Department of Psychology


– Early Detection of Brain Damage

Early detection

Devising effective therapy for perceptuo-motor disorders requires in-depth measures of the child's motor functioning. Current assessment mainly uses measures of surface behaviour, but these measures cannot reveal the underlying causes of perceptuo-motor disorders. In this section experiments from our laboratory are shown which measured in detail the functioning and development of basic movement control mechanisms.

Basic Movement Control in CP

Movement Control in Cerebral Parese

by Van der Weel, Van der Meer & Lee

Cerebral Palsy is not a homogeneous condition. Therefore, effective therapy requires assessing each individual child's problems in order to decide appropriate therapy and adjust it to the child's progress. Since underlying problems (e.g., poor (prospective) eye movement control or disorders in proprioception) can hinder performance of everyday skills such as reaching, simple assessment of overt behaviour is in many cases not adequate; it can only describe the symtoms of movement disorder. To determine the underlying causes - and so pin-point where therapy needs to be directed - it is necessary to measure basic perceptuo-motor functions that subserve the disordered everyday skills.

Cerebral palsied children initiated the hitting action much earlier with the affected hand than with the non-affected hand. Between the nursery school children's non-dominant hand and dominant hand there was no such difference. In the button-press condition no significant differences in initiation were found between the CP children's affected and non-affected hand and the nursery school children's non-dominant hand and dominant hand. This may indicate that the CP children take into account the degree of handicap of their affected arm when actually hitting the approaching ball.

Premature Reaching

Development of Prospective Control of Catching Moving Objects in Preterm at-risk Infants

by Van der Meer, Van der Weel, Lee, Laing & Lin

Healthy term infants classified as neurologically at-risk because of low birthweight and preterm birth were tested longitudinally between 20 and 48 weeks to use visual information predictively. Reaching for an object moving at different speeds was assessed; the object was occluded from view by a screen during the last part of its approach. At each infant's first reaching session, gaze anticipated the reappearance of the moving toy; however, onset of reaching and prospective control of gaze and hand varied considerably between the normal and at-risk groups. In addition, some at-risk infants geared their actions not to the time but to the distance that the toy was from the catching place, causing problems with faster-moving toys. The two children who anticipated least well were the only two of the at-risk group who were later diagnosed as having cerebral palsy.

Effect of Task on Movement Control

Effect of Task on Movement Control in Cerebral Palsy: Implications for Assessment and Therapy

by Van der Weel, Van der Meer & Lee

In order to examine the possibility that children with cerebral palsy find abstract tasks, such as extending the arm as much as possible, more difficult than concrete tasks, such as reaching to grasp an object, nine hemiparetic children with CP and 12 nursery-school children were tested with both a concrete and an abstract task. The children with CP achieved a significantly larger range of movement in the concrete task, whereas the nursery-school children showed no difference between tasks. Thus the CP children's poorer performance on the abstract did not fully reflect their movement capability. This means that conventional neurological measurements of limb function in cerebral palsy, which mainly use abstract tasks or passive movements, will give an incomplete picture of the child's action capability.

Preterm Looming

Preterm infants' timing strategies to optical collisions

by Kayed, Farstad & Van der Meer

Background: A virtual object approaching on a collision course will elicit defensive blinking in infants. Previous research has shown that when precisely timing their blinks, full-term infants shift from using a strategy based on visual angle/angular velocity to a strategy based on time between 22 and 30 weeks of age.

Aim: To investigate which timing strategy preterm infants use to determine when to make the defensive blink.
Methods: Eight preterm infants were tested at 26 weeks, corrected for prematurity. For three of these infants, longitudinal data at 22, 26, and 30 weeks were available. The virtual object approached the infants with different constant velocities and constant accelerations.
Results: At 26 weeks, three infants blinked when the virtual object's visual angle reached a threshold value causing them to have problems with fast, accelerating approaches. Four infants blinked when the virtual object was a certain time away, allowing them to blink in time on all approach conditions. One infant stood out because he relied on a timing strategy based on angular velocity on all three test sessions, causing him to blink late on a large number of trials even at 30 weeks.
Conclusion: As good timing is essential for successful interaction with the environment, the inability to switch from a timing strategy that is prone to errors to a strategy that enables successful defensive blinking reflects lack of flexibility to adjust appropriately to local circumstances. This might be an early indication of perceptuo-motor problems that warrants
further investigation.