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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.

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.

IntroductionThe administration of questionnaires presents an easy way of obtaining important knowledge about phobic patients. However, it is not well known how these subjective measurements correspond to the patient’s objective condition. Our study aimed to compare scores on questionnaires and image evaluation to the objective measurements of the behavioral approach test (BAT) and the neurophysiological effect of spiders extracted from fMRI measurements. The objective was to explore how reliably subjective statements about spiders and physiological and behavioral parameters discriminate between phobics and non-phobics, and what are the best predictors of overall brain activation.MethodsBased on a clinical interview, 165 subjects were assigned to either a “phobic” or low-fear “control” group. Finally, 30 arachnophobic and 32 healthy control subjects (with low fear of spiders) participated in this study. They completed several questionnaires (SPQ, SNAQ, DS-R) and underwent a behavioral approach test (BAT) with a live tarantula. Then, they were measured in fMRI while watching blocks of pictures including spiders and snakes. Finally, the respondents rated all the visual stimuli according to perceived fear. We proposed the Spider Fear Index (SFI) as a value characterizing the level of spider fear, computed based on the fMRI measurements. We then treated this variable as the “neurophysiological effect of spiders” and examined its contribution to the respondents’ fear ratings of the stimuli seen during the fMRI using the redundancy analysis (RDA).ResultsThe results for fear ranks revealed that the SFI, SNAQ, DS-R, and SPQ scores had a significant effect, while BAT and SPQ scores loaded in the same direction of the first multivariate axis. The SFI was strongly correlated with both SPQ and BAT scores in the pooled sample of arachnophobic and healthy control subjects.DiscussionBoth SPQ and BAT scores have a high informative value about the subject’s fear of spiders and together with subjective emotional evaluation of picture stimuli can be reliable predictors of spider phobia. These parameters provide easy and non-expensive but reliable measurement wherever more expensive devices such as magnetic resonance are not available. However, SFI still reflects individual variability within the phobic group, identifying individuals with higher brain activation, which may relate to more severe phobic reactions or other sources of fMRI signal variability.

Abstract Spiders are mostly harmless, yet they often trigger high levels of both fear and disgust, and arachnophobia (the phobia of spiders) ranks among the most common specific animal phobias. To investigate this apparent paradox, we turned to the only close relatives of spiders that pose a real danger to humans: scorpions. We adopted a unique methodology in order to assess authentic emotions elicited by arthropods. Over 300 respondents were asked to rate live specimens of 62 arthropod species (including spiders, scorpions, cockroaches, and other insects) based on perceived fear, disgust, and beauty. We found that species’ scores on all three scales depended on the higher taxon as well as on body size. Spiders, scorpions, and other arachnids scored the highest in fear and disgust, while beetles and crabs scored the highest in beauty. Moreover, all chelicerates were perceived as one cohesive group, distinct from other arthropods, such as insects or crabs. Based on these results, we hypothesize that the fear of spiders might be triggered by a generalized fear of chelicerates, with scorpions being the original stimulus that signals danger.

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.

To investigate a specificity of spiders as a prototypical fear- and disgust-eliciting stimuli, we conducted an online experiment. The respondents rated images of 25 spiders, 12 non-spider chelicerates, and 10 other arthropods on a fear and disgust 7-point scale. The evaluation of 968 Central European respondents confirmed the specificity of spiders among fear- and disgust-eliciting arthropods and supported the notion of spiders as a cognitive category. We delineated this category as covering extant spider species as well as some other chelicerates bearing a physical resemblance to spiders, mainly whip spiders and camel spiders. We suggested calling this category the spider-like cognitive category. We discussed evolutionary roots of the spider-like category and concluded that its roots should be sought in fear, with disgust being secondary of the two emotions. We suggested other chelicerates, e.g., scorpions, might have been important in formation and fixation of the spider-like category. Further, we investigated an effect of respondent's sensitivity to a specific fear of spiders on evaluation of the stimuli. We found that suspected phobic respondents were in their rating nearly identical to those with only high fear of spiders and similar to those with only moderate fear of spiders. We concluded that results based on healthy respondents with elevated fear should also be considered relevant for arachnophobia research.