Numerical Estimation of Faces: Our Personality and the Facial Expressions of Others Affect Estimation Accuracy

We examined whether high arousal (caffeine, introversion) causes overestimates of numbers of people. Participants consumed caffeine or decaf and estimated numbers of faces differing in emotionality. Larger sets were increasingly underestimated, especially for neutral and threatening faces. Personality and facial emotion, and caffeine and emotion, significantly interacted to affect estimates.