Greenfield, P.M. and Savage-Rumbaugh, E.S. (1993) Comparing communicative competence in child and chimp: the pragmatics of repetition. Journal of Child Language, 20, 1-26.
“Through an analysis of chimpanzee-human discourse, we show that two Pan troglodytes [the usual] chimpanzees and two Pan paniscus [pigmy] chimpanzees (bonobos) exposed to a humanly devised symbol system use partial or complete repetition of others’ symbols, as children do: they do not produce rote imitations, but instead use repetition to fulfil a variety of pragmatic functions in discourse. These functions include agreement, request, promise, excitement, and selection from alternatives. In so doing the chimpanzees demonstrate contingent turn-taking and the use of simple devices for lexical cohesion. In short, they demonstrate conversational competence. Because of the presence of this conversational competence in three sibling species, chimpanzees, bonobos, and humans, it is concluded that the potential to express pragmatic functions through repetition was part of the evolutionary hisotry of human language, present in our common ancestor before the phylogenetic divergence of hominids and chimpanzees. In the context of these similarities, two interesting differences appeared: (1) Human children sometimes used repetition to stimulate more talk in their conversational partner; the chimpanzees, in contrast, use repetition exclusively to forward the non-verbal action. This difference may illuminate a unique feature of human linguistic communication, or it may simply reflect a modality difference (visual symbols used by the chimpanzees, speech use by the children) in the symbol systems considered in this research. A second difference seems likely to reflect a true species difference: utterance length. The one- and two-symbol repetitions use by the chimpanzees to fulfil a variety of pragmatic functions were less than half the maximum length found in either the visual symbol combinations addressed to them by their adult human caregivers or the oral repitions of two-year-old children. This species difference probably reflects the evolution of increased brain size and consequent increased memory capacity that has occurred since the phylogenetic divergence of hominids and chimpanzees four to seven million years ago.”
METHODS (p. 7)
They used a method of discourse analysis based on that published by Ochs Keenan (1977) for children.
EXPLORATORY STUDY (p. 9)
Used Austin and Sherman when they were 7 and 8 yrs old, and had 100 lexigrams available to them. A computer printout of all symbol use by the researcher and subject was analysed in relation to detailed contextual notes made by the researcher. Two sessions of about an hour with each animal were analysed. (Transcripts had been published in 1984). 5 and 6 instances of “Confirm/agree” and “Request” were recorded for Austin, and 9, 3 and 5 instances of “Confirm/agree”, “Confirm with specification” and “Counterclaim” were observed for Sherman.
MAIN STUDY (p. 15)
Used Kanzi and Mulika when they were 5 and almost 2 years old. The analysis was based on every lexigram they produced during one month.
Mulika had 87 repetitions: 37 (43%) were “Confirm/agree” and 46 (53%) were either “Request” or “Imitate/Request”.
Kanzi had 62 repetitions: 46 (74%) were “Confirm/agree” and 10 (22%) were either “Request” or “Imitate/request”.
EXAMPLES (Table 3, p. 16: Lexigrams are capitalized)
Person: Let’s see what’s on TELEVISION
Mulika: TELEVISION (goes to video deck and gestures to it).
Person: Look Muli I found PRIVET-BERRYs in our REFRIGERATOR
Mulika: PRIVET-BERRY. (Person takes berries out of refrigerator freezer and offers Mulika one, Mulika takes it)
(Mulika reaches for Person’s Coke)
Person: COKE (showing Mulika the lexgram)
GENERAL DISCUSSION (pp 20-24)
The authors claim that repetition of symbols cannot be used as a dividing line between human and chimpanzee, since the reptitions in chimpanzees are similar to some of the simplest occurring in 1- and 2-yr old children. However, they acknowledge that children’s repitions become very different. “A principle difference was that repetitions were used by children, but not chimpanzees, to keep conversation going, to elicit further verbalization. ..... This difference .... could show that motivation to keep a conversation going and to use language for its own sake is, among primates, unique to the human species. Secondly, children develop symbolic means of referring to pragmatic functions, and the chimpanzees studied did not do this (e.g. did not have anything corresponding to “I agree”). Thirdly, chimpanzee repetitions were primarly of single lexigrams, whereas children often repeat several words. The authors accept that sentence length is probably “a true species difference” (p. 22).
Although these studies draw attention to the fact that symbol repetition by chimps is not necessarily just blind imitation, they also support the position that chimpanzee symbol use is unlike human language in being a) syntactically very limited; and b) tied very closely to immediate goals.
Thus the work by Greenfield and Savage-Rumbaugh, Jensvold and Gardner (2000) and Bodamer and Gardner (2002) does little to alter the conclusion of an immense gap between trained apes and human infants (e.g. Rivas, 2005): the 1990 chapter has Kanzi doing ‘action precedes object’ only about twice a week with 96% of his output judged to be requests, while Greenfield and S-R (1993) admit that their subjects used repetitions only for requests, not conversationally or to express agreement.
Similarly the results reported by Jensvold and Gardner (2000) and Bodamer and Gardner (2002) can readily be interpreted as Thorndikean conditioned responses reinforced by tangible goals, as opposed to human-like conversations.