Abstract
Syntax is the set of rules for combining words into phrases, providing the basis for the generative power of linguistic expressions. In human language, the principle of compositionality governs how words are combined into a larger unit, the meaning of which depends on both the meanings of the words and the way in which they are combined. This linguistic capability, i.e., compositional syntax, has long been considered a trait unique to human language. Here, we review recent studies on call combinations in a passerine bird, the Japanese tit (Parus minor), that provide the first firm evidence for compositional syntax in a nonhuman animal. While it has been suggested that the findings of these studies fail to provide evidence for compositionality in Japanese tits, this criticism is based on misunderstanding of experimental design, misrepresentation of the importance of word order in human syntax, and necessitating linguistic capabilities beyond those given by the standard definition of compositionality. We argue that research on avian call combinations has provided the first steps in elucidating how compositional expressions could have emerged in animal communication systems.
Highlights
We found that Japanese tits exhibit an equivalent response to both natural (ABC-D) and novel (ABC-taa) call sequences
When these calls are combined into reversed ordering, they reduced their responses. These results demonstrate that tits combine different meaningful signals to generate a compound message that depends on the meaning of the elements and the way in which they are combined, i.e., compositional syntax [3]
We would predict human responders to respond to the first phrase but not the second precisely because it violates syntactical rules. This is exactly what we observed in Japanese tits: combinations of ABC and D calls evoke compound responses only when they are ordered as ABC-D sequences (Fig 2C)
Summary
Playback of artificially reversed sequences (‘D-ABC’; Fig 1B) elicited reduced scanning and approaching compared to the response towards natural call sequences (ABC-D). We found that Japanese tits exhibit an equivalent response (i.e., approach with scanning) to both natural (ABC-D) and novel (ABC-taa) call sequences.
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