Repeated short presentations of morphed facial expressions change recognition and evaluation of facial expressions.

This study investigated whether sensitivity to and evaluation of facial expressions varied with repeated exposure to non-prototypical facial expressions for a short presentation time. A morphed facial expression was presented for 500 ms repeatedly, and participants were required to indicate whether each facial expression was happy or angry. We manipulated the distribution of presentations of the morphed facial expressions for each facial stimulus. Some of the individuals depicted in the facial stimuli expressed anger frequently (i.e., anger-prone individuals), while the others expressed happiness frequently (i.e., happiness-prone individuals). After being exposed to the faces of anger-prone individuals, the participants became less sensitive to those individuals' angry faces. Further, after being exposed to the faces of happiness-prone individuals, the participants became less sensitive to those individuals' happy faces. We also found a relative increase in the social desirability of happiness-prone individuals after exposure to the facial stimuli.