【行動】イルカも視覚に依存して世界を認識している

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.