Several studies point to increased impulsivity in monkeys with SIB. Therefore, one would expect monkeys with SIB to perform less well than controls on cognitive tasks that required vigilance. To test this hypothesis, we gave object permanence problems to rhesus monkeys (Macaca mulatta) with and without SIB. The experimental group consisted of 11 monkeys with a veterinary record of self-inflicted wounding. The control group consisted of 8 monkeys that did not exhibit SIB and matched insofar as possible for age and room location. Testing consisted of three types of problems. On Invisible transfers, a treat was placed into one of the three boxes, the box was moved next to another box, and the treat was transferred. Visible transfers were similar except that space was left between the two boxes so that the transfer could be observed. On No transfer problems, the object remained in the first box. This, on all problems the monkeys had to watch a complex sequence of event before they could respond. However, Invisible transfers were most difficult because the monkeys had to infer that an object displacement occurred. SIB monkeys performed better than control monkeys on all problems and all but two SIB monkeys reached a success criterion on Invisible transfers whereas only half of the control monkeys did. Thus, SIB monkeys were superior to control monkeys on cognitive tasks requiring vigilance. These results question the idea that SIB monkeys are impulsive during cognitive testing.
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