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we act on the world, we care which glass is ours, which object we already have retrieved, and whether all the cows that left the barn in the morning have returned. Object individuation consists of determining the numerically distinct (distinct in the sense of distinct one) objects that articulate a given scene. Studies of object individuation in infancy typically concern the simplest individuation problem: es- tablishing whether one single object or two distinct objects are involved in some event. Adults bring a wide variety of information to bear on the task of object indi- viduation, including spatiotemporal information (one object cannot be in two places at the same time), property information (a red plastic entity seen on one oc- casion is unlikely to be the same individual as a yellow cloth entity seen on an- other), and kind information (a dog cannot be the same individual as a table). Under many circumstances, spatiotemporal information is primary; if we see an enti

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The present studies investigate infants reliance on object kind information in solving the problem of object individuation. Two experiments explored whether adults, 10- and 12month -old infants could use their knowledge of ducks and cars to individuate an ambiguous array consisting of a toy duck perched on a toy car into two objects. A third experiment investigated whether 10-month-old infants could use their knowledge of cups and shoes to individuate an array consisting of a cup perched on a shoe into two objects. Ten-month-old infants failed to use object kind information alone to resolve the ambiguity with both pairs of objects. In contrast, infants this age succeeded in using spatiotemporal information to segment the array into two objects, i.e. they succeeded if shown that the duck moved independently relative to the car, or the cup relative to the shoe. Twelve-month-old infants, as well as adults, succeeded at object individuation on the basis of object kind information alone.

Four experiments investigated whether 12-month-old infants use perceptual property information in a complex object individuation task, using the violation-of-expectancy looking time method (Xu, 2002; Xu & Carey, 1996). Infants were shown two objects with di#erent properties emerge and return behind an occluder, one at a time. The occluder was then removed, revealing either two objects (expected outcome, if property di#erences support individuation) or one object (unexpected outcome). In Experiments 1--3, infants failed to use color, size, or a combination of color, size, and pattern di#erences to establish a representation of two distinct objects behind an occluder. In Experiment 4, infants succeeded in using cross-basic-level-kind shape di#erences to establish a representation of two objects but failed to do so using withinbasic -level-kind shape di#erences. Control conditions found that the methods were sensitive. Infants succeeded when provided unambiguous spatiotemporal information for two objects, and they encoded the property di#erences during these experiments. These findings suggest that by 12 months, di#erent properties play di#erent roles in a complex object individuation task. Certain salient shape di#erences enter into the computation of numerical distinctness of objects before other property di#erences such as color or size. Since shape di#erences are often correlated with object kind di#erences, these results converge with others in the literature that suggest that by the end of the first year of life, infants# representational systems begin to distinguish kinds and properties.

Nearly all research on concepts in cognitive psychology is research on categories of objects — categories of teapots or turnips, for example. But when it comes to things that are important to us — people, pets, works of art, special places — we also represent the individuals themselves, not just the categories they belong to. Proper nouns, such as Herman Melville, Toto, Broadway Boogie-Woogie, or Hudson Bay, can denote these individuals, but you can also represent individuals for whom you have no conventional names, like the bed you usually sleep in or your neighbor’s mulberry tree. It is Doug Medin who is mainly responsible for calling category researchers ’ attention to the importance of individual concepts. Medin and Schaffer’s (1978) Context Model proposed that much of what we know about categories we determine from our memories of their exemplars. It’s hard to overestimate the importance of this model: Not only has it produced generations of similar theories of categorization (e.g., Kruschke, 1992; Nosofsky, 1986), but it has also influenced fields as diverse as the psychology of attention (Logan, 2002), social psychology (Smith & Zarate, 1992), and phonology information that concepts afford (e.g., Medin, 1989; Medin & Ortony, 1989), but he still retains a fondness for exemplars. In fact, this tension in Doug’s thinking about concepts is characteristic of a special turn of mind, a form of reasoning that we’re tempted to call “modus medins ” and that the following schema approximates:

Manual search for totally occluded objects was investigated in 10-, 12- and 14-monthold infants. Infants responded to two types of total hiding in different ways, supporting the inference that object permanence is not a once-and-for-all attainment. Occlusion of an object by movement of a screen over it was solved at an earlier age than occlusion in which an object was carried under the screen. This dissociation was not explained by motivation, motor skill or means–ends coordination, because for both tasks the same object was hidden in the same place under the same screen and required the same uncovering response. This dissociation generalized across an experimentally manipulated change in recovery means—infants removed cloths while seated at a table in Expt 1 and were required to crawl through 3-D space to displace semi-rigid pillows in Expt 2. Further analysis revealed that emotional response varied as a function of hiding, suggesting an affective correlate of infant cognition. There are four empirical findings to account for: developmental change, task dissociation, generalization of the effects across recovery means, and emotional reactions. An identity-development theory is proposed explaining these findings in terms of infants’

When an object moves behind an occluder and re-emerges, 4-month-old infants perceive trajectory continuity only when the occluder is narrow, raising the question of whether time or distance out of sight is the important constraining variable. One hundred and forty 4-month-olds were tested in five experiments aimed to disambiguate time and distance out of sight. Manipulating the object’s visible speed had no effect on infants ’ responses, but reducing occlusion time by increasing object speed while occluded induced perception of trajectory continuity. In contrast, slowing the ball while it was behind a narrow or intermediate screen did not modify performance. It is concluded that 4-month-olds perceive trajectory continuity when time or distance out of sight is short. In everyday environments, the objects that we encounter frequently pass into and out of sight as our view of them is obstructed by nearer objects, and yet we perceive these objects as enduring entities. Additionally, when objects move, we perceive their trajectories as continuous even though they may be invisible for part of their path of movement. This ability to fill in the gaps in perception is a fundamental aspect of object perception, and important questions arise regarding its developmental origins. Early work investigating young infants ’ perception of events in which an object passes behind a screen was framed in terms of infants ’ knowledge of object permanence. For instance, Bower, Broughton, and Moore (1971) reported that 2-month-olds anticipated the re-emergence of an object from behind a screen, evidence for object permanence. Moreover, they showed tracking disruption (i.e., oculomotor search) when an object emerged from behind a screen too soon, but not when it changed its form behind the screen, and Bower et al. (1971) interpreted this as indicating a difficulty in integrating object

Using the violation-of-expectancy method, we investigated 10-month-old infants’ ability to rely on dynamic features in object individuation processes. Infants were first familiarized to events in which two different objects repeatedly appeared and disappeared, one at a time from behind a screen; at test, the screen was removed, revealing either one or two objects. In Experiment 1, one self-moving non-rigid agent and one inert object were involved in each trial, while in Experiment 2 two different agents were presented. Infants preferred to look at one-object outcomes in Experiment 1, but they did not show any preference for one- or two-object outcomes in Experiment 2. The results suggest that infants can use dynamic information to detect agents in complex individuation tasks before they can rely on shape or surface features. We propose that the sortals AGENT and INERT OBJECT appear in development before 12 months without a substantial contribution of linguistic experience. These findings may motivate a revision of current theories on the development of kind-based individuation and object files.

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