The Hidden Snake in the Grass: Superior Detection of Snakes in Challenging Attentional Conditions

Moving spiders do not boost visual search in spider fear

Previous research on attention to fear-relevant stimuli has largely focused on static pictures or drawings, and thus did not consider the potential effect of natural motion. Here, we aimed to investigate the effect of motion on attentional capture in spider-fearful and non-fearful participants by using point-light stimuli and naturalistic videos. Point-light stimuli consist of moving dots representing joints and thereby visualizing biological motion (e.g. of a walking human or cat) without needing a visible body. Spider-fearful (n = 30) and non-spider-fearful (n = 31) participants completed a visual search task with moving targets (point-light/naturalistic videos) and static distractors (images), static targets and moving distractors, or static targets and static distractors. Participants searched for a specified animal type (snakes, spiders, cats, or doves) as quickly as possible. We replicated previous findings with static stimuli: snakes were detected faster and increased distraction, while spiders just increased distraction. However, contrary to our hypotheses, spider targets did not speed up responses, neither in the group of control nor in the group of spider-fearful participants. Interestingly, stimuli-specific effects were toned down, abolished, or even changed direction when motion was introduced. Also, we demonstrated that point-light stimuli were of similar efficiency as naturalistic videos, indicating that for testing effects of motion in visual search, "pure" motion stimuli might be sufficient. As we do show a substantial modulation of visual search phenomena by biological motion, we advocate for future studies to use moving stimuli, equivalent to our dynamic environment, to increase ecological validity.

Emotional anticipation for dynamic emotional faces is not modulated by schizotypal traits: A Representational Momentum study

Schizotypy, a personality structure that resembles schizophrenia symptoms, is often associated with abnormal facial emotion perception. Based on the prevailing sense of threat in psychotic experiences, and the immediate perceptual history of seeing others' facial expressions, individuals with high schizotypal traits may exhibit a heightened tendency to anticipate anger. To test this, we used insights from Representational Momentum (RM), a perceptual phenomenon in which the endpoint of a dynamic event is systematically displaced forward, into the immediate future. Angry-to-ambiguous and happy-to-ambiguous avatar faces were presented, each followed by a probe with the same (ambiguous) expression as the endpoint, or one slightly changed to express greater happiness/anger. Participants judged if the probe was "equal" to the endpoint and rated how confident they were. The sample was divided into high (N = 46) and low (N = 49) schizotypal traits using the Schizotypal Personality Questionnaire (SPQ). First, a forward bias was found in happy-to-ambiguous faces, suggesting emotional anticipation solely for dynamic faces changing towards a potential threat (anger). This may reflect an adaptative mechanism, as it is safer to anticipate any hostility from a conspecific than the opposite. Second, contrary to our hypothesis, high schizotypal traits did not heighten RM for happy-to-ambiguous faces, nor did they lead to overconfidence in biased judgements. This may suggest a typical pattern of emotional anticipation in non-clinical schizotypy, but caution is needed due to the use of self-report questionnaires, university students, and a modest sample size. Future studies should also investigate if the same holds for clinical manifestations of schizophrenia.

No evidence of attentional prioritization for threatening targets in visual search

Throughout human evolutionary history, snakes have been associated with danger and threat. Research has shown that snakes are prioritized by our attentional system, despite many of us rarely encountering them in our daily lives. We conducted two high-powered, pre-registered experiments (total N = 224) manipulating target prevalence to understand this heightened prioritization of threatening targets. Target prevalence refers to the proportion of trials wherein a target is presented; reductions in prevalence consistently reduce the likelihood that targets will be found. We reasoned that snake targets in visual search should experience weaker effects of low target prevalence compared to non-threatening targets (rabbits) because they should be prioritized by searchers despite appearing rarely. In both experiments, we found evidence of classic prevalence effects but (contrasting prior work) we also found that search for threatening targets was slower and less accurate than for nonthreatening targets. This surprising result is possibly due to methodological issues common in prior studies, including comparatively smaller sample sizes, fewer trials, and a tendency to exclusively examine conditions of relatively high prevalence. Our findings call into question accounts of threat prioritization and suggest that prior attention findings may be constrained to a narrow range of circumstances.

Emotional interference and attentional control in schizophrenia-spectrum disorders: The special case of neutral faces

BACKGROUND AND OBJECTIVES

Schizophrenia-spectrum disorders (SSD) are characterized by impaired emotion processing and attention. SSD patients are more sensitive to the presence of emotional distractors. But despite growing interest on the emotion-attention interplay, emotional interference in SSD is far from fully understood. Moreover, research to date has not established the link between emotional interference and attentional control in SSD. This study thus aimed to investigate the effects of facial expression and attentional control in SSD, by manipulating perceptual load.

METHODS

Twenty-two SSD patients and 22 healthy controls performed a target-letter discrimination task with task-irrelevant angry, happy, and neutral faces. Target-letter was presented among homogenous (low load) or heterogenous (high load) distractor-letters. Accuracy and RT were analysed using (generalized) linear mixed-effect models.

RESULTS

Accuracy was significantly lower in SSD patients than controls, regardless of perceptual load and facial expression. Concerning RT, SSD patients were significantly slower than controls in the presence of neutral faces, but only at high load. No group differences were observed for angry and happy faces.

LIMITATIONS

Heterogeneity of SSD, small sample size, lack of clinical control group, medication.

CONCLUSIONS

One possible explanation is that neutral faces captured exogenous attention to a greater extent in SSD, thus challenging attentional control in perceptually demanding conditions. This may reflect abnormal processing of neutral faces in SSD. If replicated, these findings will help to understand the interplay between exogenous attention, attentional control, and emotion processing in SSD, which may unravel the mechanism underlying socioemotional dysfunction in SSD.

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

Responses to potentially dangerous stimuli are among the most basic animal behaviors. While research has shown that threats automatically capture the attention of human participants, research has failed to demonstrate automatic behavioral responses to threats in humans. Using a novel naturalistic paradigm, we show that two species of animals humans often report fearing trigger rapid withdrawal responses: participants withdrew their arm from photos of snakes and spiders faster, and with higher acceleration when compared to bird and butterfly stimuli. The behavior was specific to withdrawal as approach movements or button-press/release tasks failed to detect a similar difference. Moreover, between-participant differences in how aversive they found the stimuli predicted the participant's withdrawal speed, indicating that the paradigm was also sensitive to trait-level differences between individuals. Using electroencephalography (EEG), we show that the fast withdrawal was mediated by two attentional processes. First, fast withdrawal responses were associated with early amplification of sensory signals (40-110 ms after stimulus). Second, a later correlate of feature-based attention (early posterior negativity, EPN, 200-240 ms after stimulus) revealed the opposite pattern: Stronger EPN was associated with slower behavioral responses, suggesting that the deployment of attention towards the threatening stimulus features, or failure to "disengage" attention from the stimulus, was detrimental for withdrawal speed. Altogether, the results suggest that rapid behavioral withdrawal from a threatening animal is mediated by reflex-like attentional processing, and later, conscious attention to stimulus features may hinder escaping the treat.

Attentional, emotional, and behavioral response toward spiders, scorpions, crabs, and snakes provides no evidence for generalized fear between spiders and scorpions

Spiders are among the animals evoking the highest fear and disgust and such a complex response might have been formed throughout human evolution. Ironically, most spiders do not present a serious threat, so the evolutionary explanation remains questionable. We suggest that other chelicerates, such as scorpions, have been potentially important in the formation and fixation of the spider-like category. In this eye-tracking study, we focused on the attentional, behavioral, and emotional response to images of spiders, scorpions, snakes, and crabs used as task-irrelevant distractors. Results show that spider-fearful subjects were selectively distracted by images of spiders and crabs. Interestingly, these stimuli were not rated as eliciting high fear contrary to the other animals. We hypothesize that spider-fearful participants might have mistaken crabs for spiders based on their shared physical characteristics. In contrast, subjects with no fear of spiders were the most distracted by snakes and scorpions which supports the view that scorpions as well as snakes are prioritized evolutionary relevant stimuli. We also found that the reaction time increased systematically with increasing subjective fear of spiders only when using spiders (and crabs to some extent) but not snakes and scorpions as distractors. The maximal pupil response covered not only the attentional and cognitive response but was also tightly correlated with the fear ratings of the picture stimuli. However, participants' fear of spiders did not affect individual reactions to scorpions measured by the maximal pupil response. We conclude that scorpions are evolutionary fear-relevant stimuli, however, the generalization between scorpions and spiders was not supported in spider-fearful participants. This result might be important for a better understanding of the evolution of spider phobia.

Are vipers prototypic fear-evoking snakes? A cross-cultural comparison of Somalis and Czechs

Snakes are known as highly fear-evoking animals, eliciting preferential attention and fast detection in humans. We examined the human fear response to snakes in the context of both current and evolutionary experiences, conducting our research in the cradle of humankind, the Horn of Africa. This region is characterized by the frequent occurrence of various snake species, including deadly venomous viperids (adders) and elapids (cobras and mambas). We conducted experiments in Somaliland and compared the results with data from Czech respondents to address the still unresolved questions: To which extent is human fear of snakes affected by evolutionary or current experience and local culture? Can people of both nationalities recognize venomous snakes as a category, or are they only afraid of certain species that are most dangerous in a given area? Are respondents of both nationalities equally afraid of deadly snakes from both families (Viperidae, Elapidae)? We employed a well-established picture-sorting approach, consisting of 48 snake species belonging to four distinct groups. Our results revealed significant agreement among Somali as well as Czech respondents. We found a highly significant effect of the stimulus on perceived fear in both populations. Vipers appeared to be the most salient stimuli in both populations, as they occupied the highest positions according to the reported level of subjectively perceived fear. The position of vipers strongly contrasts with the fear ranking of deadly venomous elapids, which were in lower positions. Fear scores of vipers were significantly higher in both populations, and their best predictor was the body width of the snake. The evolutionary, cultural, and cognitive aspects of this phenomenon are discussed.

The bigger the threat, the longer the gaze? A cross-cultural study of Somalis and Czechs

High fear reaction, preferential attention, or fast detection are only a few of the specific responses which snakes evoke in humans. Previous research has shown that these responses are shared amongst several distinct cultures suggesting the evolutionary origin of the response. However, populations from sub-Saharan Africa have been largely missing in experimental research focused on this issue. In this paper, we focus on the effect of snake threat display on human spontaneous attention. We performed an eye-tracking experiment with participants from Somaliland and the Czechia and investigated whether human attention is swayed towards snakes in a threatening posture. Seventy-one Somalis and 71 Czechs were tested; the samples were matched for gender and comparable in age structure and education level. We also investigated the effect of snake morphotype as snakes differ in their threat display. We found that snakes in a threatening posture were indeed gazed upon more than snakes in a relaxed (non-threatening) posture. Further, we found a large effect of snake morphotype as this was especially prominent in cobras, less in vipers, and mostly non-significant in other morphotypes. Finally, despite highly different cultural and environmental backgrounds, the overall pattern of reaction towards snakes was similar in Somalis and Czechs supporting the evolutionary origin of the phenomenon. We concluded that human attention is preferentially directed towards snakes, especially cobras and vipers, in threatening postures.

Fearful snake pictures make monkeys pessimistic

Judgment bias is the cognitive tendency of animals experiencing negative (or positive) affect to expect undesirable (or favorable) outcomes in ambiguous situations. The lack of examination of judgment biases induced by ecologically relevant stimuli hampers our understanding of the adaptive role of these biases. We examined whether predator-related stimuli, i.e., pictures of snakes, induce a pessimistic judgment bias in Japanese macaques (Macaca fuscata). Our subjects underwent a touchscreen-based Go/No-go judgment bias test. We found that the subjects were less likely and slower to make Go responses to ambiguous stimuli after viewing the snake pictures, indicating that pictures of snakes induce a pessimistic evaluation of ambiguous stimuli. In environments with high levels of threat, behavioral strategies that reduce risk-taking would be evolutionarily advantageous. Hence, an affective response system that lowers expectations of favorable outcomes in ambiguous situations after encountering threat-related stimuli would serve adaptive purposes, such as curbing excessive exploratory behavior.

Slowly Making Sense: A Review of the Two-Step Venom System within Slow (Nycticebus spp.) and Pygmy Lorises (Xanthonycticebus spp.)

Since the early 2000s, studies of the evolution of venom within animals have rapidly expanded, offering new revelations on the origins and development of venom within various species. The venomous mammals represent excellent opportunities to study venom evolution due to the varying functional usages, the unusual distribution of venom across unrelated mammals and the diverse variety of delivery systems. A group of mammals that excellently represents a combination of these traits are the slow (Nycticebus spp.) and pygmy lorises (Xanthonycticebus spp.) of south-east Asia, which possess the only confirmed two-step venom system. These taxa also present one of the most intriguing mixes of toxic symptoms (cytotoxicity and immunotoxicity) and functional usages (intraspecific competition and ectoparasitic defence) seen in extant animals. We still lack many pieces of the puzzle in understanding how this venom system works, why it evolved what is involved in the venom system and what triggers the toxic components to work. Here, we review available data building upon a decade of research on this topic, focusing especially on why and how this venom system may have evolved. We discuss that research now suggests that venom in slow lorises has a sophisticated set of multiple uses in both intraspecific competition and the potential to disrupt the immune system of targets; we suggest that an exudate diet reveals several toxic plants consumed by slow and pygmy lorises that could be sequestered into their venom and which may help heal venomous bite wounds; we provide the most up-to-date visual model of the brachial gland exudate secretion protein (BGEsp); and we discuss research on a complement component 1r (C1R) protein in saliva that may solve the mystery of what activates the toxicity of slow and pygmy loris venom. We conclude that the slow and pygmy lorises possess amongst the most complex venom system in extant animals, and while we have still a lot more to understand about their venom system, we are close to a breakthrough, particularly with current technological advances.

Processing negative emotion in two languages of bilinguals: Accommodation and assimilation of the neural pathways based on a meta-analysis

Numerous functional magnetic resonance imaging (fMRI) studies have examined the neural mechanisms of negative emotional words, but scarce evidence is available for the interactions among related brain regions from the functional brain connectivity perspective. Moreover, few studies have addressed the neural networks for negative word processing in bilinguals. To fill this gap, the current study examined the brain networks for processing negative words in the first language (L1) and the second language (L2) with Chinese-English bilinguals. To identify objective indicators associated with negative word processing, we first conducted a coordinate-based meta-analysis on contrasts between negative and neutral words (including 32 contrasts from 1589 participants) using the activation likelihood estimation method. Results showed that the left medial prefrontal cortex (mPFC), the left inferior frontal gyrus (IFG), the left posterior cingulate cortex (PCC), the left amygdala, the left inferior temporal gyrus (ITG), and the left thalamus were involved in processing negative words. Next, these six clusters were used as regions of interest in effective connectivity analyses using extended unified structural equation modeling to pinpoint the brain networks for bilingual negative word processing. Brain network results revealed two pathways for negative word processing in L1: a dorsal pathway consisting of the left IFG, the left mPFC, and the left PCC, and a ventral pathway involving the left amygdala, the left ITG, and the left thalamus. We further investigated the similarity and difference between brain networks for negative word processing in L1 and L2. The findings revealed similarities in the dorsal pathway, as well as differences primarily in the ventral pathway, indicating both neural assimilation and accommodation across processing negative emotion in two languages of bilinguals.

What determines the neural response to snakes in the infant brain? A systematic comparison of color and grayscale stimuli

Snakes and primates have coexisted for thousands of years. Given that snakes are the first of the major primate predators, natural selection may have favored primates whose snake detection abilities allowed for better defensive behavior. Aligning with this idea, we recently provided evidence for an inborn mechanism anchored in the human brain that promptly detects snakes, based on their characteristic visual features. What are the critical visual features driving human neural responses to snakes is an unresolved issue. While their prototypical curvilinear coiled shape seems of major importance, it remains possible that the brain responds to a blend of other visual features. Coloration, in particular, might be of major importance, as it has been shown to act as a powerful aposematic signal. Here, we specifically examine whether color impacts snake-specific responses in the naive, immature infant brain. For this purpose, we recorded the brain activity of 6-to 11-month-old infants using electroencephalography (EEG), while they watched sequences of color or grayscale animal pictures flickering at a periodic rate. We showed that glancing at colored and grayscale snakes generated specific neural responses in the occipital region of the brain. Color did not exert a major influence on the infant brain response but strongly increased the attention devoted to the visual streams. Remarkably, age predicted the strength of the snake-specific response. These results highlight that the expression of the brain-anchored reaction to coiled snakes bears on the refinement of the visual system.

An ethologically based view into human fear

The quality of the defensive response to a threat depends on the elements that trigger the fear response. The current classification system of phobias does not account for this. Here, we analyze the fear-eliciting elements and discern the different types of fears that originate from them. We propose Pain, Disgust, Vasovagal response, Visual-vestibular and postural interactions, Movement and Speed, Distance and Size, Low and mid-level visual features, Smell, and Territory and social status. We subdivide phobias according to the fear-eliciting elements most frequently triggered by them and their impact on behavior. We discuss the implications of a clinical conceptualization of phobias in humans by reconsidering the current nosology. This conceptualization will facilitate finding etiological factors in defensive behavior expression, fine-tuning exposure techniques, and challenging preconceived notions of preparedness. This approach to phobias leads to surprising discoveries and shows how specific responses bear little relation to the interpretation we might later give to them. Dividing fears into their potentially fear-eliciting elements can also help in applying the research principles formulated by the Research Domain Criteria initiative.

Do Spiders Ride on the Fear of Scorpions? A Cross-Cultural Eye Tracking Study

Deep fear of spiders is common in many countries, yet its origin remains unexplained. In this study, we tested a hypothesis based on recent studies suggesting that fear of spiders might stem from a generalized fear of chelicerates or fear of scorpions. To this end, we conducted an eye tracking experiment using a spontaneous gaze preference paradigm, with spiders and scorpions (previously neglected but crucial stimuli) as threatening stimuli and grasshoppers as control stimuli. In total, 67 participants from Somaliland and 67 participants from the Czech Republic were recruited and presented with a sequence of paired images. Both Somali and Czech people looked longer (total duration of the gaze) and more often (number of fixations) on the threatening stimuli (spiders and scorpions) when presented with a control (grasshopper). When both threatening stimuli were presented together, Somali participants focused significantly more on the scorpion, whereas in Czech participants, the effect was less pronounced, and in Czech women it was not significant. This supports the hypothesis that fear of spiders originated as a generalized fear of scorpions. Moreover, the importance of spiders as fear-eliciting stimuli may be enhanced in the absence of scorpions in the environment.

Layered habitats: An evolutionary model for present-day recreational needs

Urbanisation and lifestyle-related illnesses increase globally. This highlights the need to shape modern human habitats to support basic recreational needs, promoting such things as physical activity and restoration of high stress levels and cognitive fatigue. Previous research suggests eight perceived qualities in the outdoor environment, described as eight perceived sensory dimensions, as universally meaningful to people in this regard. However quite extensively studied in relation to various health and wellbeing outcomes, human sensitivity and appreciation for these qualities has not yet been explicitly analysed from an evolutionary perspective. This paper investigates their possible evolutionary roots and suggests an order for their development. This is linked with empirical findings on their relative capacity to support restoration of stress and cognitive fatigue. Qualities of earlier origin are suggested to correspond to older, more fundamental adaptations. Each subsequently developed quality implies an increased complexity of our environmental relations, associated with higher demands on more recently developed capacities. The proposed model thus links the more restorative Serene, Sheltered, Natural, and Cohesive perceived sensory dimensions with earlier stages of our development while the more demanding Diverse, Open, Cultural, and Social qualities are associated with more recent transitions. It might be of relevance when shaping modern human habitats from a health-promoting perspective, and have applications in the planning and design of, e.g., health care settings, rehabilitation gardens, urban green areas, recreational forests or other similar outdoor environments.

Perception Over Personality in Lethal Force: Aggression, Impulsivity, and Big Five Traits in Threat Assessments and Behavioral Responses due to Weapon Presence and Posture

The use of lethal force is a combination of threat perception and individual judgment that sometimes warrants a behavioral response. This simplified description implicates perceptual factors and individual differences in lethal force decision making, which ongoing research continues to address. However, personality-based factors have been less explored as to how they might affect either threat perception or behavioral responses in a lethal force decision. The current investigation examined multiple personality traits with the potential to influence lethal force decision making, including aggression, impulsivity, and the Big Five traits. These measures were compared to threat perception and behavioral responses made to a variety of lethal force stimuli broadly categorized as clear threats, ambiguous threats, and clear nonthreats. Samples were recruited from combat-trained infantry, military recruits, and the civilian community to control for prior lethal force training. Although there was a strong omnibus relationship between threat perception and the likelihood of a behavioral response, neither military training nor personality differences had any impact on threat perception or a binary (e.g., shoot/don't-shoot) behavioral response. Therefore, we conclude that perception dominates personality in lethal force decision making when the threat assessment decision is limited to factors such as weapon presence or posture rather than emotion.

Task demands determine whether shape or arousal of a stimulus modulates competition for visual working memory resources

It has been posited (Öhman, 1986) that the processing of threatening stimuli became prioritized during the course of mammalian evolution and that such objects may still enjoy an advantage in visual processing to this day. It has been well-documented that both mid-level visual features (i.e., conjunctions of low-level features) and the arousal level of threatening stimuli affect attentional allocation (Cisler & Koster, 2010; Wolfe & Horowitz, 2004). Despite this, few studies have investigated the effect these factors have on visual working memory resources. Here, we investigated these factors using a rapid serial visual presentation (RSVP) paradigm, and by manipulating mid-level features (specifically, shape: similar vs. dissimilar) and the arousal level (non-threatening vs threatening) of the stimuli. Participants watched an RSVP stream in preparation for an upcoming memory test. Then, they completed a two-alternative forced-choice recognition memory test (with semantically matched foils) wherein they had to identify which item they had seen in the RSVP stream. Our results showed that when shape was a sufficient feature to discriminate the target from the other items in the stream, there was no effect of arousal (i.e., threat level) on reaction time or accuracy during the memory test. However, when the shapes of all the stimuli in the visual stream were highly similar, an effect of arousal appeared: When the target had a different arousal level than the background items (i.e., non-targets), performance was improved. Together, the results suggest that both mid-level visual features and arousal level can modulate competition for visual working memory resources.

Working Memory Performance for Differentially Conditioned Stimuli

Previous work suggests that threat-related stimuli are stored to a greater degree in working memory compared to neutral stimuli. However, most of this research has focused on stimuli with physically salient threat attributes (e.g., angry faces), failing to account for how a "neutral" stimulus that has acquired threat-related associations through differential aversive conditioning influences working memory. The current study examined how differentially conditioned safe (i.e., CS-) and threat (i.e., CS+) stimuli are stored in working memory relative to a novel, non-associated (i.e., N) stimuli. Participants (n = 69) completed a differential fear conditioning task followed by a change detection task consisting of three conditions (CS+, CS-, N) across two loads (small, large). Results revealed individuals successfully learned to distinguishing CS+ from CS- conditions during the differential aversive conditioning task. Our working memory outcomes indicated successful load manipulation effects, but no statistically significant differences in accuracy, response time (RT), or Pashler's K measures of working memory capacity between CS+, CS-, or N conditions. However, we observed significantly reduced RT difference scores for the CS+ compared to CS- condition, indicating greater RT differences between the CS+ and N condition vs. the CS- and N condition. These findings suggest that differentially conditioned stimuli have little impact on behavioral outcomes of working memory compared to novel stimuli that had not been associated with previous safe of aversive outcomes, at least in healthy populations.

Open biological negative image set

Scientists conducting affective research often use visual, emotional images, to examine the mechanisms of defensive responses to threatening and dangerous events and objects. Many studies use the rich emotional images from the International Affective Picture System (IAPS) to facilitate affective research. While IAPS images can be classified into emotional categories such as fear or disgust, the number of images per discrete emotional category is limited. We developed the Open Biological Negative Image Set (OBNIS) consisting of 200 colour and greyscale creature images categorized as disgusting, fearful or neither. Participants in Experiment 1 (N = 210) evaluated the images' valence and arousal and classified them as disgusting, fearful or neither. In Experiment 2, other participants (N = 423) rated the disgust and fear levels of the images. As a result, the OBNIS provides valence, arousal, disgust and fear ratings and 'disgusting,' 'fearful' and 'neither' emotional categories for each image. These images are available to download on the Internet (https://osf.io/pfrx4/?view_only=911b1be722074ad4aab87791cb8a72f5).

Monkeying around with venom: an increased resistance to α-neurotoxins supports an evolutionary arms race between Afro-Asian primates and sympatric cobras

Background

Snakes and primates have a multi-layered coevolutionary history as predators, prey, and competitors with each other. Previous work has explored the Snake Detection Theory (SDT), which focuses on the role of snakes as predators of primates and argues that snakes have exerted a selection pressure for the origin of primates’ visual systems, a trait that sets primates apart from other mammals. However, primates also attack and kill snakes and so snakes must simultaneously avoid primates. This factor has been recently highlighted in regard to the movement of hominins into new geographic ranges potentially exerting a selection pressure leading to the evolution of spitting in cobras on three independent occasions.

Results

Here, we provide further evidence of coevolution between primates and snakes, whereby through frequent encounters and reciprocal antagonism with large, diurnally active neurotoxic elapid snakes, Afro-Asian primates have evolved an increased resistance to α-neurotoxins, which are toxins that target the nicotinic acetylcholine receptors. In contrast, such resistance is not found in Lemuriformes in Madagascar, where venomous snakes are absent, or in Platyrrhini in the Americas, where encounters with neurotoxic elapids are unlikely since they are relatively small, fossorial, and nocturnal. Within the Afro-Asian primates, the increased resistance toward the neurotoxins was significantly amplified in the last common ancestor of chimpanzees, gorillas, and humans (clade Homininae). Comparative testing of venoms from Afro-Asian and American elapid snakes revealed an increase in α-neurotoxin resistance across Afro-Asian primates, which was likely selected against cobra venoms. Through structure-activity studies using native and mutant mimotopes of the α-1 nAChR receptor orthosteric site (loop C), we identified the specific amino acids responsible for conferring this increased level of resistance in hominine primates to the α-neurotoxins in cobra venom.

Conclusion

We have discovered a pattern of primate susceptibility toward α-neurotoxins that supports the theory of a reciprocal coevolutionary arms-race between venomous snakes and primates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01195-x.

Fear inoculation among snake experts

BACKGROUND

Fear acquisition of certain stimuli, such as snakes, is thought to be rapid, resistant to extinction, and easily transferable onto other similar objects. It has been hypothesized that due to increased survival chances, preparedness to instantly acquire fear towards evolutionary threats has been hardwired into neural pathways of the primate brain. Here, we compare participants' fear of snakes according to experience; from those who often deal with snakes and even suffer snakebites to those unfamiliar with snakes.

METHODS

The Snake Questionnaire-12 (SNAQ-12) and Specific Phobia Questionnaire (SPQ) were administered to three groups of participants with a different level of experience with snakes and snakebites: 1) snake experts, 2) firefighters, and 3) college students.

RESULTS

This study shows that individuals more experienced with snakes demonstrate lower fear. Moreover, participants who have suffered a snakebite (either venomous or not) score lower on fear of snakes (SNAQ-12), but not of all other potentially phobic stimuli (SPQ).

CONCLUSIONS

Our results suggest that a harmless benign exposure might immunize people to highly biologically prepared fears of evolutionary threats, such as snakes.

Slower access to visual awareness but otherwise intact implicit perception of emotional faces in schizophrenia-spectrum disorders

Schizophrenia-spectrum disorders are characterized by deficits in social domains. Extant research has reported an impaired ability to perceive emotional faces in schizophrenia. Yet, it is unclear if these deficits occur already in the access to visual awareness. To investigate this question, 23 people with schizophrenia or schizoaffective disorder and 22 healthy controls performed a breaking continuous flash suppression task with fearful, happy, and neutral faces. Response times were analysed with generalized linear mixed models. People with schizophrenia-spectrum disorders were slower than controls in detecting faces, but did not show emotion-specific impairments. Moreover, happy faces were detected faster than neutral and fearful faces, across all participants. Although caution is needed when interpreting the main effect of group, our findings may suggest an elevated threshold for visual awareness in schizophrenia-spectrum disorders, but an intact implicit emotion perception. Our study provides a new insight into the mechanisms underlying emotion perception in schizophrenia-spectrum disorders.

Neutral and threatening distracter word stimuli are unnecessarily stored in working memory but do not differ in their degree of working memory storage

Evidence suggests that threatening stimuli induce attentional biases compared to neutral stimuli, leading to subsequent storage in working memory. The current study examined how threatening versus neutral word distracters influence attention, and how this affects the unnecessary storage of these task-irrelevant stimuli in working memory. We measured the N2pc and contralateral delay activity (CDA), two event-related potentials (ERPs) that index attentional selection and the number of items maintained in WM, respectively, as participants completed a lateralized change detection task using word stimuli. Our results replicated work demonstrating a CDA effect for word stimuli, and found that distracter words are unnecessarily stored in working memory. However, we observed non-significant differences in attentional bias and working memory storage between distracter word conditions, and individual variation in anxiety was not associated with these processes. Bayes Factor analyses supported these null effects, suggesting that differences between neutral and threatening distracter words are unlikely.

Preferential Neuronal Responses to Snakes in the Monkey Medial Prefrontal Cortex Support an Evolutionary Origin for Ophidiophobia

Ophidiophobia (snake phobia) is one of the most common specific phobias. It has been proposed that specific phobia may have an evolutionary origin, and that attentional bias to specific items may promote the onset of phobia. Noninvasive imaging studies of patients with specific phobia reported that the medial prefrontal cortex (mPFC), especially the rostral part of the anterior cingulate cortex (rACC), and amygdala are activated during the presentation of phobogenic stimuli. We propose that the mPFC-amygdala circuit may be involved in the pathogenesis of phobia. The mPFC receives inputs from the phylogenically old subcortical visual pathway including the superior colliculus, pulvinar, and amygdala, while mPFC neurons are highly sensitive to snakes that are the first modern predator of primates, and discriminate snakes with striking postures from those with non-striking postures. Furthermore, the mPFC has been implicated in the attentional allocation and promotes amygdala-dependent aversive conditioning. These findings suggest that the rACC focuses attention on snakes, and promotes aversive conditioning to snakes, which may lead to anxiety and ophidiophobia.

Effects of cognitive load and type of object on the visual looming bias

According to the behavioral urgency hypothesis, organisms have evolved various mechanisms that facilitate their survival by focusing attention and resources on approaching danger. One example of such mechanisms is the looming bias-the tendency for an individual to judge an approaching object's distance as being closer or time-to-collision as being sooner than receding or stationary objects. To date, most research on the looming bias has explored the ways in which human factors and object characteristics influence the strength and direction of the bias. The current study expanded on this field of research in two novels ways by exploring (a) whether cognitive vulnerabilities may influence the strength of the looming bias in the visual domain, and (b) whether the combination of human factors (i.e., cognitive load) and object characteristics (i.e., object threat) interact to create an additive effect on looming bias strength. Findings appear to only partially support the hypotheses that cognitive vulnerabilities can influence looming bias strength in the visual domain, and that factors related to both the individual and the looming object may interact to create a stronger looming bias. These findings help to highlight possible evolutionary advantages of the looming bias and its presence across modalities, as well as add some strength to the claims that the margin of safety theory can be generalized to include psychological factors.

Preferential snake detection in a simulated ecological experiment

OBJECTIVES

According to Isbell's snake detection theory (SDT), the need to rapidly detect and thus avoid snakes had a major impact on the evolution of the primate visual system, and thus the origin and evolution of the primate lineage, as expansion of the visual sense is a key characteristic of primates. The SDT rests on the assumption that there are both cortical (conscious) and subcortical (unconscious) brain structures and pathways that are responsible for rapid visual detection of and quick avoidance reactions to snakes. Behavioral evidence for the SDT primarily comes from visual search tasks and presentations of images on a computer screen; our aim was to evaluate the SDT under more ecologically valid circumstances.

MATERIALS AND METHODS

We asked participants to take a virtual hike in which a realistic model of a snake, rabbit, or bottle had been placed on the trail. Subjects were instructed simply to imagine themselves as the hiker while watching the video. We measured heart rate and skin conductance reactions while the participants viewed the video. After the video, the participants were shown pictures of the three stimuli and asked if they had seen any of them.

RESULTS

We found that snakes were detected more often than rabbits or bottles, and that participants showed greater changes in heart rate and greater skin conductance responses in the snake condition than in the other two conditions, even when the participant did not report having seen the snake.

DISCUSSION

A critical component of the SDT is that primates must be able to quickly detect snakes even when their attention is directed elsewhere. Using a novel experimental context-a simulated hike-we assessed arousal and detection without directing participants to attend to any particular stimulus or event. Our data support the SDT by providing evidence of enhanced detection and autonomic arousal even in the absence of detection. Replication of these results using additional controls and experimental contexts will help refine our understanding of snake avoidance by primates.

Early posterior negativity in humans to pictures of snakes and spiders: effects of proximity

Snakes have proven to drive early attentional capture due to their evolutionary importance, as reflected by the early posterior negativity (EPN). The EPN snake effect might be partly driven by the proximity of the animal. In this study, by employing full-body (medium shot) and head-focused (close-up) pictures, we investigated whether the relative nearness (proximity) of the animal on the picture affects the snake EPN effect. We presented thirty participants with medium shot and close-up snake, spider and bird pictures in a rapid serial presentation paradigm at a presentation rate of three frames per second. We extracted the mean EPN activity from the 225–330 ms time frame after stimulus onset at the parietal–occipital cluster (PO3, O1, Oz, O2, PO4). The results indicate enhanced EPN for snake pictures as compared to spider and bird pictures. In addition, medium-shot snake pictures elicited higher EPN amplitudes than close-up snake pictures, suggesting that the EPN is higher when local, high spatial frequency attributes are visible. Spatial frequency analysis of the stimuli indicated that medium-shot snake pictures possess more power in the high spatial frequency bands, compared to medium-shot spider and bird pictures.

Negative content enhances stimulus-specific cerebral activity during free viewing of pictures, faces, and words

Negative visual stimuli have been found to elicit stronger brain activation than do neutral stimuli. Such emotion effects have been shown for pictures, faces, and words alike, but the literature suggests stimulus-specific differences regarding locus and lateralization of the activity. In the current functional magnetic resonance imaging study, we directly compared brain responses to passively viewed negative and neutral pictures of complex scenes, faces, and words (nouns) in 43 healthy participants (21 males) varying in age and demographic background. Both negative pictures and faces activated the extrastriate visual cortices of both hemispheres more strongly than neutral ones, but effects were larger and extended more dorsally for pictures, whereas negative faces additionally activated the superior temporal sulci. Negative words differentially activated typical higher-level language processing areas such as the left inferior frontal and angular gyrus. There were small emotion effects in the amygdala for faces and words, which were both lateralized to the left hemisphere. Although pictures elicited overall the strongest amygdala activity, amygdala response to negative pictures was not significantly stronger than to neutral ones. Across stimulus types, emotion effects converged in the left anterior insula. No gender effects were apparent, but age had a small, stimulus-specific impact on emotion processing. Our study specifies similarities and differences in effects of negative emotional content on the processing of different types of stimuli, indicating that brain response to negative stimuli is specifically enhanced in areas involved in processing of the respective stimulus type in general and converges across stimuli in the left anterior insula.

Brain networks mediating the influence of background music on selective attention

Prevalent across societies and times, music has the ability to enhance attention, a property relevant to clinical applications, but the underlying brain mechanisms remain unknown. It is also unclear whether music produces similar or differential effects with advancing age. Here, we used event-related functional magnetic resonance imaging to investigate the influence of music exposure evoking four types of emotions on distinct attentional components measured with a modified attention network test, across 19 young (21 ± 2.6) and 33 old participants (72 ± 5.4). We then determined whether music-related effects differed across age groups and whether they were associated with particular acoustic features. Background music during selective attention requiring distractor conflict resolution was associated with faster response times and greater activations of fronto-parietal areas during happy and high-arousing music, whereas sad and low-valence music was associated with slower responses and greater occipital recruitment. Shifting and altering components of attention were unaffected. The influence of music on performance and brain networks was similar between age groups. These behavioral and neuroimaging results demonstrate the importance of affective music dimensions, particularly arousal, in enhancing selective attention processes. This study adds novel support to the benefits of music in the rehabilitation of attention functions.

Snakes elicit specific neural responses in the human infant brain

Detecting predators is essential for survival. Given that snakes are the first of primates' major predators, natural selection may have fostered efficient snake detection mechanisms to allow for optimal defensive behavior. Here, we provide electrophysiological evidence for a brain-anchored evolved predisposition to rapidly detect snakes in humans, which does not depend on previous exposure or knowledge about snakes. To do so, we recorded scalp electrical brain activity in 7- to 10-month-old infants watching sequences of flickering animal pictures. All animals were presented in their natural background. We showed that glancing at snakes generates specific neural responses in the infant brain, that are higher in amplitude than those generated by frogs or caterpillars, especially in the occipital region of the brain. The temporal dynamics of these neural responses support that infants devote increased attention to snakes than to non-snake stimuli. These results therefore demonstrate that a single fixation at snakes is sufficient to generate a prompt and large selective response in the infant brain. They argue for the existence in humans of an inborn, brain-anchored mechanism to swiftly detect snakes based on their characteristic visual features.

Increased attention to snake images in cynomolgus monkeys: an eye-tracking study

Previous studies have revealed faster detection of snake images in humans and non-human primates (NHPs), suggesting automatic detection of evolutionary fear-relevant stimuli. Furthermore, human studies have indicated that general fear-relevance rather than evolutionary relevance is more effective at capturing attention. However, the issue remains unclarified in NHPs. Thus, in the present study, we explored the attentional features of laboratory-reared monkeys to evolutionary and general fear-relevant stimuli (e.g., images of snakes, capturing gloves). Eye-tracking technology was utilized to assess attentional features as it can provide more accurate latency and variables of viewing duration and frequency compared with visual search task (VST) and response latency adopted in previous studies. In addition, those with autism spectrum disorder (ASD) show abnormal attention to threatening stimuli, including snake images. Rett syndrome (RTT) is considered a subcategory of ASD due to the display of autistic features. However, the attentional features of RTT patients or animal models to such stimuli remain unclear. Therefore, we also investigated the issue in MECP2 gene-edited RTT monkeys. The influence of different cognitive loads on attention was further explored by presenting one, two, or four images to increase stimulus complexity. The eye-tracking results revealed no significant differences between RTT and control monkeys, who all presented increased viewing (duration and frequency) of snake images but not of aversive stimuli compared with control images, thus suggesting attentional preference for evolutionary rather than general fear-relevant visual stimuli. Moreover, the preference was only revealed in visual tasks composed of two or four images, suggesting its cognitive-load dependency.

Animacy effects extend to working memory: results from serial order recall tasks

Words that represent animate entities (e.g., dog) are recalled from long-term memory more accurately than words representing inanimate entities (e.g., pan). In this research, we examined whether the animacy effect extends to working memory (WM). The potential roles of WM maintenance strategies (rehearsal and directed attention) were also examined. Participants performed serial order recall tasks with sets of 3, 4, 5 or 6 words that were either animate or inanimate. In stage 1 of Experiment 1, participants received no instructions regarding how to maintain the words. In stage 2, participants received either no instructions, sub-vocal rehearsal or directed attention instructions. In all instruction groups and at both stages, significant animacy effects were observed at set sizes of 4, 5 and 6 but not set size 3. The animacy effect was larger at set size 5 than other set sizes. In Experiment 2, participants completed the task with and without articulatory suppression. In both conditions, animacy effects were observed at set sizes 4, 5 and 6, but not at set size 3. The magnitude of the animacy effect declined as set size increased from 4 to 6. Animacy appears to enhance serial recall, but the effect is not dependent on rehearsal.

Spider Venom: Components, Modes of Action, and Novel Strategies in Transcriptomic and Proteomic Analyses

This review gives an overview on the development of research on spider venoms with a focus on structure and function of venom components and techniques of analysis. Major venom component groups are small molecular mass compounds, antimicrobial (also called cytolytic, or cationic) peptides (only in some spider families), cysteine-rich (neurotoxic) peptides, and enzymes and proteins. Cysteine-rich peptides are reviewed with respect to various structural motifs, their targets (ion channels, membrane receptors), nomenclature, and molecular binding. We further describe the latest findings concerning the maturation of antimicrobial, and cysteine-rich peptides that are in most known cases expressed as propeptide-containing precursors. Today, venom research, increasingly employs transcriptomic and mass spectrometric techniques. Pros and cons of venom gland transcriptome analysis with Sanger, 454, and Illumina sequencing are discussed and an overview on so far published transcriptome studies is given. In this respect, we also discuss the only recently described cross contamination arising from multiplexing in Illumina sequencing and its possible impacts on venom studies. High throughput mass spectrometric analysis of venom proteomes (bottom-up, top-down) are reviewed.

Does Threat Have an Advantage After All? - Proposing a Novel Experimental Design to Investigate the Advantages of Threat-Relevant Cues in Visual Processing

The automatic visual attentional procession of threatening stimuli over non-threatening cues has long been a question. The so-called classical visual search task (VST) has quickly become the go-to paradigm to investigate this. However, the latest results showed that the confounding results could originate from the shortcomings of the VST. Thus, here we propose a novel approach to the behavioral testing of the threat superiority effect. We conducted two experiments using evolutionary relevant and modern real-life scenes (e.g., forest or street, respectively) as a background to improve ecological validity. Participants had to find different targets in different spatial positions (close to fovea or periphery) using a touch-screen monitor. In Experiment 1 participants had to find the two most often used exemplar of the evolutionary and modern threatening categories (snake and gun, respectively), or neutral objects of the same category. In Experiment 2 we used more exemplars of each category. All images used were controlled for possible confounding low-level visual features such as contrast, frequency, brightness, and image complexity. In Experiment 1, threatening targets were found faster compared to neutral cues irrespective of the evolutionary relevance. However, in Experiment 2, we did not find an advantage for threatening targets over neutral ones. In contrast, the type of background, and spatial position of the target only affected the detection of neutral targets. Our results might indicate that some stimuli indeed have an advantage in visual processing, however, they are not highlighted based on evolutionary relevance of negative valence alone, but rather through different associational mechanisms.

Are Humans Prepared to Detect, Fear, and Avoid Snakes? The Mismatch Between Laboratory and Ecological Evidence

Since Seligman (1971) statement that the vast majority of phobias are about objects essential to the survival of a species, a multitude of laboratory studies followed, supporting the finding that humans learn to fear and detect snakes (and other animals) faster than other stimuli. Most of these studies used schematic drawings, images, or pictures of snakes, and only a small amount of fieldwork in naturalistic environments was done. We address fear preparedness theories and automatic fast detection data from mainstream laboratory data and compare it with ethobehavioral information relative to snakes, predator-prey interaction, and snakes' defensive kinematics strikes in order to analyze their potential matching. From this analysis, four main findings arose, namely that (1) snakebites occur when people are very close to the snake and are unaware or unable to escape the bite; (2) human visual detection and escape response is slow compared to the speed of snake strikes; (3) in natural environments, snake experts are often unable to see snakes existing nearby; (4) animate objects in general capture more attention over other stimuli and dangerous, but recent objects in evolutionary terms are also able to be detected fast. The issues mentioned above pose several challenges to evolutionary psychology-based theories expecting to find special-purpose neural modules. The older selective habituation hypothesis (Schleidt, 1961) that prey animals start with a rather general predator image from which specific harmless cues are removed by habituation might deserve reconsideration.

Superior Neuronal Detection of Snakes and Conspecific Faces in the Macaque Medial Prefrontal Cortex

Snakes and conspecific faces are quickly and efficiently detected in primates. Because the medial prefrontal cortex (mPFC) has been implicated in attentional allocation to biologically relevant stimuli, we hypothesized that it might also be highly responsive to snakes and conspecific faces. In this study, neuronal responses in the monkey mPFC were recorded, while monkeys discriminated 8 categories of visual stimuli. Here, we show that the monkey mPFC neuronal responses to snakes and conspecific faces were unique. First, the ratios of the neurons that responded strongly to snakes and monkey faces were greater than those of the neurons that responded strongly to the other stimuli. Second, mPFC neurons responded stronger and faster to snakes and monkey faces than the other categories of stimuli. Third, neuronal responses to snakes were unaffected by low-pass filtering of the images. Finally, activity patterns of responsive mPFC neurons discriminated snakes from the other stimuli in the second 50 ms period and monkey faces in the third period after stimulus onset. These response features indicate that the mPFC processes fast and coarse visual information of snakes and monkey faces, and support the hypothesis that snakes and social environments have shaped the primate visual system over evolutionary time.

Human Attitude toward Reptiles: A Relationship between Fear, Disgust, and Aesthetic Preferences

Focusing on one group of animals can bring interesting results regarding our attitudes toward them and show the key features that our evaluation of such animals is based on. Thus, we designed a study of human perception of all reptiles focusing on the relationship between perceived fear, disgust, and aesthetic preferences and differences between snakes and other reptiles. Two sets containing 127 standardized photos of reptiles were developed, with one species per each subfamily. Respondents were asked to rate the animals according to fear, disgust, and beauty on a seven-point Likert scale. Evaluation of reptile species shows that people tend to perceive them as two clearly distinct groups based on their similar morphotype. In a subset of lizards, there was a positive correlation between fear and disgust, while disgust and fear were both negatively correlated with beauty. Surprisingly, a positive correlation between fear and beauty of snakes was revealed, i.e., the most feared species also tend to be perceived as beautiful. Snakes represent a distinct group of animals that is also reflected in the theory of attentional prioritization of snakes as an evolutionary relevant threat.

Snakes Represent Emotionally Salient Stimuli That May Evoke Both Fear and Disgust

Humans perceive snakes as threatening stimuli, resulting in fast emotional and behavioral responses. However, snake species differ in their true level of danger and are highly variable in appearance despite the uniform legless form. Different snakes may evoke fear or disgust in humans, or even both emotions simultaneously. We designed three-step-selection experiments to identify prototypical snake species evoking exclusively fear or disgust. First, two independent groups of respondents evaluated 45 images covering most of the natural variability of snakes and rated responses to either perceived fear (n = 175) or disgust (n = 167). Snakes rated as the most fear-evoking were from the family Viperidae (Crotalinae, Viperinae, and Azemiopinae), while the ones rated as the most disgusting were from the group of blind snakes called Typhlopoidea (Xenotyphlopinae, Typhlopinae, and Anomalepidinae). We then identified the specific traits contributing to the perception of fear (large body size, expressive scales with contrasting patterns, and bright coloration) and disgust (thin body, smooth texture, small eyes, and dull coloration). Second, to create stimuli evoking a discrete emotional response, we developed a picture set consisting of 40 snakes with exclusively fear-eliciting and 40 snakes with disgust-eliciting features. Another set of respondents (n = 172) sorted the set, once according to perceived fear and the second time according to perceived disgust. The results showed that the fear-evoking and disgust-evoking snakes fit mainly into their respective groups. Third, we randomly selected 20 species (10 fear-evoking and 10 disgust-evoking) out of the previous set and had them professionally illustrated. A new set of subjects (n = 104) sorted these snakes and confirmed that the illustrated snakes evoked the same discrete emotions as their photographic counterparts. These illustrations are included in the study and may be freely used as a standardized assessment tool when investigating the role of fear and disgust in human emotional response to snakes.

The evil eye effect: vertical pupils are perceived as more threatening

Popular culture has many examples of evil characters having vertically pupilled eyes. Humans have a long evolutionary history of rivalry with snakes and their visual systems were evolved to rapidly detect snakes and snake-related cues. Considering such evolutionary background, we hypothesised that humans would perceive vertical pupils, which are characteristics of ambush predators including some of the snakes, as threatening. In seven studies (aggregate N = 1458) conducted on samples from American and Turkish samples, we found that vertical pupils are perceived as more threatening on both explicit (Study 1) and implicit level (Studies 2-7) and they are associated with physical, rather than social, threat (Study 4). Findings provided partial support regarding our hypothesis about the relevance of snake detection processes: Snake phobia, and not spider phobia, was found to be related to perceiving vertical pupils as threatening (Study 5), however an experimental manipulation of saliency of snakes rendered no significant effect (Study 6) and a comparison of fears of snakes, alligators, and cats did not support our prediction (Study 7). We discuss the potential implications and limitations of these novel findings.

Walking with perturbations: a guide for biped humans and robots

This paper provides an update on the neural control of bipedal walking in relation to bioinspired models and robots. It is argued that most current models or robots are based on the construct of a symmetrical central pattern generator (CPG). However, new evidence suggests that CPG functioning is basically asymmetrical with its flexor half linked more tightly to the rhythm generator. The stability of bipedal gait, which is an important problem for robots and biological systems, is also addressed. While it is not possible to determine how biological biped systems guarantee stability, robot solutions can be useful to propose new hypotheses for biology. In the second part of this review, the focus is on gait perturbations, which is an important topic in robotics in view of the frequent falls of robots when faced with perturbations. From the human physiology it is known that the initial reaction often consists of a brief interruption followed by an adequate response. For instance, the successful recovery from a trip is achieved using some basic reactions (termed elevating and lowering strategies), that depend on the phase of the step cycle of the trip occurrence. Reactions to stepping unexpectedly in a hole depend on comparing expected and real feedback. Implementation of these ideas in models and robotics starts to emerge, with the most advanced robots being able to learn how to fall safely and how to deal with complicated disturbances such as provided by walking on a split-belt.

Gender Differences in the Automatic Attention to Romantic Vs Sexually Explicit Stimuli

INTRODUCTION

Gender differences in sexual responses and cognitive and emotional processing to romantic and sexually explicit stimuli have been reported. However, these differences seem to depend on the automaticity of the task that is being used, thus suggesting that gender differences may be the result of specific mechanisms rather than a generalized effect.

AIM

To expand previous basic processes research on gender differences to romantic vs sexually explicit stimuli, focusing on potential differentiating mechanisms influencing male and female sexual responses, we aim to investigate gender differences on automatic attention to sexual stimuli, and to test its relationship with sexual excitation proneness.

METHODS

26 women and 30 men (heterosexual) performed an automatic attention task, in which romantic and sexually explicit stimuli were presented as distractors, that is, stimuli to be ignored, while a concurrent letter discrimination task was performed, followed by a self-report task assessing subjective sexual and emotional responses to the stimuli.

MAIN OUTCOME MEASURES

Percentage of accuracy and response times (RTs) to discriminate the target letters were used as markers of automatic attention, with lower accuracy and longer RTs reflecting a higher degree of attentional capture by the distractor stimuli (romantic and sexually explicit). Participants completed self-report ratings on emotional valence, general arousal, and sexual arousal toward romantic and sexually explicit stimuli. They further reported on their sexual excitation proneness.

RESULTS

Findings revealed that sexually explicit pictures yielded more automatic attention capture. However, this effect was superseded by pornography consumption, which likely reflects a habituation mechanism. Also, data revealed gender-x type of picture interaction effects only at the self-report task, with men rating sexually explicit stimuli as more sexually exciting, and women rating these stimuli as less pleasant. No relationship was found between automatic attention proxies and sexual excitation proneness.

CLINICAL TRANSLATION

While therapeutic strategies are used as tools to improve attention to sexual stimuli (and, hence, increase sexual arousal), the current findings suggest that the specific pathways by which attention influences sexual response are still to be established. Also, gender differences on the subjective appraisal of sex stimuli suggest that therapeutic approaches, consisting on exposure techniques, must recognize gender specificities.

STRENGTHS & LIMITATIONS

To our knowledge, this is the first study applying an automatic attention task to the field of sex research, thus adding new inputs to the topic of attention, gender differences, and sexual response. However, there is very limited research in the field of automatic attention, which may limit the interpretation of our findings, at the moment.

CONCLUSION

Whereas both genders do not seem to differ in automatic attention toward romantic and sexually explicit stimuli, their responses do differ in their subjective appraisal of the stimuli. Furthermore, despite theoretical assumptions on the relationship between attention and sexual response, automatic attention seemed not to be related to sexual excitation proneness. Carvalho J, Czop O, Rocha M, et al. Gender differences in the automatic attention to romantic vs sexually explicit stimuli. J Sex Med 2018;15:1083-1092.

Count on arousal: introducing a new method for investigating the effects of emotional valence and arousal on visual search performance

There is a large body of research, indicating that threatening stimuli with evolutionary history are prioritised in visual processing. It has been proposed that all threatening stimuli are prioritised, irrespective of evolutionary age, but it was argued that the method used to produce the results was not suitable for investigating the phenomenon. We present a new visual search task and provide evidence that it is an appropriate tool for future research. In Experiment 1, we investigated how the influence of emotional stimuli on visual search performance varies with valence (negative, positive, and neutral) and arousal (medium and high). Negative valence found to have a greater impact. Furthermore, our results underscore the importance of controlling for arousal. Experiment 2 confirmed these findings and also revealed that negative valence decreases performance by diverting attention away from the task, but arousal can compensate for this by increasing attentional capacity. This mechanism does not seem to be affected by the evolutionary history of the stimulus. In Experiment 3, we reproduced these results using a touchscreen monitor and controlling for variance in low-level visual features. We claim that these results support the notion of preferential processing of threatening cues, regardless of evolutionary origin. However, the level of threat, i.e., how arousing the cue is, has to be taken into account to explain the findings.

Subcortical Facilitation of Behavioral Responses to Threat

Behavioral responses to threat are critical to survival. Several cortical and subcortical brain regions respond selectively to threat. However, the relation of these neural responses and their underlying representations to behavior is unclear. We examined the contribution of lower-order subcortical representations to behavioral responses to threat in adult humans. In Experiments 1 and 2, participants viewed pairs of images presented to the same eye or to different eyes. We observed a monocular advantage, which indicates subcortical facilitation, for ancestral threats (snakes, spiders), but not for modern threats, positive images, or neutral images. In Experiment 3, we presented pairs of snakes or neutral images into the temporal or nasal hemifield. For snakes only, we observed a temporal hemifield advantage, which indicates facilitation by the retino-tectal subcortical pathway. These results advance the current understanding of processing of threat by adult humans by revealing the characteristics of behaviors driven by a lower-order neural mechanism that is specialized for the processing of ancestral threats. The results also contribute to ongoing debates concerning the biological generality of neural mechanisms for processing of complex, emotionally-relevant stimuli by providing evidence for conservation of lower-order neural mechanisms for processing of ancestral threats across both ontogeny and phylogeny.

Food or threat? Wild capuchin monkeys (Sapajus libidinosus) as both predators and prey of snakes

Snakes present a hazard to primates, both as active predators and by defensive envenomation. This risk might have been a selective pressure on the evolution of primate visual and cognitive systems, leading to several behavioral traits present in human and non-human primates, such as the ability to quickly learn to fear snakes. Primates seldom prey on snakes, and humans are one of the few primate species that do. We report here another case, the wild capuchin monkey (Sapajus libidinosus), which preys on snakes. We hypothesized that capuchin monkeys, due to their behavioral plasticity, and cognitive and visual skills, would be capable of discriminating dangerous and non-dangerous snakes and behave accordingly. We recorded the behavioral patterns exhibited toward snakes in two populations of S. libidinosus living 320 km apart in Piauí, Brazil. As expected, capuchins have a fear reaction to dangerous snakes (usually venomous or constricting snakes), presenting mobbing behavior toward them. In contrast, they hunt and consume non-dangerous snakes without presenting the fear response. Our findings support the tested hypothesis that S. libidinosus are capable of differentiating snakes by level of danger: on the one hand they protect themselves from dangerous snakes, on the other hand they take opportunities to prey on non-dangerous snakes. Since capuchins and humans are both predators and prey of snakes, further studies of this complex relationship may shed light on the evolution of these traits in the human lineage.

Exogenous attention to fear: Differential behavioral and neural responses to snakes and spiders

Research has consistently shown that threat stimuli automatically attract attention in order to activate the defensive response systems. Recent findings have provided evidence that snakes tuned the visual system of evolving primates for their astute detection, particularly under challenging perceptual conditions. The goal of the present study was to measure behavioral and electrophysiological indices of exogenous attention to snakes, compared with spiders - matched for rated fear levels but for which sources of natural selection are less well grounded, and to innocuous animals (birds), which were presented as distracters, while participants were engaged in a letter discrimination task. Duration of stimuli, consisting in a letter string and a concurrent distracter, was either presented for 180 or 360ms to explore if the stimulus duration was a modulating effect of snakes in capturing attention. Results showed a specific early (P1) exogenous attention-related brain potential with maximal amplitude to snakes in both durations, which was followed by an enhanced late attention-related potential (LPP) showing enhanced amplitudes to spiders, particularly under the longer exposure durations. These results suggest that exogenous attention to different classes of threat stimuli follows a gradual process, with the most evolutionary-driven stimulus, i.e., snakes, being more efficient at attracting early exogenous attention, thus more dependent on bottom-up processes.