Perceptuo-motor calibration and the perception of affordances following rapid growth in adolescence
Adolescence is usually considered to be a time of transition from child to adult. However, studies of perceptuo-motor control have tended to focus on infants and young children or on adults, despite indications that the actions of adolescent children are poorly coordinated. This thesis examines the adolescent growth spurt and resulting recalibration of perceptuo-motor control with respect to the coordination of movement. The first four experiments compared the performance of boys aged 12 and 13 (the age when a growth spurt is most likely to be in progress) with older (aged 14 and 15) and younger (aged 10 and 11) boys on tasks where their knowledge of their ability to perform certain actions was observed. These tasks examined actions ranging from placing objects on surfaces in front of them, reaching up to place objects on high shelves, stepping across gaps and walking along balance beams. In agreement with previous research, the younger children tended to overestimate their ability more than the older children. However, overall the poorest match between predictions and actual actions was observed in the 12 and 13 year old boys. In particular, they appeared to have a problem identifying the critical point beyond which they could no longer maintain balance during an action. This was linked to complex changes which take place in conjunction with height increases at adolescence: moments of inertia of body segments change and this must be taken into account when planning actions. The last three experiments examined the relationship between growth and performance on forward and upward reach as well as on a task where children used long sticks to increase their forward reach. In this case, the performance of boys aged 12 and 13 who had grown substantially over the previous six months differed substantially from that of boys of the same age who had grown only a small amount. Again, differences were most notable when it was necessary to identify the critical point beyond which balance could not be maintained: this was particularly apparent when reaching with long sticks. The High Growth boys greatly overestimated their ability in comparison to the Low Growth boys. The results of the thesis highlight the perceptuo-motor changes which accompany rapid growth and demonstrate that adult patterns of movement are unlikely to be in place until the child has learned to take account of changes in height, limb length and the moments of inertia of their body and limb segments. Until this has happened, it is likely that the adolescent will occasionally perform poorly planned and coordinated movements, especially in unfamiliar situations.