NEURAL RESPONSES TO OMISSION DEVIANTS AND THE INFLUENCE OF GLOBAL PREDICTABILITY IN INFANTS AND ADULTS

Abstract

The human auditory system excels at detecting patterns necessary for processing speech and music. This system is adept at detecting changes to the incoming sounds. According to predictive coding theories, the brain generates hypothesis about what the incoming tone should be, and if the incoming tone does not match the hypothesis, a prediction error response is elicited. This process can be estimated in electroencephalography (EEG) by the mismatch negativity and P3a event related potentials (ERPs) in adults or the mismatch response in infants. It remains unclear is how this system responds to unexpected absence of a sound created by silences. In this thesis, we compared ERPs in adults (Chapter 2) elicited by infrequent sound omissions — i.e. unexpected silences or omission deviants — in various sequences of tones to those elicited by regularly occurring omissions — i.e., expected silences or predictable omissions. We found that unexpected silences elicited both the MMN and P3a, although the magnitude of these components was considerably smaller than we would expected from previous research with omission deviants and auditory deviants. We also found that infants (Chapter 3) exhibited a neural response to omission deviants similar to the mismatch response. Unexpectedly this was not influenced by the global predictability of the omission deviants, which typically attenuates the ERPs to a deviant when it is globally predictable. Adults also showed a lack of difference between globally predictable and globally unpredictable omission deviants (Chapter 4). Furthermore, in adults, we did not find the typical deviance detection ERP responses. Overall, we found evidence of robust neural responses to omission deviants in both adults and infants, but the context in which the omission deviants can change the ERP components elicited. This dissertation is the first to investigate the direct effect of global predictability on the neural responses to omission deviants, as well as 6-month-old infants’ response to omission deviants.