Distinct Computational and Temporal Mechanisms Underlie the Joint Effects of Motivation and Working Memory on Perceptual Sensitivity

Human perception is continuously shaped by internal cognitive states, yet how motivation and working memory jointly influence perceptual sensitivity remains poorly understood. Here, we combined behavioural experiments, computational modelling, and pupillometry to determine whether motivation enhances perception by amplifying working memory (WM)-driven facilitation or whether both exert independent influences. Participants performed a near-threshold visuospatial discrimination task under systematically manipulated motivational and WM states. Behaviourally, both motivation and WM independently improved perceptual performance, producing the greatest enhancement when both were present. A Bayesian generalized linear psychometric model revealed that these improvements were best explained by independent additive contributions to effective perceptual sensitivity, rather than motivational amplification of WM. Consistent with this computational framework, pupil dynamics tracked trial-by-trial fluctuations in effective perceptual sensitivity while revealing temporally dissociable influences of WM and motivation during perceptual decision making. Together, our findings demonstrate that the joint effects of motivation and working memory arise from distinct computational and temporal mechanisms, providing a unified framework for understanding top-down regulation of human perception.