Karen E. Brakke

Spontaneous class grouping behavior by bonobos (Pan paniscus) and common chimpanzees (P. troglodytes)

Abstract Two experiments investigated spontaneous class grouping behavior by human-enculturated and language-reared bonobos (Pan paniscus) and common chimpanzees (P. troglodytes). In experiment 1, three chimpanzees ranging in age from 6 to 18 years were presented with six objects. The objects embodied three conditions: additive, multiplicative and disjoint classes. All chimpanzees spontaneously produced single- and two-category classifying. In experiment 2, six chimpanzees ranging in age from 6 to 21 years were presented with 12 objects in the same class conditions. Chimpanzees mainly produced single-category classifying. Their two-category classifying was more rudimentary than that found in experiment 1. Chimpanzees did not produce any three-category classifying which would be necessary to construct the hierarchies that humans begin to construct during early childhood.

Early postural behavior in pan: Influences on development☆

Abstract The development of postural control is fundamental to virtually any other behavior, yet data on its ontogeny in anthropoid species are lacking. In this study, the Riesen and Kinder (1952) Postural Schedule for Infant Chimpanzees was used to compare the postural development of an infant bonobo (Pan paniscus) and an infant chimpanzee (Pan troglodytes) to that of each other, to that of nursery-reared chimpanzees ( Riesen & Kinder, 1952 ), and to that of normative humans ( Gesell & Thompson, 1938 ). These subjects, although of different species, displayed similar development and attained many behaviors earlier than the nursery-reared chimpanzees. All ape subjects, especially those in the current study, developed most behaviors several weeks earlier than did humans. Results support Riesen and Kinders finding that rate of early motor development differs in Pan and Homo infants, but this study also suggests that within a genus or species there are rearing effects which can facilitate or retard development of certain skills.

Spontaneous logicomathematical constructions by chimpanzees (Pan troglodytes, P. paniscus)

Abstract Two experiments investigated the spontaneous construction of precursory logicomathematical operations by human-enculturated and language-reared chimpanzees (Pan troglodytes, Pan paniscus) when they were interacting freely with objects. In experiment 1, three chimpanzees ranging in age from 6 to 18 years were presented with sets of six objects. Chimpanzees constructed equivalence, order and reversibility relations within single sets of objects as well as between two or three contemporaneous sets of objects. The chimpanzees’ logicomathematical operations were more advanced, including infrequent and minimal operations on three sets, than those of some previously investigated younger nonenculturated common chimpanzees. In experiment 2, six chimpanzees ranging in age from 6 to 21 years were presented with sets of 12 objects. Chimpanzees constructed more advanced operations on single sets, but not on contemporaneous sets. The results suggest partial convergence and partial divergence between development of logicomathematical cognition in chimpanzees and humans.

COMPREHENSION SKILLS OF LANGUAGE-COMPETENT AND NONLANGUAGE-COMPETENT APES

Initial language studies of humans and of apes revealed that humans, unlike apes, already have a solid understanding of the nature of linguistic reference when they begin to produce language (Huttenlocher, 1974). Overlooking the sophisticated comprehension that undergirds a child’s understanding of language, the first studies with apes began simply by teaching rote symbol-object associations wherein an ape looked at an object and responded by producing a sign or selecting a symbol. Production learned in this way, however, did not generalize across communicative function; nor did production generalize to receptive competence (Savage-Rumbaugh, 1981). More recent work has stressed the comprehension of language as a communicative instrument prior to the onset of production and has shown that apes, like children, can learn to differentiate speech sounds, attach communicative intent to those sounds and even link specific sounds with appropriate environmental events and referents (Savage-Rumbaugh, 1986; Sevcik and SavageRumbaugh, 1994). In 1993, Savage-Rumbaugh and her colleagues demonstrated the ability of a young child and a bonobo chimpanzee to comprehend simple sentences and simple syntactic structures in an experimental setting (Savage-Rumbaugh et al., 1993). The level of comprehension required in this setting was quite advanced, since experimental controls strictly precluded both child and bonobo from using any contextual assists in understanding the sentences spoken to them. In a normal language-acquisition environment, context and speech are often paired and so entrenched in the culture that the learner acquires the meaning of words and syntactical structures by exposure to speech uttered in a context that may convey the speaker’s intent. Examples of such contexts include turn-taking games and interindividual routines promoting joint attention, such as diaper-changing, playing, eating, preparing food, etc. (Brunei-, 1975; Bruner, 1983; Bakeman and Adamson, 1984). Since context can determine and/or clarify a speaker’s intent, it is important to ascertain the extent to which this may or may not be occurring in language comprehension studies with both children and apes (e.g. Benedict, 1979; Savage-Rumbaugh, 1991; Bates, 1993). It is all too easy to assume that language comprehension is occurring when indeed it is actually comprehension of overall context and what should be done in that context that is really happening. This does not mean that comprehension of context and what to do in context is in itself a trivial phenomenon. For example, a caretaker may ask a nonlanguage-using ape to ‘Make the chimp doll tickle your foot.’ The caretaker may say this in the context of just having demonstrated this action upon herself. In order to respond appropriately, even without understanding the sentence, the ape has to recognize that it is being asked to act