Thinking More Lowers Hand Waving: Dual Task Damps Hand Movements During Mental Rotation

We report a dual task experiment investigating complementary actions (such as hand movements) that arise during cognitive tasks (such as counting). The ‘orphan model’ of the mechanism underlying such parallel actions predicts that a dual task would raise the frequency of such actions. However, rather than leading to more complementary actions, the dual task actually lowered usage of hands during mental rotation. This result fits models that consider motor area activation to be modulated by working memory load, such as models where motor area recruitment is initiated and driven by mental rotation, rather than by movement perception, as assumed by the orphan model. But studies on mental rotation show that there is no activation of the motor area during mental rotation of objects. Given this conflict, we propose two models that explain the dual task’s damping effect on hand activation, and outline current experiments to test these models.