Changes in expectation impact multiple steps of the visual perceptual decision process in adults

Perceptual decision-making processes, particularly in the context of eye movements and reaction times (RT), have been studied to better understand how the brain integrates and responds to sensory information. Recent models have decomposed the process into multiple intermediate steps, including detection, instruction processing, decision, and motor response. To investigate the impact of the observer's expectations on each of these steps, we conducted two experiments on 24 participants (including both female and male participants), manipulating respectively the stimuli's location expectation (left or right) and the eye movement expectation (saccade or antisaccade). The results revealed limited evidence for the influence of location expectation on saccadic RT and moderate evidence for antisaccadic RT. Conversely, there was strong evidence of the influence of movement expectations on both movements' RT. This suggests an asymmetric impact of expectations on the different steps of perceptual decision-making, with strong impact on motor response and instruction processing. These findings challenge the common attribution of expectation effects solely to the decision-making module from previous works, emphasizing the importance of considering multi-module integration in perceptual decision models.