Abstract
In real life, facial expressions are fleeting occurrences that appear suddenly, like a burst of happiness or flash of anger, and then, just as quickly, the expression vanishes from the face. What are the brain mechanisms that allow us to discern the rapid onset and offset of facial expressions quickly and effortlessly? In this study, we examine the neural correlates of dynamic facial expressions using event-related potentials (ERPs). Participants were presented with happy, angry or neutral faces while EEG was recorded from 36 scalp electrodes. In the expression onset condition, a neutral face was presented for 500 ms, immediately followed by either a happy or angry face for 500 ms. In the expression offset condition, the happy or angry face was shown for 500 ms, immediately followed by a face with a neutral expression for 500 ms. The onset and offset conditions were compared to a static condition in which a single happy, angry and neutral face was shown for 500 ms. The EEG data showed that in the right posterior scalp sites, the onset of the happy or angry expression elicited a larger potential than their static versions suggesting that dynamic faces are more salient than static images. Moreover, the direction of the dynamics appears to be critical where the onset expressions produced larger brain potentials than offset expressions. These findings indicate that observers are more sensitive to the dynamic expressions than static expressions. However, the direction of the facial dynamics also seems important where the sudden appearance of a facial expression elicited more brain activity than its abrupt disappearance.