Mouthing and grasping in neonates: Evidence for the early detection of what hard or soft substances afford for action

Newborns and 2- and 3-month-old infants were presented for 3 min with a rigid or an elastic object either introduced into their mouths for mouthing or into their right hands for grasping. Each object was connected to an air pressure transducer allowing polygraphic recording of the positive pressure variations applied by the infant to the object. Results indicate that, from birth, infants haptically discriminate between the rigidity and elasticity of objects by generating different rates and patterns of responses. Furthermore, the differential haptic responding by the infant does not manifest itself in an analogous manner for the oral or the manual modality of response but is reversed relative to the two objects' properties. During the first 3 months, a developmental trend is observed wherein the infant's oral response rates and patterns begin to align themselves with her/his manual responding to either one of the two objects. Relative to a similar output of positive pressures generated orally or manually, these observations show that from birth the infant's response is both object-dependent (hard vs. soft substance) and modality-dependent (oral vs. manual condition). These results are interpreted as suggesting that early mouthing and grasping are not merely controlled by reflexive (automatic) mechanisms but rather are guided by what objects afford for functional actions.