When you watch someone put chocolate into a cabinet, you know where to find the treat, even when you can’t see it. If a person shows you a gold coin in their hand, reaches into their pocket, and then, when they remove their hand, they are no longer holding the coin, you’ll have no problem figuring out where that gold must be. This ability to reason about things that have disappeared from view is known as object permanence. It has been studied in many land animals, and now Dolphin Research Center (DRC), located in Grassy Key, FL, is the first to explore this ability with marine mammals. Dolphin Research Center’s research paper on What Do Dolphins (Tursiops truncatus) Understand About Hidden Objects was recently published by the prestigious scientific journal Animal Cognition.
“When you show an object to a human infant who’s only a few months old and then hide it, as far as the baby is concerned, it’s as though the object ceases to exist. They won’t look for it,” explains Research Director Dr. Kelly Jaakkola. “By the time humans are around 12 months old, they seem to realize that the object still exists and search for it even if they can’t see it.”
For this study, DRC’s researchers hid an object—a plush toy alligator—in one of three containers while the dolphins watched. They then asked the animals to choose the container holding the alligator. The dolphins chose correctly with a high rate of accuracy.
Several other non-human species have demonstrated this ability—which scientists call “visible displacement”—including gorillas, chimpanzees, parrots and dogs. DRC next explored a harder condition called “invisible displacement”. This time, they showed dolphins the plush alligator being hidden in a cylinder. They then placed the cylinder in one of three containers and emptied the alligator into the container where the dolphin could not see this action take place. They showed the dolphin the empty cylinder, and again asked it to choose the container holding the alligator. Apes are the only animals besides humans that demonstrate they can solve these kinds of trials. Since apes, humans and dolphins share other specific cognitive skills – including mirror self-recognition, ability to imitate and to understand symbols– DRC’s scientists fully expected that dolphins would also succeed with invisible displacement. Surprisingly, they didn’t.
“The reasons why remain unknown,” Jaakkola said. “There are many possibilities. They might lack an understanding of containment, since containers as we understand them do not exist in the sea. Also, in their underwater world, dolphins use echolocation, which is their natural sonar. If a fish disappears beneath the sand, for example, dolphins can echolocate and still perceive exactly where the fish is located. Perhaps they just don’t need this ability in the first place. Further research could address this puzzle.”
Even though the dolphins did not demonstrate the ability they expected, DRC’s research team is anything but disappointed. “Our studies are helping to build a more complete picture of dolphin cognition,” Jaakkola adds. “To do that, it’s just as important and fascinating to figure out what they can’t do as well as what they can, so that we can really begin to understand how they think and learn.”
For over 25 years, Dolphin Research Center has dedicated itself to learning more about marine mammals and then sharing that information with the world. The nonprofit education and research facility is home to a family of Atlantic bottlenose dolphins and California sea lions. DRC is open daily to the public and visitors can see a variety of narrated behavior sessions, including current research projects, and other educational presentations throughout the day. The facility also offers several different interactive programs, and other educational programs such as their weeklong college accredited DolphinLab courses. For more information about the center and its activities, visit http://www.dolphins.org or call 305-289-1121.