Eye movements reveal sustained implicit processing of others' mental states

The ability to attribute mental states to others is crucial for social competency. To assess mentalizing abilities, in false-belief tasks participants attempt to identify an actor's belief about an object's location as opposed to the object's actual location. Passing this test on explicit measures is typically achieved by 4 years of age, but recent eye movement studies reveal registration of others' beliefs by 7 to 15 months. Consequently, a 2-path mentalizing system has been proposed, consisting of a late developing, cognitively demanding component and an early developing, implicit/automatic component. To date, investigations on the implicit system have been based on single-trial experiments only or have not examined how it operates across time. In addition, no study has examined the extent to which participants are conscious of the belief states of others during these tasks. Thus, the existence of a distinct implicit mentalizing system is yet to be demonstrated definitively. Here we show that adults engaged in a primary unrelated task display eye movement patterns consistent with mental state attributions across a sustained temporal period. Debriefing supported the hypothesis that this mentalizing was implicit. It appears there indeed exists a distinct implicit mental state attribution system.