The line copy task for kinesthesia and internal movement representation: Application in children

In the present study a new test is proposed and tested, which requires ability to use information both from kinesthesia and from mental rotation of previously produced cyclic movements over a distinct trajectory. This Line Copy Test (LICT) was performed by 58 children aged 7–11 years. For the S-part, the participants first had to make movements till they reached a barrier and then they were required to reproduce the same (S) movements without the barrier. For the O-part of the test the participants had to rely on an internal representation of a felt trajectory length, and reproduce the movement orthogonal (O) to the ones felt. Trajectory Length Error (TLE) and variable error (VE) were measured. Furthermore, results of the LICT were correlated to the Kinesthetic Acuity Test and a pegboard task. The general finding was that the TLE, capturing the spatial calibration of the movement, and the VE, used as a measure of noise or inconsistency in the 10 reproductions, was largest for the youngest children, but this developmental effect was not significant in the O-part of the test. Although participants of all age groups made much larger TLE in the rotated task (O-part) than in the LICT_S-part, the VE was much smaller. This can be explained by assuming that different underlying control mechanisms underlie each task. Also differences in correlations of the two parts of the test with the other measures infer that they measure dissimilar underlying entities. It is likely that at least some portion of the increased movement variability in the S-part seen during development in young children can be attributed to partly unstable kinesthetic representations for hand movements. The finding that no significant development was found on the O-part indicates that changes in the use of internal models must occur outside the age window studied.