An electroencephalography study of the neural correlates of visual habituation in infants with hearing loss

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The goal of this research project is to compare brain development between babies who are deaf, and babies with normal hearing while they see and process a novel visual stimulus. Past research has shown that babies and children with hearing loss perform less well on commonly used tests of nonverbal cognition, such as attention, working memory, and learning. These findings have led scientists to believe that hearing loss negatively affects cognitive development, in addition to causing difficulties with language development. However, there are several crucial gaps in this research: first, simply demonstrating a difference in performance does not allow us to infer the underlying brain mechanisms that cause the difference. In this case, we still do not know whether the difference reflects a deficit, as hypothesized, or whether it could reflect an adaptation of the deaf infants to their unusual sensory environment. Secondly, most of the prior research has been done with older children and not babies. This project will be the first to examine the brain activity that underlies early cognitive development in babies who are born with hearing loss. This knowledge is crucial for understanding how hearing and hearing loss affect brain and cognitive development in babies. To achieve this goal, this project will build upon a previous study that tested visual habitation in deaf and hearing babies. Visual habituation is a well-established phenomenon that reflects information processing: babies will eventually lose interest in a visual stimulus that is continuously shown to them. Initially, they will be very interested, as infants are generally curious about the world around them, but after a while they will lose interest and stop looking at it. This is because they have fully encoded a memory for the stimulus and there is no longer any new information to learn. In a recent study by the Principal Investigator, deaf babies took longer to habituate to a new visual stimulus (a colourful object) compared to a group of hearing babies of the same age. The main interpretation of these findings, based on the assumptions discussed earlier, is that the deaf infants are slower to encode the visual information into memory and therefore slower to habituate. However, it could also be that the deaf babies are slower to habituate because they are, in fact, encoding a stronger memory for the object or showing deeper sustained attention to visual stimuli. These alternative possibilities would also lead to longer looking times. Therefore, we cannot infer the underlying brain processes that cause the observed differences between deaf and hearing infants from behavioural measures alone. In other words, the underlying reasons for differences in visual processing in deaf infants may not be reflected in observable infant behaviour, making them ideally suited for neuroimaging methods. This research study will use electroencephalography (EEG) to measure brain activity during visual habituation in order to arbitrate between these competing hypotheses about why we have observed differences between deaf and hearing infants in visual processing.This research project will also examine whether measures of brain development in young infants are related to their language development one year later. This information will be crucial in helping families and clinicians understand the developmental trajectories of babies with hearing loss and those with normal hearing. The findings from this project will be shared with families via a community workshop and will be shared with the academic and medical communities through peer-reviewed publications and presentations at conferences.