Sensory adaptation and pupil-linked arousal support flexible evidence accumulation during perceptual decision making

Effective decision making in dynamic environments requires flexible evidence accumulation. Although models often express this flexibility as a property of the accumulator, its implementation in the brain may involve adaptive mechanisms operating at other stages of the decision process. We examined two such mechanisms: 1) stimulus-specific sensory adaptation at the level of evidence encoding; and 2) arousal-related neuromodulation, which could, in principle, affect both evidence encoding and accumulation. We measured single-unit activity in the middle temporal area (MT) and pupil-linked arousal while monkeys performed a modified random-dot motion direction-discrimination task in which an adap