Sense of agency for a new motor skill emerges via the formation of a structural internal model.

Sense of agency (SoA) refers to the feeling of controlling one's body and the external environment. The traditional comparator model posits that SoA arises from a match between predicted and actual action outcomes. However, when learning new motor skills, individuals initially lack outcome predictions and gradually develop an internal model of action-outcome mapping through trial-and-error, a process known as motor exploration. To investigate the development of SoA in such scenarios, we employed a de novo motor learning task that participants had never experienced before. Using a data glove, participants controlled a cursor on a screen through finger movements. In Experiment 1, participants learned a spatial hand-to-screen mapping from scratch via motor exploration. At different learning phases, we measured and compared participants' SoA for cursor movements that either conformed to the learned mapping or incorporated spatial or temporal biases. Initially, SoA was driven solely by temporal contiguity between finger and cursor movements. As learning progressed, SoA increased for cursor movements following the learned mapping compared to those following the spatially biased, unlearned mapping. In contrast, such changes did not occur in Experiment 2, where participants only imitated gesture images and memorized corresponding screen positions. The findings enhance existing SoA theories by elucidating the origins of the comparator process and highlighting the critical role of motor exploration.