Human Sight Especially Sensitive To Snakes

The human eye can spot snakes from blurred images faster than non-threatening animals such as cats or fish.

AsianScientist (Nov. 21, 2016) – A pair of researchers at Nagoya University have found that the visual system of human beings is uniquely sensitive to snakes, as compared to other animals. Their results have been published in PLOS ONE.

Although previous studies have suggested that the visual systems of humans and other primates are finely tuned to identify dangerous creatures such as snakes and spiders, it has been difficult to compare the recognition of different animals in an unbiased way because of their different shapes, anatomical features, and levels of camouflage.

Instead, Associate Professor Nobuyuki Kawai and PhD student Mr. He Hongshen used an image manipulation tool called Random Image Structure Evolution (RISE) to create a series of 20 images of snakes, birds, cats and fish, ranging from completely blurred to completely clear. The pair then asked subjects to views these images in order of increasing clarity until they could identify the animal in the picture.

“Because of the algorithm that it uses, RISE produces images that allow unbiased comparison between the recognition of different animals,” Kawai said. “In the images, the animals are ‘camouflaged’ in a uniform way, representing typical conditions in which animals are encountered in the wild.”

The snakes were increasingly well-identified in the sixth to eighth of 20 images, while the subjects often needed to see the less blurred ninth or tenth images to identity the other animals.

“This suggests that humans are primed to pick out snakes even in dense undergrowth, in a way that isn’t activated for other animals that aren’t a threat,” He explained.

The findings confirm the Snake Detection Theory; namely, that the visual system of humans and primates has specifically evolved in a way that facilitates picking out of dangerous animals. This work augments understanding of the evolutionary pressures placed on our ancestors.

The article can be found at: Kawai et al. (2016) Breaking Snake Camouflage: Humans Detect Snakes More Accurately than Other Animals under Less Discernible Visual Conditions.


Source: Nagoya University; Photo: Pixabay.
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