Françoise Morange-Majoux

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.

Right-left approach and reaching arm movements of 4-month infants in free and constrained conditions

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.

Early manifestations of manual specialisation in infants: A longitudinal study from 20 to 30 weeks

This longitudinal study examined lateral differences between latency time of the two hands during the development of prehension in 12 infants from 20 to 30 weeks. Latency time (LT) is defined as the delay between the visual localisation of a reachable target and the beginning of the movement and could be considered as a phase in the preparation of action. If LT varies with the hand used and the type of movement, this would suggest differences in information processing (nature and/or quantity). Results show that the latency time is shorter for the left hand approach movements and shorter for the right hand grasping movements. These findings are in favour of a manual specialisation—clearly present from 20 weeks—and are discussed in a possible hemispheric specialisation perspective.

Do Preterm Infants Perceive Temporal Synchrony? An Analysis with the Eye-Tracking System

The aim of this study was to investigate auditory–visual temporal asynchrony in preterm infants using a habituation procedure coupled with an eye-tracking system in order to examine visual behavior accurately and determine specific visual areas of interest. Sixteen term infants, twelve low-risk near-term (LBW) preterm infants and eight Very Low Birth Weight (VLBW) preterm infants were tested at four months post term. Infants were habituated with an auditory–visual synchronic situation: a visual ball bounced back in synchrony with an auditory sound. In the test phase, an asynchronized situation and a synchronized situation were presented alternately three times. The results showed that VLBW infants spent more time looking at the target before being habituated compared to LBW preterm infants and full-term infants.Specific areas of interest showed that VLBW infants spent less time on the target than LBW and full-term infants and had a more heterogeneous visual exploration. Nevertheless, VLBW infants had the same novelty reaction as the other infant groups. Moreover, the study of areas of interest revealed that whatever the age group, infants looked more at the area where the sound was produced during the asynchronized trial. This result suggests that infants perceive asynchrony. We suggest that VLBW preterm infants show the same ability to habituate and novelty recovery through an early learning experience due to earlier additional extra-uterine exposure.