Pulling to scale: Motor planning for sequences of repeated actions by cotton-top tamarins (Saguinus oedipus).

Previous research has demonstrated that nontool-using primates are capable of sophisticated motor planning for a single action. The present study extends this work by asking whether monkeys are capable of planning a sequence of repetitive motor actions to accommodate a task demand. We presented tamarins with a tape measure baited with a food reward at near or far distances and measured their manual intergrasp distances as they reeled in the food. In Condition 1, subjects viewed the reward as they pulled, whereas in Condition 2, they received no visual feedback during pulling. Across both experiments, we found that the intergrasp distance in Near trials was significantly smaller than in Far trials, an effect that was demonstrated even during the first two pulls of each trial. These results suggest that tamarins prospectively scale their intergrasp distances in accordance with the distance to the goal. These findings provide further support for the lengthy evolutionary history of sophisticated motor planning abilities in primates.