Abstract
Beyond seeing objects in terms of their lower-level features, such as color and motion, we also see them in terms of seemingly higher-level properties, such as their masses, and the physical forces acting upon them. Determining objects’ masses from sensory data is not always straightforward: for example, if we see one object accelerate more slowly than another object, this could reflect the same force acting on objects of different masses, different forces acting on objects of the same mass, etc. In Experiments 1 and 2, we asked whether the visual perception of the relative masses of two ‘launched’ objects influences our perception of those objects’ relative sizes on the screen. When two stationary objects were simultaneously struck by a common launching object, observers reliably saw the slower-accelerating of the two as larger on the screen (a visual ‘weight-size illusion’) — and this effect was attenuated when the objects were instead struck independently by two unconnected launchers (rendering ambiguous whether their different accelerations were due to a difference in mass or to a difference in imparted force). In Experiments 3 and 4, we tested whether the apparent relative mass of two objects on either side of a fulcrum influences our perception of their relative size on the screen. Observers tended to see the heavier-looking object (when the seesaw ‘tipped’, the descending object; when the seesaw remained still, the lower object) as larger — an effect which depended critically on drawing the connecting ‘seesaw’ line between the two objects to convey their participation in the same force system. All four experiments support the conclusion that we automatically see objects in terms of their masses in a way that (1) depends on sophisticated analysis of the forces at play in a scene, and (2) influences the perception of other visual properties.