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Recent theories on the evolution of language (e.g. Corballis, 2009) emphazise the interest of early manifestations of manual laterality and manual specialization in human infants. In the present study, left- and right-hand movements towards a midline object were observed in 24 infants aged 4months in a constrained condition, in which the hands were maintained closed, and in a free condition. A left-hand dominance for approach movements without contact with the object, and a right-hand dominance for reaching movements with object contact was observed in the free condition. In the constrained condition reaching movements of the right hand decreased dramatically. These results are interpreted as strong evidence of manual specialization in 4-month olds, with approach movements having a localization role and reaching movements announcing future right-hand dominance for prehension and object manipulation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the influence of social encouragement on infants' hand movements, in particular on manual preference. Thirty-six infants were observed at 5.5 months. In a first step, their spontaneous manual preference was recorded with an object placed at the midline position. The second step consisted in encouraging infants to use their non-preferred hand by putting the object near that hand and congratulating them. The third step was similar to the first one (object placed at the midline position) except that the infant continued to be congratulated when (s)he used the non-preferred hand for reaching the object. Results showed that half of the infants exhibited a spontaneous manual preference and that a majority of these infants could use their non-preferred hand when verbally encouraged. Moreover, infants showing a left hand preference modified their hand-use more easily than infants showing a right hand preference. Although our findings reveal only a temporary and short-term influence of the social context, results are discussed in light of a socio-cognitive perspective whereby social encouragement can model manual preference, in particular its strength and stability. Highlights • At 5.5 months, a manual preference was observed in 47.2% of the infants. • The preference for the left hand was observed in 35.3% of the infants who presented a manual preference. • Left-handers change more easily their hand-use than right handers.

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.