The Effect of Stress on the Understanding of Goal-Directed Actions in 6- to 8-Month-Old Infants

Mild stress is present in infants’ everyday life, but its effect on their cognition is largely unexplored experimentally. The present pre-registered study tested whether stress leads to a shift from a goal-directed to a movement-based interpretation of others’ actions. Eighty-eight infants aged 6 to 8 months were tested in a stress or a control condition. Pre- and post-stress levels were assessed via parental rating and salivary cortisol. In a subsequent visual habituation paradigm, infants watched videos showing a human hand repeatedly grasping one of two objects. At test, infants watched videos showing the objects in reversed positions and the objects were grasped alternately. Salivary cortisol concentrations and parental ratings indicated higher stress levels of infants in the stress condition than in the control condition after stress manipulation. No statistically significant difference in looking behavior at test as a function of condition (stress, control) was found. Across conditions infants looked longer to the test trials showing a hand grasping the new object using the old grasping path, indicating that they had habituated to the goal of the grasping movement and thereby showed an encoding of the goal of the actor. Additionally, infants in the stress condition showed a longer accumulated looking time during the habituation than non-stressed infants. These results suggest that acute stress does not influence infants’ interpretation of actions as goal-directed. Nevertheless, the slower speed of habituation in stressed infants suggests that identifying the action target may have been more difficult for them.