NEURAL REPRESENTATION OF ACOUSTIC ELEMENTS OF SPEECH

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Auditory learning disabilities and attention deficit disorders are among the most common disorders found in children. Recent estimates are that 5-9 percent of school-age children in the United States have learning disabilities and that an additional 3-5 percent of school-age children have been diagnosed with an attention deficit disorder. The focus of this multi-year project is to examine the hypothesis that an inability to process certain basic acoustic parameters of speech is a significant contributing factor to learning and attention problems in these children. Behavioral and electrophysiologic techniques will be used to investigate psychophysical abilities and to delineate the underlying central auditory neural representation of acoustic elements of speech. At the same time, neurophysiologic responses to the same acoustic elements will be examined in an animal model, which is important because the surface-recorded neurophysiologic responses measured in human subjects cannot be traced directly to their anatomical sources. The ultimate goal of this project is to understand the neurophysiologic bases of speech perception in normal and impaired children, and to develop improved diagnostic and rehabilitative methods of the management of individuals with auditory learning disabilities. Specifically, it is known that some acoustic speech cues are better perceived than others, particularly by children with auditory-based learning disabilities. This project will look at the behavioral discrimination of rapidly changing spectro-temporal cues, which appear to be especially difficult for impaired children to hear. At the same time, neurophysiologic responses elicited by those same important acoustic cues will be measured. Then these neurophysiologic measures will be related to listening, learning, and academic achievement in normal and impaired children. For potential clinical use, techniques will be developed for measurment and objective analysis of neurophysiologic responses in individual subjects. Concurrently, an animal model will serve to determine the neurophysiologic encoding of the acoustic speech parameters under investigation along the auditory thalamo-cortical pathway, thereby providing an indicator of the pathology that may underlie certain auditory learning disabilities. Specifically, this project will (1) characterize evoked potentials recorded from several locations (epidural surface, primary and non-primary regions of the auditory thalamus and cortex) to the experimental acoustic elements, (2) investigate the contribution of each thalamo-cortical region to the aggregate response by observing the effects of pharmacologic inactivation of specific anatomical regions, and (3) compare the responses in each region to right and left ear stimulation.