Chimpanzee sign language and Darwinian continuity: evidence for a neurological continuity for language.

The current article addresses the empirical validity of the Cartesian view of language by first examining a sample of the results generated by over 30 years of chimpanzee sign language studies and then examining some neurological and behavioral data that accounts for the similarity between human and nonhuman communication systems. Finally an attempt will be made to propose a unified model of language that accounts for these findings and shows how the Cartesian world view has proposed a theory of language that is incomplete.

Use of temporary and semipermanent enrichment objects by five chimpanzees.

At the Chimpanzee and Human Communication Institute, caregivers provide the 5 chimpanzees who reside there with many different forms of social, food, habitat, and object enrichment. In this study, we examined the chimpanzees' use of both semipermanent and temporary objects. Semipermanent objects included cargo nets, climbing structures, a treat mound, and other objects that were present at the chimpanzees' enclosure throughout the duration of this study. Each day, 50 temporary objects were placed in the chimpanzees' outdoor enclosure or indoor exercise rooms. Frequency of use was examined in 2 conditions: rotated and same. In the rotated condition, temporary objects were replaced with different temporary objects after 3 hr. In the same condition, temporary objects were presented for the entire day. Focal and scan sampling were used to record the chimpanzees' use of enrichment objects. Observers collected focal sample data to record the chimpanzees' initial reaction to objects when entering the indoor exercise rooms, outdoor enclosures, or both at 9:00 a.m. and 1.00 p.m. A total of 35 hr of focal data and 156 hr of scan data were collected over an 8-week period. Temporary object rotation increased the overall frequency of temporary object use both in the initial 15 min of focal sample data and during the following 6 hr of scan sample data for 4 of the chimpanzees. All of these chimpanzees used both semipermanent and temporary objects throughout the day. Each chimpanzee's pattern of use was unique. The results of this study emphasize the importance of temporary object rotation and presentation of both temporary and semipermanent objects to captive chimpanzee environments.

Chimpanzee (Pan troglodytes) pointing: hand shapes, accuracy, and the role of eye gaze.

The manual pointing of 2 signing chimpanzees, Moja and Tatu, was examined in 2 experiments. Experiment 1 investigated eye-gaze direction, hand use, and hand shape while pointing. Both chimpanzees obtained the attention of a human before pointing toward an unreachable object. During 100 trials, the chimpanzees alternated their eye gaze between the object and the human while pointing. Moja's points were left-hand biased, and Tatu showed no lateral hand bias. Both indexical and whole hand points were recorded. Experiment 2 tested the chimpanzees' ability to point accurately toward objects in close proximity to each other. Humans were able to reliably determine the locations toward which the chimpanzees pointed. Both chimpanzees showed left-hand biases, and a higher proportion of indexical points were observed than in Experiment 1. These results are compared and contrasted with recent hypotheses pertaining to the topography of chimpanzee pointing and the role of eye gaze in deictic interactions.

Acquisition of American sign language by a noncommunicating autistic child.

Experiments in the perception and language abilities of autistic children indicate that the children have auditory-visual association problems. These findings, combined with the findings that autistic communication is primarily gestural, led to the teaching of elements of American Sign Language to a 5-year-old nonverbal autistic boy. Results after 20 hours of training indicate that the child did acquire signs, that increasing signing led to increasing vocal speech, and that the child has rudimentary English syntax. The use of Ameslan signs spontaneously generalized to other situations and the training resulted in increased social interaction.

Acquisition and testing of gestural signs in four young chimpanzees.

Two male and two female chimpanzees were each taught ten signs of American Sign Language. The acquisition rates of the signs were compared on the basis of the number of minutes required in training to reach a criterion of five consecutive unprompted correct responses. After the ten signs had been acquired, the chimpanzees were tested in a double-blind procedure for nine of the signs. All four chimpanzees acquired all of the signs. Some signs were consistently easier to acquire than others, and individual differences between the four chimpanzees were found in the acquisition rates and tests.