**1. Introduction**

318 Neuroimaging – Cognitive and Clinical Neuroscience

Zhao, H., Tanikawa, Y., Gao, F., Onodera, Y., Sassaroli, A., Tanaka, K., Yamada, Y., (2002).

*Biol* 47, 12, (Jun 21), pp. (2075-2093), ISSN 0031-9155.

Maps of optical differential pathlength factor of human adult forehead, somatosensory motor and occipital regions at multi-wavelengths in NIR. *Phys Med* 

> Until recently, newborns had typically been described as displaying mainly involuntary reactions and clumsy arm movements. However, in recent years investigation of exploratory perception of objects has emerged as key area research. Newborns' hands have often been described as closed or exhibiting either grasping or avoidance reactions which are inappropriate behaviors for holding an object and gathering and processing information (Katz, 1925; Roland and Mortensen 1987; Twitchell, 1965). However, besides possessing manual brief reactions (reflex), newborns are also able to handle small objects and to perceive their properties. To reveal this tactile ability, researchers have applied a habituation-dishabituation procedure to the tactile modality, just as in the visual modality (Streri & Pêcheux, 1986a). This procedure, which is controlled by the infant, is effective in revealing the early perceptual capacities of young babies (cf. Streri, 1993). It unfolds in two phases. The first phase, habituation, includes a series of trials in which the infants receive a small object in one hand. A trial begins when the infant holds the object and ends when the infant drops it or after a maximum duration defined by the experimenter. This process is repeated several times. As a consequence, the habituation process entails several grasps of determined duration (usually between 1 sec to 60 sec of holding). Trials continue until the habituation criterion is met. The newborn is judged to have been habituated when the duration of holding on any two consecutive trials, from the third onwards, totals a third (or a quarter, depending on age) or less of the total duration of the first two trials. Total holding time is taken as an indicator of the duration of familiarization. The mean number of trials taken to reach habituation ranges from four to twelve, and often varies with shape complexity. The decrease in holding times is considered to reveal the infants' ability to perceive and form a memory of the shape and subsequently recognize it. Then, in the dishabituation phase, a novel object is put in the infant's hand. If an increase in holding time of the novel object is observed, it is inferred that the baby is reacting to novelty, having noticed the difference between novel and familiar objects. That these processes reveal a form of mental representation of stimuli is now well established (cf. Pascalis & De Haan, 2003; Rovee-Collier & Barr, 2001).

> Using this experimental procedure, Streri, Lhote, and Dutilleul (2000) showed that full-term newborns (the youngest was 16 hours old) were able to detect differences in the contours of

Intermanual and Intermodal Transfer in Human Newborns:

in accordance with the early maturation of touch.

tactile information (Fabri et al., 2001, 2005).

adults.

Neonatal Behavioral Evidence and Neurocognitive Approach 321

results revealed that when an object is placed in a preterm newborn's hand, holding time decreases trial by trial until the habituation criterion is reached. In the test phase, the experimental group held the novel object significantly longer compared to the preceding two habituation trials, in contrast to the control group in which this was not the case. These results suggest that preterm babies react differentially to a novel shape. These findings are

Taken together, these results show that preterm and full-term babies are able to memorize the shape of an object with each hand. These abilities reflect the very early existence of some internal representation of a stimulus. However, what is the nature of this internal representation? If it has some level of abstraction, newborns should be able to transfer object information from one hand to the other (low level of abstraction) or from one hand to the visual modality (high level of abstraction). Thus, the first goal of this chapter was to show that full-term and preterm newborns are capable of transferring shape and texture information from one hand to the other. The second goal was to show that full-term newborns are capable of transferring information between touch and vision in some, but not all, conditions. These limits or failures may be explained by neuroimaging evidence in

One reason for interest in intermanual transfer is its potential value in assessing communication between the two hemispheres and cerebral plasticity during cognitive development. Sann and Streri (2008a) investigated the inter-manual transfer of shape in twenty-four 2-day-old full-term newborns. After tactual habituation to a shape (prism or cylinder) in one hand, full-term newborns held the familiar shape longer in the opposite hand, and not the novel shape as usually expected in such procedure (Soroka, Corter, & Abramovitch, 1979). But in the same study, infants also exhibited inter-manual transfer of texture (smooth or granular), with a preference for the novel texture in the opposite hand. According to Sann and Streri (2008a), these discrepancies in performance between object properties indicate that the property of shape requires a more abstract and elaborate representation relative to texture. However, given the design of the study, it is not possible to draw definite conclusions about the type of shape information that was transferred: the entire shape of the object, edge information (round vs. angled), or other contrasts or differences. Regardless, these results provided evidence of intermanual transfer of shape in full-term newborns, confirming the hypothesis that the development of the corpus callosum at this stage is sufficient to permit some transfer of shape information between the two hands. Indeed, an fMRI study has demonstrated the essential contribution of posterior corpus callosum to the inter-hemispheric transfer of

Considering that the corpus callosum is less mature in preterm infants than full-term infants (Anderson, Laurent, Woodward, & Inder, 2006) and that very preterm birth (before 33 GW) may be associated with perinatal brain injury including the corpus callosum (Kontis et al., 2009), Lejeune et al. (in press) explored whether preterm infants are capable of inter-manual transfer of shape after the age of 33 GW. Using a classic tactile habituation-dishabituation procedure the authors predicted that after successive presentations of the same object, each preterm infant would show a decrease in holding time regardless of the hand tested or

**2. Intermanual perception of object shape in human newborns** 

two small objects (a smoothly curved cylinder versus a sharply angled prism) with both right and left hands. After habituation with one of the two objects placed in the right or left hand, the newborns reacted to novelty when a new object (the prism or cylinder) was put in their hand. This was the first evidence of habituation and reaction to novelty observed with the left as well as the right hand in human newborns. Thus, newborns are able to discriminate between curvilinear and rectilinear contours in small objects. However, this behavior does not show that babies have a clear representation of what they are holding in their hand. Because young infants are unable to perform the integration and synthesis of information in working memory required for haptic exploration, their shape perception is probably partial or limited to the detection of clues such as points, curves, presence or absence of a hole, etc. The information gathered is provided by the enclosure of the object (cf. Lederman & Klatzky, 1987), which seems to be an effective exploratory procedure for these limited purposes. To understand the emergence of these manual abilities in full-term newborns, it is important to recall the early maturation of touch (first among the senses to begin functioning) in the foetal period (from a cephalo-caudal point of view). Tactile receptors can be found in the epithelium of the mouth and the dermis of the peri-oral area as early as 8-9 gestational weeks. Meissner and Pacini corpuscles develop soon after. Tactile receptors are found on the face, the palms and the soles of the feet by 11 weeks. By the 15th week they are found on the trunk and proximal zones of arms and legs, and on the whole skin by the 20th week (Humphrey, 1964). Taken together, these data suggest that this ability to perceive various shapes with both hands observed in full-term newborns may be a "core ability" already present in the foetus. To investigate this hypothesis, the study of this manual ability in preterm babies is relevant and may reveal continuity in sensory functioning between foetal and neonatal periods, by determining whether preterm babies are able to extract information with their hands.

The current World Health Organization definition of premature is a baby born before 37 weeks of gestation, counting from the first day of the last menstrual period, where 40 weeks of gestation is the normal term. Moreover, the viability of foetuses is between 22 and 24 weeks of gestation, depending on the country. Studies about preterm babies and touch have generally focused on pain and developmental concerns (Sizun & Browne, 2005). They have shown that neonates' pain responses are influenced by the number of painful procedures previously experienced by the infant (Johnston & Stevens, 1996). Bartocci, Bergqvist, Lagercrantz and Anand (2006) showed that tactile and painful stimuli specifically activate somatosensory cortical areas. This result indicates that central integration of tactile information occurs in preterm newborns at 28-36 weeks of gestation. A link between hand movements and somatosensory cortical activation has also been shown in preterm newborns at 29-31 weeks of gestation (Milh *et al*., 2007). Recently, Lejeune, Audéoud, Marcus, Streri, Debillon and Gentaz (2010) investigated the ability of preterm babies' hands to discriminate between various shapes. Twenty-four preterm babies underwent a habituation phase followed by a test phase. The entire observation is performed in such a way the newborns cannot see their hands and the held object. In the test phase, twelve babies (experimental group) were tested with a novel object whereas twelve babies (control group) were tested with a familiar object (the one presented during the habituation phase). The shapes used were similar to those used by Streri *et al* (2000): a cylinder and a prism with identical object/hand surface ratio. These objects were smaller than those used by Streri *et al.* (2000) because preterm babies' hands are smaller than those of full term babies. The

two small objects (a smoothly curved cylinder versus a sharply angled prism) with both right and left hands. After habituation with one of the two objects placed in the right or left hand, the newborns reacted to novelty when a new object (the prism or cylinder) was put in their hand. This was the first evidence of habituation and reaction to novelty observed with the left as well as the right hand in human newborns. Thus, newborns are able to discriminate between curvilinear and rectilinear contours in small objects. However, this behavior does not show that babies have a clear representation of what they are holding in their hand. Because young infants are unable to perform the integration and synthesis of information in working memory required for haptic exploration, their shape perception is probably partial or limited to the detection of clues such as points, curves, presence or absence of a hole, etc. The information gathered is provided by the enclosure of the object (cf. Lederman & Klatzky, 1987), which seems to be an effective exploratory procedure for these limited purposes. To understand the emergence of these manual abilities in full-term newborns, it is important to recall the early maturation of touch (first among the senses to begin functioning) in the foetal period (from a cephalo-caudal point of view). Tactile receptors can be found in the epithelium of the mouth and the dermis of the peri-oral area as early as 8-9 gestational weeks. Meissner and Pacini corpuscles develop soon after. Tactile receptors are found on the face, the palms and the soles of the feet by 11 weeks. By the 15th week they are found on the trunk and proximal zones of arms and legs, and on the whole skin by the 20th week (Humphrey, 1964). Taken together, these data suggest that this ability to perceive various shapes with both hands observed in full-term newborns may be a "core ability" already present in the foetus. To investigate this hypothesis, the study of this manual ability in preterm babies is relevant and may reveal continuity in sensory functioning between foetal and neonatal periods, by determining whether preterm babies

The current World Health Organization definition of premature is a baby born before 37 weeks of gestation, counting from the first day of the last menstrual period, where 40 weeks of gestation is the normal term. Moreover, the viability of foetuses is between 22 and 24 weeks of gestation, depending on the country. Studies about preterm babies and touch have generally focused on pain and developmental concerns (Sizun & Browne, 2005). They have shown that neonates' pain responses are influenced by the number of painful procedures previously experienced by the infant (Johnston & Stevens, 1996). Bartocci, Bergqvist, Lagercrantz and Anand (2006) showed that tactile and painful stimuli specifically activate somatosensory cortical areas. This result indicates that central integration of tactile information occurs in preterm newborns at 28-36 weeks of gestation. A link between hand movements and somatosensory cortical activation has also been shown in preterm newborns at 29-31 weeks of gestation (Milh *et al*., 2007). Recently, Lejeune, Audéoud, Marcus, Streri, Debillon and Gentaz (2010) investigated the ability of preterm babies' hands to discriminate between various shapes. Twenty-four preterm babies underwent a habituation phase followed by a test phase. The entire observation is performed in such a way the newborns cannot see their hands and the held object. In the test phase, twelve babies (experimental group) were tested with a novel object whereas twelve babies (control group) were tested with a familiar object (the one presented during the habituation phase). The shapes used were similar to those used by Streri *et al* (2000): a cylinder and a prism with identical object/hand surface ratio. These objects were smaller than those used by Streri *et al.* (2000) because preterm babies' hands are smaller than those of full term babies. The

are able to extract information with their hands.

results revealed that when an object is placed in a preterm newborn's hand, holding time decreases trial by trial until the habituation criterion is reached. In the test phase, the experimental group held the novel object significantly longer compared to the preceding two habituation trials, in contrast to the control group in which this was not the case. These results suggest that preterm babies react differentially to a novel shape. These findings are in accordance with the early maturation of touch.

Taken together, these results show that preterm and full-term babies are able to memorize the shape of an object with each hand. These abilities reflect the very early existence of some internal representation of a stimulus. However, what is the nature of this internal representation? If it has some level of abstraction, newborns should be able to transfer object information from one hand to the other (low level of abstraction) or from one hand to the visual modality (high level of abstraction). Thus, the first goal of this chapter was to show that full-term and preterm newborns are capable of transferring shape and texture information from one hand to the other. The second goal was to show that full-term newborns are capable of transferring information between touch and vision in some, but not all, conditions. These limits or failures may be explained by neuroimaging evidence in adults.
