Local Motion Pooling Is Continuous, Global Motion Perception Is Discrete

Perceiving the motion of an object is thought to involve two stages: Local motion energy is measured at each point in space, and these signals are then pooled across space to build coherent global motion. There are several theories of how local-to-global pooling occurs, but they all predict that global motion perception is a continuous process, such that increasing the strength of motion energy should gradually increase the precision of perceived motion directions. We test this prediction against the alternative that global motion perception is discrete: Motion is either perceived with high precision or fails to be perceived altogether. Data from human observers provides clear evidence that, whereas pooling local motion energy is continuous, the segmentation of local signals into coherent global motion patterns is a discrete process. This result adds motion perception to the growing list of processes that exhibit evidence of all-or-none visual awareness. Public Significance Statement Visual perception requires that objects are isolated from other objects, a process that is accomplished in part by analyzing motion energy across space. For example, although individual parts of a running dog may be moving in many directions at any moment, all of them share motion energy in the direction he's running, which helps the visual system to build the perception of a coherently moving object. This global motion process develops early in life, and deficits in it have been identified in disorders including autism, dyslexia, and schizophrenia. Whereas current theories of global motion perception predict that motion perception is analog, taking on any value from weak to strong, here we show that it is discrete: coherent motion is either perceived nearly perfectly, or not at all. This finding suggests that current models of global motion perception, and theories of why deficits in this process occur, may require substantial revision.