Perception of biological motion in schizophrenia

Abstract

This dissertation aimed to investigate perception of socially-relevant visual stimuli in schizophrenia. Past studies have revealed that schizophrenia patients (SZ) are deficient in processing rapid visual stimuli (e.g. motion). It is also known that impaired social functioning characterizes SZ. Humans are very sensitive to motion signals that are generated by others (i.e. biological motion, BM). Therefore, BM perception is important for both visual perception and social functioning. Nevertheless, there have been no systematic attempts to investigate BM perception in SZ. BM (portrayed using point-light animations) discrimination and detection ability was investigated in SZ and healthy controls across three psychophysical tasks. The results revealed that SZ are deficient in both detecting BM, and in discriminating BM from non-BM compared to healthy controls. Interestingly, this impairment was due to an increased tendency for patients to perceive non-BM as containing BM, rather than failure to perceive BM. An fMRI study investigated activation to BM and non-BM within the superior temporal sulcus (STS); a region selectively responsive to BM in the normal brain. Consistent with past findings, strong selective STS activation to BM was observed in controls. Interestingly, strong STS activation was also found when a healthy subject mistakenly perceived a non-BM stimulus as containing BM, emphasizing the role of top-down processing in BM perception. On the other hand, SZ did not show differential STS activation between BM and non-BM stimuli, suggesting abnormal neural mechanism for BM perception, which may be associated with impaired top-down processing in perceiving BM. Correlation between STS activation with social functioning scores suggested that deficient BM perception might be one of the behavioral manifestation of impaired social functioning. An expanded study with obsessive-compulsive disorder (OCD) patients revealed that OCD also show impaired BM perception, suggesting this deficit is not restricted to SZ. In this research, impaired BM perception in SZ and OCD was demonstrated for the first time, and the neural mechanisms underlying BM perception in SZ and healthy people were explored.