Complexity in Language Acquisition
Article first published online: 17 JAN 2013
Copyright © 2013 Cognitive Science Society, Inc.
Topics in Cognitive Science
Volume 5, Issue 1, pages 89–110, January 2013
How to Cite
Clark, A. and Lappin, S. (2013), Complexity in Language Acquisition. Topics in Cognitive Science, 5: 89–110. doi: 10.1111/tops.12001
- Issue published online: 17 JAN 2013
- Article first published online: 17 JAN 2013
- Manuscript Accepted: 2 NOV 2012
- Manuscript Received: 21 SEP 2011
- Manuscript Revised: 21 SEP 2011
- Computational complexity;
- Language acquisition;
- Computational learning theory
Learning theory has frequently been applied to language acquisition, but discussion has largely focused on information theoretic problems—in particular on the absence of direct negative evidence. Such arguments typically neglect the probabilistic nature of cognition and learning in general. We argue first that these arguments, and analyses based on them, suffer from a major flaw: they systematically conflate the hypothesis class and the learnable concept class. As a result, they do not allow one to draw significant conclusions about the learner. Second, we claim that the real problem for language learning is the computational complexity of constructing a hypothesis from input data. Studying this problem allows for a more direct approach to the object of study—the language acquisition device—rather than the learnable class of languages, which is epiphenomenal and possibly hard to characterize. The learnability results informed by complexity studies are much more insightful. They strongly suggest that target grammars need to be objective, in the sense that the primitive elements of these grammars are based on objectively definable properties of the language itself. These considerations support the view that language acquisition proceeds primarily through data-driven learning of some form.