11/08/2006

Nativist Perspectives on "Late Talkers"

In novel noun generalization tasks, children tend to show a “shape bias” by 2.5 years of age – that is, they will extend known object names to other objects of the same shape. More recent work has shown that children with abnormally small vocabularies do not demonstrate this shape bias (Jones, 2003); furthermore, this relationship appears to be causal, in that training normal children to show the shape bias drastically improves word learning even outside the laboratory (Smith et al., 2002).

Interactionist, connectionist, and nativist theories of language acquisition each make novel predictions for the underlying mechanism giving rise to a lack of shape bias among so called “late-talkers,” and also for ways to improve their rate of word learning. Predictions motivated by the nativist account are discussed in today's post, while predictions motivated by the other two accounts will be discussed in tomorrow and Friday's posts.

Nativist accounts suggest that language acquisition is guided by mechanisms that are innately specified. These mechanisms may be language specific, such as in the Chomskian concept of a “universal grammar,” or as in Pinker’s “words-and-rules” theory (2002). Alternatively, these mechanisms may be relatively domain-general, such as the computations required for combinatorial (Spelke, 2003) or recursive cognitive processing (Hauser, Chomsky & Fitch, 2002). In either case, the assumption is that a bias to preferentially attend to shape features is somehow innate, and therefore largely determined by intrinsic biological properties as opposed to being developed through experience.

According to hard-line nativist accounts, the failure of late-talkers to demonstrate a shape bias might be purely genetic in origin. Therefore, late-talking could be associated with a maladaptive gene for word learning in a language-specific faculty, or one that codes for how general-purpose attention is distributed to objects in the environment. In the latter case, nativist accounts would predict that late-talkers would show early deficits in a variety of other domains (for example in ignoring distractors or in focusing attention), whereas the former case would predict only language-specific deficits. In either case, the prognosis and possibilities for intervention would be particularly bleak, since language learning is presumed to be innately-specified and relatively unaffected by learning.

A less extreme nativist account would still suggest that word learning strategies like the shape bias are innately specified, but may only become active after certain “linguistic triggering experiences” (as cited by Tomasello, 2000). In this case, late-talkers may fail to show a shape bias simply because they have not yet encountered these environmental triggers, either as a result of less language exposure or deficits in auditory processing. Alternatively, late-talkers may just be developmentally delayed. In either of these cases, the prognosis is much more favorable than what is suggested by hard-line nativist accounts; intervention would simply involve continued exposure to natural language and, if auditory deficits are suspected, possibly hearing aids.

References:

Hauser MD, Chomsky N, & Fitch WT. (2002) The faculty of language: what is it, who has it, and how did it evolve? Science. 2002 Nov 22;298(5598):1565-6.

Pinker S, & Ullman MT. (2002). The past and future of the past tense. Trends Cogn Sci. 2002 Nov 1;6(11):456-463

Smith LB, Jones SS, Landau B, Gershkoff-Stowe L, & Samuelson L. (2002). Object name learning provides on-the-job training for attention. Psychol Sci.;13(1):13-9.

Spelke, E., 2003. What Makes Us Smart? Core Knowledge and Natural Language. In: Gentner, D. & Goldin-Meadow, S., Language in Mind: Advances in the Study of Language and Thought. Bradford Books/MIT Press, Cambridge, MA.

Tomasello M. (2000). The item-based nature of children's early syntactic development. Trends Cogn Sci. 2000 Apr;4(4):156-163.

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