Repository 12-1999 Scale-Model Comprehension by Chimpanzees ( Pan troglodytes )

The ability of chimpanzees (Pan troglodytes) to recognize the correspondence between a scale model and its real-world referent was examined. In Experiments 1 and 2, an adult female and a young adult male watched as an experimenter hid a miniature model food in 1 of 4 sites in a scale model. Then, the chimpanzees were given the opportunity to find the real food item that had been hidden in the analogous location in the real room. The female performed significantly above chance, whereas the male performed at chance level. Experiments 3 and 4 tested 5 adult and 2 adolescent chimpanzees in a similar paradigm, using a scale model of the chimpanzees' outdoor area. Results indicate that some adult chimpanzees were able to reliably demonstrate an understanding of the relationship between a scale model and the larger space it represented, whereas other subjects were constrained by inefficient and unsuccessful search patterns. Flexible symbol use and comprehension have recently been a significant focus in the study of the cognitive abilities of chimpanzees (Pan troglodytes; e.g., Matsuzawa, 1985; Savage-Rumbaugh, 1986). Chimpanzees have demonstrated the capacity for understanding sophisticated representational concepts related to rudimentary language-like skills (e.g., Premack, 1971, 1986) as well as other representational systems, such as numbers (e.g., Boysen & Berntson, 1989; Matsuzawa, 1985; Murofushi, 1997). However, in an early attempt to test chimpanzees' understanding of another representational relationship, juvenile chimpanzee subjects failed to recognize the correspondence between a scale model of a familiar room and the actual room (Premack & Premack, 1983). However, important procedural details were not reported, making it difficult for one to compare these chimpanzees' difficulties with children's performance on similar tasks and also with the results of the present set of studies with chimpanzees. Human children show a striking age difference in understanding scale models (DeLoache, 1987, 1991, 1995). DeLoache reported that during a task in which children who witnessed a miniature toy being hidden in a model were asked to find the analogous full-size toy in a real room, 3-year-old children readily retrieved the real toy, whereas 21⁄2-year-old children had difficulty with the task. The younger children's poor performances were not due to a memory failure for the original hiding site, because they were able to find the miniature toy when they were asked to do so after returning to the model (DeLoache, 1987, 1991). DeLoache (1987, 1991, 1995) explained the performance problems of the younger children as reflecting more limited abilities to form a "dual orientation" to the model. To solve the task, the children must be able to represent the model as both a tangible, real object and a symbol for something else. The dualorientation hypothesis was supported by additional findings when the same children were presented with photographs of the hiding sites instead of the model. With photographs, both age groups were able to find the hidden toy. Thus, in situations in which the younger children (21⁄2-year-olds) had to form a dual orientation (scale-model task), their performance was poorer, whereas photographs were readily interpreted representationally (DeLoache, 1991). In contrast, the older children recognized the model as both symbol and object. In light of the negative findings of Premack and Premack (1983) as well as the developmental differences noted by DeLoache (e.g., 1987, 1991), we designed the present study to explore the ability of chimpanzees to understand the topographic relationship between a scale model and its corresponding real-world space by using an approach closely modeled after DeLoache's (1987) research. The first study used a scale model of an indoor room that was very familiar to the 2 chimpanzee subjects, which were able to interact safely with Sarah T. Boysen outside of their home cage. A second scale model of a familiar outdoor enclosure was used in Experiment 3 and allowed all7 chimpanzees (5 adults and 2 adolescents) in the Ohio State University colony to be tested.