FBS Colloquia No.415Center for Information and Neural Networks

Apparent forgetting in human motor memory reflects contextual drift over time

Motor memories often appear weakened when tested after a delay, yet whether this reflects degradation of the stored memory or incomplete expression remains unclear. Here, in a human force-field adaptation task, we show that motor memories dropped after a delay recovered rapidly over successive error-free probe trials that minimized relearning. This apparent forgetting and recovery occurred after delays ranging from minutes to 24 h, arguing against simple passive trace loss and instead indicating incomplete reinstatement of a retained memory. A contextual inference model captured both the apparent forgetting and recovery, and trial-by-trial pupil fluctuations tracked transient increases in model-derived contextual uncertainty as a function of delay length, consistent with transient failure to reinstate the internal context associated with the learned response. Together, these findings suggest that forgetting-like losses in motor learning across time scales partly reflect reversible failures to reinstate task-relevant internal context.