Tool-using in rhesus monkeys and 36-month-old children: Acquisition, comprehension, and individual differences

The main objective of this dissertation was to characterize the tool-using ability of rhesus monkeys and children by examining the acquisition and comprehension of tool-using behavior, and by identifying factors that might be related to individual differences in the ability to use tools. The first study examined whether twenty rhesus monkeys could use a rake to extend reach, whether they understood the required properties of the tool, and whether tool-using ability was correlated with behavioral characteristics. Fifteen monkeys used the rake to retrieve treats placed out-of-reach; however, none of the monkeys tested selected an effective rake from an ineffective rake. The level of tactile oral exploration in non-tool-using contexts was positively correlated with the number of rewards retrieved. The second study examined whether rhesus monkeys could use a rod to insert and probe and whether they understood the effects of using the tool. Only two monkeys used a rod to push a reward out of a clear tube. Subsequent manipulations involving multi-tube combinations, in which only one tube was baited, indicated that the monkeys were unable to select the correct path or tube. However, these monkeys correctly selected the baited tube over empty tubes when the tubes were presented on separate walls. The third study examined whether rhesus monkeys and 36-month-old children were able to use two different tools in series to retrieve a desired object. Both of the two monkeys tested used a rake to retrieve a rod and then used the rod to push a reward out of a clear tube, and all but one of the children tested used the tools in series either on their own or following hints or demonstrations. The fourth study revealed that certain types of object manipulation and behavior were related to tool-using ability in monkeys. In summary, this dissertation characterized tool-using in rhesus monkeys and children, validated new procedures for assessing comprehension in tool-using tasks, and identified certain factors related to individual differences in tool-using ability. The implications of these results are discussed