Repeated within-session rule switching in the marmoset: a paradigm for tracking the dynamics of cognitive flexibility

Adapting behaviour when reward contingencies change is a core function of cognitive control, but the underlying trial-by-trial computations are hard to observe when tasks cue each rule or allow only one switch per session. We developed the Feature-Rule Switching Task (FRST), in which common marmosets (Callithrix jacchus) repeatedly switch, without cues and under a fixed stimulus set, among the visual features that earn reward, inferring each switch from feedback alone. All four animals acquired the task within two days and sustained several switches per session across months of testing. A reinforcement-learning model with a learned weighting of stimulus dimensions best explained choices in every animal, outperforming complexity-matched perseveration controls. Learning-rate estimates fell within the human range, and in almost every session the animals weighted a stimulus dimension rather than individual features alone, with a dimensional commitment comparable in strength to that of humans. FRST thus provides a primate paradigm, amenable to laminar recording, for tracking the dynamics of cognitive flexibility.