One of the major distinctions between human and nonhuman animals is language. At the beginning of the animal language projects, the object was to show that an individual from a nonhuman species could acquire and use language. Apes have been the primary participants in these projects. One of the first attempts to teach language to an ape was that of Keith and Cathy Hayes, who reared Viki the chimpanzee in their home from 1947 to 1954. With much effort, Viki learned to say four words, "mama, papa, cup, and up." She had great difficulty producing these words, and they were barely intelligible. We now know that great apes lack vocal structures necessary to produce speech. However, they appear to have the cognitive ability to acquire aspects of language using symbols in communicative interactions with humans.

Washoe, a chimpanzee reared by Beatrice and Allen Gardner beginning in 1966, was taught American Sign Language (ASL). Washoe's acquisition and use of ASL were interpreted to demonstrate that a great ape could acquire a human language. The strong version of this interpretation was questioned from two perspectives. First, H. S. Terrace, who in the late 1970s trained a chimpanzee named Nim Chimpsky to learn ASL, questioned the referential nature of a chimpanzee's use of ASL. Terrace suggested that the primary basis for Nim's "linguistic" ability was not linguistic or referential in the way that human language is used to refer to objects, concepts, and experiences, but was more likely based on associative learning and imitation in goal-oriented situations. That is, Nim appeared to reply to questions posed by his teachers in a manner that was more imitative of the teacher's gestures than suggestive that he was generating linguistic utterances of his own that referred to objects, concepts, and experiences in his environment.

A second related question addressed syntax, or grammar. Chimpanzees who learned ASL (and there were more than Washoe and Nim involved in such studies) did not follow strict grammatical rules of word order required in human linguistic utterances, whether spoken or signed. Rather, the chimpanzees would repeat words or phrases, often varying the order of words as the utterances were repeated. Such behavior was consistent with Terrace's suggestion that the chimpanzees were not using signs to communicate. Beginning in 1973, Duane Rumbaugh trained a chimpanzee named Lana to produce sentences through the use of a computer-operated keyboard containing abstract symbols that represented verbs, nouns, adjectives, and adverbs. These symbols, called lexi-grams, were composed of abstract geometric shapes combined to form unique configurations, each of which referred to a particular word or concept. Rumbaugh developed a language he called "Yerkish" named for the Yerkes Regional Primate Research Center where the Lana project began. Lana's symbols followed rules of grammar and the results of this project showed that Lana and other chimpanzees in the project could learn rules of syntax and use abstract visual symbols in a communicative manner. Chimpanzees Sherman and Austin later showed the ability to use this computer-based system to communicate information to each other.

Although for some investigators of animal cognition the question of ape language is still at issue, the ape language projects have expanded in content and have provided important discoveries about ape cognitive abilities. In such a project, Chantek, an orangutan reared by Lynn Miles beginning in 1977, learned ASL. In this project Chantek's acquisition of symbolic communication was studied in the context of overall cognitive development. This project is unique in its breadth, providing understanding of the development of symbolic communication as one feature of a suite of cognitive abilities.

In 1971, David Premack first reported results of a project in which he trained chimpanzee Sarah to communicate using arbitrary abstract symbols. These symbols were colored plastic shapes. Sarah learned concepts such as "same" and "different," as well as nouns, verbs, and adjectives. That these

Bottlenosed dolphins (Tursiops truncatus) have a complex language that may eventually help humans to communicate with them. (Photo by © Stuart Westmorland/Corbis. Reproduced by permission.)

symbols were representational to Sarah was demonstrated when she was provided with the symbol for apple, and asked to describe its physical features. Although the symbol for apple was a blue triangle, Sarah described the object presented to her as "red" and "round," referring to attributes of the object rather than of the symbol. She also showed the ability to reason analogically through her understanding of "same" and "different." The primary contribution of this language project was not Sarah's linguistic abilities, but how Premack used Sarah's representational capacity to show the breadth of cognitive flexibility and conceptual understanding available to a chimpanzee provided with Sarah's rich cognitive environment.

In a similar fashion, two current ape language projects use the animals' symbolic ability to uncover cognitive representational abilities that would be difficult to access without this means of symbolic communication. In 1995 Robert Shumaker began to work with orangutans Azy and Indah, who are learning an abstract symbolic communication system presented as lexigrams on a touch-sensitive video screen. When questions are posed, the orangutans indicate the appropriate symbol from an array of symbols by touching it. Shumaker is using the animals' symbolic abilities as a window into other related cognitive processes such as number comprehension. In a project begun in 1978 by Kiyoko Murofushi, Toshio Asano, and Tetsuro Matsuzawa, chimpanzee Ai continues to demonstrate her sophisticated cognitive abilities using a touch-sensitive video screen and a vocabulary of lexigrams and Arabic numerals. For example, Ai labels objects and their characteristics such as color and number; she clearly understands numbers conceptually, and counts using Arabic numerals from zero to nine; and she "spells" by constructing lexigrams from their components. Ai's infant Ayumu, born in 2000, is learning to use the touch-screen system, providing insight into the development of symbolic cognitive skills as he interacts with his mother and observes her using the system.

The symbolic ability of great apes in the context of a language-learning setting was most strongly demonstrated by Sue Savage-Rumbaugh who in 1979 extended the Lana project to another great ape species, the bonobo (Pan paniscus). Kanzi, a young bonobo who lived with his mother during her training with Rumbaugh's computer-based language, surprised researchers when he showed clear understanding of the task and of particular symbols simply as a result of having been passively exposed to the symbols while his mother was learning the task. Following this discovery, Savage-Rumbaugh focused on Kanzi's ability and motivation to use abstract communicative symbols. Kanzi not only uses the abstract symbolic language system, he also has a demonstrated understanding of spoken language, and Savage-Rumbaugh has reported that he appears to attempt to communicate vocally by imitating acoustic properties of human speech. Her interpretation of Kanzi's behavior is that bonobos appear to have not only the ability to acquire abstract human-derived symbols, but that they may have additional communicative skills that can provide insight into the evolution of human language.

Koko the gorilla has been using ASL under the tutelage of Francine Patterson since 1976. She is probably the most publicly recognizable language-trained ape. Indeed, Patterson has extended her project into conservation efforts in the United States by promoting Koko to the public. Further, Patterson translated a children's book about Koko into French to distribute in French-speaking Africa as a way to educate children about the cognitive and emotional capacities of gorillas and the importance of preserving them in the wild.

The importance of the ape language projects has not been in the demonstration of a human capacity in great apes, but rather in exposing the complex symbolic skills available to animals in a rich interactive environment. The cognitive skills shown by the nonhuman participants in these projects extend beyond the specific symbolic skills trained in individual projects. They have opened a window into the minds of animals that enriches our understanding of the animal mind, while also providing new theoretical perspectives on the evolution of human cognition and language.

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