Symmetry in emotional and visual similarity between neutral and negative faces
Is Mr Hyde more similar to his alter ego Dr Jekyll, because of their physical identity, or to Jack the Ripper, because both evoke fear and loathing? The relative weight of emotional and visual dimensions in similarity judgements is still unclear. We expected an asymmetric effect of these dimensions on similarity perception, such that faces that express the same or similar feeling are judged as more similar than different emotional expressions of same person. We selected 10 male faces posing different expressions. Each male posed one neutral expression and one emotional expression (5 disgust, 5 fear). We paired these expressions, resulting in 190 pairs, which differed either in emotional expressions, physical identity, or both. Twenty healthy participants rated the similarity of paired faces on a 7-points scale. We report a symmetric effect of emotional expression and identity on similarity judgements, suggesting that people may perceive Mr Hyde to be just as similar to Dr Jekyll (identity) as to Jack the Ripper (emotion). We also observed that emotional mismatch decreased perceived similarity, suggesting that emotions play a prominent role in similarity judgements. From an evolutionary perspective, poor discrimination between emotional stimuli may not be advantageous to the individual.