Cues to object persistence in infancy: Tracking objects through occlusion vs. implosion

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Abstract

Objects in the real world frequently move in and out of view, as when they pass behind occluding surfaces. Even infants are able to keep track of objects over time and motion in such situations, despite long occlusion intervals. What factors support and constrain this ability? Research on mid-level vision in adults suggests that persisting object representations are constrained by the precise manner of an item's disappearance at an occluding boundary. Here we explore the power of this cue, in a study of infants' numerical representations. Infants were habituated to dynamic displays of either 2 or 3 randomly moving identical items, which disappeared and reappeared from behind occluders. In the Occlusion condition, the items disappeared and reappeared gradually, via normal accretion and deletion cues along a single edge. In the Implosion condition, the items still disappeared and reappeared gradually (and at the same rate), but did so from all contours simultaneously — ‘imploding’ out of existence and then ‘exploding’ into existence. In a test phase, which was identical across both conditions, infants' looking times were then assessed to 2 versus 3 moving objects without occluders. Infants in the Occlusion condition looked longer to test displays with a novel number of objects compared to habituation, but infants in the Implosion condition showed no such preference for the number of objects. Thus, only infants in the Occlusion condition were able to establish representations of a constant number of items over habituation. We conclude that the local manner in which an item disappears and reappears serves as a fundamental cue to the maintenance of numerical identity over time: occlusion is a cue that an object has gone out of sight, while implosion is a cue that an object has gone out of existence. More generally, these results are consistent with the idea that the same types of representations are being studied in adult mid-level vision and infant object cognition.

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