Do infants come to understand other people's actions through a mirror neuron system that maps an observed action onto motor representations of that action? We demonstrate that a specialized system for action perception guides proactive goal-directed eye movements in 12-month-old but not in 6-month-old infants, providing direct support for this view. The activation of this system requires observing an interaction between the hand of the agent and an object.

Reaches, performed by 5 infants, recorded at 19 weeks of age and every third week thereafter until 31 weeks of age, were studied quantitatively. Earlier findings about action units were confirmed. At all ages studied, movements were structured into phases of acceleration and deceleration. Reaching trajectories were found to be relatively straight within these units and to change direction between them. It was also found that at all ages, there was generally one dominating transport unit in each reach. The structuring of reaching movements changed in four important ways during the period studied. First, the sequential structuring became more systematic with age, with the dominating transport unit beginning the movement. Second, the duration of the transport unit became longer and covered a larger proportion of the approach. Third, the number of action units decreased with age, approaching the two-phase structure of adult reaching. Finally, reaching trajectories became straighter with age.

No abstract

The development of visually controlled grasping actions was studied in two experiments. An optoelectronic technique (SELSPOT) was used to monitor the opening and closing of the hand during reaching actions by measuring the change in the distance between thumb and index finger. The purpose of Experiment 1 was to establish an adult criterion for the development. It was shown that adults started closing the hand around the target well before touch and that the timing was dependent on the size of the target. The hand started to close earlier when grasping a small rather than a large target. In addition, the degree of hand opening was also less for a small than for a large target. In Experiment 2 it was shown that infants who were 5-6, 9, and 13 months of age also controlled their grasping actions visually and started closing the hand around the target in anticipation of the encounter rather than as a reaction to the encounter. However, the strategy of the two younger age groups was different from that of adults. They started closing the hand closer to the time of contact with the target than did the 13-month-olds, who were comparable to adults in this respect. The timing was not dependent on the size of the target in any of the infant groups. In all age groups, reaching and grasping were most commonly organized in a continuous way; that is, the hand started to close without any interruption in the approach. The opening of the hand was found to be adjusted to target size in the 9- and 13-month-olds but not in the 5-6 month olds.

The current review offers a unique introduction to the use of corneal reflection eye tracking in infancy research. We provide a detailed description of how to calibrate, collect, and analyze infants' gaze in a series of experimental paradigms, focusing specifically on the analysis of visual tracking, point of gaze, and the latency of gaze shifts (prediction and reactive gaze shifts). The article ends with a critical discussion about the pros and cons of corneal reflection eye tracking.