Auditory congnition in the chimpanzee

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In the first year, a chimpanzee acquired an audio-visual intermodal matching to sample task using sound producing objects. And the performance was transfered to different pairs and new pairs of sound producing objects. However, compared with a visual or audio-visual sample stimulus, it was very difficult for the chimpanzee to choose a picture of an object based on sound of the object. Even if the subject showed a high level of performance, reaction time was two to three times longer than that for a visual or an audio-visual sample stimulus. In the second year, working memory of an auditory sample was examined. The delay interval was inserted between the auditory sample and visual choice stimuli. The decay of auditory sample was abrupt and performance dropped to a chance level at the 16-s delay interval. Then, the formation of "human" and "object" concepts was examined. The sample stimulus was human voices or sounds of an object. The choice stimuli were picture of a human face and an object which produced these acoustic stimuli. Twenty-two human and object pairs (fourty-four stimuli) were gradually introduced. Matching performance was improved as new pairs were added. And for thirty-four out of the 44 stimuli the subject showed a correct response in the first trial. These results suggest that the chimpanzee acquired the concepts of "human" and/or "object" .