Prior expectations modulate unconscious evidence accumulation

•Participants made decisions using noisy motion stimuli.•This requires information to be gradually accumulated.•We titrated conscious awareness of these stimuli using a dynamic dichoptic mask.•Unconscious decisional processes are modulated by statistical regularities.•Such modulation produces flexible and adaptive behaviour that optimises performance.•A computational model shows evidence changes in unconscious evidence accumulation.•Ruling out changes in performance as a conscious change in strategy.