Noisy Perceptual Expectations: Multiple Object Tracking Benefits When Objects Obey Features of Realistic Physics

When objects move, their motion is governed by the laws of physics. We investigated whether multiple objects that move while correctly obeying aspects of Newtonian physics are easier to track than those that do not accurately obey the laws of physics. Participants were asked to track multiple objects that either did or did not take on the correct angles and/or speeds after collisions with each other. We found an advantage for tracking when objects obeyed realistic physics, such that people were more accurate when objects reflected from each other at proper angles and when objects varied in speed after collisions (as opposed to always maintaining the same speed). This advantage was independent of a variety of low-level factors that would be expected to affect object tracking, such as object spacing. However, we also found that performance was not affected when objects' speed changed randomly after each collision (so long as it varied), nor when the reflection angles were jittered moderately after collisions. We conclude that perceptual noise seriously limits many aspects of object trajectory estimation, but nevertheless people are sensitive to at least a subset of the Newtonian laws of physics under demanding attentional tracking conditions.