Eye movements reveal the intuitive understanding of materials and their behavior

Abstract

Does a metal ball sink or float when dropped into water? Answering this intuitively simple question relies on our understanding of materials and their physics1. Knowing materials helps us to recognize objects, estimate their properties, and predict how they will behave when interacting with other objects or materials2,3. This leads to expectations about material behaviors already in young infants4,5, for example, that a metal ball should sink in water. Typically, properties and affordances of materials have been studied with perceptual tasks. But even though explicit perceptual judgments allow us to identify important determinants of material understanding, it is not clear how they relate to dynamic predictions of material behavior -- which we need for successful interactions with objects3. Here, we tap into material understanding by leveraging anticipatory eye movements, which have been shown to be direct readouts of trajectory predictions6 and can also reflect expectations about material properties such as elasticity or mass7. This allows us to reveal the temporal evolution of dynamic predictions based on material properties. Furthermore, by using novel stimuli that violate intuitive expectations about material behavior, we demonstrate that even though dynamic predictions can be learned over time, there remains a fundamental difference between predictions in line with and against our intuitive expectations.