Categorical Perception of Facial Expressions Is Not a Homogeneous Effect

We studied the categorical perception on transitions between seven basic emotional facial expressions and explored the influencing factors. In Experiment 1, participants performed a multiple-choice emotion labeling task while observing basic or morphed (blended between a pair of basic emotions) facial expressions. In Experiment 2, other participants completed AB-X discrimination task. They observed pairs of images adjacent in a morphing continuum, and matched the test image to one of the pair. The results of Experiment 1 revealed influence of emotional context, formed by the presented expressions, on perception of surprise, anger, disgust, and neutral face. The “categorical field” of morphed expressions includes not only the two relevant emotions (morphing basis) but a number of additional ones. Based on the data of Experiment 1, we selected the pairs of stimuli crossing the categorical boundary, and pairs falling within the category, to predict the discriminability obtained it the Experiment 2. A generalized linear mixed model was fitted to the data. We show the main effect of within/between category pair, type of continuum and continuum/category interaction on the probability of correct discrimination. Overall, our results showed the categorical perception, but its strength depends on particular pair of emotional categories.