Spatial representations of touch in infancy and early childhood

The primary aim of this thesis was to examine how infants, and young children, represent touches in space (i.e. with respect to their external environment). Studying infants in the first year of life allows us to map the emergence of the complex processes needed in order to correctly locate touches to the body (and, by extension, the location of the limbs and body parts on which those touches impinge). In a series of seven experiments, I examined the development of the spatial representation of touch. To do this, I explored the development of an external reference frame in which touches are coded, the modulatory effect of changes in posture on the neural representation of a touch and the relationship between vision and touch when locating a stimulus from these sensory modalities in space. To investigate the development of an external reference frame for touch, I used a ‘crossed-hands’ task. This task has been used as a marker of the influence of an external frame of reference for localizing touch and is considered to arise out of conflict (when the hands are crossed) between the anatomical and external frames of reference within which touches can be perceived. Previous research with children had found that this reference frame does not develop until after 5.5-years; I extended this finding by determining that children as young as 4-years are able to locate touches in external co-ordinates. Additionally, in a further study, I found that an external reference frame develops between 4 and 6 months of age. The modulatory role of vision on tactile localization was also investigated. These studies showed that when 4-year-old children are provided with current vision of the hand being touched, this interfered with the benefits of using an external reference frame. However, this interference was limited to when the limbs were in canonical postures. As such, it seems that young children are still refining the ways in which sensory cues to the body help them to locate touches in the world. Considering that early visual experience was implicated in the development of an external frame of reference I also examined the development of an ability to perceive visual and tactile stimuli in a common spatial location. Here, it was found that 6-month-olds demonstrated this ability, with tentative findings suggesting that it may develop even earlier in life (e.g., at 4 months of age). As such, the ability to co-locate tactile and visual stimuli at 6 months is consistent with a role for visual experience in the development of an external frame of reference for touch at this age. Further to this, I examined interactions between vision and touch using a crossmodal cueing event-related potential (ERP) paradigm. In this study, it was found that at 7 months of age visual cues to the hand modulate processing of a subsequent tactile stimulus on that same hand. This provides further evidence of early acquired crossmodal links, but this was the first demonstration of crossmodal attentional cuing effects in infancy. Finally, in a set of two experiments, I investigated how infants (in the first year of life) were able to update the location of a felt touch across changes in arm posture, using an ERP measure. Although these studies demonstrated a null relationship between sensorimotor experience and somatosensory remapping, it was found that only those 8-month-old infants that displayed contralateral reaching behaviours were able to update to the location of a touch across a change in posture. As such, the relationship between sensorimotor experience and somatosensory remapping may not be simple, with other factors (such as brain maturation) also influencing this relationship.