Thinking About Dolphins
What are the dimensions of dolphin intelligence? In seeking the answer, scientists are learning volumes about the animals' abilities
Wearing sunglasses to conceal his eyes, Louis Herman stands next to a large outdoor tank not far from the hustle of Waikiki Beach and waves his arms like a symphony conductor. "Is the Frisbee in the water?" he asks with his hands, using a modified form of American Sign Language. A few feet away, a bottlenose dolphin correctly responds by pushing a paddle for "yes."
Herman gestures again, telling the dolphin to take the Frisbee and place it on top of a surfboard. There's just one problem: There is no surfboard in the tank. The animal swims over and grabs the Frisbee in its mouth, pauses for a moment, then carries it to a second floating paddle, which she pushes to signify "no."
The dolphin is telling Herman that she can respond to his first request by picking up the Frisbee, but not the second because there is no surfboard. In effect, the animal has thought through the problem and reacted appropriately. "She hasn't been trained to do this." says the University of Hawaii psychologist. "It's a spontaneous response."
Another clever Honolulu tourist attraction? Hardly. Even Hawaii residents are unlikely to have heard of the university's Kewalo Basin Marine Mammal Laboratory, where for the past 23 years Herman and a staff of graduate students and Earthwatch volunteers have repeatedly challenged captive bottlenose dolphins to solve a wide range of problems.
To scientists who concern themselves with questions about animal intelligence, however, the work at Kewalo Basin is recognized as the most thorough research ever conducted on the ability of dolphins to comprehend simple language. "It has revolutionized the way we think about dolphins by giving us new insight into their memories and learning abilities," says Kenneth Norris, a University of California, Santa Cruz, biologist and one of the world's leading authorities on dolphins and other marine mammals.
Intelligence, maintains Herman, is a matter of flexibility-adjusting to new situations. Rather than only studying what dolphins can do in their own environment, the researcher is also attempting to find out what they can do in conditions that are totally foreign to their natural lives. "We're trying to map out the dimensions of their intelligence," he says, "so we can better understand what it's like cognitively to be a dolphin."
Herman is using language comprehension to help map out that intelligence. He has demonstrated that dolphins can understand not only a complex vocabulary but also syntax, or word order-a basic rule of sentence formation that constitutes language as humans define the term. Two dolphins have learned a vocabulary of about 50 words, which Herman and his staff use to construct more than 1,000 different commands given in sentences with as many as five words. Each command produces an unrehearsed response, involving the animals' understanding of word order.
"Syntax is what tells us that a venetian blind is not a blind Venetian," says Herman. In the tests he administers, the dolphins have to take into account both word meaning and word sequence. And almost without fail, the animals have demonstrated consistently that they can distinguish between such commands as "get the Frisbee and take it to the surfboard" and "get the surfboard and take it to the Frisbee."
When a dolphin responds in a spontaneous way to one of Herman's commands, it may be a signal that the creature is thinking on a level humans would call "conscious"- an idea that challenges some traditional notions about the capabilities of most animals.
"Scientists have tended to cling to the conservative assumption that all animal behavior is unconscious, but recent studies like those of Lou Herman have made it more and more difficult to minimize animal versatility," says Donald Griffin, a Harvard Museum of Comparative Zoology biologist who has written three books on animal awareness. "The precursors of language are evident throughout the animal kingdom," adds Kenneth Norris.
In the wild, dolphins emit a variety of sounds. These include a range of echolocation clicks, which the animals can vary to identify objects in the water-the so-called dolphin sonar system. Studies by the U.S. Navy have found that using its sonar, a dolphin can accurately locate a 3-inch sphere nearly 400 yards away.
"We think the echolocation image is very well developed in a dolphin's brain, similar to a visual image," says Herman. When a dolphin locates through its sonar an object that it can't yet see, adds Kewalo Basin researcher Adam Pack, "it probably can determine what that object will actually look like."
Among the world's 33 dolphin species, herds sometimes number more than 1,000 strong. In such groups, researchers have documented complex social systems that include forming cooperative defenses against threatening sharks, "babysitting" other animals' young, and females creating lasting bonds with their offspring. To communicate with each other, the animals produce a medley of whistlelike sounds.
A few years ago, Peter Tyack, a biologist at Woods Hole Oceanographic Institution on Cape Cod, Massachusetts, invented a device that enables researchers to determine which dolphin in a group is vocalizing at any point in time. Known as the vocalight, the harmless device illuminates a set of light-emitting diodes when the animal wearing it whistles. Studying captive animals, Tyack has found that when dolphins swim together, at least half of the sounds that each creature produces are distinct signature whistles that identify the sender to the other members of the group.
Studies also indicate that the creatures can vary the length or pitch of their signature whistles. "As far as we know," says Herman, "marine mammals like dolphins are the only animals that modify what they say in response to what they hear." When stressed, for instance, a dolphin may alter its signature whistle to alert its companions: "I'm over here and I need assistance."
Despite such abilities, experts have found no evidence that dolphins convey complex messages to one another. "Dolphins taken from the sea can use parts of speech, but that doesn't mean they use actual language to communicate," says Norris. "It just means they have the mental capacity to deal with syntax, verbs and other elements of language."
Louis Herman set out to explore the boundaries of a dolphin's capacity to understand simple language in the late 1970s-a time when a number of researchers were conducting language studies with chimpanzees and other primates. "I think of dolphins and chimps as `cognitive cousins,- he says. "They tend to perform very similarly on intellectually challenging tasks. And both have complex social networks that depend on communication."
Concerned about the difficulties other U.S. scientists had encountered trying to teach primates to "speak" by using sign language, Herman decided instead to test only whether dolphins can comprehend language. Comprehension appealed to the psychologist because, he believed, it represented the most fundamental place to begin looking for language competency in animals. Human infants understand words before they begin to produce them, and even in adults the comprehension vocabulary greatly exceeds the speech vocabulary.
Funded by the University of Hawaii and a National Science Foundation grant, Herman took over an abandoned outdoor tourist facility at Honolulu's Kewalo Basin that once held sharks in two 50-foot pools. He surrounded the oceanfront site with a high fence, built an observation tower that now houses a bank ofcomputers and audio equipment, and put two captive bottlenose dolphins into the tanks. (He has since acquired two additional dolphins.)
To test the animals' comprehension, Herman put a variety of objects into the tanks and devised two artificial languages that described the objects. He taught one animal a vocabulary of hand signals. Another dolphin learned an acoustic language composed of computer-generated whistlelike sounds, broadcast into the pool through an underwater speaker. Each hand gesture or sound represented an object like "Frisbee," a verb such as "put" or a description of a particular location, as in "on top of."
To help reduce the chances of pure guesswork playing a role in the animals' performances, the researcher placed a large assortment of objects in the water for the dolphins to choose from. In some tests, they had to distinguish between identical objects based on whether the toys were to their left or right, floating at the surface or on the bottom. The creatures have had no trouble picking the correct objects.
The dolphins appear to be able to generalize the meaning of words beyond the context in which they were learned. For instance, they respond correctly to commands involving the word "hoop," no matter if the hoop involved is round, triangular or square, large or small, floating or flat on the bottom. What this means, says Herman, is that "dolphins develop an understanding of the words of their artificial languages at the level of a concept."
Perhaps a more telling example of the dolphins' cognitive skills is in their ability to report the absence of an object. In experiments at Kewalo Basin, the animals are asked to report whether, for example, a swimmer is in the tank with them. By pushing "yes" and "no" paddles, the dolphins respond. Their success in giving the correct responses is evidence that they can refer to objects symbolically, says Herman.
What is the difference between how the dolphins respond and symbolic actions by other species? Scientists have observed, for instance, that when a bee flies back to the hive after foraging, it will indicate a large amount of nectar at a certain distance and direction from the nest through a ritualized dance. However, says Herman, the bee can only give positive reports. "In our studies," he notes, "dolphins can report the absence as well as the presence of objects."
Are dolphins capable of producing language beyond the simple responses of "yes" and "no"? In Orlando, Florida, two of Herman's former graduate students, John Gory and Mark Xitco, currently are investigating the possibility of dolphin-tohuman communication, using a large keyboard placed on the bottom of a tank. Each of the 16 keys has a symbol representing a different word. When a dolphin presses one of the symbols, it hears through an underwater speaker a spoken word, referring to a type of action, an object or a location. The dolphins in the study are observing people using the keyboard to announce their intentions, such as a desire to swim to a particular location in the tank. And the animals are beginning to use the keyboard to indicate their own intentions to swim to a specific tank location, particularly when food is found there.
For all of the marine mammals' apparent learning abilities, Herman admits that dolphins are a long way from humans in their grasp of language. "We should never expect them to approach even the capabilities of young children in language performance," he says, "much like we could never approach their performance as swimmers."
Nevertheless, says Kenneth Norris, the work at Kewalo Basin is significant beyond its success in demonstrating potential linguistic competence in animals. "It provides an invaluable window on dolphin cognition, a chance for us to better understand these complex creatures," he says. And understanding the cognitive abilities of animals, adds Donald Griffin, "presents us with one of the supreme scientific challenges of our time."
Editor Mark Wexler visited with psychologist Louis Herman at the Kewalo Basin Marine Mammal Laboratory in preparation for this article.