Resource bounds on mental simulations: Evidence from a liquid-reasoning task

People are able to reason about the physical dynamics of everyday objects. But, there are theoretical disagreements about the computations that underlie this ability. One proposal is that people are running an approximate mental simulation of their environment. However, such a simulation must be limited in its resources. We applied the notion of a resource-bound simulation to a task of reasoning about liquids, and show that people’s changing behavior can be explained by an approximate simulation that hits a resource limit after some time elapses. In Experiments 1 and 2, people performed well on tasks that asked them to estimate the time-to-fill and water level of different containers, when filled over short periods of time (1-7 seconds). Experiment 3 shows systematic biases in visual volumeestimation, which further strengthens the proposal that people are using a simulation to solve the first two experiments. Experiment 4 extends the reasoning time for the time-to-fill task, and shows the existence of a ‘switch point’, as expected from a resource-bound simulation model. The model also accounts for individual differences: People who perform worse on a digit-span task have an earlier switch point. Our work argues for the theoretical proposal that people are using mental simulations to reason about intuitive physics, but further informs the suggestion that these simulations are limited in resources.