Do monkeys fidget? Using movement analysis to understand the role of gaze direction on non-instrumental object manipulation: stone handling in Balinese long-tailed macaques

Abstract

Stone handling (SH) is a form of playful and repetitive object-directed manipulation performed by some non-human primates. SH includes approximately 40 behavioural patterns using the hands, feet, and mouth. Within a SH pattern, there are subtle variations in the manner they are performed (e.g., less rigid appearance). Currently, the psychological mechanisms underlying the performance of SH are poorly understood. This thesis aimed to examine the performance variations and subsequent structural variations in two SH patterns performed by Balinese long-tailed macaques: rubbing a stone on the ground and pounding a stone on the ground. Movement analyses revealed, for each SH pattern, two distinct variations correlated with gaze direction. The implications of these results were explored using information about fidgeting to hypothesize about potential relationships between SH, object play, and fidgeting.