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. 2015 Sep 23;10(9):e0136492.
doi: 10.1371/journal.pone.0136492. eCollection 2015.

Infants Time Their Smiles to Make Their Moms Smile

Paul Ruvolo  1 , Daniel Messinger  2 , Javier Movellan  3
Affiliations

Infants Time Their Smiles to Make Their Moms Smile

Paul Ruvolo et al. PLoS One. .

Abstract

One of the earliest forms of interaction between mothers and infants is smiling games. While the temporal dynamics of these games have been extensively studied, they are still not well understood. Why do mothers and infants time their smiles the way they do? To answer this question we applied methods from control theory, an approach frequently used in robotics, to analyze and synthesize goal-oriented behavior. The results of our analysis show that by the time infants reach 4 months of age both mothers and infants time their smiles in a purposeful, goal-oriented manner. In our study, mothers consistently attempted to maximize the time spent in mutual smiling, while infants tried to maximize mother-only smile time. To validate this finding, we ported the smile timing strategy used by infants to a sophisticated child-like robot that automatically perceived and produced smiles while interacting with adults. As predicted, this strategy proved successful at maximizing adult-only smile time. The results indicate that by 4 months of age infants interact with their mothers in a goal-oriented manner, utilizing a sophisticated understanding of timing in social interactions. Our work suggests that control theory is a promising technique for both analyzing complex interactive behavior and providing new insights into the development of social communication.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Comparison of Infant and Mother Goals.
Means of the probability distributions of potential mother and infant goals. Error bars are 95% confidence intervals of the mean.
Fig 2
Fig 2. When to Smile? Performance for different strategies derived from different possible infant goals (each displayed in a different panel) versus the observed probability of infant actions.
Mother is smiling and infant has just stopped smiling. On the x-axis are wait times until the infant smiles again. The y-axis displays the modeled performance (dashed lines) of various wait times (different plots show different possible goals) versus the empirical probability (dots) that the infant selects a particular wait time.
Fig 3
Fig 3. Diego-San’s Expressions.
Diego-San, the robot used to interact with adults smiling (left) and not smiling (right).
See this image and copyright information in PMC

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