Early posterior negativity in humans to pictures of snakes and spiders: effects of proximity
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RESEARCH ARTICLE
Early posterior negativity in humans to pictures of snakes and spiders: effects of proximity Nick Beligiannis1 · Jan W. Van Strien1 Received: 13 April 2020 / Accepted: 11 September 2020 © The Author(s) 2020
Abstract 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. Keywords Early posterior negativity (EPN) · Snake detection hypothesis · Proximity · Spatial frequency · Phylogenetic fear
Introduction Snakes have been proven to trigger fast detection and early attentional capture in humans and primates, due to their evolutionary importance (Öhman et al. 2001). That is, an evolutionary forced readiness of the visual system seems to be active in the presence of phylogenetic fear (Mühlberger et al. 2006). This suggests a visual attentional mechanism responsible to rapidly detect dangerous stimuli in order to avoid danger and promote survival. The “Snake Detection Theory” (SDT) (Isbell 2006), suggests that snakes, as evolutionary agents, have shaped the development of the primate visual system and have also set vision as the primary sense for threat detection in humans and primates. Previous studies have examined visual attributes of snakes, such as the curvilinear body shape and the snake’s skin patterns, that Communicated by Melvyn A. Goodale. * Nick Beligiannis [email protected] 1
Erasmus School of Social and Behavioral Sciences, Brain and Cognition, Erasmus University Rotterdam, PO Box 1738, 3000 DR Rotterdam, The Netherlands
may play a role in snake detection. The present study was conducted to explore the role of proximity and its role in snake-related attentional capture. Many studies have acknowledged that there is attentional modulation of the human visual system caused by snakes that is reflected at an electrophysiological level, as measured by event-related potentials (ERPs) (He et al. 2014; Grassini et al. 2016;
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