Dolphins possess ability to use sound, or echolocation, to identify objects under water. But their visual perception of the world isn’t properly studied now.
Masaki Tomonaga and his team of scientists from Kyoto University in Japan conducted a new study in attempt to find out how bottlenose dolphins perceive a range of simple, two-dimensional objects compared with chimpanzees and humans.
During previous experiments, researchers used complicated, three-dimensional shapes, which made it complicated to define the types of visual “cues” — like curves or diagonal lines — that dolphins use to suss out differences or similarities among objects.
This species of mammals are said to have limited color vision and poor clearness of vision from a specific distance, both in air and under water than primates.
“Despite these differences, bottlenose dolphins perceive the world in fundamentally similar ways” to other primates, the study authors wrote in the journal Scientific Reports.
This time the group of scientists tested the visual perception of three dolphins who were born in natural conditions— Peace, Tino, and Eagle — and now living in the Port of Nahoya Public Aquarium in Japan.
Within the framework of the experiment nine simple geometric shapes with distinguishing features were used. A bottlenose dolphin was trained to touch to a sample shape that was shown above the water by a person.
After the mammal remembered the shape of the sample, it was removed and was required to choose the shape it had just remembered.
“Comparable matching tests, using pictures of the 36 pairs, were done with chimpanzees and humans. Seven chimpanzees were presented on a computer screen with color photographs of the same shapes shown to the dolphins,” The Business Insider writes.
“When given two choices, the chimpanzees had to touch the shape that was identical to the sample. In the human experiment, 20 volunteers used a rating scale to judge the similarity of each pair, which were printed on a single sheet of paper,” the publication explains.
The results of the experiments appeared to be quite surprising. All three dolphins and the chimpanzees demonstrated similar patterns of confusion — they had a tougher time discriminating between shapes with the same features, meaning they view these shapes as “similar.”
However, there was one difference— all three species relied on different details to determine “similarity.” “The weight given to each feature in determining perceptual similarity differed slightly among species,” the researchers wrote.
“It’s still not clear why these differences emerged,” the researchers said, “but point to some procedural inconsistencies. Humans, for example, were shown shapes that were much smaller than the shapes presented to the dolphins and chimpanzees. It’s possible that the reduced size caused the human group to pay more attention to features like closure.”
According to the Japanese scientists, humans first notice the whole shape, while other animals pay more attention to finer details.