Movements, however, do not always need to be acted out overtly to support mental simulations.
Even an imagined hand movement improved adults’ performance (Schwartz & Black, 1999). This result
is in line with recent theories on embodied cognition (Wilson, 2002), which claim that mental
structures that originally evolved to control action can also be used ‘‘off-line” to mentally simulate
external events decoupled from the physical inputs and outputs. Thus, motor functions may be used
to recruit motor knowledge in a covert way and without overt movement. However, the lack of an active
hand movement seemed to make the water tilting task more difficult. Schwartz and Black (1999)
argued that there might be situations where the extra information and the constraints provided by a
motor activity are necessary to sustain imagery. The questions of when, why, and for whom motor
activity has a beneficial effect are still an unresolved theoretical issue.