Fast unconscious processing of emotional stimuli in early stages of the visual cortex

Abstract

Several cortical and subcortical brain areas have been reported to be sensitive to the emotional content of subliminal stimuli. However, the timing of these activations remains unclear. Our scope was to detect the earliest cortical traces of emotional unconscious processing of visual stimuli by recording event-related potentials (ERPs) from 43 participants. Subliminal spiders (emotional) and wheels (neutral), sharing similar low-level visual parameters, were presented at two different locations (fixation and periphery). The differential (peak-to-peak) amplitude from CP1 (77 ms from stimulus onset) to C2 (100 ms), two early visual ERP components originated in V1/V2 according to source localization analyses, was analyzed via Bayesian and traditional frequentist analyses. Spiders elicited greater CP1-C2 amplitudes than wheels when presented at fixation. This fast effect of subliminal stimulation - not reported previously to the best of our knowledge - has implications in several debates: 1) The amygdala cannot be mediating these effects, 2) latency of other evaluative structures recently proposed, such as the visual thalamus, is compatible with these results, 3) the absence of peripheral stimuli effects points to a relevant role of the parvocellular visual system in unconscious processing.