's degree in Psychology and Philosophy (double major) at Koç University in Istanbul, Turkey. She then pursued a master's degree in Brain and Cognitive Sciences at the University of Amsterdam. For her master's thesis, Melis moved to Cambridge, UK, to study the development of prosocial trust in infants. Upon completing her master’s, she joined the Language Development Department at the Max Planck Institute for Psycholinguistics as a PhD candidate, focusing on the neural underpinnings of early language acquisition. In addition to her research, Melis actively engaged in scientific outreach, contributing to events such as the Kletskoppen Kindertaalfestival and the TalkLing science blog at the Max Planck Institute for Psycholinguistics. In 2023, she worked as a researcher and lecturer in the Department of Experimental Psychology at Utrecht University while completing her dissertation. She is currently a postdoctoral researcher in the Department of Cognitive Neuropsychology at Tilburg University.