Spontaneous Encoding of Event Roles in Hominids

When observing social interactions, humans rapidly and spontaneously encode events in terms of agents, patients and causal relations. This propensity can be made visible empirically with the switch cost paradigm, a reaction time experiment and well-established tool of cognitive psychology. We adapted the paradigm for non-human primates to test whether non-linguistic animals encoded event roles in the same way. Both human and non-human participants were requested to attend to different social interactions between two artificially coloured (blue or green) actors and to target the actor masked by a specified colour (e.g., blue), regardless of her role. We found that when we switched the targeted colour mask from agents to patients (or vice versa) the processing time significantly increased in both hominid species (i.e., human and chimpanzee), suggesting that event roles were spontaneously encoded and subsequently interfered with our simplistic colour search task. We concluded that the propensity to encode social events in terms of agents and patients was a common feature of hominid cognition, as demonstrated in several human and one chimpanzee participant, pointing towards an evolutionarily old and phylogenetically shared cognitive mechanism central to language processing.