Differential magnocellular versus parvocellular pathway contributions to the combinatorial processing of facial threat.

Recently, speed of presentation of facially expressive stimuli was found to influence the processing of compound threat cues (e.g., anger/fear/gaze). For instance, greater amygdala responses were found to clear (e.g., direct gaze anger/averted gaze fear) versus ambiguous (averted gaze anger/direct gaze fear) combinations of threat cues when rapidly presented (33 and 300ms), but greater to ambiguous versus clear threat cues when presented for more sustained durations (1, 1.5, and 2s). A working hypothesis was put forth (Adams et al., 2012) that these effects were due to differential magnocellular versus parvocellular pathways contributions to the rapid versus sustained processing of threat, respectively. To test this possibility directly here, we restricted visual stream processing in the fMRI environment using facially expressive stimuli specifically designed to bias visual input exclusively to the magnocellular versus parvocellular pathways. We found that for magnocellular-biased stimuli, activations were predominantly greater to clear versus ambiguous threat-gaze pairs (on par with that previously found for rapid presentations of threat cues), whereas activations to ambiguous versus clear threat-gaze pairs were greater for parvocellular-biased stimuli (on par with that previously found for sustained presentations). We couch these findings in an adaptive dual process account of threat perception and highlight implications for other dual process models within psychology.