A Spatiotemporal Hierarchy for Social Interaction Perception in the Lateral Visual Stream

The lateral visual stream has been recently proposed as a third visual stream, in addition to the ventral and dorsal streams, specialized for processing dynamic social content. While prior work has suggested that the regions of this pathway form a hierarchy representing increasingly abstract information, the computations along this pathway are still largely unknown. High spatiotemporal resolution data are particularly informative for characterizing the information flow and thus neural computations across different brain regions. Using a novel regression approach, we combine data from EEG, fMRI, and behavior in response to the same videos to leverage the high temporal resolution of EEG and whole-brain spatial resolution of fMRI. We find that low-level visual features are represented in early visual cortex with a short temporal latency and are not represented in higher-level regions of the lateral stream. Further, we find that mid-level features are represented in mid-level lateral regions with a shorter latency than high-level features in more anterior regions of the lateral pathway. However, both mid- and high-level features were decodable in anterior regions of the lateral pathway with a similar latency. Together, these results provide evidence that features of social actions are processed rapidly in the lateral visual stream in a manner that is consistent with hierarchical processing, but the lateral stream does not exhibit a strict temporal sequence of representational transformations along the posterior-to-anterior axis.