How to pour a cup of coffee
- 1Technical University of Darmstadt
Abstract
Pouring a drink feels deceptively trivial, yet it requires guiding a boundary-free fluid into a vessel without spilling, overflowing, or toppling it -- a task at which robots remain notoriously brittle. How humans achieve this so effortlessly is unknown, as motor control has predominantly been studied in brief, highly constrained laboratory tasks, leaving the control principles underlying ecological tasks largely unknown. Here we measured continuous sensorimotor control during liquid pouring across various containers, vessels, and speed demands. Despite substantial variation in movement trajectories and durations, individuals maintained a strikingly invariant preferred fill level. Counterintuitively, fill level variability decreased at higher fill levels, and precision was maintained even under time pressure. A stochastic optimal control model combining a data-driven nonlinear approximation of flow dynamics with a cost that balanced individualised fill level, energy expenditure and flow-rate reproduced the behaviour. Humans thus pour optimally, given their sensorimotor limits and idiosyncratic notion of "full".
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BibTeX
@misc{midlagajni2026pour,
title = {{How to pour a cup of coffee}},
author = {N. Midlagajni and R. W. Fleming and C. A. Rothkopf},
howpublished = {bioRxiv},
year = {2026},
month = aug,
doi = {10.64898/2026.08.26.746627},
url = {https://www.biorxiv.org/content/10.64898/2026.08.26.746627v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - How to pour a cup of coffee
AU - N. Midlagajni
AU - R. W. Fleming
AU - C. A. Rothkopf
PY - 2026
DA - 2026/08/26
PB - bioRxiv
DO - 10.64898/2026.08.26.746627
UR - https://www.biorxiv.org/content/10.64898/2026.08.26.746627v1
AB - Pouring a drink feels deceptively trivial, yet it requires guiding a boundary-free fluid into a vessel without spilling, overflowing, or toppling it -- a task at which robots remain notoriously brittle. How humans achieve this so effortlessly is unknown, as motor control has predominantly been studied in brief, highly constrained laboratory tasks, leaving the control principles underlying ecological tasks largely unknown. Here we measured continuous sensorimotor control during liquid pouring across various containers, vessels, and speed demands. Despite substantial variation in movement trajectories and durations, individuals maintained a strikingly invariant preferred fill level. Counterintuitively, fill level variability decreased at higher fill levels, and precision was maintained even under time pressure. A stochastic optimal control model combining a data-driven nonlinear approximation of flow dynamics with a cost that balanced individualised fill level, energy expenditure and flow-rate reproduced the behaviour. Humans thus pour optimally, given their sensorimotor limits and idiosyncratic notion of "full".
ER -