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In this study, we presented computer‐morphing animations of the facial expressions of six emotions to 43 subjects and asked them to evaluate the naturalness of the rate of change of each expression. The results showed that the naturalness of the expressions depended on the velocity of change, and the patterns for the four velocities differed with the emotions. Principal component analysis of the data extracted the structures that underlie the evaluation of dynamic facial expressions, which differed from previously reported structures for static expressions in some aspects. These results suggest that the representations of facial expressions include not only static but also dynamic properties.
Sato et al. (Sat,) studied this question.