An extremely fast neural mechanism to detect emotional visual stimuli: A two-experiment study.

Defining the brain mechanisms underlying initial emotional evaluation is a key but unexplored clue to understanding affective processing. Event-related potentials (ERPs), especially suited for investigating this issue, were recorded in two experiments (n = 36 and n = 35). We presented emotionally negative (spiders) and neutral (wheels) silhouettes homogenized regarding their visual parameters. In Experiment 1, stimuli appeared at fixation or in the periphery (200 trials per condition and location), the former eliciting a N40 (39 milliseconds) and a P80 (or C1: 80 milliseconds) component, and the latter only a P80. In Experiment 2, stimuli were presented only at fixation (500 trials per condition). Again, an N40 (45 milliseconds) was observed, followed by a P100 (or P1: 105 milliseconds). Analyses revealed significantly greater N40-C1P1 peak-to-peak amplitudes for spiders in both experiments, and ANCOVAs showed that these effects were not explained by C1P1 alone, but that processes underlying N40 significantly contributed. Source analyses pointed to V1 as an N40 focus (more clearly in Experiment 2). Sources for C1P1 included V1 (P80) and V2/LOC (P80 and P100). These results and their timing point to low-order structures (such as visual thalamic nuclei or superior colliculi) or the visual cortex itself, as candidates for initial evaluation structures.

Menstrual cycle and exogenous attention toward emotional expressions.

Several studies suggest that the menstrual cycle affects emotional processing. However, these results may be biased by including women with premenstrual syndrome (PMS) in the samples. PMS is characterized by negative emotional symptomatology, such as depression and/or anxiety, during the luteal phase. This study aimed to explore the modulation of exogenous attention to emotional facial expressions as a function of the menstrual cycle in women without PMS. For this purpose, 55 women were selected (from an original volunteer sample of 790) according to rigorous exclusion criteria. Happy, angry, and neutral faces were presented as distractors, while both behavioral performance in a perceptual task and event-related potentials (ERPs) were recorded. This task was applied during both phases of the menstrual cycle (luteal and follicular, counterbalanced), and premenstrual symptomatology was monitored daily. Traditional and Bayesian ANOVAs on behavioral data (reaction times and errors in the task) and ERP indices (P1, N170, N2, and LPP amplitudes) confirmed the expected lack of an interaction of phase and emotion. Taken together, these results indicate that women free of PMS present steady exogenous attention levels to emotionally positive and negative stimuli regardless of the menstrual phase.

Exogenous Attention to Emotional Stimuli Presenting Realistic (3D) Looming Motion.

Previous research shows that dynamic stimuli, on the one hand, and emotional stimuli, on the other, capture exogenous attention due to their biological relevance. Through neural (ERPs) and behavioral measures (reaction times and errors), the present study explored the combined effect of looming motion and emotional content on attentional capture. To this end, 3D-recreated static and dynamic animals assessed as emotional (positive or negative) or neutral were presented as distractors while 71 volunteers performed a line orientation task. We observed a two-phase effect: firstly (before 300 ms), early components of ERPs (P1p and N2po) showed enhanced exogenous attentional capture by looming positive distractors and static threatening animals. Thereafter, dynamic and static threatening distractors received enhanced endogenous attention as revealed by both late ERP activity (LPC) and behavioral (errors) responses. These effects are likely explained by both the emotional valence and the distance of the stimulus at each moment.

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

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.

Realistic (3D) looming of emotional visual stimuli: Attentional effects at neural and behavioral levels.

Previous research shows that endogenous attention (the controlled selection of certain aspects of our environment) is enhanced toward emotional stimuli due to its biological relevance. Although looming affective stimuli such as threat seem even more critical for survival, little is known about their effect on endogenous attention. Here, we recorded neural (event-related potentials, ERPs) and behavioral responses (errors and reaction times) to explore the combined effect of emotion and looming motion. 3D-recreated static and moving animals assessed as emotionally positive, negative, and neutral, were presented to participants (n = 71), who performed an indirect categorization task (vertebrate vs. invertebrate). Behavioral results showed better task performance, as reflected by lower number of errors and reaction times, in response to threatening stimuli. Neural indices revealed significant early (P1p, 150 milliseconds), intermediate (P2p, 240), and late (LPP, 450) effects, the latter being more intensely associated with behavior, as revealed by regression analyses. In general, neural indexes of attention to both static and dynamic stimuli showed a positivity offset in early stages and a negativity bias in subsequent phases. However, and importantly, the progressive inclusion of negative stimuli in the attentional focus is produced earlier in the case of dynamic (at P2p latency) than in static versions (at LPP). These results point to an enhancement of attention, particularly in temporal terms, toward stimuli combining motion and biological significance.

Enhanced N170 to outgroup faces: Perceptual novelty or prejudice?

Habituation to ethnic ingroup members has been reported to be greater than to ethnic outgroup members. This pattern could be due to the lack of perceptive experience (familiarity) with outgroup facial morphs or, alternatively, to the prejudice held toward that outgroup. We explored this disjunctive in 71 participants, all Spanish, who were experimentally habituated to faces from their Ingroup and to faces from two unfamiliar outgroups, one for which there is low probability of prejudice in this population (Non-prejudiced Outgroup), and one for which the probability of prejudice is higher (Prejudiced Outgroup). We indexed habituation through event-related potentials, concretely as the differential amplitude of the face-sensitive N170 component from Initial to Final trials of each group. Afterward, participants completed several prejudice measures. N170 showed significant habituation to all faces, though it did not differ among groups. However, a regression analysis revealed that individual habituation to the Outgroup faces was inversely related to implicit prejudice scores. Importantly, N170 amplitudes were maximal for the Prejudiced Outgroup in both Initial and Final trials. We conclude that these effects are explained by the prejudice held toward a specific outgroup rather than perceptive experience.

Prejudice drives exogenous attention to outgroups.

Exogenous attention allows the automatic detection of relevant stimuli and the reorientation of our current focus of attention towards them. Faces from an ethnic outgroup tend to capture exogenous attention to a greater extent than faces from an ethnic ingroup. We explored whether prejudice toward the outgroup, rather than lack of familiarity, is driving this effect. Participants (N = 76) performed a digit categorization task while distractor faces were presented. Faces belonged to (i) a prejudiced outgroup, (ii) a non-prejudiced outgroup and (iii) their ingroup. Half of the faces were previously habituated in order to increase their familiarity. Reaction times, accuracy and event-related potentials (ERPs) were recorded to index exogenous attention to distractor faces. Additionally, different indexes of explicit and implicit prejudice were measured, the latter being significantly greater towards prejudiced outgroup. N170 amplitude was greater to prejudiced outgroup-regardless of their habituation status-than to both non-prejudiced outgroup and ingroup faces and was associated with implicit prejudice measures. No effects were observed at the behavioral level. Our results show that implicit prejudice, rather than familiarity, is under the observed attention-related N170 effects and that this ERP component may be more sensitive to prejudice than behavioral measures under certain circumstances.

Retinotopy of emotion: Perception of negatively valenced stimuli presented at different spatial locations as revealed by event-related potentials.

Scarce previous data on how the location where an emotional stimulus appears in the visual scene modulates its perception suggest that, for functional reasons, a perceptual advantage may exist, vertically, for stimuli presented at the lower visual field (LoVF) and, horizontally, for stimuli presented at the left visual field (LeVF). However, this issue has been explored through a limited number of spatial locations, usually in a single spatial dimension (e.g., horizontal) and invariant eccentricities. Event-related potentials (ERPs) were recorded from 39 participants perceiving brief neutral (wheels) and emotional stimuli (spiders) presented at 17 different locations, one foveal and 16 at different peripheral coordinates. As a secondary scope, we explored the role of the magnocellular (M) and the parvocellular (P) visual pathways by presenting an isoluminant/heterochromatic (P-biased) and a heteroluminant/isochromatic version (M-biased) of each stimulus. Emo > Neu effects were observed in PN1 (120 ms) for stimuli located at fovea, and in PN2 (215 ms) for stimuli located both at fovea and diverse peripheral regions. A factorial approach to these effects further revealed that: (a) emotional stimuli presented in the periphery are efficiently perceived, without evident decrease from para- to perifovea; (b) peripheral Emo > Neu effects are reflected 95 ms later than foveal Emo > Neu effects in ERPs; (c) LoVF is more involved than UVF in these effects; (d) our data fail to support the LeVF advantage previously reported, and (e) Emo > Neu effects were significant for both M and P stimuli.

Binocular rivalry and emotion: Implications for neural correlates of consciousness and emotional biases in conscious perception.

Studies of the neural correlates of consciousness (NCCs) combining MEG/EEG with behavioral data have described two main time ranges relating to conscious perception: 130-320 (the visual awareness negativity; VAN) and 300-500 (P3a) ms after stimulus onset. At the same time, two event-related potential (ERP) peaks have shown an emotional modulation of endogenous attention: the early posterior negativity (EPN; peaking around 250 msec) and the late positive potential (LPP, peaking around 600 msec). Furthermore, an emotional bias on conscious perception has been reported in Binocular Rivalry (BR) studies. Here, we combined an intermittent BR paradigm with neutral and emotional stimuli while recording the behavioral subjective perception and ERPs with two aims: i) to explore the NCCs of emotional content in the time ranges previously described, and ii) to study the emotional bias in conscious perception as first percept when neutral and emotional images rival against each other. First, results revealed a specific ERP emotional modulation (emotional content awareness modulation; ECAM) at the VAN time range. This was the first time window sensitive to the emotional information and showing the strongest modulation in conscious emotional content. Second, results revealed an emotional bias in conscious perception towards the positive valence. This work shows how conscious perception pertaining to emotional content relates to perceptual areas at the VAN latency, which supports the claim of the 130-320 msec time window as the earliest NCC and extends the claim to apply to more than visual perceptual features. Additionally, our findings show that positive and negative content modulates the conscious perception differently.

Haptic recognition memory following short-term visual deprivation: Behavioral and neural correlates from ERPs and alpha band oscillations.

In the current study, we investigated the effects of short-term visual deprivation (2 h) on a haptic recognition memory task with familiar objects. Behavioral data, as well as event-related potentials (ERPs) and induced event-related oscillations (EROs) were analyzed. At the behavioral level, deprived participants showed speeded reaction times to new stimuli. Analyses of ERPs indicated that starting from 1000 ms the recognition of old objects elicited enhanced positive amplitudes only for the visually deprived group. Visual deprivation also influenced EROs. In this sense, we observed reduced power in the lower-1 alpha band for the processing of new compared to old stimuli between 500 and 750 ms. Overall, our data showed improved haptic recognition memory after a short period of visual deprivation. These effects were thought to reflect a compensatory mechanism that might have developed as an adaptive strategy for dealing with the environment when visual information is not available.

Effects of negative content on the processing of gender information: an event-related potential study.

Previous research on emotion in language has mainly concerned the impact of emotional information on several aspects of lexico-semantic analyses of single words. However, affective influences on morphosyntactic processing are less understood. In the present study, we focused on the impact of negative valence in the processing of gender agreement relations. Event-related potentials (ERPs) were recorded while participants read three-word phrases and performed a syntactic judgment task. Negative and neutral adjectives could agree or disagree in gender with the preceding noun. At an electrophysiological level, the amplitude of a left anterior negativity (LAN) to gender agreement mismatches decreased in negative words, relative to neutral words. The behavioral data suggested that LAN amplitudes might be indexing the processing costs associated with the detection of gender agreement errors, since the detection of gender mismatches resulted in faster and more accurate responses than did the detection of correct gender agreement relations. According to this view, it seems that negative content facilitated the processes implicated in the early detection of gender agreement mismatches. However, gender agreement violations in negative words triggered processes involved in the reanalysis and repair of the syntactic structure, as reflected in larger P600 amplitudes to incorrect than to correct phrases, irrespective of their emotional valence.