Neurodynamics of reading crowd emotion: Independent visual pathways and hemispheric contributions

Abstract

Introduction: The visual system exploits redundancies by extracting summary statistics from groups of similar items. In social situations, extracting average emotion from crowds of faces helps us to avoid potential threats (e.g., mob violence or panic). We conducted fMRI, MEG, and behavioral experiments to investigate contributions of magnocellular (M) and parvocellular (P) visual pathways, and of hemispheric lateralization in reading of crowd emotion. Methods: Participants in fMRI (N=32), MEG (N=38), and behavioral (N=36) experiments were presented bilaterally with either arrays of faces or single faces with varying emotional expressions. Participants performed a 2AFC task as to which facial crowd, or single face comparison to avoid. In the behavioral experiment, the original stimuli were converted to M-biased (low-luminance contrast) or P-biased (isoluminant chromatic) stimuli to isolate visual field contributions. Results: fMRI and MEG results revealed that reading crowd emotion evoked highly lateralized activations along the dorsal stream, including the prefrontal and parietal cortex. Conversely, individual emotion processing activated the ventral stream, including the FFA. MEG activity in the precuneus (dorsal stream) differentially increased for facial crowds from 180 ms after stimulus onset, indicating early engagement of M-pathway, whereas the FFA (ventral stream) showed higher activation for individual faces 200 ms after stimulus onset. Furthermore, we found goal-dependent hemispheric asymmetry for crowd emotion processing: the right hemisphere was superior for task-congruent (e.g., angry crowd to avoid) decisions and the left hemisphere for processing task-incongruent cues (e.g., happy crowd). However, the right hemisphere was superior for individual emotion processing regardless of task demands. Finally, in the behavioral task, we found crowd emotion extraction to be more accurate from M- than P-stimuli, and observed goal-dependent hemispheric asymmetry only for M-stimuli. Conclusion: Unlike individual emotion processing, reading crowd emotion is predominantly carried out by the M/dorsal stream, with the right hemisphere superiority for task-congruent decisions.

Meeting abstract presented at VSS 2017