The Role of Motor Representation in Infant’s Sensitivity to Emotional Information in Action Kinematics

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Background: Emotional information can be conveyed by deviations in action kinematics (Montepare et al., 1999; Pollick et al., 2001). By 11- to 12-months of age, infants showed sensitivity to the emotional valence of action kinematics (Addabbo et al., in preparation). Whilst the underlying mechanisms of this sensitivity remain unclear, it is widely accepted that our motor system represents observed actions of others. A recent study provided the first evidence that perceived emotional states of others are dependent on our own movement kinematics (Edey et al., 2017). This suggests that infants might become sensitive to emotional information conveyed in kinematics once they have a sufficiently detailed motor representation allowing them to detect deviations in another person’s movement kinematics. Aims: This study aimed to understand how young infants become sensitive to emotional information conveyed in kinematics. Firstly, this study examined whether it could replicate the results of Addabbo and colleagues (in preparation) in a large sample. Secondly, this study investigated whether infants who have a better detailed motor representation, indicated by less kinematic variability in their movement, were more sensitive to deviations in kinematics conveying emotional information. Method: Action kinematics of 12- to 13-month-old infants were investigated in two transport tasks using motion tracking. Infants’ sensitivity to kinematics of angry and happy transport actions was investigated using facial electromyography (EMG) (following Addabbo et al., in preparation). Forty-six infants with sufficient EMG data were included in the analysis to examine whether infants were sensitive to emotional information conveyed in kinematics. Twenty-four infants with sufficient data for both tasks were included in the analysis to investigate whether infants with a more detailed motor representation were more sensitive to emotional information conveyed in kinematics. Results: The EMG data did not provide evidence that infants this age are already sensitive to emotional information conveyed in action kinematics. The combined data of both tasks indicated a significant correlation between the measurement of motor representation and infants’ sensitivity to happy kinematics. However, in contrast to our predictions, infants with higher variability, hypothesized as a less detailed motor representation, showed more zygomaticus muscle activation in response to happy stimulus videos. Discussion: This unexpected finding that more variable infants were more sensitive to emotional information (i.e. more zygomaticus compared to corrugator activation to happy stimuli) might be due to expressive infants that were more active and happy overall over both sessions, resulting in more variability in their movement and more zygomaticus activation in the EMG session. There was no evidence for a relationship between the measurement of movement representation and the sensitivity to emotional information conveyed in kinematics. However, it might be that our motor task did not capture the detailedness of the infant’s motor representations as assumed. Future research should design an age-appropriate task in order to measure the detailedness of motor representation.
Faculteit der Sociale Wetenschappen