- Trainers asked captive bottlenose dolphins to fetch an object with their eyes either open or closed.
- Dolphins took longer when the trainer’s eyes were closed and when the trainer’s face was turned away.
- Captive dolphins may understand eye cues due to their social intelligence and experience with humans.
For humans, eyes are an important indicator of attention. By the time they are one year old, babies appear to understand how visual perception works and will consistently follow their mother’s gaze. However, the evidence for this ability in other species is mixed. Even studies of chimpanzees, our closest living relatives, do not reliably show that they use eyes as an attentional cue.
In a new study, researchers investigated this ability in a much more distantly related animal—the bottlenose dolphin. Dolphins live in complex social environments that demand a sophisticated toolkit of socio-cognitive skills, including the ability to pay attention to what others attend to. In addition, captive dolphins often undergo specialized training in which they must attend to and interact with human trainers in exchange for rewards. In other words, captive dolphins’ skills and experience may make them sensitive to human attentional states. Could dolphins understand visual attention in humans?
The Eyes Have It
James Davies of the University of Cambridge and Elias Garcia-Pelegrin of the National University of Singapore explored this question using an object retrieval task. In the task, the researchers asked a dolphin to fetch an object under four conditions involving the trainer’s eyes and face orientation: “eyes open” (in which the trainer’s head faced the dolphin’s, and their eyes were open), “eyes closed” (in which the trainer’s head faced the dolphin, but their eyes were closed), “half-looking” (in which the trainer’s head was at a right angle to the dolphin with their eyes open), and “not looking” (in which the trainer’s head was turned away from the dolphin so their face and eyes were out of view).
In trials with eight dolphins, the team measured how long it took for the dolphin to retrieve the object in each condition.
“The main results were that the dolphins showed an increased latency to retrieve the object in conditions where the trainer lacked visual attention towards them,” says Davies. “There was a significant difference between the ‘eyes open’ and ‘not looking’ conditions, the ‘half-looking’ and ‘not looking’ conditions, and, most interestingly, the ‘eyes open’ and ‘eyes closed’ conditions.
“This tells us that dolphins can be sensitive to human attentional features, including eye functionality.”
The ability of the dolphins in this study to understand visual attention is interesting for a few reasons, says Davies. One is the inconsistent evidence for this ability in chimpanzees and other nonhuman primates. Another is the difference in eye placement between humans and dolphins.
Plus, dolphins’ primary method of communicating and exploring the world is not visual. Acoustic signals, including high-pitched whistles and echolocation clicks, are more reliable in murky waters and over long underwater distances. Where another dolphin is directing its eyes is probably not very relevant.
“The ability to attend to eye cues is impressive considering the lack of evidence that dolphins would have specifically evolved this ability,” says Davies. “It provides further evidence of the sophisticated and flexible social intelligence of dolphins.”
Davies, J.R., Garcia-Pelegrin, E. Bottlenose dolphins are sensitive to human attentional features, including eye functionality. Sci Rep 13, 12565 (2023). DOI: 10.1038/s21598-023-39031-7.