Date: 17-May-2006
From: Geoffrey Pullum <pullumsoe.ucsc.edu>
Subject: Re: 17.1317, Disc: Starling Study: Recursion
Tim Gentner and his colleages recently published a paper in Nature about learning of artificially constructed recursive "grammars" by songbirds, with patterns like AAAABBBB (Gentner TQ, Fenn KM, Margoliash D, Nusbaum HC, 2006: Recursive syntactic pattern learning by songbirds, Nature 440: 1204-1207). The work has been widely reported in newspaper articles. We (Ray Jackendoff, Mark Liberman, Geoff Pullum, and Barbara Scholz) wrote a letter to Nature to warn against over-interpretation of the Gentner group's results. The letter presented four reasons for thinking the paper's conclusion, that the experiment "opens a new range of complex syntactic processing mechanisms to physiological investigation", was not sufficiently supported. Within 18 hours, Nature declined to publish the letter. (In our experience, this is what usually happens when linguists write to general science journals like Nature and Science commenting on the content of papers with linguistic content that have been published by non-linguists.) Readers of the LINGUIST List might like to read here the four points that were expressed in the letter, which were expressed thus: (i) Even if it were true that starlings could grasp a recursive grammar, this could hardly provide direct evidence about the evolution of human language. It would be at best an analogous rather than homologous capacity -- surely not an inheritance from some common ancestor of birds and mammals. (ii) It is not clear that the starlings learned a recursive rule. Becoming habituated to a pattern like AAABBB does not necessarily imply grasping recursively center-embedded structures like A(A(A(...)B)B)B. This pattern could equally be detected by comparing the number of A's and B's, given that some birds such as pigeons can subitize numbers up to 4 or more (Dehaene S, The Number Sense, Oxford University Press, 1997). (iii) Humans do not perform well on center-embedded syntax. Even for n = 2, they are often baffled by A^nB^n structures ("People people cheat cheat" is all but unintelligible). Few can handle n = 3. Are starlings outperforming humans syntactically? (iv) Recursion is not the unique core property of the human language faculty anyway (Pinker S & Jackendoff R, `The faculty of language: What's special about it?', 2005, Cognition 95, 201-36). Recursion is arguably involved in comprehension of complex visual fields, planning of action, and understanding social environments. These human capacities are shared with other primates. Unique to human language is a very large learned vocabulary consisting of long-term memory associations between meanings and structured pronunciations plus varied phrasal syntax. The Gentner experiment may help us understand animal pattern recognition and learning abilities, some of them possibly prerequisites for linguistic abilities; but the implications are being considerably exaggerated, especially in popular media accounts with headlines like "Songbirds May Be Able to Learn Grammar." Ray S. Jackendoff (Center for Cognitive Studies, Tufts University) Mark Y. Liberman (Institute for Research in Cognitive Science, University of Pennsylvania) Geoffrey K. Pullum, Barbara C. Scholz (Radcliffe Institute for Advanced Study, Harvard University)
Linguistic Field(s):
Philosophy of Language
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