| Summary: | The main goal of this dissertation was to examine rhesus macaque and preschool child performance on invisible displacement tasks. In Study 1, rhesus monkeys were tested on a ramp task wherein an object rolled down a ramp behind four doors. An obstacle was placed along the ramp at one of four doors, and monkeys had to open the door nearest to the obstacle. Macaques were unable to locate the object until they were provided with cuing trials. In Study 2, macaques were tested on a vertical tube task. The tube had an occluding panel with three doors and an obstacle that was placed beneath one of the doors. Three of six monkeys were able to solve this task without any cuing. Subsequent studies manipulating the number of available doors identified the length of trajectory of the falling object as aiding performance. In Study 3, monkeys were tested on a trajectory task consisting of an apparatus with three tubes, each extending from the top of the apparatus into three widely spaced cups. The animals were shown a predetermined length of the object's trajectory (ranging from 15 cm to 35 cm) before it disappeared behind an occluding panel. Ten of eleven monkeys were able to solve the task. Young adults were initially affected by the trajectory length but were able to solve the task after minimal experience. In contrast, both elderly and juvenile macaques partially solved the task when given the maximum amount of information. Subsequent tests showed that performance of juvenile macaques was related to trajectory information whereas elderly macaques used a strategy of searching where the object was last seen. In the final four studies, we investigated the failure of preschool children to solve the ramp task. We conducted various manipulations to promote integration of the obstacle into the child's solution, none of which markedly improved performance. In conclusion, macaques appear to (1) have difficulty understanding the contact-mechanics between objects and obstacles and (2) use trajectory information to solve invisible displacement tasks. Children, however, appear unable to incorporate the obstacle into their solution even with the addition of cues.
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