What are the early skills which help children to develop language? An important part of learning language, for typically developing children, is watching the way that other people move their mouths whilst they are speaking. For example, researchers found that 6-month-olds who focus on their mother’s mouth tend to develop better language skills later in life, than 6-month-olds who focus on their mother’s eyes (Young, Merin, Rogers, & Ozonoff, 2009).
Why would this be the case? Some researchers suggest that looking at speakers’ mouth movements help infants perceive important differences in basic speech sounds (called “phonemes”) such as “b” or “d”. This helps infants to tell the difference between words such as “bad” and “dad”. Looking at a speaker’s mouth may also help an infant to accurately perceive the speech sounds in noisy environments.
Given the fact that word learning is seriously delayed in most children with neurodevelopmental disorders, including fragile-X, we wondered whether this delay partly results from differences in how children with neurodevelopmental disorders observe speakers’ faces.
But do children with neurodevelopmental disorders differ from typically developing infants in the way they look at faces? There is evidence that this may be the case. For example, many children with fragile-X look away from unfamiliar faces, perhaps due to social anxiety. There is also evidence that children with neurodevelopmental disorders differ from each other in the way they look at faces. For example, children with Williams syndrome (a rare genetic disorder) are fascinated by faces, but compared to typically developing children they spend significantly more time looking at the eyes rather than the mouth of a face. Might differences in looking at faces partly explain why different neurodevelopmental disorders find it difficult to learn language? This was the question that motivated our research.
We decided to investigate the question by measuring how toddlers with fragile-X and other neurodevelopmental disorders (namely, Down syndrome and Williams syndrome) scan the face of a speaker who is uttering simple syllables. We wanted to know whether these children look at faces in a different way to typically developing children, and whether the patterns are related to language development. To do this, we presented infants and toddlers with video-clips of faces and different sounds (“ba”, “ga”). Face-scanning behaviour was measured using eye-tracking technology (click here to see our previous article).
Because observing speakers’ mouth movements help typically developing children understand new words, we predicted that typically developing infants who focus more on the mouth would have larger vocabularies than those who focus more on the eyes. And this is indeed what we found in our typically developing participants. Interestingly, no relationship was found between gaze to the mouth and language ability in any of the three atypically developing groups (who were matched to the typically developing group on mental age). However, there were individual differences such that the number of times a toddler with fragile-X (or Williams syndrome) looked at the eyes, the more likely it was that he or she had a relatively large vocabulary. No such relationship emerged in the Down syndrome group.
Figure 1. Face-scanning patterns of children observing a talking face: orange and red blobs represent a greater number of looks to that part of the face; green blobs represent a fewer number of looks to that part of the face.
(a) The picture on the left shows the face-scanning pattern of typically developing infants.
(b) The picture on the right shows the face-scanning pattern of toddlers with fragile-X.
Why do those children with fragile-X who have also a relatively large vocabulary look more at the eyes instead of the mouth? Although focusing on the mouth may help an infant to understand unfamiliar, noisy, or confusing speech, the mouth is not the part of the face to which very young babies naturally look. In fact, typically developing newborns look more at a person’s eyes, which are the most salient features of the face. It seems that infants focus more on the eyes during the first half-year of life, but they later learn that the mouth region carries important information for learning language. So, by 6 months of age they look equally long at the eyes and the mouth. Still later, when they are learning their first words, they tend to look longer at the mouth area. Maybe children with fragile-X are failing to use this typical word learning strategy. Moreover, the children with fragile-X who looked more at the eyes had a larger vocabulary. This suggests that children with fragile-X who engage more generally with faces (even if they do so in a way that only younger babies would) develop better language.
In summary, we demonstrated that different attentional processes underpin word learning across different groups. Typically developing children with a relatively large vocabulary make more fixations to the speaker’s mouth, while those with fragile-X or Williams syndrome who also have a relatively large vocabulary make more fixations to the eyes. By contrast, no relationship was found in the Down syndrome group. These findings indicate that different strategies are likely involved in language learning across these neurodevelopmental disorders, at least at certain points in development.
Moreover, our findings reveal an important association between face scanning and language ability which points to intervention strategies for language delay outside language itself (e.g., by designing computer games that improve language learning by changing how children scan faces). It may be useful to ascertain whether training on precisely where to look for visual input (e.g. eyes to follow gaze or read emotions, mouth to learn words) would facilitate the understanding and learning of spoken language in children with neurodevelopmental disorders.
Finally, the findings from our study raise a number of important questions. For instance, why do the children with fragile-X or Williams syndrome who focus more on the eyes of a speaker tend to have larger vocabularies? Should interventions encourage infants with these neurodevelopmental disorders to focus more on the mouth of the speaker when learning words? Would it improve their word learning ability? We hope future research will be able to answer these questions.