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

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

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

Intermanual and Intermodal Transfer in Human Newborns:

**3. Cross-modal transfer between touch and vision** 

Here we present a series of studies that illustrate these constraints.

**3.1 Initial evidence in newborns** 

cross-modal transfer between these senses.

infants from 33 GW.

Neonatal Behavioral Evidence and Neurocognitive Approach 323

procedures during their first 15 days of life (Simons et al., 2003). Furthermore, Gimenez et al. (2008) showed that the maturation of brain tissue may be accelerated by factors associated with preterm birth, perhaps through the direct effects of the extrauterine environment. These particular tactile experiences could enhance the development of the intermanual transfer of information in preterm infants, even among younger infants who are at least 9 days old. In this case, according to the hypothesis proposed by Sann and Streri (2008a), preterm infants could have a more elaborate representation of shape than full-term newborns, leading to a preference for the novel shape in the opposite hand. However, these interpretations remain entirely speculative and post-hoc and require further investigation. More generally, the explanation of direction of preference is still debated in the infant studies literature, and seems to depend on several factors (e.g., Kerzerho, Streri, Gentaz, 2009; cf. Pascalis & De Haan, 2003). A preference indicates the presence of discrimination, whatever its direction, and suggests that the development of the corpus callosum is sufficient to permit some transfer of shape information between the two hands in preterm

In conclusion, these results show that intermanual transfer of shape information is present at 33 GW in preterm infants. The occurrence of these intermanual abilities in full-term and preterm newborns suggests that some internal representation of a stimulus already has some level of abstraction. A second set of findings in favor of the existence of a higher-level internal representation stems from cross-modal studies on vision and touch in newborns.

In cognitive psychology, amodal perception is usually considered to be present at birth (see Streri, in press; Streri & Gentaz, 2009) as suggested by E. J. Gibson (1969). Beyond the details provided by individual sensory modalities, newborns are able to perceive a multimodal object as unified. However, the links between the haptic and the visual modalities are not fully established and will not be it until about the age of 15 years. Because newborns cannot engage in bimodal visual-haptic exploration of an object, a cross-modal transfer paradigm can be used to uncover the nature of these links and thereby evaluate young infants' ability to match the same object property captured by two modalities. However, cross-modal transfer tasks involve two successive phases (familiarization with an object in one modality and recognition test in a second modality). These tasks require cognitive processes (manual and visual information-processing capacities, memory load, etc.) that can weaken the links between sensory modalities and reveal failures in the establishment of amodal perception.

Newborns' visual abilities are weak. Nevertheless, numerous studies have revealed that babies can perceive speaking faces, photographs, objects, pictures, discriminate between large numbers, etc. (Coulon, Guellai and Streri, 2011; Féron, Gentaz, and Streri 2006; Guellai and Streri, 2011; Izard, Sann, Spelke and Streri, 2009; Meary, Kitromilides, Mazens, Graff and Gentaz, 2007; cf. Kellman and Arteberry, 1988, for a review). As discussed above, various studies have provided evidence that newborns are able to detect differences between shapes and textures with their hands (Streri et al. 2000; Molina and Jouen, 1998). All of these findings show that the prerequisites in both modalities are present to obtain

object shape. Second, the hypothesis of discrimination in intermanual transfer would be confirmed by differential treatment of novel and familiar objects in the opposite hand, as demonstrated previously in full-term newborns (Sann & Streri, 2008a). Thus, discrimination would be considered to have occurred when mean holding time for novel and familiar objects in the opposite hand differed significantly. Firstly, the results confirmed the occurrence of haptic manual habituation for each hand and for each shape in preterm infants between 33 and 34+6 GW. The second and main result was that, after habituation to the shape of an object in one hand, preterm infants held the novel object longer in the opposite hand. These results revealed intermanual transfer of shape in preterm infants between 33 and 34+6 GW for the first time. Fabri et al. (2005) showed the essential contribution of posterior corpus callosum to the inter-hemispheric transfer of tactile information: its development thus seems to be sufficient to permit the transfer of some shape information between hands in preterm infants between 33 and 34+6 GW. However, preterm infants' holding time in the opposite hand increased with both novel and familiar objects, although this increase was significantly greater for the novel object than for the familiar one. While the increase in holding time was expected for the novel object, confirming the presence of discrimination, the increase in holding time for the familiar object was more surprising. This second result relates to the influence of changing hands on manual discrimination. This pattern of results could be due to two factors, one peripheral and one central. At a peripheral level, the tactile receptors were not the same as those stimulated during habituation and the information collected by the opposite hand had to be sent to the central nervous system by another pathway. In addition, given that the infant participants had underdeveloped muscle tone, the increase in holding time could also be caused by muscle fatigue in the habituated hand, compared to the unfatigued contralateral hand. Any form of tactile stimulation of the contralateral hand would induce some degree of recovery from habituation. At a central level, comparing objects information collected from the two hands may require more time than during an intramanual discrimination. This increase in holding time could reflect the time required to transfer information between the two hemispheres via the corpus callosum.

Finally, the direction of preference (preference for novelty) differed from that observed in 2 day-old full-term newborns with a similar procedure. Lejeune et al. (in press) propose two interpretations for this difference. First, because it is impossible to determine what type of shape information was transferred (entire shape, edge information or other contrasts or differences), one possible interpretation could be that full-term and preterm infants extract different types of shape information, leading to this discrepancy of preference. A second interpretation could be that experience prevails over maturation. Preterm infants were tested at a lower post-conceptional age (34+3 GW) than full-term newborns (40+2 GW) but at a higher postnatal age (30 days *vs.* 2 days). Consequently, the results could be explained by a greater tactile experience *ex utero* than for the full-term newborns. However, 2-monthold full-term infants have also been found to demonstrate a familiar preference (Streri, Lemoine, & Devouche, 2008) even though their postnatal age was higher than that of our preterm infants. A second factor that could explain this second discrepancy is the type of tactile experience which, combined with the length of experience, might influence the direction of preference. Preterm infants in their incubators receive a great deal of repetitive and stereotyped tactile stimulations (daily care, feeding, medical examinations, etc.). Hospitalized infants experience up to 14 painful procedures per day and up to 53 different

object shape. Second, the hypothesis of discrimination in intermanual transfer would be confirmed by differential treatment of novel and familiar objects in the opposite hand, as demonstrated previously in full-term newborns (Sann & Streri, 2008a). Thus, discrimination would be considered to have occurred when mean holding time for novel and familiar objects in the opposite hand differed significantly. Firstly, the results confirmed the occurrence of haptic manual habituation for each hand and for each shape in preterm infants between 33 and 34+6 GW. The second and main result was that, after habituation to the shape of an object in one hand, preterm infants held the novel object longer in the opposite hand. These results revealed intermanual transfer of shape in preterm infants between 33 and 34+6 GW for the first time. Fabri et al. (2005) showed the essential contribution of posterior corpus callosum to the inter-hemispheric transfer of tactile information: its development thus seems to be sufficient to permit the transfer of some shape information between hands in preterm infants between 33 and 34+6 GW. However, preterm infants' holding time in the opposite hand increased with both novel and familiar objects, although this increase was significantly greater for the novel object than for the familiar one. While the increase in holding time was expected for the novel object, confirming the presence of discrimination, the increase in holding time for the familiar object was more surprising. This second result relates to the influence of changing hands on manual discrimination. This pattern of results could be due to two factors, one peripheral and one central. At a peripheral level, the tactile receptors were not the same as those stimulated during habituation and the information collected by the opposite hand had to be sent to the central nervous system by another pathway. In addition, given that the infant participants had underdeveloped muscle tone, the increase in holding time could also be caused by muscle fatigue in the habituated hand, compared to the unfatigued contralateral hand. Any form of tactile stimulation of the contralateral hand would induce some degree of recovery from habituation. At a central level, comparing objects information collected from the two hands may require more time than during an intramanual discrimination. This increase in holding time could reflect the time required to transfer information between the

Finally, the direction of preference (preference for novelty) differed from that observed in 2 day-old full-term newborns with a similar procedure. Lejeune et al. (in press) propose two interpretations for this difference. First, because it is impossible to determine what type of shape information was transferred (entire shape, edge information or other contrasts or differences), one possible interpretation could be that full-term and preterm infants extract different types of shape information, leading to this discrepancy of preference. A second interpretation could be that experience prevails over maturation. Preterm infants were tested at a lower post-conceptional age (34+3 GW) than full-term newborns (40+2 GW) but at a higher postnatal age (30 days *vs.* 2 days). Consequently, the results could be explained by a greater tactile experience *ex utero* than for the full-term newborns. However, 2-monthold full-term infants have also been found to demonstrate a familiar preference (Streri, Lemoine, & Devouche, 2008) even though their postnatal age was higher than that of our preterm infants. A second factor that could explain this second discrepancy is the type of tactile experience which, combined with the length of experience, might influence the direction of preference. Preterm infants in their incubators receive a great deal of repetitive and stereotyped tactile stimulations (daily care, feeding, medical examinations, etc.). Hospitalized infants experience up to 14 painful procedures per day and up to 53 different

two hemispheres via the corpus callosum.

procedures during their first 15 days of life (Simons et al., 2003). Furthermore, Gimenez et al. (2008) showed that the maturation of brain tissue may be accelerated by factors associated with preterm birth, perhaps through the direct effects of the extrauterine environment. These particular tactile experiences could enhance the development of the intermanual transfer of information in preterm infants, even among younger infants who are at least 9 days old. In this case, according to the hypothesis proposed by Sann and Streri (2008a), preterm infants could have a more elaborate representation of shape than full-term newborns, leading to a preference for the novel shape in the opposite hand. However, these interpretations remain entirely speculative and post-hoc and require further investigation. More generally, the explanation of direction of preference is still debated in the infant studies literature, and seems to depend on several factors (e.g., Kerzerho, Streri, Gentaz, 2009; cf. Pascalis & De Haan, 2003). A preference indicates the presence of discrimination, whatever its direction, and suggests that the development of the corpus callosum is sufficient to permit some transfer of shape information between the two hands in preterm infants from 33 GW.

In conclusion, these results show that intermanual transfer of shape information is present at 33 GW in preterm infants. The occurrence of these intermanual abilities in full-term and preterm newborns suggests that some internal representation of a stimulus already has some level of abstraction. A second set of findings in favor of the existence of a higher-level internal representation stems from cross-modal studies on vision and touch in newborns.
