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

Abstract

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.

Keywords: Eye gaze; Facial expression; Fear expression; Magnocellular; Parvocellular; Shared signal hypothesis; Threat; Threat perception; Threat-related ambiguity.

FIG. 1

Illustrates a sample trial of the main experiment. After a jittered ISI (200–400ms), a face stimulus was presented for 1000ms, followed by a blank screen (1100–1300ms). Participants were required to indicate whether a face image presented on the screen looked fearful or neutral. Key-target mapping was counterbalanced across participants such that a half of the participants pressed the left key for neutral and the right key for fearful and the other half pressed the left key for fearful and the right key for neutral. The participants were presented with 384 trials total and feedback was provided every trial.

FIG. 2

(A) ROI analysis depicting differential activation in the right and left amygdala in response to M- versus P-biased stimuli. (B) Activations evoked by M-biased clear minus ambiguous threat stimuli (shown in orange), and by P-biased ambiguous minus clear threat stimuli (shown in green).