The sense of agency is reduced by stimulus variability but has a limited effect on perceived variability.

Research has shown that the sense of agency depends on various sources of information and can influence other cognitive processes such as visual attention and memory. This study examines whether stimulus variability is another factor that either influences or is influenced by the sense of agency. Stimulus variability reflects environmental uncertainty, which is closely linked to the sense of agency. We hypothesized that a reduced sense of agency increases perceived variability and that higher stimulus variability diminishes the sense of agency. Participants in four experiments moved 40 circle stimuli for 3 s, with a 1 s delay introduced in half the trials to reduce the sense of agency. In Experiments 1-3, color variability was manipulated. Participants reported the perceived color variability (Experiment 1), their sense of agency (Experiment 3), or both (Experiment 2). While the delay manipulation did not influence perceived color variability, color variability reduced the agency ratings. Notably, the effect of color variability emerged only when participants reported both perceived color variability and their agency ratings (Experiment 2), and it disappeared when the color variability was task-irrelevant (Experiment 3). Experiment 4 extended this design to motion-direction variability, and a similar pattern was observed where direction variability reduced the agency ratings but the delay had no effect on perceived direction variability. Together, these results suggest that stimulus variability can influence the sense of agency in a unidirectional manner and that this effect is modulated by the task relevancy of variability information.