Troy G. Steiner

Differential hemispheric and visual stream contributions to ensemble coding of crowd emotion

In crowds, where scrutinizing individual facial expressions is inefficient, humans can make snap judgments about the prevailing mood by reading ‘crowd emotion’. We investigated how the brain accomplishes this feat in a set of behavioural and functional magnetic resonance imaging studies. Participants were asked to either avoid or approach one of two crowds of faces presented in the left and right visual hemifields. Perception of crowd emotion was improved when crowd stimuli contained goal-congruent cues and was highly lateralized to the right hemisphere. The dorsal visual stream was preferentially activated in crowd emotion processing, with activity in the intraparietal sulcus and superior frontal gyrus predicting perceptual accuracy for crowd emotion perception, whereas activity in the fusiform cortex in the ventral stream predicted better perception of individual facial expressions. Our findings thus reveal significant behavioural differences and differential involvement of the hemispheres and the major visual streams in reading crowd versus individual face expressions.Im et al. examine how people process crowd facial expressions as opposed to individual ones, finding significant behavioural and neural differences.

Neurodynamics and connectivity during facial fear perception: The role of threat exposure and signal congruity

Fearful faces convey threat cues whose meaning is contextualized by eye gaze: While averted gaze is congruent with facial fear (both signal avoidance), direct gaze (an approach signal) is incongruent with it. We have previously shown using fMRI that the amygdala is engaged more strongly by fear with averted gaze during brief exposures. However, the amygdala also responds more to fear with direct gaze during longer exposures. Here we examined previously unexplored brain oscillatory responses to characterize the neurodynamics and connectivity during brief (~250 ms) and longer (~883 ms) exposures of fearful faces with direct or averted eye gaze. We performed two experiments: one replicating the exposure time by gaze direction interaction in fMRI (N = 23), and another where we confirmed greater early phase locking to averted-gaze fear (congruent threat signal) with MEG (N = 60) in a network of face processing regions, regardless of exposure duration. Phase locking to direct-gaze fear (incongruent threat signal) then increased significantly for brief exposures at ~350 ms, and at ~700 ms for longer exposures. Our results characterize the stages of congruent and incongruent facial threat signal processing and show that stimulus exposure strongly affects the onset and duration of these stages.

Reading the lines in the face: The contribution of angularity and roundness to perceptions of facial anger and joy.

Through 3 studies, we investigated whether angularity and roundness present in faces contributes to the perception of anger and joyful expressions, respectively. First, in Study 1 we found that angry expressions naturally contain more inward-pointing lines, whereas joyful expressions contain more outward-pointing lines. Then, using image-processing techniques in Studies 2 and 3, we filtered images to contain only inward-pointing or outward-pointing lines as a way to approximate angularity and roundness. We found that filtering images to be more angular increased how threatening and angry a neutral face was rated, increased how intense angry expressions were rated, and enhanced the recognition of anger. Conversely, filtering images to be rounder increased how warm and joyful a neutral face was rated, increased the intensity of joyful expressions, and enhanced recognition of joy. Together these findings show that angularity and roundness play a direct role in the recognition of angry and joyful expressions. Given evidence that angularity and roundness may play a biological role in indicating threat and safety in the environment, this suggests that angularity and roundness represent primitive facial cues used to signal threat−anger and warmth−joy pairings.

Differential hemispheric and visual stream involvement in ensemble coding of emotion in facial crowds

The visual system takes advantage of redundancies in the scene by extracting summary statistics from groups of similar items. Similary, in social situations, we routinely make snap judgments of crowds of people. Reading “crowd emotion” is critical for guiding us away from danger (e.g., mass panic or violent mobs) and towards help from friendly groups. Scrutinizing each individual’s expression would be too slow and inefficient. How the brain accomplishes this feat, however, remains unaddressed. Here we report a set of behavioral and fMRI studies in which participants made avoidance or approach decisions by choosing between two facial crowds presented in the left and right visual fields (LVF/RVF). Behaviorally, participants were most accurate for crowds containing task-relevant cues-avoiding angry crowds/approaching happy crowds. This effect was amplified by sex-linked facial cues (angry male/happy female crowds), and highly lateralized with greater recognition of task-congruent stimuli presented in LVF. In a related fMRI study, the processing of facial crowds evoked right-lateralized activations in the dorsal visual stream, whereas similar processing of single faces preferentially activated the ventral stream bilaterally. Our results shed new light on our understand of ensemble face coding, revealing qualitatively different mechanisms involved in reading crowd vs. individual emotion.

Cross-Cultural Effects On Ensemble Coding Of Emotion In Facial Crowds

In many social situations, we make a snap judgment about crowds of people relying on their overall mood (termed “crowd emotion”). Although reading crowd emotion is critical for interpersonal dynamics, the sociocultural aspects of this process have not been explored. The current study examined how culture modulates the processing of crowd emotion in Korean and American observers. Korean and American participants were briefly presented with two groups of faces that were individually varying in emotional expressions and asked to choose which group between the two they would rather avoid. We found that Korean participants were more accurate than American participants overall, in line with the framework on cultural viewpoints: Holistic versus analytic processing in East Asians versus Westerners. Moreover, we found a speed advantage for other-race crowds in both cultural groups. Finally, we found different hemispheric lateralization patterns: American participants were more accurate for angry crowds presented in the left visual field and happy crowds presented in the right visual field, replicating previous studies, whereas Korean participants did not show an interaction between emotional valence and visual field. This work suggests that culture plays a role in modulating our crowd emotion perception of groups of faces and responses to them.