Tuesday, October 12, 2010

iPost Research Byte: New approaches needed to study language disorders?

New Approaches to the Study of Childhood Language Disorders
Susan Nittrouer and Bruce Pennington
Curr Dir Psychol Sci 2010;19 308-313
Select sections (quotes) and summary of this interesting article below.

Although considerable progress has been made in understanding the etiology and risk factors associated with disorders of speech, language, and reading acquisition (Pennington & Bishop, 2009), the exact nature of the problem underlying these related conditions is still puzzling. Much research on children with these disorders has reliably shown that something is awry with their phonological representations, but precisely what that problem is remains elusive. Here we suggest that at least one factor impeding progress toward identifying that problem is that our collective notion of phonological representations has fallen out of line with current directions in perceptual psychology. The goal of this paper is to review trends in this area that bear on how we think about phonological representations in typical and atypical spoken and written language development, to help redirect our research efforts. In turn, that redirection should affect how we intervene with children experiencing difficulty learning language.

As described above, speech perception is typically viewed as the recovery of strings of phonetic segments from the acoustic signal. Historically, investigators have examined (a) what acoustic properties are used to make decisions about specific phonetic segments and (b) what values or settings on those properties specify each phonetic label. These acoustic properties are traditionally termed cues, defined as temporally brief (several tens of milliseconds long) bits of the spectral array that, when experimentally manipulated, can be shown to affect phonetic labeling (Repp, 1982). For decades, speech perception experiments have involved manipulating these spectro-temporal bits of the signal in a well-controlled manner and measuring how those manipulations influence phonetic labeling. This line of investigation led to the development of another cornerstone of speech perception research: categorical perception.

This brief historical review of speech perception research indicates that we can no longer view the human listener as merely a passive recipient of acoustic cues specifying a string of phonemes. There is more to speech perception. Typical listeners use signal components not exclusively affiliated with individual phonetic segments to recover the linguistically significant object, as long as those components can be organized properly. Results congruent with this suggestion emphasize that the job of our sensory systems is to fuse all signal components reaching us in order to create coherent perceptual objects. Accordingly, phonological representations arise when various levels of signal structure, both detailed and more global, are integrated over time. By this view, phonemes are not recoverable as separate entities; rather, phonetic structure emerges from ongoing perceptual processes. Being able to organize signal components in a certain manner is clearly an important skill, yet little effort has been expended investigating how well children with language deficits are able to perform these sorts of perceptual feats. Numerous studies have measured the sensitivity of children or adults with language impairments to the acoustic cues that underlie phonetic labeling, and they have come up empty handed in terms of unequivocal explanation for those impairments (e.g., Hazan et al., 2009). It is time to consider other perceptual processes as possible culprits in the problems faced by these individuals..


It is tempting for cognitive and developmental scientists whose main interest is in the acquisition of language or literacy to relinquish concern about the details of phonological development—to simply assume that such development happens and provides the child with phonological representations like phonemes that can then be used in other language processes. But the intricacies of how listeners recover phonologically significant structure turn out to be very important for understanding both typical and atypical spoken and written language acquisition. Relying too heavily on older theories of speech perception to explain this phenomenon is a mistake. It is time that we incorporate alternative experimental approaches such as those we reviewed here into our study of childhood language disorders, and consider the theoretical implications in our accounts of those disorders.

Sent from Kevin McGrew's iPad

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