Differential reliance of chimpanzees and humans on automatic and deliberate control of motor actions

Humans are often unaware of how they control their limb motor movements. People pay attention to their own motor movements only when their usual motor routines encounter errors. Yet little is known about the extent to which voluntary actions rely on automatic control and when automatic control shifts to deliberate control in nonhuman primates. In this study, we demonstrate that chimpanzees and humans showed similar limb motor adjustment in response to feedback error during reaching actions, whereas attentional allocation inferred from gaze behavior differed. We found that humans shifted attention to their own motor kinematics as errors were induced in motor trajectory feedback regardless of whether the errors actually disrupted their reaching their action goals. In contrast, chimpanzees shifted attention to motor execution only when errors actually interfered with their achieving a planned action goal. These results indicate that the species differed in their criteria for shifting from automatic to deliberate control of motor actions. It is widely accepted that sophisticated motor repertoires have evolved in humans. Our results suggest that the deliberate monitoring of one’s own motor kinematics may have evolved in the human lineage.     

Perceptual mechanism underlying gaze guidance in chimpanzees and humans

Previous studies comparing eye movements between humans and their closest relatives, chimpanzees, have revealed similarities and differences between the species in terms of where individuals fixate their gaze during free viewing of a naturalistic scene, including social stimuli (e.g. body and face). However, those results were somewhat confounded by the fact that gaze behavior is influenced by low-level stimulus properties (e.g., color and form) and by high-level processes such as social sensitivity and knowledge about the scene. Given the known perceptual and cognitive similarities between chimpanzees and humans, it is expected that such low-level effects do not play a critical role in explaining the high-level similarities and differences between the species. However, there is no quantitative evidence to support this assumption. To estimate the effect of local stimulus saliency on such eye-movement patterns, this study used a well-established bottom-up saliency model. In addition, to elucidate the cues that the viewers use to guide their gaze, we presented scenes in which we had manipulated various stimulus properties. As expected, the saliency model did not fully predict the fixation patterns actually observed in chimpanzees and humans. In addition, both species used multiple cues to fixate socially significant areas such as the face. There was no evidence suggesting any differences between chimpanzees and humans in their responses to low-level saliency. Therefore, this study found a substantial amount of similarity in the perceptual mechanisms underlying gaze guidance in chimpanzees and humans and thereby offers a foundation for direct comparisons between them.     

Slowly walking down to the more food: relative quantity discrimination in African spurred tortoises (Centrochelys sulcata)

Animal Cognition - Quantity discrimination, is thought to be highly adaptive as it allows an organism to select greater amounts of food or larger social groups. In contrast to mammals, the...     

Perception of the motion trajectory of objects from moving cast shadows in infant Japanese macaques (Macaca fuscata)

The shadows cast by moving objects enable human adults and infants to infer the motion trajectories of objects. Nonhuman animals must also be able to discriminate between objects and their shadows and infer the spatial layout of objects from cast shadows. However, the evolutionary and comparative developmental origins of sensitivity to cast shadows have not been investigated. In this study, we used a familiarity/novelty preferential looking procedure to assess the ability of infant macaques, aged 7–24 weeks, to discriminate between a ‘depth’ display containing a ball and cast shadow moving diagonally and an ‘up’ display containing a ball with a diagonal trajectory and a shadow with a horizontal trajectory. The infant macaques could discriminate the trajectories of the balls based on the moving shadows. These findings suggest that the ability to perceive the motion trajectory of an object from the moving shadow is common to both humans and macaques.