Just for you, I've transcribed an excerpt from one of my university-level textbooks:
"Using each type of training technique, some researchers have made remarkable claims for the ability of other species to approximate language use. In one of the better-known projects, a chimp named Washoe was trained in ASL from a very early age (Gardner & Gardner, 1969, 1975). According to the Gardners, Washoe acquired a vocabulary of several hundred signs and displayed the rudiments of syntax by putting signs together with some regularity of ordering. In addition, Washoe reportedly displayed productivity in language by coining new words. Upon seeing a swan, Washoe is said to have signed "water-bird." Similar claims were made for a groilla named Koko, who also was schooled in sign language (Patterson, 1978).
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Do these examples demonstrate the rudiments of a syntax-governed language, or can the data on primate language training be interpreted in other ways? We should always maintain a healthy, objective skepticism in science, but it is especially important to take a skeptical attitude when scientific investigation seek to prove something that we really want to believe. Even the subjects who have been among the fastest learners in this research, such as Kanzi, require an enormous investment of time and energy to train, and they learn much more slowly than humans learn language. Some critics charge that, for these reasons, investigators are particularly prone to interpret often subjective data in ways that support the continuity view, even if such interpretations are not warranted by the data (Umiker-Sebeok & Sebeok, 1981).
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Let's first consider the efforts to teach ASL to chimps and gorillas. Terrace and colleagues attempted to teach ASL to a chimp they dubbed Nim Chimpsky, after the famous linguistic Noam Chomsky. They found, however, that Nim's communications bore little resemblance to the language abilities of his namesake. As in other projects involving signing among chimps, Nim acquired a fairly extensive vocabulary and strung together two-word "sentences" that often followed a predictable word order. For excample, when Nim asked for something with the sign for "more," the "more" sign was used in the first position 85% of the time, as in "more drink" or "more banana." However, when the project ended and Terrace looked back at his data, he came to suspect that it was not a language-like ability that Nim had displayed.
Even though Nim's vocabulary increased as he was trained, the length of his utterances showed little development over time. The average "sentence" length remained around 1.5 signs. In addition, Nim's longer utterances were not novel or sentence-like. They were characterized by repetition...When Terrace closely watched the tapes of Nim's signing, he observed that what was originally taken to be spontaneous and syntactically organized utterances could be explained as imitations of the teachers in order to get specific rewards (Terrace, 1983). Other animal language researchers critized the teaching methods used in the Nim project and claimed that Nim's limitations were not representative of the abilities of other language-trained chimps (e.g., Gardner, 1981). However, when Terrace and colleagues examined films of the training of chimps or gorillas in other studies, they saw the same problem that they themselves had experienced: The experimenters failed to distinguish between language utterances and the imitation of the signs (Terrace et al., 1980; Seidenberg & Petitto, 1979).
A number of other criticisms have been leveled against studies supporting the claim that chimps can learn language (Wallman, 1992). For instance, fluent users of ASL have noted that it takes a very generous interpretation of the chimps' use of signs mixed with pointing and other natural gestures to come up with vocabulary estimates in the hundreds. And because the trainers possess language, it is all to easy for them to extrapolate beyond the chimps' behavior. When Washoe signed "water-bird," was this a novel label for a swam? Or did Washoe merely give a sign for water and a sign for bird, thus separately naming each object?"
I could go on, but hopefully you get the idea from that.