Unconscious processing of emotional faces and its probable neural mechanism

With the advancement of techniques in probing unconscious visual processing, an increasing number of researches have demonstrated that unconscious visual information could have an impact on human being’s cognition and behavior. This review mainly introduces those studies regarding processing of fearful faces which are rendered subconscious through weak bottom-up inputs rather than insufficient top-down attentional resources. Studies that adopted backward masking, binocular rivalry, and interocular suppression paradigms and those conducted on patients who suffered from visual cortex lesion have shown converging evidence that some subcortical structures, like superior colliculus, thalamus, and amygdala, and the functional connectivity between these regions contribute to the unconscious processing of fearful faces. It is thus suggested that the human brain is able to process unconscious emotional faces through a rapid subcortical route bypassing early visual cortex. However, this route still needs further studies to delineate its causal instead of correlational relationship with unconscious processing. In addition, how the highly efficient subcortical route adds to the conscious processing of emotional faces is worthy of future investigations.