Preliminary Assessment of Siamang (Symphalangus syndactylus) Cognition Using Digital Cognition Testing Software and Touchscreen Technology

Studies of nonhuman primate cognition have traditionally employed subjects from the monkey (Cercopithecoidea) and ape (Hominidae) lineages, with relatively much less examination of the phylogenetically intermediate gibbons (Hylobatidae). To begin to rectify this gap in our understanding of primate cognition, we used a short-term training and testing method to preliminarily evaluate siamang gibbon (Symphalangus syndactylus) performance on a battery of standardized cognitive tasks, using Monkey CANTAB cognition testing software (Lafayette-Campden Neuroscience) and a computer touchscreen apparatus. Five different operant tasks examining distinct perceptual and cognitive functions were used to train and test each subject over a period of five weeks. Over 1900 cognitive testing trials were completed with three subjects. Despite limited training and testing opportunity, all siamangs achieved proficiency scores well above chance (> 65%) in both Concurrent Discrimination and Spatial Working Memory tasks. Over the limited training opportunities available, our subjects did not achieve proficiency in Delayed Match-to-Sample, Paired Associates Learning, or Conditional Visual Discrimination tasks; however, subjects did exhibit (to varying degrees) improved performance in these tasks, suggesting that additional training may lead to higher proficiency and that siamangs demonstrate effective, task-based learning capabilities. We present one of the first successful tests of a hylobatid ape using touchscreen cognitive testing methods and demonstrate that hylobatids can be evaluated using the same methods now commonly employed in tests of other nonhuman primates. Further, our testing regime proved to be behaviorally rewarding for our subjects, suggesting that hylobatids may benefit from advanced forms of interactive cognitive enrichment.