Analysis of a constraint on perception, cognition, and development: one object, one place, one time

It has become increasingly common for theories to rely on a constraint that 1 object cannot be in more than 1 place at the same time. Analysis suggests that a 1 object–1 place–1 time constraint as literally stated is false, that a modified constraint is biased toward the visual modality, that it may not be a correct description of the physical world, is not true of how objects must appear on sensory surfaces, and does not mean that 2 simultaneous spatially separated samples must be interpreted as 2 different objects, even for vision. However, once such object numerosity or identity is determined in some other way, then a modified constraint can be used to trigger learning, such as prism adaptation. A far-removed implication is that “Where is an object? ” may be a misleading question. A number of psychological theories assume that one object cannot be in more than one place at one time. For instance, in attention theories, “object files ” (Kahneman, Treisman, & Gibbs, 1992) are created on the basis of location. Similarly, “indexes ” (Pylyshyn, 1989, 1994) are assigned and accessed by location. In both theories, entities in two locations at the same time get two distinct object files or indexes, one for each location. The assumption is even more promi-nent when location-based theories are extended to infants ’ perception of objects: “Because objects are indexed by location, seeing two objects in different locations at the same time forces the assignment of two indexes: therefore two individual objects are inferred ” (Leslie