Indirect feedback hinders explicit sensorimotor adaptation.

Motor adaptation-the process of reducing motor errors through feedback-is an essential feature of human competence, allowing us to move accurately in dynamic and novel environments. Adaptation typically results from direct sensory feedback, with most learning driven by visual and proprioceptive feedback that arises with the movement. In humans, motor adaptation can also be driven by indirect numerical feedback. In the present study, we examine how implicit and explicit components of motor adaptation are modulated by indirect numerical feedback. We conducted three reaching experiments involving over 400 human participants to compare direct sensory feedback and indirect numerical feedback using a task in which both types of learning processes could be present (experiment 1) or tasks in which learning was expected to be limited to only an explicit process (experiments 2 and 3). Adaptation with indirect feedback was dominated by explicit strategy use, with minimal evidence of implicit recalibration. When matched for information content, adaptation to both rotational and mirror-reversal perturbations was slower with indirect feedback than with direct feedback, due to increased random and systematic exploration. These results suggest that the nature of feedback shapes strategic discovery, offering new insights into how feedback type influences the mechanisms of sensorimotor learning.