Sensory adaptation supports flexible evidence accumulation during perceptual decision making.

Effective decision making in dynamic environments requires flexible evidence accumulation. Although models often express this flexibility as an adaptive "leak" parameter governing accumulator dynamics, its implementation in the brain may involve adaptive mechanisms operating at other stages of the decision process. We tested whether such mechanisms include adjustments in evidence encoding. We recorded single-unit activity in the middle temporal area (MT) while monkeys performed a modified random-dot motion direction-discrimination task in which an adapting stimulus with varied temporal stability preceded a behaviorally relevant test stimulus. Monkeys flexibly adjusted their decision-making behavior in a manner consistent with an adaptive leak that depended on temporal-context stability. Behavioral adjustments were reflected in context-dependent differences in sensory adaptation in MT that were independent of changes in pupil-linked arousal. These findings identify a novel role for stimulus-specific sensory adaptation in shaping the evidence available for perceptual decisions to support flexible, context-dependent evidence accumulation.