Our continuing research focuses on higher order cognitive processing in nonhuman primates In addition to our work on spatial memory, we are now determining whether monkeys can make inferences about hidden movements (complex Piagetian tasks) or understand cause-effect relationships A total of 15 monkeys were tested in various paradigms involving hidden movements These included tasks in which objects were moved to different containers behind a screen and the animal had to infer the movement from seeing that the containers were now empty (transfer task) as well as tasks in which a treat rolled down an inclined ramp and disappeared behind a screen containing several doors (ramp task) In general, monkeys failed to comprehend these hidden movements suggesting that their representational skills are more limited than those of the great apes The monkeys were also exposed to tool using tasks in which the animals were given access to both a working tool (i e , pullin g it resu lted in retrieving a treat) and a nonworking tool (i e , pulling it resulted in the treat falling into a hole or getting stuck by a barrier) In general, the monkeys did not appear to understand cause-effect relationships and showed no initial ability to differentiate between types of tools In all the tests, a few monkeys got better with repeated trials However, their improved performance appeared to be related to the development of simple strategies rather than to comprehension of the problem itself Monkeys with SIB were also tested in this paradigm and interestingly performed better than controls on most tasks Future research will be directed to understanding the differences in performance between monkeys with SIB and controls PUBLICATIONS deBlois, S T , Novak, M A , & Bond, M (1998) Object permanence in orangutans (Pongo pygmaeus) and squirrel monkeys (Saimiri sciureus) Journal of Comparative Psychology, 112, 137-152 Platt, D M , & Novak, M A (1999) Perception of novel changes in a familiar environment by socially housed rhesus monkeys American Journal of Primatology, 47, 117-131 de Blois, S T , & Novak, M A (1998) Do monkeys with self-injurious behavior (SIB) act impulsively in cognitive tasks? American Journal of Primatology 45, 176
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