Evaluating the empirical evidence for the two-stage-model of infant imitation. A commentary on Paulus, Hunnius, Vissers, and Bekkering (2011)

Reduced Mu Power in Response to Unusual Actions Is Context-Dependent in 1-Year-Olds

During social interactions infants predict and evaluate other people's actions. Previous behavioral research found that infants' imitation of others' actions depends on these evaluations and is context-dependent: 1-year-olds predominantly imitated an unusual action (turning on a lamp with one's forehead) when the model's hands were free compared to when the model's hands were occupied or restrained. In the present study, we adapted this behavioral paradigm to a neurophysiological study measuring infants' brain activity while observing usual and unusual actions via electroencephalography. In particular, we measured differences in mu power (6 - 8 Hz) associated with motor activation. In a between-subjects design, 12- to 14-month-old infants watched videos of adult models demonstrating that their hands were either free or restrained. Subsequent test frames showed the models turning on a lamp or a soundbox by using their head or their hand. Results in the hands-free condition revealed that 12- to 14-month-olds displayed a reduction of mu power in frontal regions in response to unusual and thus unexpected actions (head touch) compared to usual and expected actions (hand touch). This may be explained by increased motor activation required for updating prior action predictions in response to unusual actions though alternative explanations in terms of general attention or cognitive control processes may also be considered. In the hands-restrained condition, responses in mu frequency band did not differ between action outcomes. This implies that unusual head-touch actions compared to hand-touch actions do not necessarily evoke a reduction of mu power. Thus, we conclude that reduction of mu frequency power is context-dependent during infants' action perception. Our results are interpreted in terms of motor system activity measured via changes in mu frequency band as being one important neural mechanism involved in action prediction and evaluation from early on.

Fourteen-Month-Olds Adapt Their Imitative Behavior in Light of a Model’s Constraints

Rather than reenacting every action they observe, preverbal infants adapt their imitative behavior. Although previous studies have revealed the capability of preverbal infants to imitate selectively, the question about the adaptability of this behavior on an individual level did not attract considerable scientific attention until now. In the current study, we investigated whether 14-month-old infants flexibly alternate their imitative response in accordance with a model’s changing physical constraints in a body-part imitation paradigm. Participants were presented with two novel actions whereby a model illuminated a light-box and turned on a sound-box, either by using her forehead (head touch) or by sitting on the apparatus (sit-touch). Each participant observed these tasks in two conditions: once where the model’s hands were occupied and once where her hands were free while executing the head or sit-touch. Participants were more likely to reenact the observed novel behavior when the model had freely chosen to perform it than when she had to do so due to physical constraints. Not only did we replicate a number of previous findings, we show here that preverbal infants adapt their imitative behavior across conditions based on the physical constraints of the model. These results point towards the adaptable nature of imitative behavior also on an individual level. This ability might be one of the building blocks for children for learning their social group’s specific action repertoire.

The relation between contingency preference and imitation in 6–8-month-old infants

Detecting self-generated actions and imitating other-generated actions are important abilities in order to interact with others. The relationship between these domains was investigated in 6–8-month-old infants. In a contingency-preference task, infants observed their own legs on a real-time and a delayed video display. In an imitation task, the experimenter demonstrated a three-step action directed at a puppet mouse. The Cognitive Scale of the Bayley Scales of Infant and Toddler Development was administered in order to control for the infants’ cognitive developmental status. A negative correlation was found between the proportion of time spent looking at the delayed display in the contingency-preference task and the imitation score in the imitation task. This indicates that the lower the infants’ preference for the delayed video image, the more likely they were to imitate. The correlation between contingency preference and imitation remained even after controlling for cognitive developmental status. Thus, a basic interest in high contingency might underlie the preference for observing self-generated actions and imitating other-generated actions.