Symposium
Chairs: Louise Ronnqvist and Brian Hopkins
Discussant: Brian Hopkins
Both Freud (1927) and Werner (1948) were advocates for studying pathological manifestations as a means of improving insights and knowledge about normal functioning. This approach, widely adopted in neuropsychology with its concern for identifying double dissociation effects in adults with specified brain lesions, has not been a major focus of concern in the study of developmental disorders. Generally speaking, disorders such as cerebral palsy (CP) and 'clumsiness' as well as others associated with prematurity have been studied in their own right relative to some set of standards held to constitute 'normality'. The rationale for such clinically-based studies has been to improve the prospects for the diagnosis and treatment of children with particular developmental disorders. In this symposium, these sorts of issues will be addressed from a number of different theoretical perspectives. More importantly, however, it will also attend to the theme of if and how research on children with developmental disorders can inform us about the mechanisms and processes involved in normal development. In order to achieve coherence between presentations, the symposium will take as its departure point research concerned with the development of perception-action systems in specified clinical populations. Thus, presentations will cover preterm infants relative to gaze behaviour (Geuze et al.) and prehensile movements (Rnnqvist), and bimanual coordination in children with hemiplegic CP (Rsblad) or who are considered to be 'clumsy' (Sigmundsson). Based on their own findings, each speaker will illustrate how they provide answers to the two main topics that have motivated the symposium: the need for more theoretically-based approaches to diagnosis and treatment and in what ways the study of 'abnormal' development can be beneficial to obtaining deeper (and perhaps novel) insights into 'normal' development.
Details of individual items:
paper
Infants' ability to shift gaze develops rapidly in the first few months after birth. It plays a central role in early exploration and communication, thus contributing to the development of the infant. An important question is whether adverse pre-and perinatal conditions constitute a risk factor in the development of the ability to shift gaze efficiently. The development of gaze shifting abilities in preterm infants is particularly interesting. On the one hand, the early development of processes which are mediated by early maturing structures, and which are sensitive to environmental input may be accelerated by preterm infants' early exposure to visual input. On the other hand, the medical complications that often accompany a preterm birth may lead to brain damage, and this may delay development. Evidence from studies of visual orienting suggests that the development of the ability to shift gaze to peripheral stimuli that appear suddenly in an empty visual field is accelerated in very young preterm infants. How long this advantage persists is not known. Indirect evidence from studies of social interaction and habituation suggests that the more complex process of shifting gaze from a fixated stimulus to a suddenly appearing peripheral target is delayed in preterm infants. Shifting gaze from a fixated stimulus to a suddenly appearing peripheral target requires not just the ability to shift gaze, but also the ability to disengage attention and gaze. There is as yet no direct evidence on the development of the ability to shift gaze from fixation in preterm infants. An intensive, longitudinal study of the development of gaze shifting in preterm and full-term infants between 6 and 26 weeks of age was carried out to increase our understanding of the impact of a preterm birth on the development of the ability to shift gaze. Healthy preterms and preterms with minor brain damage were included in the study. Both groups could be expected to benefit from early experience, however, development in the second group may have been affected by brain damage. The frequency and latency of shifts of gaze to peripheral targets were measured in a competition condition (the fixation stimulus persisted after the target appeared), and in a non-competition condition (the fixation stimulus disappeared when the target appeared). A preliminary analysis comparing full-term infants with the entire group of preterm infants showed that, at 6 weeks of age, preterms shifted gaze more frequently and faster than full-terms in the non-competition condition. There was no difference in the frequency of gaze shifts in the competition condition. However, when preterms did shift gaze in this condition, they tended to do so faster than the full-terms. At 26 weeks of age, there were no differences in either frequency or latency in the non-competition condition. In the competition condition, both groups shifted gaze equally frequently but full-term's shifts of gaze were faster. These results suggest that the very early development of simple shifts of gaze was accelerated in the preterm group, presumably because of their extra visual experience. However, the full terms had caught up by 26 weeks. An analysis of the impact of perinatal brain damage on development within the preterm group is currently being carried out. Although we found that preterm infants are less efficient in shifting gaze when using abstract stimuli, we do not know the functional significance of this finding. In a following study with infants Ôat risk' we will use ecologically more relevant visual stimuli such as a dynamic recording of an emerging smile on the mothers' face, and real objects (toys) which elicit a reaching and grasping response. Also independent physiological measures of attention (heart rate response) will be used. Some data from a pilot study will be presented.
paper
Most studies of the development of prehensile movements have focused on changes in the control of uni- or bimanual reaching and its coordination with grasping. Surprisingly few have investigated what an infant actually does with object once it has been grasped in particular way. In other words, why does an infant reach out and grasp an object? The research discussed in this presentation has addressed this neglected issue within the context of kinematic analyses of the reaching movements of fullterm (FT) and preterm (PT) infants. In asking what an infant does with an object after grasping it, one is dealing with how intentions and their goals are built into an action during its early development. An obvious strategy to investigate this issue is to set the infant different goals in tasks involving prehensile movements, where goals can be defined in terms of varying the intrinsic and extrinsic properties of objects to be grasped. The question can then be posed as to when an infant begins to modify the kinematics of reaching before object contact to take account of such variations. More specific questions include: Are these modifications apparent first to changes in the object's intrinsic properties (e.g., size, shape, salience relative to other objects) or to its extrinsic properties (e.g., location, distance)? How are these modifications reflected in specific kinematic parameters (e.g., speed, straightness, number of movement units)? Which modifications result in the clearest distinction between a dominant and a non-dominant hand and at what age? These sorts of questions prompted a series of experiments and a longitudinal study involving reaching, grasping and subsequent manipulation in both FT and PT infants from 6- to 12 months of age. In the case of PT infants, it may be the case that the real problem they have is in selecting an action appropriate to the goal of the task and that this should be revealed in the kinematics of their reaching movements. More generally, the data presented will provide a foundation for discussing how the development of intention is incorporated into improvements in the control and coordination of prehensile movements.
paper
Functional plasticity is a key feature of the developing central nervous system. One expression of this is the capacity of the central nervous system for reorganisation after an early onset of brain damage. Children suffering from hemiplegia as a consequence of brain damage occurring before or around the time of birth show significantly better hand function compared to when similar damage happens later in development or during adulthood. Early onset hemiplegia (i.e., hemiplegic cerebral palsy) is not only connected with relatively good hand function, but also with a high incidence of persistent mirror movements. This means that movements of the unaffected forelimb will elicit symmetrical movements in the affected forelimb, typically most pronounced in the hand and forearm. This coupling between the hands in children with hemiplegic cerebral palsy could be explained by control of both hands from the undamaged motor cortex (Carr et al 1993). Activation of both forelimbs symmetrically will accordingly enhance the function of the affected limb in children with hemiplegic cerebral palsy (Utley & Sugden 1998). However, in many bimanual tasks asymmetric activation of the hands are required. If the child has mirror movements activation of one hand could then disturb the function of the other hand. Results from a study in which reaching movements in children with hemiplegic cerebral palsy were investigated will be presented. The movements were studied in situations in which the reaching hand was activated unimanually or when asymmetrical movements of the hands were required. The implications of the study's findings for clinical practice and for understanding the development of bimanual coordination in general will be discussed. ReferencesCarr, L.J., Harrison, L.M., Evans, A.L., & Stephens, J.A. (1993). Patterns of central motor reorganization in hemiplegic cerebral palsy. Brain,116,1223-1247. Utley, A., & Sugden, D. (1998). Interlimb coupling in children with hemiplegic cerebral palsy during reaching and grasping at speed. Developmental Medicine and Child Neurology, 40, 396-404.
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Much of the previous research involving motor-impaired children has been characterized by a focus on test outcomes (i.e., a product-based approach), which simply describes the problems, but cannot explain them. To achieve the latter requires the adoption of a process-oriented approach, which attempts by appropriate experimentation to tease out the ways in which these children organise their moments in time and space. This has been the focus of the present research. Its initial emphasis has been on the difficulties experienced by particular groups of motor-impaired children in terms of sensory integration. In this way, it has been possible to draw parallels between behavioural manifestations of 'clumsiness' and potential underlying neurological information-processing disorders. Using tasks requiring bimanual (and interlimb) coordination with and without vision, we have been able to identify whether these disorders involve the intra-hemispheric or inter-hemispheric transfer of information in 'clumsy' children and specifically those with eye-hand coordination problems. The findings to be reported not only have consequences for the remedial teaching of such children, but also for our understanding of the development of cerebral functions, especially those concerned with the transfer of sensory information via the corpus callosum.