In our daily life, adequate social interaction arises from action observation and reading others' intentions and feelings. The human visual system detects visual information of others' actions, i.e., biological motion (BM), and can obtain various information from only point-light animations, which depicts the movement of actor's main joints. Recently it has been reported that schizophrenia patients have impairments of BM perception, which relates to their social functions and symptomatic severities. In this study, we recorded eye movements during detection of BM with background noise to investigate the effect of selective attention on BM perception. We also examined the relationship between BM perception and empathic ability, and explored the neural basis of BM perception using MRI analyses.
Behavioral data revealed lower accuracy and longer reaction times for patients compared to healthy controls, indicating that schizophrenia represents impaired BM perception. As for eye movements, patients tended to fixate longer than controls, indicating slower BM processing in schizophrenia. With regard to the relationship between accuracy and eye movements, the control group showed a larger number of fixations and shorter fixation duration for higher accuracy, while the patient group showed a larger number of fixations and shorter fixation duration for lower accuracy. This inverse correlation may stem from impaired selective attention in schizophrenia which makes efficient target selection difficult.
Affective empathy was positively correlated with accuracy in the patient group. In addition, voxel-based morphometry using MRI showed that gray matter volume of the right temporal pole and left temporoparietal junction were positively correlated with accuracy in patients.
In conclusion, impaired attention as well as impaired central processing of BM might contribute to an overall BM perception deficit, which leads to social cognitive impairments.