Can an Ape Create a Sentence? Based on Comparisons Between Washoe and Children, As
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23 November 1979, Volume 206, Number 4421 SCIENCE quences produced and understood by their pongid subjects were governed by grammatical rules. The Gardners, for ex- ample, note that "The most significant results of Project Washoe were those Can an Ape Create a Sentence? based on comparisons between Washoe and children, as ... in the use of order H. S. Terrace, L. A. Petitto, R. J. Sanders, T. G. Bever in early sentences" (3, p. 73). If an ape can truly create a sentence there would be a reason for asserting, as Patterson (11) has, that "language is no longer the exclusive domain of man." The innovative studies of the Gardners song when asserting territory. Such ri- The purpose of this article is to evaluate (1-3) and Premack (4-6) show that a gidity is typical of the communicative be- that assertion. We do so by summarizing chimpanzee (Pan troglodytes) can learn havior of other genera, for example, bees the main features of a large body of data substantial vocabularies of "words" of communicating about the location and that we have collected from a chim- visual languages. The Gardners taught quality of food or sticklebacks engaging panzee exposed to sign language during Washoe, an infant female chimpanzee, in courtship behavior (14). its first 4 years. A major component of signs of American Sign Language (ASL) Human language is most distinctive these data is the first corpus of the multi- (7, 8). Premack taught Sarah, a juvenile because of a second level of structure sign utterances of an ape. Superficially, female, an artificial language of plastic that subsumes the word-the sentence many of its utterances seem like sen- on November 15, 2013 tences. However, objective analyses of our data, as well as of those obtained by Summary. More than 19,000 multisign utterances of an infant chimpanzee (Nim) other studies, yielded no evidence o an were analyzed for syntactic and semantic regularities. Lexical regularities were ob- ape's ability to use a grammar............ .... Each in- served in the case of two-sign combinations: particular signs (for example, more) stance of presumed grammatical compe- tended to occur in a particular position. These regularities could not be attributed to tence could be explained adequately by memorization or to position habits, suggesting that they were structurally constrained. simple nonlinguistic processes. That conclusion, however, was invalidated by videotape analyses, which showed that most of Nim's utterances were prompted by his teacher's prior utterance, and that www.sciencemag.org Nim interrupted his teachers to a much larger extent than a child interrupts an adult's Project Nim speech. Signed utterances of other apes (as shown on films) revealed similar non- human patterns of discourse. Our subject was a male chimpanzee, Neam Chimpsky (Nim for short) (16, 17). Since the age of 2 weeks, Nim was raised chips of different colors and shapes. In a (15). A sentence characteristically ex- in a home environment by human surro- et al. presses a complete semantic proposition related study, Rumbaugh (9) taught gate parents and teachers who communi- Downloaded from Lana, also a juvenile chimpanzee, to use through a set of words and phrases, each cated with him and amongst themselves Yerkish, an artificial visual language. bearing particular grammatical relations in ASL (7,8). Nim was trained to sign by These and other studies (10), one of to one another (such as actor, action, ob- a method modeled after the techniques which reports the acquisition of more ject). Unlike words, most sentences can- that the Gardners (2) and Fouts (18) have than 400 signs of ASL by a female gorilla not be learned individually. Psycholo- referred to as molding and guidance. Our named Koko (11), show that the shift gists, psycholinguists, and linguists are methods of data collection paralleled from a vocal to a visual medium can in general agreement that using a human those used in studies of the development compensate effectively for an ape's in- language indicates knowledge of a gram- of language in children (19-24). During ability to articulate many sounds (12). mar. How else can one account for a their sessions with Nim, his teachers That limitation alone might account for child's ultimate ability to create an 'in- whispered into a miniature cassette re- earlier failures to teach chimpanzees to determinate number of meaningful sen- corder what he signed and whether his communicate with spoken words (13). tences from a finite number of words? Human language makes use of two Recent demonstrations that chim- H. S. Terrace is a professor of psychology at Co- levels of structure: the word and the sen- panzees and gorillas can communicate lumbia University, 418 Schermerhorn Hall, Colum- tence. The meaning of a word is arbi- with humans via arbitrary "words" pose bia University, New York 10027. L. A. Petitto is a graduate student in the Department of Human De- trary. This is in contrast to the fixed a controversial question: Is the ability to velopment at Harvard University, Cambridge, Mas- character of various forms of animal create and understand sentences unique- sachusetts 01238. R. J. Sanders is a graduate student in the Department of Psychology at Columbia Uni- communication. Many bird species, for ly human? The Gardners (1, 3), Premack versity and a visiting instructor at the State Univer- sity of New York in Utica. T. G. Bever is a professor example, sing one song when in distress, (6), Rumbaugh (9), and Patterson (11) of psychology and linguistics at Columbia Universi- one song when courting a mate, and one have each proposed that the symbol se- ty. SCIENCE, VOL. 206, 23 NOVEMBER 1979 0036-8075/79/1123-0891$02.00/0 Copyright C 1979 AAAS 899 signs were spontaneous, prompted, Table 1. Number of tokens and types of com- turn of the hands to a relaxed position molded, or approximations ofthe correct binations containing two, three, four, and five (29). Of Nim's combinations, 95 percent sign (25). or more signs. consisted of sequences of distinct signs Nim satisfied our criterion of acquiring Length of Tokens Types that occurred successively. These are re- a sign when (i) on different occasions, combination ferred to as "liiear sequences." Two three independent observers reported its Two signs 11,845 1,138 other kinds of combinations were not in- spontaneous occurrence and (ii) it oc- Three signs 4,294 1,660 cluded in the corpus: contractions of two curred spontaneously on each of five Four signs 1,587 1,159 or more signs and simultaneous combi- successive days. By spontaneously we Five or more signs 1,487 1,278 nations in which two distinct signs oc- mean that Nim signed the sign in an ap- curred at the same time. Even though propriate context and without the aid of such combinations can occur in ASL, molding, prompting, or modeling on the stances of more tickle, the conventional they were excluded from our corpus be- part of the teacher. As of 25 September English juxtaposition of these signs. Ac- cause it was impossible to specify the 1977, Nim had acquired 125 signs (26). cordingly, there is no basis for deciding temporal order of the signs they con- whether Washoe's multisign combina- tained. Figure 1 shows a typical linear tions obeyed rules of sign order (28). One combination, me hug cat, in which there Combinations of Signs could conclude that Washoe had learned is no temporal overlap between any of that both more and tickle were appropri- the signs. The Gardners' analyses of Washoe's ate ways of requesting that tickling reoc- In no instance were specific se- sign combinations prevents one from cur and that when Washoe signed both quences, contractions, or simultaneous studying their grammatical structure. signs it was because of her prior training combinations reihforced differentially. With but two minor exceptions, the to sign each sign separately. Indeed, Nim was never required to make Gardners did not report the order of We defined a combination of signs as a combination of signs as opposed to a signs of Washoe's multisign combina- the occurrence of two or more different single sign. However, Nim's teachers of- tions (27). For example, more tickle and signs that were not interrupted by the oc- ten signed to him in stereotyped orders tickle more were both reported as in- currence of other behavior or by the re- modeled after English usage, and they I Fig. 1. Nim signing the linear combination, me hug cat to his teacher (Susan Quinby). (Photographed in classroom by H. S. Terrace.) 892 SCIENCE, VOL. 206 may also have unwittingly given him spe- consisting of all transitive verbs com- we observed. A conservative inter- cial praise when he signed an interesting bined with all references to himself (me pretation of these regularities, one that combination. Such unintentional reac- or Nim), is shown in Table 3 (32). The does not require the postulation of syn- tions do not, however, appear to differ number of tokens with the verb in the tactic rules, would hold that Nim used from the reactions parents exhibit when first position substantially exceeds the certain categories as relatively initial or their child produces an interesting utter- reverse order. Also, Nim combined tran- final irrespective of the context in which ance or one that conforms to correct sitive verbs as readily with Nim as with they occur. If this were true, it should be English. me (33). Nim's preference for using me possible to predict the observed frequen- Nim's linear combinations were sub- and Nim in the second position of two- cy of different constructions, such as jected to three analyses.