Investigators have traditionally claimed that infants do not begin to view objects as permanent until 9 or 10 months of age. However, preliminary studies indicate that infants as young as 5 months of age recognize that objects continue to exist when occluded. The research described in this proposal builds on the results of these initial studies. Three general issues will be addressed. The first concerns infants' ability to represent the physical and spatial properties of objects and to use this information to reason about simple occlusion events. Two types of occlusion events will be investigated. In one, a stationary object will be placed in the path of a moving screen. The proposed experiments will test whether infants represent information about the height and location of the object and use this information to predict when the screen should stop. In the second type of occlusion sequence, an object will travel along a track, part of which will be occluded by a screen. The proposed experiments will test whether infants represent information about the height of the object and use this information to determine whether a portion of the object should remain visible above the screen. The second issue is closely related to the first. It concerns infants' ability to make inferences about properties of occluded objects. One experiment will examine whether infants can infer the distance an object travels behind a screen, based on its speed of movement and the duration of its occlusion. Other experiments will test whether infants can infer where an object is hidden, based on specific types of cues. For instance, if shown a flat cover and a cover with a distinct lump, will infants realize that the object must be hidden under the lumpy cover? The third issue concerns the development of infants' reasoning about occluded objects. At what age do infants understand that a stationary object continues to exist when occluded, or that a moving object continues to exist and pursues its trajectory behind an occluder? At what age do infants become able to represent and use information about the physical and spatial properties of occluded objects? Finally, when do infants become able to make inferences about the physical features and spatial properties of occluded objects? The research described in this proposal has implications for two, hitherto disjoint areas of infancy research: infants' object concept, and infants' knowledge of the physical world.