Two experiments used error-detection to determine the reason for 3-year olds' perseverative errors on the postswitch phase of the Dimensional Change Card Sort. Results implied that perseveration cannot be attributed to difficulty inhibiting prepotent motor responses, but that changes in rule use between 3 and 5 years are more likely to increase…

Three experiments explored determinants of two-year olds' perseverative errors in a search task. Found that active search, even in the absence of observation, produced perseveration on post-switch trails, but mere observation did not. Results indicated that active search is required to elicit perseveration, which points to failures of response…

Provided 2- and 2.5-year-olds with partial visual information about a ball's path as it moved toward a hiding place. Found that both age groups were equally proficient at tracking the ball as it rolled behind a transparent screen with 4 opaque doors, but 2.5-year-olds were more likely to reach to the correct door when asked to find the ball.…

Investigated 3-year-olds' understanding of the appearance-reality distinction using verbal response and nonverbal response paradigms in 4 experiments. Found that about 30 percent of children were correct in verbal paradigm; over 90 percent of same children were correct in nonverbal paradigm. Participating in the verbal paradigm impeded children's…

Four experiments examined 8- to 12-month olds on search and nonsearch A not B tasks, a one-location task, and control tasks. Results indicated memory for where object was hidden and expectations of where it should be found. The effect occurred at delays at which infants made the A not B error when searching, and at a longer 15-second delay.…