Cortical Contributions to Local and Global Biological Motion Perception: Insights from Transcranial Magnetic Stimulation

Humans have an extraordinary ability to detect and recognize biological motion (BM). This sophisticated perception relies on two fundamental visual cues: local kinematics and global structure-from-motion information, which are processed along subcortical-cortical pathways. However, it remains unclear how key motion-sensitive regions, such as the posterior superior temporal sulcus (pSTS) and the medial temporal complex (MT+), contribute to the processing of distinct BM cues. In this study, we employed transcranial magnetic stimulation (TMS) to explore the causal roles of these two cortical regions in BM perception. TMS was delivered to the pSTS and MT+, which were individually localized in the right hemisphere, and participants performed direction discrimination tasks with intact BM, scrambled BM, and simple coherent motion stimuli. Results demonstrated that TMS over the pSTS selectively impaired intact BM discrimination, whereas MT+ stimulation only disrupted coherent motion perception. Importantly, neither site showed significant impairment in scrambled BM direction discrimination. These findings suggest that while pSTS and MT+ are critical for global BM and coherent motion perception, respectively, they are not obligatory for local BM processing. The detection of local BM signals may rely on a specialized mechanism operating at an early stage of visual processing.