Development of prospective control of blinking and catching in full-term and preterm infants
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- Institutt for psykologi 
Prospective control is dependent on perceptual information guiding an action so that an extrapolation of the movement can be made into the future (Lee, 1998, 2005; Von Hofsten, 2004, 2007). Infants become increasingly better at predictively using the perceptual information available to time their actions. Earlier research has found that infants use information variables such as distance, velocity, or time when performing interceptive actions (Out, Savelsbergh, & Van Soest, 2001; Van der Meer, Van der Weel, & Lee, 1994; Van der Meer, Van der Weel, Lee, Laing, & Lin, 1995; Van Hof, Van der Kamp, & Savelsbergh, 2006, 2008). Infants can use different timing strategies by initiating an action when an information variable reaches a certain criterion value, for example every time an object is a certain distance away from them. There are differences in how well different timing strategies aid the infants to time their actions. Strategies based on distance or velocity are susceptible to errors, while a strategy based on time enables successful timing independently of the task requirements. In the current thesis, development of prospective control is studied in full-term and preterm infants on defensive blinking to optical collisions and catching of moving objects. The aim is to investigate which information variables infants use to time their actions. Strategies based on distance (or the equivalent angle-strategy), velocity, and time are explored. A shift to a timing strategy that lead to improved performance is considered a successful coupling of perception and action by the infants to better time their actions. When a looming virtual object approaches on a collision course, infants blink to protect their eyes. In a series of three experiments, using a combination of cross sectional and longitudinal design, it is investigated which timing strategies twenty fullterm and eight preterm infants between 22 and 30 weeks of age (corrected for prematurity) use to make a defensive blink. Results show that infants at the youngest ages tend to use an angle-strategy and make many late defensive blinks, while older infants use a time-strategy and blink in time on all approach conditions. One preterm infant uses a velocity-strategy at 22, 26, and 30 weeks. Unlike all the other full-term and preterm infants he does not switch to a time-strategy with age, and makes a high number of late blinks. When catching a moving toy, ten full-term and five preterm infants are tested longitudinally at 22, 26, 30, 40, and 48 weeks of age (corrected for prematurity). Results show that the youngest infants use a distance- or velocity-strategy to initiate the catch, and make many unsuccessful catches. With age, infants switch to a time-strategy and increase the number of successful catches. In addition to studying the timing strategies infants use to initiate the catch, it is investigated how infants continuously guide their hands to the toy, and whether this guidance is influenced by their use of timing strategy. The tau-coupling analysis show that when using a time-strategy, infants perform longer and more functional tau-couplings between the hand and the toy, compared to when they are using a distance- or velocity-strategy. The same preterm infant as mentioned above does not switch to a time-strategy when catching a moving toy and makes a high number of unsuccessful catches. In addition, this preterm infant shows a less functional tau-coupling with non-controlled collisions between the hand and the toy. Results from both defensive blinking to optical collisions and catching of moving toys demonstrate that the need for a more robust strategy lead to a shift towards a timing strategy that allows the infants to perform actions that require precise timing more successfully. These studies are among the few developmental studies showing attunement in infants’ perceptual systems enabling them to perform their actions in accordance with the requirements of the environment. Also, the studies are among the few performed on timing in preterm infants, and contribute to the understanding of the processes underlying this group’s coupling of perception and action. Whether timing problems in preterm infants can be used as an indication of later perceptuo-motor problems needs further investigation.