An 'Aha!' moment precedes the strategic response to a visuomotor rotation

Strategic behaviour in sensorimotor adaptation tasks is typically described as either a gradual error minimisation process or as a process of learning through trial-and-error. The former predicts a gradual monotonic reduction in error, until some asymptote, while the latter predicts behavioural exploration to discover an efficacious solution. Another explanation is that a sufficiently rich understanding of the task culminates in an "Aha!" moment, and that this richer understanding naturally entails a new strategy. This predicts some period of perseveration in baseline behaviour, followed by an abrupt shift to a new strategic solution. To avoid obfuscation caused by the motor system, we first investigate these hypotheses in a strategy-only aiming game, where participants aim and fire a cannon at targets. Most participants exhibited a period of baseline perseveration followed by a single-trial shift to a distinct strategy. This strategy typically appears to produce the correct compensatory magnitude for a noisily estimated perturbation, but also substantial variability in compensatory sign. We then applied the same analyses to reaching data from a visuomotor rotation task that inhibited implicit adaptation through delaying feedback presentation. Similarly, we found that participants typically perseverated in reaching towards the target before suddenly switching, in a single trial, to good performance in compensatory magnitude. We fit our generative "Aha!" model to 1337 participants across several datasets and show that it faithfully captures these phenomena. Our findings highlight the need to update existing models to account for the abrupt, insight-driven shifts that characterise individual human responses to sensorimotor perturbations.