The effect of task constraints on infants' (bi)manual strategy for grasping and exploring objects

Fluctuations in handedness and in the choice of one-handed versus two-handed grasping have often been observed in infants. From a dynamic systems perspective, these fluctuations are considered to reflect the emergence of other developing skills. The fluctuations within session reflect the variability inherent to the infant's motor behavior. The goal of this study was to examine to what extent task constraints can modulate this variability during object grasping and exploration. Forty-one 6- to 12-month-olds, forty-two 18- to 24-month-olds, forty-three 30- to 36-month-olds and twelve 48-month-old children were tested on different tasks: simple grasping, precision grasping, grasping involving bimanual manipulation, and, for a few subjects, object exploratory behavior. Results showed that the variability of the hand used for simple grasping decreases particularly between 36 and 48 months. Increasing the precision required for grasping decreased the variability of the grasping patterns and increased the frequency of right-handed strategies. When grasping involved bimanual manipulation, handedness emerged more clearly than for simple grasping, at least for 18- to 36-month-old infants. In contrast, grasping of objects affording various explorations and subsequent exploratory behaviors were even less clearly lateralized than simple grasping. Thus, variability of infants' hand patterns during object grasping and manipulation, while reflecting the more general variability of infants' motor output, can be modulated by different task constraints.