Prospective Control and Object Representation in Yound Infants : An action-based account

Abstract: The aim of the present thesis was to study the age-related differences of prospective control and object representation in young infants. The overall set of theoretical and empirical issues addressed in this thesis consists of how infants represent and react to visible and non-visible moving objects. This involves understanding the interrelationship between different actions, such as head and trunk movements, and reaching. Questions about infants’ ability to negotiate different kinds of motions and the notion that infant representation of an occluded object can be graded in strength are also addressed in the present thesis. The hypothesis of graded representation proposed that a concept of object representation is not a clear-cut distinction between whether one has a representation or not. It is rather a graded process, evolving with experience and becoming embedded in processes underlying overt behaviour. Study I showed that perturbing an object affected the quality of grasp, which seems to indicate that the approach and grasp components are, at least partially, integrated by nine months of age. The analysis of the relationship between head and hand movements showed tightness in the coupling between these movements, as indicated by a small correction time difference between them. Study III showed that 6-month-old infants, under certain conditions, can form a dynamical representation of a moving and temporarily occluded object, taking into account the velocity and the direction of the object’s motion. It also revealed three other interesting findings: firstly, that an occluder could provide landmark information about object reappearance; secondly, that reaching was dramatically disrupted when the object was temporarily non-visible either due to occlusion or blackout of the room lights and thirdly, that reaching recovered markedly after a few trials, but only when subject to blackout. Overall, the results supported the hypothesis of graded representations. In Study IV, when infants observed a circular object motion, it was shown that while head tracking is functional in 6-month-old infants, it continues to develop and become more refined up to, and beyond, the age of 12 months. The structural organization of head tracking in both 6 and 12-month-old infants complied with an organizational pattern of accelerations and decelerations, or so-called movement units, which is in line with earlier studies of both goal-directed and spontaneous arm movements. The intersegmental coupling between the head and the trunk showed that the infants tried to stabilise head movements by adjustments of the trunk. In addition, study II presents a method for coding prehensile movements by means of a touch screen system, which is used in study III.