Manual exploration of consistency (soft vs hard) and handedness in infants from 4 to 6 months old.

In infants the developmental course of haptic perception is constrained by the development of attention to object properties and of the ability to execute various movements with the hands. The purpose of this study is to consider how infants, aged 4 to 6 months, become able to use their hands to assess qualities of objects such as consistency (softness vs hardness). The object that the infants explored was a cylinder, divided into four equal parts that were alternately hard and soft. It was tactually heterogeneous but visually homogeneous. Two aspects of exploration according to age, hand used, and consistency touched were considered: (1) the mode of exploration, contact, pressure, and tapping; and (2) the means of exploration, whole hand or fingers. The results show that infants adjust their movements to the quality of the object they are testing. That is, the infant varies the distribution of investigative and manipulative behaviours according to the nature of the specific object being explored. Pressure movements were the predominant exploratory procedures used for the soft parts, whereas passive contacts were the predominant movements for the hard parts. Concerning manual laterality, the results show that the left hand is used for touching objects (passive contact) more than the right one, whereas the right hand is used to press the soft parts and tap the hard parts more than the left hand.