Quantification of object manipulation in children with cerebral palsy

A shape-posting task was studied in 30 control, eight hemiplegic and 10 diplegic children, to determine how differences in object manipulation between such children could be quantified. Conical, cylindrical and triangular-shaped objects were posted through a hole in a perspex screen, three times each with both preferred and non-preferred hands. Four variables were defined to describe kinematic aspects of the task: adjustment inefficiency, mean transport velocity, adjustment distance to be completed in the placing phase and adjustment velocity in the placing phase. As expected, total task time was increased in subjects with cerebral palsy and with more complex shapes, and reduced by repetition. The four kinematic variables reduced the variation in task time between individual children by 79%, between sets of like objects by 62%, and the residual variation by 63%. Adjustment inefficiency was increased and mean transport velocity reduced in subjects with cerebral palsy, whereas repetition had the opposite effect. It is suggested that combined alterations in adjustment inefficiency and transport velocity reflect changes in the intrinsic uncertainty of a movement and that this quantity is decreased by repetition and increased in cerebral palsy.