Breaking Snake Camouflage: Humans Detect Snakes More Accurately than Other Animals under Less Discernible Visual Conditions

<div><p>Humans and non-human primates are extremely sensitive to snakes as exemplified by their ability to detect pictures of snakes more quickly than those of other animals. These findings are consistent with the Snake Detection Theory, which hypothesizes that as predators, snakes were a major source of evolutionary selection that favored expansion of the visual system of primates for rapid snake detection. Many snakes use camouflage to conceal themselves from both prey and their own predators, making it very challenging to detect them. If snakes have acted as a selective pressure on primate visual systems, they should be more easily detected than other animals under difficult visual conditions. Here we tested whether humans discerned images of snakes more accurately than those of non-threatening animals (e.g., birds, cats, or fish) under conditions of less perceptual information by presenting a series of degraded images with the Random Image Structure Evolution technique (interpolation of random noise). We find that participants recognize mosaic images of snakes, which were regarded as functionally equivalent to camouflage, more accurately than those of other animals under dissolved conditions. The present study supports the Snake Detection Theory by showing that humans have a visual system that accurately recognizes snakes under less discernible visual conditions.</p></div

Examples of a Random Image Structure Evolution (RISE) sequence for snake pictures.

<p>Includes a sequence of 20 pictures with interpolation ratio starting from 95% to 0% with steps of 5%. RISE sequence will gradually change from unorganized to well discernible.</p

Mean identification rates for each type of stimuli (snake, fish, cat, bird).

<p>Asterisks on the line graph indicate significantly different accuracies from ANOVA results. Chance performance (0.25) is indicated by the horizontal dotted line. Error bars denote <i>SEM</i>.</p

The 14 photographs of snakes which were used as target stimuli.

<p>In 7 of them, a typical striking posture was displayed (Striking) while a resting snake was displayed in the remaining 7 (Resting).</p

The asymmetry indexes for each group were displayed in the baseline and the insult periods.

<p>The open circles illustrate the no-apology group (<i>N</i> = 24). The closed circles illustrate the apology group (<i>N</i> = 24). Each vertical line illustrates the standard error for each condition.</p

Mean rating scores and standard error of subjective scales (PANAS and STAXI) for the no-apology group and the apology group.

*<p>:baselineps<.05).</p

The results of HR (A) and SCL (B) for each group were displayed in the baseline and the insult periods.

<p>Each vertical line illustrates the standard error for each condition.</p

Synthesis of the 1‑Phenethyltetrahydroisoquinoline Alkaloids (+)-Dysoxyline, (+)-Colchiethanamine, and (+)-Colchiethine

Asymmetric total syntheses of the 1-phenethyl-1,2,3,4-tetrahydroisoquinoline alkaloids (+)-dysoxyline (<b>1</b>), (+)-colchiethanamine (<b>2</b>), and (+)-colchiethine (<b>3</b>) are described. In the synthetic routes, coupling of a key, enatiomerically pure 1-(sulfonylmethyl)­tetrahydroisoquinoline with aromatic aldehydes, performed by using the Julia–Kocienski reaction, afforded the corresponding 1-(β-styryl)-substituted tetrahydroisoquinolines with complete retention of the absolute configuration at the C1 carbon atom. Functionalization of the products generated in these processes by using four- or five-step sequences gave the target alkaloids <b>1</b>–<b>3</b>

Schematic_Representation_Exchange

Schematic illustration of the exchang

Results of Experiment 1.

<p>Mean values of the controller bars on FaceTool software for the four conditions to make changes to the facial parts are indicated using FACS (facial action coding system) names, accompanied by AU (Action Unit) numbers. Standard errors of the mean are shown in parentheses. Asterisks indicate values significantly larger than zero. ⁺: <i>p</i><0.10; *: <i>p</i><0.05; **: <i>p</i><0.01; ***: <i>p</i><0.001.</p