Co-speech gestures have been proposed to strengthen sensorimotor knowledge related to objects’ weight and manipulability.
This pre-registered study (https ://www.osf.io/9uh6q /) was designed to explore how gestures affect memory for sensorimotor
information through the application of the visual-haptic size-weight illusion (i.e., objects weigh the same, but are experienced
as different in weight). With this paradigm, a discrepancy can be induced between participants’ conscious illusory
perception of objects’ weight and their implicit sensorimotor knowledge (i.e., veridical motor coordination). Depending on
whether gestures reflect and strengthen either of these types of knowledge, gestures may respectively decrease or increase
the magnitude of the size-weight illusion. Participants (N = 159) practiced a problem-solving task with small and large
objects that were designed to induce a size-weight illusion, and then explained the task with or without co-speech gesture
or completed a control task. Afterwards, participants judged the heaviness of objects from memory and then while holding
them. Confirmatory analyses revealed an inverted size-weight illusion based on heaviness judgments from memory and we
found gesturing did not affect judgments. However, exploratory analyses showed reliable correlations between participants’
heaviness judgments from memory and (a) the number of gestures produced that simulated actions, and (b) the kinematics of
the lifting phases of those gestures. These findings suggest that gestures emerge as sensorimotor imaginings that are governed
by the agent’s conscious renderings about the actions they describe, rather than implicit motor routines.