Increasing convergence between imagined and executed movement across development: evidence for the emergence of movement representations.

Motor imagery (MI) has become a principal focus of interest in studies on brain and behavior. However, changes in MI across development have received virtually no attention so far. In the present study, children (N = 112, 6 to 16 years old) performed a new, computerized Virtual Radial Fitts Task (VRFT) to determine their MI ability as well as the age-related confluence between performance in executed and imagined movement conditions. Participants aimed at five targets, which were positioned along radial axes from a central target circle. The targets differed in width (2.5, 5, 10, 20 or 40 mm), resulting in an index of difficulty (ID) that varied from 6.9 to 2.9 bits. Performance was indexed by the linear relationship between ID and Movement Time (MT). The findings showed that executed task performance was slower than imagined performance. Moreover, conformance to Fitts' Law during executed movement performance was obtained from a very young age. Most importantly, correlations between imagined and executed movements were low in the young participants but gradually increased across age. These age-related changes in MI are hypothesized to reflect the children's emerging ability to represent internal models for prospective actions, consistent with the gradual unfolding of feedforward control processes.