Dolphins Preception Of The World Is Similar To Higher Primates, Including Humans

By Ajit Jha on January 18, 2014 2:05 PM EST

dolphin
For a long time, we've known that dolphins were intelligent, using echolocation to navigate. But little was known about their visual perception until now, with tests discovering that their sight isn't much different from primates and humans. (Photo: Just Taken Pics, CC BY 2.0)

Echolocation is pretty common for navigating in the animal world. Dolphins have it to help them move get around, yet their visual perception of the world is not clearly understood. Past studies on dolphin vision didn't yield useful results as researchers couldn't identify the visual cues, like circular or rectangular shapes the dolphins were supposed to use to identify similarities and differences among objects.

A new study, published in Scientific Reports, by a team of researchers from Kyoto University in Japan, compared the visual perception of dolphins with chimpanzees and humans. Researchers found that bottlenose dolphins and primates are pretty similar in how they see the world. However, dolphins have not only limited color vision, but their clarity both underwater and outside is relatively poorer from after a certain distance.

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Three wild-born bottlenose dolphins - Peace, Tino, and Eagle - which are currently living in the Port of Nahoya Public Aquarium in Japan, were chosen for the test. They were shown nine simple geometric shapes, which had features like open-endedness or right angles, and were used in a matching task known as delayed matching. The trained dolphins were told to touch their noses to a sample shape, and were later required to choose the identical shape when it was presented with another one, Business Insider reported. 

When paired with others, the nine shapes created 36 combinations. Chimpanzees and human volunteers were also shown the same set of shapes, and underwent the same testing. The results of the test showed that chimpanzees along with all the dolphins displayed similar kinds of confusion. All of them nearly failed to discriminate between shapes that looked somewhat similar, such as circle, D-shapes, U-shapes, and H-shapes.

The researchers were surprised to learn that dolphins and primates shared the same visual abilities despite coming from different environments. However, the three species made use of different details to perceive similarity. "The weight given to each feature in determining perceptual similarity differed slightly among species," the researchers wrote.

To human beings, for instance, curved shapes appeared more similar when compared to how dolphins saw them. Shapes with acute angles appeared less similar to humans when compared to both dolphins and chimpanzees. Meanwhile, open-ended shapes appeared more similar to chimpanzees than to the other two.  

These differences are not clearly explicable, the researchers said. They also pointed out some factors that could have swayed the results. Humans, for instance, were shown comparatively smaller shapes than those shown to chimpanzees and dolphins, which could have caused them to pay more attention to shapes with features like closure. The research also highlighted that while humans noticed the complete shape with one look, other animals focused their attention on finer details.

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