Niteesh Midlagajni¹, Carola Stork¹, Jolande Fooken¹, Constantin Rothkopf¹; ¹Centre for Cognitive Science, Technical University of Darmstadt

Many everyday activities, such as pouring a glass of water, require continuous visuomotor control. Interaction between gaze and motor control during such naturalistic tasks remains poorly understood. Here, we designed a novel experimental setup, combining mobile eye tracking, object tracking, and a custom-made digital scale to investigate the visuomotor control of pouring. Twenty participants poured water from three different jugs into three different cups under two conditions: ‘self-paced’, where they poured naturally, and ‘fast’, where they were instructed to pour as quickly as possible. In both conditions, participants received no explicit instructions regarding visuomotor behavior, target fill-levels, or time constraints. Our results reveal that participants had preferred fill-levels and that gaze behavior during the task was highly consistent. Participants looked at the jug before grasping it, then rapidly shifted their gaze to the cup and held it there until pouring began. During pouring, gaze remained confined to the cup region, hovering either on the wall of the cup, the liquid surface, or the rising fill-level. Once pouring was complete, gaze became task-irrelevant, and participants returned the jug without visual guidance. To determine when gaze is most critical, we quantified the variability in gaze position as a function of fill-level. Gaze density systematically decreased as participants approached their preferred fill-level, reflecting increased visual monitoring towards the end. In the 'fast’ condition, gaze was even more concentrated throughout the task, suggesting a stronger reliance on continuous visual feedback to pour quickly. Finally, we observed individual differences in visuomotor strategies: some participants tracked the rising liquid via smooth pursuits, whereas others monitored only near the end. Notably, these differences did not affect task performance. Overall, this work demonstrates that structured visuomotor strategies emerge even in simple, naturalistic tasks, underscoring the importance of studying everyday tasks to better understand the role of natural vision.

Acknowledgements: This research was supported by the European Research Council (ERC; Consolidator Award ‘ACTOR’- project number ERC-CoG-101045783).