Anti-expressions: Artificial control stimuli for the visual properties of emotional facial expressions

The perceptual/cognitive processing for emotional facial expressions is effective compared to that for neutral facial expressions. To investigate whether this effectiveness can be attributed to the expression of emotion or to the visual properties of the facial expressions, we used computer morphing to develop a form of control stimuli. These “anti-expressions” changed the features in emotional facial expressions in the opposite direction from neutral expressions by amounts equivalent to the differences between emotional and neutral expressions. To examine if anti-expressions are usable as emotionally neutral faces, 35 participants were asked to categorize and rate the valence and arousal dimensions of six basic emotions for normal and anti-expressions. The results indicate that anti-expressions were assessed as neutral for anger, disgust, fear, and happiness, and these can be used as control stimuli in emotional facial expressions regarding visual properties.