An emerging hypothesis posits that reflexive processing of clear threat cues may be predominantly associated with the more primitive, coarse, and action‐oriented M pathway, while reflective, sustained processing of threat ambiguity may preferentially engage the slower, analysis‐oriented P pathway (Adams et al., 2012 Adams & Kveraga, 2015 Kveraga, 2014). Recent work proposes that visual threat stimuli may differentially engage the major visual streams-the magnocellular (M) and parvocellular (P) pathways. Such interactions between gaze direction and a specific emotional facial expression (e.g., fear, joy, or anger) have been reported in many studies (e.g., Adams & Kleck, 2003, 2005 Adams, Gordon, Baird, Ambady, & Kleck, 2003 Akechi et al., 2009 Bindemann, Burton, & Langton, 2008 Hess, Adams, & Kleck, 2007 Milders, Hietanen, Leppänen, & Braun, 2011 Sander, Grandjean, Kaiser, Wehrle, & Scherer, 2007), suggesting that perceiving an emotional face involves integration of different types of social cues available in the face. When a fearful expression is combined with direct gaze, however, it tends to look less fearful due to the incongruity that direct gaze (an approach signal) creates in combination with the fearful expression (an avoidance signal), requiring more reflective processing to resolve the ambiguity inherent in the conflicting signal and the source of threat. Furthermore, in a fearful face this “pointing with the eyes” (Hadjikhani et al., 2008) to the source of threat disambiguates whence the threat is coming. For example, a fearful face tends to be perceived as more fearful when presented with an averted eye gaze because the combination of fearful facial expression and averted gaze provides a congruent social signal (both the expression and the gaze direction signal avoidance), leading to facilitated processing of the congruent signals (e.g., Adams et al., 2012 Adams & Kleck, 2003, 2005 Cushing et al., 2018 Hadjikhani, Hoge, Snyder, & de Gelder, 2008 Im et al., 2017a). Prior work has investigated how observers read such signals from a facial expression combined with direct or averted eye gaze, which imparts different meanings. For example, a happy facial expression implies to an observer that either the expresser or the environment surrounding the observer is safe and friendly, and thus approachable, whereas a fearful facial expression can imply the existence of a potential threat to an expresser or even to an observer. It enables both observers and expressers of facial cues to communicate nonverbally about the social environment. Our findings suggest that M and P processing of facial threat cues is modulated by functional and structural differences in the amygdalae associated with observer's sex.įace perception, particularly assessment of facial emotion during social interactions, is critical for adaptive social behavior. Conversely, in males only the right amygdala volume was positively correlated with accuracy for M‐biased fear faces. In addition to functional reactivity differences, females had proportionately greater bilateral amygdala volumes, which positively correlated with behavioral accuracy for M‐biased fear. Conversely, males showed greater right amygdala activation only for M‐biased averted‐gaze fear faces. Female observers showed more accurate behavioral responses to faces with averted gaze and greater left amygdala reactivity both to fearful and neutral faces. We adjusted luminance and color of face stimuli to selectively engage M or P processing and asked observers to identify emotion of the face. Because growing evidence has identified a variety of sex differences in emotional perception, here we also investigated how M and P processing of fear and eye gaze might be modulated by observer's sex, focusing on the amygdala, a structure important to threat perception and affective appraisal. It has been proposed that the processing of different combinations of threat cues is mediated by dual processing routes: reflexive processing via magnocellular (M) pathway and reflective processing via parvocellular (P) pathway. For example, fear with averted gaze provides a congruent avoidance cue, signaling both threat presence and its location, whereas fear with direct gaze sends an incongruent cue, leaving threat location ambiguous. During face perception, we integrate facial expression and eye gaze to take advantage of their shared signals.
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