Normal Speech Development

This project is funded through a grant from the National Institutes of Health-National Institute on Deafness and Other Communication Disorders awarded to Dr. Susan Nittrouer. It seeks to examine how normally developing children learn to recognize phonetic segments from the ongoing speech signal, which lacks any explicit segmental structure, as well as how they learn to produce speech in the precisely organized fashion of adult speech. So far, results suggest that the ability of language users to apprehend phonetic structure in the speech they hear depends on how well they recognize structure in the speech signal. There are perceptual strategies that are optimal in terms of allowing the listener to access phonetic structure. These optimal perceptual strategies differ across languages. We suggest that children learn these optimal strategies through experience with their native language. This project continues to test the basic premises of this theoretical position, and to extend our understanding of the developmental process involved in acquiring mature perceptual strategies.

Many procedures used in the laboratory involve labeling experiments. The acoustic structure of stimuli is varied such that several properties can provide information about phonetic identity. Procedures are crafted to allow the estimation of the relative weights assigned to each property in the labeling decision.

Fricative-vowel syllables were used regularly during the early stages of theory building. In these examples, the fricative noise is a single-pole, synthetic noise. The vowel portions are natural, with formant transitions appropriate for a preceding ‘sh’ or ‘s.’
Because stimuli are designed around the acoustic properties that are being studied, category labels may be nonsense syllables, and children have had no trouble reliably learning the labels to nonsense syllables. To facilitate the process of learning label names for nonsense syllables, children are taught that the labels are names of funny creatures or animals. For example, ‘sa’ is a little space creature. Stories are then created about these creatures, and presented to the children: first with [natural speech] and then with [synthetic speech]. The presentation of stories using synthetic speech provides children with some opportunity to listen to this kind of signal.
More recently we have been interested in how children discover the global structure of their native language.  In these experiments we process speech either to preserve amplitude envelope information only or to preserve dynamic spectral structure (i.e., sine wave speech).  Examples of such processed signals are below.  The sentence is Knees talk with mice.

[Natural speech] [Amplitude envelope speech] [Sine wave speech]