There is a significant need for objective assessment methods for schizophrenia. Therefore, this study examined the emotional characteristics of facial stiffness—one of the indicators for estimating patients' flat affect—using average faces. First, we conducted an experiment for psychological evaluation of facial stiffness in 16 Japanese patients with schizophrenia. Twelve medical professionals rated the patients' facial stiffness in 147 videos. Their gaze data were also collected. To extract the physical characteristics of facial stiffness, 11 average faces of 14 male patients and one average face of a group of healthy subjects were generated. The average faces were subjected to an emotion evaluation test by the existing application and 33 medical experts. The results showed that most of the average faces differed in the proportions of the eight emotions between two tests. The most common emotions were anger for the stiffest average face and calm for the healthy average face. In the application analysis, the percentage of emotions other than calm, such as anger and sadness, ranged from 15–65%. In contrast, in the judgment by medical experts ranged from 55–97% for emotions other than calm. The results suggest that “the perception of anger” or “the perception of complex emotions with a mix of anger, confusion, disgust, fear or sadness” is related to the judgment of facial stiffness by medical professionals
