Caricatured facial movements enhance perception of emotional facial expressions.

Although faces "in the wild" constantly undergo complicated movements, humans adeptly perceive facial identity and expression. Previous studies, focusing mainly on identity, used photographic caricature to show that distinctive form increases perceived dissimilarity. We tested whether distinctive facial movements showed similar effects, and we focussed on both perception of expression and identity. We caricatured the movements of an animated computer head, using physical motion metrics extracted from videos. We verified that these "ground truth" metrics showed the expected effects: Caricature increased physical dissimilarity between faces differing in expression and those differing in identity. Like the ground truth dissimilarity, participants' dissimilarity perception was increased by caricature when faces differed in expression. We found these perceived dissimilarities to reflect the "representational geometry" of the ground truth. However, neither of these findings held for faces differing in identity. These findings replicated across two paradigms: pairwise ratings and multiarrangement. In a final study, motion caricature did not improve recognition memory for identity, whether manipulated at study or test. We report several forms of converging evidence for spatiotemporal caricature effects on dissimilarity perception of different expressions. However, more work needs to be done to discover what identity-specific movements can enhance face identification.

Face space representations of movement.

The challenging computational problem of perceiving dynamic faces "in the wild" goes unresolved because most research focuses on easier questions about static photograph perception. This literature conceptualizes face representation as a dissimilarity-based "face space", with axes that describe the dimensions of static images. Some versions express positions in face space relative to a central tendency (norm). Are facial movements represented like this? We tested for representations that accord with an a priori hypothesized motion-based face space by experimentally manipulating faces' motion-based dissimilarity. Because we caricatured movements, we could test for representations of dissimilarity from a motion-based norm. Behaviorally, participants perceived these caricatured expressions as convincing and recognizable. Moreover, as expected, caricature enhanced perceived dissimilarity between facial expressions. Functional magnetic resonance imaging showed that occipitotemporal brain responses, including face-selective and motion-sensitive areas, reflect this face space. This evidence converged across methods including analysis of univariate mean responses (which additionally exhibited norm-based responses), repetition suppression and representational similarity analysis. This accumulated evidence for "representational geometry" shows how perception and visual brain responses to facial dynamics reflect representations of movement-based dissimilarity spaces, including explicit computation of distance from a norm movement.