The platyrrhine primate Cebus imitator uses gaze to adjust grasp posture for food handling and withdraw to the mouth

Abstract

Orienting a food item held in the hand to withdraw it to the mouth for eating is mediated by vision in catarrhine anthropoids and by nonvisual strategies in strepsirrhines. The present study asks whether vision contributes to the withdraw in a platyrrhine anthropoid, a member of a monophyletic primate suborder whose stem group diverged from catarrhines about 40 million years ago. We examined gaze and hand use in arboreal fruit picking by the Costa Rican capuchin, Cebus imitator, a platyrrhine known for its skilled object-handling and tool use. Videos clips of reach, grasp and withdraw movements and associated gaze were examined frame-by-frame to assess hand shaping and sensory control of eating. Cebus imitator used vision and touch to reach for and grasp food items with precision or whole hand grasps. They used vision to orient food items held inhand into a precision grip and their withdraw of food items to the mouth was assisted with a vertically oriented hand. The conjoint use of vision, grasp and hand posture by capuchins is discussed in relation to the staged evolution of visual manipulation of objects, one of which is featured in this platyrrhine primate.