其他摘要 | Recognizing others' movements in a complex environment is a crucial ability, which is related to adaptive survival and social development. Biological motion could convey life signals and social information. For example, humans could decipher goal-directed actions to engage in social interaction and group behavior. Previous studies have mainly focused on the biological information of biological motion, and rarely examined social information conveyed by biological motion. With the enrichment of experimental materials and the development of experimental technology, researchers can explore the neural mechanism underlying biological motion perception from a new perspective. Accordingly, we investigated how our visual system represents social information carried by biological motion.
First, identifying living creatures of the same species constitutes a prerequisite for humans to process social information of biological motion. Therefore, in the first part, we explored how humans process same- and cross一species biological motion. Are there specialized mechanisms for detecting the same-species biological motion? By adopting human and macaque biological motion, we explored this issue at behavioral, physiological, and neural levels. In study 1,subjects were asked to judge the walking direction of biological motion masked by noises. It was found that the perception of human and macaque biological motion was subject to an inversion effect for both the intact and scrambled versions. In addition, observers' performance was significantly better on recognizing intact human biological motion compared with intact macaque biological motion. This study demonstrates that the visual system processes biological motion across species in a similar way but is highly sensitive to conspecifics. In study 2, using pupillometry method, we explored the pupillary response when people perceived the biological motion across species. We found that pupil size was larger when observers viewed an upright human biological motion walker than an inverted one. Such an effect was attributed to kinematic characteristics rather than static configuration. Intriguingly, this pupil dilation effect could be extended to local feet motion, but can't be generalized to macaque biological motion. These findings demonstrate biological motion signals can be mirrored by pupil size, and provide direct physiological evidence for the specific processing of same-species biological motion. In study 3, we used the functional magnetic resonance imaging technology to further assess its brain basis. The univariate whole-brain analysis showed that middle temporal area (hMT+) generally responded to biological motion across species, while posterior superior temporal sulcus (pSTS) only responded to same-species biological motion. The multivariate decoding results also found that whereas hMT+ and pSTS can represent same-species biological motion, only hMT+ was able to represent cross-species biological motion. Moreover, a specialized modulation of effective connectivity between hMT+ and pSTS by human biological motion perception rather than macaque biological motion perception was found. These results together demonstrate that the pSTS region at a higher hierarchy is specialized for processing the same-species biological motion that is closely relevant to social information, whereas the upstream hMT+ region may act as a generalized processor tuned to cross-species biological motion. The above three studies jointly reveal the privileged detection of conspecific biological motion.
Secondly, the social information carried by biological movement is more reflected in the social interaction between multiple agents. Therefore, in the second part, we mainly focused on the specific cognitive and neural mechanisms of processing social interaction information. Study 4 assessed whether perceived social relations could induce a contextual effect. The study used a spatial contextual paradigm and a direction judgment task, and created implicit social relations by systematically manipulating the movement alignment of biological entities. Observers were required to judge the walking direction of the central walker when surrounding inducers were uniformly walked leftward and rightward, respectively. We found that the perceived walking direction of the central walker was attracted by the direction of those surrounding walkers, i.e., a contextual attraction effect. Through a series of control experiments, we found that this effect was not affected by the gender and speed of the surrounding people. In addition, this effect could not extend to the context of non-biological motion and static figure, but depended on simultaneous presentation and local motion clues. These findings provide new support for the distinctiveness of perceived social relations on contextual modulation, indicating that there may be a specialized contextual mechanism tuned to social group movements. Study 5 investigated whether the perception of social interaction can be reflected by our eyes. We found that observers' pupil size was significantly enlarged either when they viewed a single agent that sends interactive intention toward them than toward others in a "second person" perspective task, or when they viewed facing interactive dyads compared to non-facing dyads in a "third person" perspective task. Moreover, we confirmed that this pupil dilation effects depends on the communicative intention conveyed by the interactive agents. The present study substantiated that human visual system is highly sensitive to social interaction information, which paves the way for the potential application of pupil dilation as an index for high-level social cognitive processing. Study 6 explored the neural mechanisms underlying social interaction perception. We focused on μ suppression index, which is an EEG indicator reflecting activities of the mirror neuron system. We adopted a similar task as in Study 5, and recorded observers' EEG signals when they viewed social interaction displays from different person perspective. It was found that perceived social interaction induced stronger } suppression relative to non-interaction, while there was no difference in a suppression which showed comparable attentional states. These results provide a direct neural basis for the specific mechanism of processing social information embedded in biological motion. Taken together, the above three studies confirm that the visual system is highly sensitive to social interaction perception, as demonstrated by contextual effects, pupil responses, and neural indicators.
To sum up, these studies highlight the specific visual representation of social information in biological movement from two aspects: the species specificity of biological motion processing and the cognitive characteristics of social interaction processing. They may lead to a promising application for the early diagnosis of social-cognitive disorders (such as autism) with deficits in animacy perception and social proficiency. |
修改评论