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Snake scales, partial exposure, and the Snake Detection Theory: A human event-related potentials study

View Article: PubMed Central - PubMed

ABSTRACT

Studies of event-related potentials in humans have established larger early posterior negativity (EPN) in response to pictures depicting snakes than to pictures depicting other creatures. Ethological research has recently shown that macaques and wild vervet monkeys respond strongly to partially exposed snake models and scale patterns on the snake skin. Here, we examined whether snake skin patterns and partially exposed snakes elicit a larger EPN in humans. In Task 1, we employed pictures with close-ups of snake skins, lizard skins, and bird plumage. In task 2, we employed pictures of partially exposed snakes, lizards, and birds. Participants watched a random rapid serial visual presentation of these pictures. The EPN was scored as the mean activity (225–300 ms after picture onset) at occipital and parieto-occipital electrodes. Consistent with previous studies, and with the Snake Detection Theory, the EPN was significantly larger for snake skin pictures than for lizard skin and bird plumage pictures, and for lizard skin pictures than for bird plumage pictures. Likewise, the EPN was larger for partially exposed snakes than for partially exposed lizards and birds. The results suggest that the EPN snake effect is partly driven by snake skin scale patterns which are otherwise rare in nature.

No MeSH data available.


Related in: MedlinePlus

(A) Grand-average waveforms for the early posterior negativity (EPN) in response to pictures of snake skin (red line), lizard skin (blue line), and bird plumage (black line) at the occipito-parietal cluster (collapsed across O1, Oz, O2, PO3, PO4, P7, P8). The vertical bar depicts the EPN time window. (B) Grand-average topographic maps of the differences in the 225–300 ms mean area amplitudes between pictures of snake skin vs. bird plumage (left), snake skin vs. lizard skin (middle), and lizard skin vs. bird plumage (right). 3D head view created with BrainVision Analyzer 2.1, Brain Products GmbH, Gilching, Germany.
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f3: (A) Grand-average waveforms for the early posterior negativity (EPN) in response to pictures of snake skin (red line), lizard skin (blue line), and bird plumage (black line) at the occipito-parietal cluster (collapsed across O1, Oz, O2, PO3, PO4, P7, P8). The vertical bar depicts the EPN time window. (B) Grand-average topographic maps of the differences in the 225–300 ms mean area amplitudes between pictures of snake skin vs. bird plumage (left), snake skin vs. lizard skin (middle), and lizard skin vs. bird plumage (right). 3D head view created with BrainVision Analyzer 2.1, Brain Products GmbH, Gilching, Germany.

Mentions: Figure 3A shows the grand average EPN potentials at the occipital cluster (O1, Oz, O2, PO3, PO4, P7, P8) for pictures of snake skin, lizard skin, and bird plumage. Snake skin pictures yielded the largest negative-going wave form, lizard skin pictures an intermediate negative-going wave form, and plumage pictures the smallest negative-going wave form. The ANOVA revealed a significant stimulus category effect, F(2, 46) = 35.84, epsilon = 0.912, p < 0.001. Bonferroni-corrected pairwise comparisons revealed that the EPN was significantly more negative for snake skin pictures than for lizard skin pictures and bird plumage pictures (both p-values < 0.001). Lizard skin pictures evoked a more negative EPN than plumage pictures (p = 0.013).


Snake scales, partial exposure, and the Snake Detection Theory: A human event-related potentials study
(A) Grand-average waveforms for the early posterior negativity (EPN) in response to pictures of snake skin (red line), lizard skin (blue line), and bird plumage (black line) at the occipito-parietal cluster (collapsed across O1, Oz, O2, PO3, PO4, P7, P8). The vertical bar depicts the EPN time window. (B) Grand-average topographic maps of the differences in the 225–300 ms mean area amplitudes between pictures of snake skin vs. bird plumage (left), snake skin vs. lizard skin (middle), and lizard skin vs. bird plumage (right). 3D head view created with BrainVision Analyzer 2.1, Brain Products GmbH, Gilching, Germany.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384215&req=5

f3: (A) Grand-average waveforms for the early posterior negativity (EPN) in response to pictures of snake skin (red line), lizard skin (blue line), and bird plumage (black line) at the occipito-parietal cluster (collapsed across O1, Oz, O2, PO3, PO4, P7, P8). The vertical bar depicts the EPN time window. (B) Grand-average topographic maps of the differences in the 225–300 ms mean area amplitudes between pictures of snake skin vs. bird plumage (left), snake skin vs. lizard skin (middle), and lizard skin vs. bird plumage (right). 3D head view created with BrainVision Analyzer 2.1, Brain Products GmbH, Gilching, Germany.
Mentions: Figure 3A shows the grand average EPN potentials at the occipital cluster (O1, Oz, O2, PO3, PO4, P7, P8) for pictures of snake skin, lizard skin, and bird plumage. Snake skin pictures yielded the largest negative-going wave form, lizard skin pictures an intermediate negative-going wave form, and plumage pictures the smallest negative-going wave form. The ANOVA revealed a significant stimulus category effect, F(2, 46) = 35.84, epsilon = 0.912, p < 0.001. Bonferroni-corrected pairwise comparisons revealed that the EPN was significantly more negative for snake skin pictures than for lizard skin pictures and bird plumage pictures (both p-values < 0.001). Lizard skin pictures evoked a more negative EPN than plumage pictures (p = 0.013).

View Article: PubMed Central - PubMed

ABSTRACT

Studies of event-related potentials in humans have established larger early posterior negativity (EPN) in response to pictures depicting snakes than to pictures depicting other creatures. Ethological research has recently shown that macaques and wild vervet monkeys respond strongly to partially exposed snake models and scale patterns on the snake skin. Here, we examined whether snake skin patterns and partially exposed snakes elicit a larger EPN in humans. In Task 1, we employed pictures with close-ups of snake skins, lizard skins, and bird plumage. In task 2, we employed pictures of partially exposed snakes, lizards, and birds. Participants watched a random rapid serial visual presentation of these pictures. The EPN was scored as the mean activity (225&ndash;300&thinsp;ms after picture onset) at occipital and parieto-occipital electrodes. Consistent with previous studies, and with the Snake Detection Theory, the EPN was significantly larger for snake skin pictures than for lizard skin and bird plumage pictures, and for lizard skin pictures than for bird plumage pictures. Likewise, the EPN was larger for partially exposed snakes than for partially exposed lizards and birds. The results suggest that the EPN snake effect is partly driven by snake skin scale patterns which are otherwise rare in nature.

No MeSH data available.


Related in: MedlinePlus