Are Facial Identity and Expression Perceived Independently? A Study Controlling Stimulus and Decisional Confounds

Numerous studies have investigated processing of emotional expressions and facial identity and the possible integrality between the two. However, the results of these studies have not come into an agreement on whether facial expression and identity are processed integrally or they are perceptually separable, which may be due to a general lack of control of stimulus and decisional factors. This makes it necessary to develop experiments that overcome the shortcomings of the previous research and may shed light on this debate. In this study, we performed an experiment with highly controlled stimuli using 3-D realistic computer-generated faces for which the discriminability of identities and expressions, the intensity of the expressions, and low-level features of the faces were controlled. A large number of participants, distributed across twelve experiments, performed identification tasks for the six basic emotional expressions and the neutral expression. General recognition theory with individual differences was utilized to model the data, which allowed us to dissociate between perceptual and decisional processes. Results showed robust violations of perceptual independence and decisional separability, which were consistent across most experiments. Perceptual separability results were inconsistent for most expressions, except for the case of happiness and anger. Anger was exceptional in that it showed perceptual separability from identity, and vice-versa. Happiness was perceptually separable from identity, but not vice-versa. Interestingly, discriminability of identity was consistently reduced by happiness compared to a neutral expression.