Objectives: To examine the subliminal face processing pathway in neuro-typical young adults, using a binocular rivalry task and fMRI.
Methods: During fMRI data collection, 12 young adult participants performed a consonant/vowel identification task of the first letter of consciously perceived words, while alternating blocks of subliminal faces or houses were presented through the non-dominant eye.
Results: : In a whole brain, random-effects analysis, participants exhibited significantly greater activation for subliminally suppressed faces than suppressed houses in the precuneus and left inferior parietal cortices– areas not evaluated by Pasley due to a narrow EPI data collection window. A priori ROI analysis of bilateral amygdalae revealed significantly greater left amygdala response for subliminal faces compared to houses. Psycho-physiological interaction (PPI) analysis was used to test for regional specific connections to the amygdala, using individually defined ROIs. Results demonstrated task dependent correlations between the left amygdala and bilateral pulvinar, as well as early visual cortices.
Conclusions: The current results present a more complete subliminal face processing pathway, in addition to replicating previous findings. The pulvinar nucleus is implicated in orienting towards salient stimuli. The precuneus has bidirectional connections to the pulvinar nucleus as well as cortico-cortical projections to parietal cortex, a region critical for spatial attention. One interpretation is that a subcortical pulvinar response to a potentially salient stimulus is followed by an increase in amygdala activity and an allocation of spatial resources in parietal cortex, directed by the precuneus. This research builds on previous work identifying a subcortical visual processing pathway, which may aid in revealing more specific deficits underlying the origin of face processing difficulties in ASD.