Seeing happy emotion in fearful and angry faces: qualitative analysis of facial expression recognition in a bilateral amygdala-damaged patient

Neuropsychological studies reported that bilateral amygdala-damaged patients had impaired recognition of facial expressions of fear. However, the specificity of this impairment remains unclear. To address this issue, we carried out two experiments concerning the recognition of facial expression in a patient with bilateral amygdala damage (HY). In Experiment 1, subjects matched the emotion of facial expressions with appropriate verbal labels, using standardized photographs of facial expressions illustrating six basic emotions. The performance of HY was compared with age-matched normal controls (n = 13) and brain-damaged controls (n = 9). HY was less able to recognize facial expressions showing fear than normal controls. In addition, the error pattern exhibited by HY for facial expressions of fear and anger were distinct from those exhibited by both control groups, and suggested that HY confused these emotions with happiness. In Experiment 2, subjects were presented with morphed facial expressions that blended happiness and fear, happiness and anger, or happiness and sadness. Subjects were requested to categorize these expressions by two-way forced-choice selection. The performance of HY was compared with age-matched normal controls (n = 8). HY categorized the morphed fearful and angry expressions blended with some happy content as happy facial expressions more frequently than normal controls. These findings support the idea that amygdala-damaged patients have impaired processing of facial expressions relating to certain negative emotions, particularly fear and anger. More specifically, amygdala-damaged patients seem to give positively biased evaluations for these negative facial expressions.