Embodied simulations improve memory, but which is the most effective? The crucial role of action observation and its dynamic interplay with motor imagery ability.

Literature has shown that memory can be influenced by sensorimotor simulations at encoding as those involved in motor imagery (MI), action observation (AO), or affordances elicited by visual object presentation (OBJ). Such simulations can improve memory by creating multimodal and thus, more accessible memory traces. However, no research has yet compared all these simulations within a single study and investigated their relationship with participants' imagery ability. The current study aimed to fill this gap by assessing the effects of different simulations on episodic memory for objects that initially were encoded as part of a sentence in which the action was 'grasping' (e.g., You are grasping a fork). By applying a between-subject design, 163 participants were assigned to different sensorimotor encoding conditions, and their memory was tested in a free recall task 15 min after encoding. Our results showed a main effect of AO, indicating an overall AO benefit to memory enhancement. Moreover, a three-way interaction between AO, MI and OBJ showed how the facilitating role of AO can be dampened by MI and OBJ. Finally, we found that the individual trait of kinesthetic imagery (KI) interacts with AO in recall performance, as higher levels of KI interfere with AO encoding, suggesting potential different mechanisms underlying the mental simulations involved in motor imagery and action observation.