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.

Rapid withdrawal from a threatening animal is movement-specific and mediated by reflex-like neural processing

“…Our results show that snake stimuli evoked amplified ERP responses already 70-110 ms after stimulus onset (P1 wave). The main source of the P1 localizes to early visual cortices 33,34 , suggesting that that relatively low-level visual processes signaled the presence of a potentially threatening stimulus when snakes were presented. In line with this, while rapid unconscious responses to threat-relevant stimuli are sometimes attributed to subcortical structures [35][36][37] , recent studies indicate that rapid cortical processing also plays a key role in threat processing 9,34,38,39 .…”

“…The main source of the P1 localizes to early visual cortices 33,34 , suggesting that that relatively low-level visual processes signaled the presence of a potentially threatening stimulus when snakes were presented. In line with this, while rapid unconscious responses to threat-relevant stimuli are sometimes attributed to subcortical structures [35][36][37] , recent studies indicate that rapid cortical processing also plays a key role in threat processing 9,34,38,39 . The P1 response is typically assumed to precede the earliest correlate of conscious visual perception 40 , suggesting that snake detection may be mediated by unconscious perception.…”

“…The main source of the P1 localizes to early visual cortices (Carretié et al, 2022; di Russo et al, 2002), suggesting that that relatively low-level visual processes signaled the presence of a potentially threatening stimulus when a snake was presented. In line with this, while rapid unconscious responses to threat-relevant stimuli are sometimes attributed to subcortical structures(Evans et al, 2018; Salay et al, 2018; Wei et al, 2015), recent studies indicate that rapid cortical processing also plays a key role in threat processing (Carretié et al, 2022; Li & Keil, 2023; Miskovic & Keil, 2012; West et al, 2011).…”

“…The main source of the P1 localizes to early visual cortices (Carretié et al, 2022; di Russo et al, 2002), suggesting that that relatively low-level visual processes signaled the presence of a potentially threatening stimulus when a snake was presented. In line with this, while rapid unconscious responses to threat-relevant stimuli are sometimes attributed to subcortical structures(Evans et al, 2018; Salay et al, 2018; Wei et al, 2015), recent studies indicate that rapid cortical processing also plays a key role in threat processing (Carretié et al, 2022; Li & Keil, 2023; Miskovic & Keil, 2012; West et al, 2011). Given that the present stimuli were not designed to measure the C1 wave, it remains open whether the initial wave of visual stimulus driven cortical activity is sensitive to threat-relevance and predicts behavioral responding, as suggested by fear conditioning studies (Hintze et al, 2014; Sperl et al, 2021; Stolarova et al, 2006; Thigpen et al, 2017).…”

“…This early response likely indicates that relatively low-level visual processes signaled the presence of a potentially threatening stimulus when snakes were presented. The main source of the P1 localizes to early visual cortices 31,32 , and it is often assumed to precede the earliest correlate of conscious visual perception 33 . This suggests that snake detection may be mediated by processes that precede conscious perception.…”