Babies can tell whether you made a mistake or not from the tone of your voice

For decades, psychologists have been trying to find out when and how children develop the ability to step outside of themselves and understand other people's minds. Piaget, the great Swiss developmental psychologist, had children study a model of the mountains around Geneva and describe what the scene would look like from another perspective. His results led him to conclude that children younger than about seven are stuck with an ego-centric perspective. Since then, with ever more ingenious techniques, psychologists have demonstrated that even infants as young as one year old have a rudimentary sense that other people have a mind, perspective and intentions of their own. Betty Repacholi and Alison Gopnik, for example, observed how 18-month-olds would choose to feed an adult disgusting broccoli, rather than yummy crackers, if they'd seen the adult enjoying the dreaded vegetable earlier.

Now Elena Sakkalou and Merideth Gattis have performed a study looking specifically at the role of prosody in the ability of infants to infer whether an adult intended to perform an action or made a mistake. Prosody refers to the sing-song, rise and fall of speech - its tempo and fluctuating pitch. It's the quality of speech we can hear through a wall or ceiling. We might not be able to distinguish any of our next-door neighbour's actual words, but we can still get a sense of the mood and emotion of what they're saying.

This study combines what we know about the importance of prosody to children's learning, with what we know about their emerging ability to think about other people's minds and intentions. For example, past research has shown how mothers use prosody to convey approval and prohibition, and that 5-month-olds smile more in response to the former.

Sakkalou and Gattis first replicated an earlier study by showing that infants aged 14 to 18-months can use an adult's vocal utterances, specifically including the words "There" vs. "Whoops", to infer whether they intended an action or not. Twenty-eight toddlers saw an experimenter perform two actions on a toy (for example, pushing it or rolling it), one of which was accompanied by the word "There" as if the action were intended; the other by "Whoops". Given a chance to handle the toy themselves, the infants were more likely to imitate the action that was accompanied by the word "There" - as if they knew that it had been a deliberate action.

Next, Sakkalou and Gattis analysed the prosody of the experimenter utterances: "There" and "Whoops". The former was characterised by higher amplitude, longer duration and falling pitch; the latter by a rising pitch contour. The earlier experiment was then replicated with 56 more toddlers (mean age 16 months), but this time the words "There" and "Whoops" were replaced with the Greek words "Nato" and "Ochi" (or vice versa). Crucially, the words signifying a mistake or intentional action were always delivered with the prosodic profile established earlier as being associated with a mistake or intended action. The toddlers were raised in English-speaking homes so there's no way they could have known the meaning of the words. Nonetheless, the toddlers older than 16 months still imitated more "intentional" actions than accidental actions on the toys, thus suggesting strongly they were able to use the way the words were said to infer which actions were intended and which were accidental.

It's important to note that the "mistake" vs. "intent" prosodic patterns in the current study do not map simply onto approval/ disapproval - they were more complex, which could explain why it was only the older toddlers who could interpret the difference. This fits with other research showing that infants' preference for different types of vocalisations changes as they develop, with older infants preferring prosodic patterns that direct their attention whereas younger infants prefer comforting prosody.

"We propose that infants' understanding of vocal patterns supports their growing understanding of intentions," Gattis told The Digest. "Together these two forms of understanding shape the development of imitation and communication."

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Sakkalou, E., and Gattis, M. (2012). Infants infer intentions from prosody. Cognitive Development, 27 (1), 1-16 DOI: 10.1016/j.cogdev.2011.08.003

Post written by Christian Jarrett for the BPS Research Digest.

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