Visual and auditory conditional position discrimination in chimpanzees (Pan troglodytes)

L. Martinez & T. Matsuzawa

チンパンジーの認知について、視覚の研究は多いが聴覚の研究は少ない。本研究の目的は、視覚処理と聴覚処理を比較することだ。新たな課題として、条件付位置弁別課題（CPD）と呼ぶ弁別課題を考案した。視覚あるいは聴覚の手がかりをもとに左右の位置を識別する課題である。 刺激は、同じチンパンジーの顔と声である。被験者はチンパンジー６個体だった。その結果、視覚と聴覚では大きな違いがあった。視覚性のCPDは聴覚性のそれよりも容易に習得した。従来の結果と同様に聴覚性の弁別課題はチンパンジーには学習が困難だった。個体差もあった。過去の経験で象徴的見本合わせの経験の豊富な個体は両方の課題を習得できた。それに対し、聴覚ー視覚の異種感覚間見本あわせの経験の豊富な個体は、弁別学習という意味では同様に豊富な経験があるにもかかわらず、両条件ともまったく学習がすすまなかった。今後さらに、こうした視覚と聴覚の弁別学習を規定する要因を検討する必要がある。

Behavioural Processes 82: 90–94

Chimpanzee cognition has been studied predominantly through the visual modality, and much less through the auditory modality. The aim of this study was to explore possible differences in chimpanzees’processing of visual and auditory stimuli.We developed a new conditional position discrimination (CPD) task requiring the association between a stimulus (from either the auditory or the visual modality), and a spatial position (left or right). The stimuli consisted of the face and voice of two individuals well known to the subjects (one chimpanzee and one human). Six chimpanzees participated in both the visual and the auditory conditions.We found contrasting results between the two conditions: the subjects acquired the CPD more easily in the visual than in the auditory condition. This supports previous findings on the difficulties encountered by chimpanzees in learning tasks involving auditory stimuli. Our experiments also revealed individual differences: the chimpanzee with the most extensive experience in symbolic visual matching tasks showed good performance in both conditions. In contrast, the chimpanzee expert in an auditory--visual intermodal matching task showed no sign of learning in either condition. Future work should focus on finding the most appropriate procedure for exploring chimpanzees’ auditory--visual cognitive skills.

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