Macaques can predict social outcomes from facial expressions

There is widespread acceptance that facial expressions are useful in social interactions, but empirical demonstration of their adaptive function has remained elusive. Here, we investigated whether macaques can use the facial expressions of others to predict the future outcomes of social interaction. Crested macaques (Macaca nigra) were shown an approach between two unknown individuals on a touchscreen and were required to choose between one of two potential social outcomes. The facial expressions of the actors were manipulated in the last frame of the video. One subject reached the experimental stage and accurately predicted different social outcomes depending on which facial expressions the actors displayed. The bared-teeth display (homologue of the human smile) was most strongly associated with predicted friendly outcomes. Contrary to our predictions, screams and threat faces were not associated more with conflict outcomes. Overall, therefore, the presence of any facial expression (compared to neutral) caused the subject to choose friendly outcomes more than negative outcomes. Facial expression in general, therefore, indicated a reduced likelihood of social conflict. The findings dispute traditional theories that view expressions only as indicators of present emotion and instead suggest that expressions form part of complex social interactions where individuals think beyond the present.     

Long-tailed macaques display unexpected waiting abilities in exchange tasks

The ability of animals to delay gratification is crucial for complex goal-directed action. It may help them in making effective decisions when facing a choice. We tested the ability of nine long-tailed macaques (Macaca fascicularis) to delay gratification in several experiments. In exchange tasks, subjects had to keep a small piece of cookie before returning it to an experimenter in order to get a larger food amount. Results showed that animals could wait between 10 s and 10 min depending on individual and sizes of reward. In another experiment, subjects could immediately give back the initial piece of cookie then wait for the return. Their performances more than doubled, demonstrating the role of consumption inhibition in postponing gratification. Such achievements underscore delays of gratification which until now were not thought possible in monkeys. Finally, subjects were presented with an accumulation of food pieces added at short intervals until they seized them. They mostly waited between 30 s and 1 min, which points at the consistency of our data, compared to those of other studies. Our results indicate that long-tailed macaques anticipated the duration of delays. We may account for their remarkable performances by their achievements in the social context.     

Tolerant macaque species are less impulsive and reactive

Animal Cognition - Inhibitory control, the inhibition of impulsive behaviours, is believed to be key in navigating a complex social environment. Species characterised by higher social tolerance,...