Abstract # 4388 Poster # 141:

Scheduled for Friday, June 22, 2012 07:00 PM-09:00 PM: Session 22 (Gardenia) Poster Presentation


CAPTIVE SQUIRREL MONKEYS DEMONSTRATE END-STATE COMFORT ON A GRASPING TASK

S. L. Zander1, P. G. Judge1 and D. J. Weiss2
1Bucknell University, Animal Behavior Program, Lewisburg, PA 17837, USA, 2Psychology Department, The Pennsylvania State University, University Park, PA, 16802, USA
line
     Humans demonstrate motor planning when initially grasping an object in an uncomfortable position in order to allow for a more comfortable end-state position. An example of this “end-state comfort” effect occurs when a waiter grasps an upside-down glass with the thumb pointing downward so that the ending position will be comfortable for pouring into the cup. This form of motor planning has only been demonstrated in humans and a few species of nonhuman primates. We tested for the same effect in six squirrel monkeys (Saimiri sciureus) by presenting them with a transparent stemmed cup with a desired food item secured within the bowl of the cup. Once a monkey grasped the cup by the stem, it could place its head into the cup and retrieve the reward. The cup was presented in either an upright or an inverted position. When the cup was presented with the bowl facing upward, all subjects in all trials grasped the cup with a comfortable, thumb-up hand orientation. Conversely, when the bowl of the cup was facing downward, 4 of the 6 subjects spontaneously adopted the uncomfortable, thumb-down grasp on their first presentation, thus exhibiting end-state comfort (Fisher’s Exact Test, p=.03). Ours was the first demonstration of this type of motor planning in squirrel monkeys and provides comparative data for understanding the phylogenetic origin of complex planning processes in nonhumans.