Research press release


Scientific Reports

Behaviour: How do dolphins see the world?


イルカは、空中の視力も水中の視力も霊長類より劣っているが、それでも複雑な物体と身ぶりを視覚によって知覚し、判別しているように思われる。しかし、イルカの視知覚の能力を調べる系統的研究は少なかった。今回、友永雅己(ともなが まさき)たちは、さまざまな特徴(曲線、開いた形状など)を有する2次元幾何学図形(例えば、○や×)を使って、バンドウイルカ3個体に対して視覚的な見本合わせ課題を実施した。この課題で、イルカに、水面より上の位置で提示された図形(見本刺激)に鼻先で触れさせ、次に、その図形と別の図形を同時に提示して、最初に掲示された図形に触れるかどうかを調べた。チンパンジーとヒトについても同等の課題を実施し、チンパンジー7個体に対してはコンピューターを用いた見本合わせ課題を実施し、ヒト被験者20名は、類似度評価を行った。


Despite being adapted for life in aquatic environments, dolphins seem to perceive the world in fundamentally similar ways to humans and chimpanzees. The study is published in the journal Scientific Reports this week.

Dolphins have poorer in-air and underwater visual acuity than primates, but still seem to visually recognise and discriminate complex objects and gestures. Yet few systematic studies have examined dolphins’ visual perception abilities. Masaki Tomonaga and colleagues tested three bottlenose dolphins on a visual-matching task using two-dimensional geometric forms (such as a circle and an X-shape) comprising various features, including curvature and open-endedness. Dolphins had to touch with their nose a stimulus that was displayed above the water and then, when presented with two objects, had to tap the original stimulus again. The authors conducted comparable tests with a group of seven chimpanzees, who completed a computer-controlled matching test, and 20 humans, who completed a rating test.

The team found that all three species perceived shapes sharing the same features as similar, although the weight given to each feature in determining perceptual similarity differed slightly among species. For example, dolphins and chimpanzees relied on an acute-angled feature; open-ended features strongly affected the chimpanzees’ perceptual judgments; and curvature was important for human perceptual classifications. The results suggest that the visual world is perceived similarly by these three mammal species, even though each has adapted to a different environment and has differing degrees of dependence on vision.

doi: 10.1038/srep03717


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