Humans proven to recognize partially obscured snakes more easily than other animals

Humans proven to recognize partially obscured snakes more easily than other animals
Examples of a Random Image Structure Evolution (RISE) sequence for snake pictures. Participants looked at a sequence of 20 pictures with interpolation ration starting from 95 percent to 0 percent with steps of 5 percent. RISE sequence gradually changes from unorganized to well discernible. Credit: Nobuyuki Kawai

Some studies have suggested that the visual systems of humans and other primates are finely tuned to identify dangerous creatures such as snakes and spiders. This is understandable because, among our ancestors, those who were more able to see and avoid these animals would have been more likely to pass on their genes to the next generation. However, 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.

In a study reported recently in PLOS ONE, a pair of researchers at Nagoya University obtained strong support for the idea that humans have heightened visual awareness of snakes. The researchers applied an image manipulation tool and revealed that subjects could identify snakes in much more blurry images than they could identify other harmless animals in equivalent images.

The tool, called Random Image Structure Evolution (RISE), was used 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," first author Nobuyuki Kawai says. "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 to identity the other animals. "This suggests that humans are primed to pick out even in dense undergrowth, in a way that isn't activated for other animals that aren't a threat," co-author Hongshen He explains.

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 . This work augments understanding of the evolutionary pressures placed on our ancestors.

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More information: Nobuyuki Kawai et al, Breaking Snake Camouflage: Humans Detect Snakes More Accurately than Other Animals under Less Discernible Visual Conditions, PLOS ONE (2016). DOI: 10.1371/journal.pone.0164342
Journal information: PLoS ONE

Provided by Nagoya University
Citation: Humans proven to recognize partially obscured snakes more easily than other animals (2016, November 8) retrieved 31 July 2021 from
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