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Joshua Susskind, Melissa Ellamil, Adam Anderson; Emotional anti-faces reveal contrastive coding of facial expressions. Journal of Vision 2009;9(8):453. doi: 10.1167/9.8.453.
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It is widely thought that facial expressions are recognized in relation to one of six or more basic prototypes, with cross cultural and neuropsychological studies supporting these prototypes as the fundamental building blocks of emotional representation (Ekman, 1999). However, little work has examined directly whether there is a non-arbitrary underlying logic based on physical movements of the face that can explain why expressions look the way they do. Why do we raise our brows in fear and wrinkle our noses in disgust? According to evolutionary accounts, facial movements serve adaptive functions to regulate an organism's interaction with the environment. Confirming this view, we recently demonstrated that production of fear and disgust expressions has opposing effects on sensory intake, with fear increasing and disgust decreasing visual field size, saccadic velocity, and nasal inspiration (Susskind et al, 2008, Nature Neuroscience 11, 843–850). We reasoned that these opposing physical actions have come to represent important social cues for recognizing emotions in the face. Specifically, we hypothesized that the brain would represent expressions as perceptual opposites through opponent neural coding. Employing a computational model of facial appearance, we created a set of photorealistic expression prototypes and their visual-statistical opposites (i.e., emotional anti-faces). Categorization data revealed that not only do emotional anti-faces physically oppose basic emotion prototypes, but subjectively convey opposing emotional meanings. We next tested the effects of perceptually adapting to emotional faces and anti-faces on expression discrimination. As predicted by opponent coding, adapting to facial expressions impaired expression discrimination, and adapting to their anti-faces enhanced expression discrimination. Analogous results were found for discrimination of fear, disgust, happiness, and sadness. These results provide evidence for a new theory that emotional expressions are decoded not only as discrete categories, but by opponent representations that highlight contrasting facial actions.
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