THE SPECIAL STATUS OF LANGUAGE: NEURAL PROCESSING OF SPEECH IN NEWBORNS AND YOUNG INFANTS WITH TYPICAL AND ATYPICAL AUDITORY EXPERIENCE

After only a year of exposure to speech, and without explicit training, infants start to produce their first words and soon afterwards short sentences, displaying a knowledge of language that increases considerably in only a few months. How do infants acquire their native language(s) so rapidly and easily? This question interests many researchers and numerous studies have highlighted the remarkable speech perception abilities that young infants display during their first months of life, before producing their first words, helping them discover their language from a very early stage. The current thesis addresses one of the most fundamental and earliest tasks young learners need to face: How to identify the speech signal among the multitude of sounds they hear in their environment? What auditory stimuli do newborns categorize as speech and thus pay special attention to, in order to develop language? Does the newborn brain already exhibit a specific processing in response to speech compared to other auditory stimuli or some months of experience with language are required to shape the infant brain? The current thesis aims at bring new insights about these exciting questions. In order to address these questions, the thesis will first briefly review newborn infants’ perceptual abilities (Chapter 1) and the experimental methods most commonly used to investigate them (Chapters 1 and 2). It will then present four empirical studies with newborns and young infants using the brain imaging technique near-infrared spectroscopy (NIRS) exploring how babies with typical and atypical hearing perceive speech and various other auditory stimuli. Experiment 1 (Chapter 3) will investigate how the newborn brain processes speech as well as newborn’s cries. Experiment 2 (Chapter 3), as a subsequent study, will explore the newborn’s brain processing of laughters. In experiment 3 (Chapter 4), we will study how the newborn’s brain processes repetition-based regularities when presented with piano tones vs with syllables. Finally, experiment 4 (Chapter 5) will investigate how hearing loss influences the brain responses to languages, both native and unfamiliar.