Chimpanzee's language-like skill having a two-level structure comparable to the duality in human language.

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Cognitive function in chimpanzees was discussed, referring to studies on language-like skills mastered by chimpanzees. Ai, a female chimpanzee, served as the main subject in the present study. When the project started in April. 1978, her age was estimated to be about 1.5 years. A computer-controlled console terminal was used in the experiments. 'Words' were represented by visual symbols such as geometric figures or Arabic numerals. Some of them could be disassembled into nine fundamental figures called 'graphemes'. Each symbol and each grapheme were drawn on a key and would appear in various positions on a maximal l5x7 key matrix on the console. The chimpanzee learned to name various objects. 11 colors. and the numbers from one to six. Ai favored two sequences (Object/Color/Number and Color/Object/Number) in particular when naming the three attributes of a referent, for example, "five red pencils". The favored sequences continued to be used when naming new items. The chimpanzee also learned to construct the 'words' by assembling their corresponding graphemes. These results show the chimpanzee's language -like skill as having a two-level structure comparable to the duality in human language. Some of the experiments were carried out without direct food reward. The cognitive abilities of chimpanzees and humans can be studied using the same apparatus and following the same procedures. Although there was no fundamental difference between the two species in visual sensation and perception. a difference was found among the higher cognitive functions such as the acquisition of self-embedding rules. The differences found between the two species was discussed in terms of the depth of hierarchical structure in cognitive function.