Abstract
Introduction: Relatively greater amygdalar response has been found to rapidly presented fear faces when coupled with averted gaze (offering clear signal of threat location), and to sustained presentations of ambiguous threat (direct gaze fear; Adams et al., 2012). To help explain these results, the parvocellular (P) and magnocellular (M) pathways have been implicated in the processing ambiguous versus clear threat, respectively. We tested another presentation parameter relevant to these visual pathways, manipulating stimulus size as a natural spatial filter (Smith & Schyns, 2009). Methods: Twenty-nine (15 female) participants passively viewed fearful faces in an ABA design alternating between averted and direct gaze, for 16 blocks. Fourteen participants (8 female) were presented small faces (visual angle of 3.9̊ by 5°) while fifteen participants (6 female) were presented large faces (visual angle of 9.7° by 12.5 ̊). Each block consisted of 16 trials; stimuli were presented for 300 ms then a 1200 ms fixation. Results: For small presentations favoring (M) pathway, clear threat (averted gaze fear) minus ambiguous threat (direct gaze fear) yielded activation in many regions, including: right-amygdala, PMC, SMA, left-IFC, right-OFC, thalamus, insula, and left-TPJ. Ambiguous threat-gaze minus clear threat yielded fewer areas of activation including the OFC, right-mPFC, right-ITG, CG, and posterior cingulate. The pattern was in many ways reversed for large stimuli: Ambiguous minus clear threat elicited activation in the amygdala, mPFC regions, right-STS, bilateral-iFG, and right-insula. Clear minus ambiguous threat elicited fewer activations including in the right-insula and SMA, left-caudate, cingulate, and MT. Conclusion: Our findings with small versus large presentations of clear versus ambiguous threat-gaze pairs yielded similar patterns of activations previously found for rapid versus sustained presentations of the same threat-gaze pairs (Adams et al., 2012). These findings highlight that presentation parameters yield highly variable effects, presumably due to differential magnocellular versus parvocellular involvement.
Meeting abstract presented at VSS 2017