Developmental changes of the biomechanical effect in motor imagery.

Motor imagery has been investigated in childhood and early adolescence, but not across adolescence stages; moreover, available evidence did not clarify whether the involvement of motor information in mental rotation of body parts becomes stronger or weaker during development. In the present study, we employed the hand laterality task to assess motor imagery in ninety-seven typically developing adolescents divided into three age groups (i.e., 11-12, 14-15, and 17-18 years); mental rotation of objects and letters were also assessed. As a specific marker of the motor involvement in mental rotation of body parts, we assessed the so-called biomechanical effect, that is, the advantage for judging hand pictures showing physically comfortable positions with respect to hand pictures showing physically impossible or awkward positions. Results demonstrated that the biomechanical effect did not significantly affect early adolescents' performance, whereas it became significant in 14- to 15-year-old participants and even more stronger in 17- to 18-year-old participants; this pattern did not depend on an increase in processing speed to mentally rotate both corporeal and non-corporeal (objects and letters) stimuli. The present findings demonstrated that: (1) motor imagery undergoes a continuous and progressive refinement throughout adolescence, and (2) full exploitation of motor information to mentally transform corporeal stimuli can be attained in late adolescence only.