Gesture changes thought by grounding it in action.

When people talk, they gesture. We show that gesture introduces action information into speakers' mental representations, which, in turn, affect subsequent performance. In Experiment 1, participants solved the Tower of Hanoi task (TOH1), explained (with gesture) how they solved it, and solved it again (TOH2). For all participants, the smallest disk in TOH1 was the lightest and could be lifted with one hand. For some participants (no-switch group), the disks in TOH2 were identical to those in TOH1. For others (switch group), the disk weights in TOH2 were reversed (so that the smallest disk was the heaviest and could not be lifted with one hand). The more the switch group's gestures depicted moving the smallest disk one-handed, the worse they performed on TOH2. This was not true for the no-switch group, nor for the switch group in Experiment 2, who skipped the explanation step and did not gesture. Gesturing grounds people's mental representations in action. When gestures are no longer compatible with the action constraints of a task, problem solving suffers.