Auditory Temporal Change Experiments  Electrocortical and behavioral measures of temporal integration as predictors of speech development   Naseem Choudhury, Ph.D. Paavo H. T. Leppänen, Ph.D. April A. Benasich, Ph.D. Asst. Professor of Neuroscience and Director of the Infancy Studies Laboratory   Infancy Studies Laboratory Center for Molecular & Behavioral Neuroscience Rutgers, The State University of New Jersey 197 University Avenue, Newark, NJ 07102 USA

 

Research Aims The purpose of this research is to examine the long-term relations between early information processing abilities (as indexed by auditory temporal processing [ATP], habituation, and recognition memory) and later cognitive and linguistic development. The project combines two promising converging techniques which, to our knowledge, have not previously been integrated in the study of young infants: brain electrophysiological activation measures employing event-related potentials (ERPs) to rapidly changing auditory temporal cues and behavioral assessment using a perceptual-cognitive battery sensitive to individual differences in perceiving fine acoustic discriminations. The specific focus will be on the relation between the electrophysiological and behavioral measures and later language (both receptive and expressive) and cognitive outcomes in children at high risk of language impairment (LI) and appropriate matched controls. Determining in more detail the nature of the relationship between early information processing abilities in the time frame of tens of milliseconds and later language abilities should elucidate the perceptual and cognitive substrates of speech and language processes. The development of more precise measures for the early identification of children most at risk for later LI would also be facilitated. This is an important long-term goal, so that intervention and remediation can begin during the most critical early periods of language development. Importantly, these investigations would also clarify whether the differences in language development between LI and control children are related to underlying basic neurocognitive differences as reflected in cortical electrical activation to rapidly changing auditory information.   Participants Two groups of infants will participate: normal control infants and infants born into families with a history of language-based learning disorders. Infants are tested between 6 and 24 months of age.   The tasks Behavioral measures:   A go/no-go (G/N-G) head-turn procedure is used to assess ATP. Infants are operantly conditioned to make a head-turn to the reinforcer following a target tone sequence embedded within a standard repeating sequence. Infants also receive several AV habituation tasks that evaluate their ability to discriminate consonant-vowel pairings and complex tone pairs. ERP paradigm: The stimuli are presented in a paradigm, which is particularly suitable for studying the brain's capability to detect small acoustic changes embedded in a sound stream. Rarely occurring deviant stimuli embedded among frequently repeated standard stimuli typically elicit in adults the mismatch negativity-component (MMN) reflecting passive detection of change at the level of the auditory sensory memory. MMN can be automatically elicited without an overt behavior or focused attention making the paradigm easy to use with very young infants. The EEG is recorded from 64 scalp sites using a 64-channel Geodesic Sensor Net (Electrical Geodesics, Inc.).   Significance of the Research Uniting data derived from studies of infant perceptual-cognitive development and studies of developmental language disorders with data obtained using sophisticated electrophysiological methodology (allowing examination of cortical temporal relations across development) will inform existing theories of perceptual, cognitive and language development. Hopefully, cross-fertilization of theory as well as techniques across fields will result. For example, although a substantial literature exists linking ATP abilities to developmental LI and dyslexia/ reading disorder (RD), and a small literature is emerging linking early perceptual-cognitive abilities, ATP thresholds and later language, examination of brain functioning related to ATP by means of ERPs in these populations has been very sparse. However, these studies show that response to both pure tones and speech stimuli of school age LI and RD children differ from those of normal control children, suggesting altered cortical processing of auditory information. Most recent studies have investigated young children at risk for these disorders on the basis of the familial history of LI and dyslexia showing that at both the behavioral and in brain activation levels at-risk children manifest deviancies in temporal processing. For example, my dissertation research has shown that brain electrical activity distribution over scalp areas, especially over the left temporo-centro-parietal regions, generated by a change in consonant duration (a critical temporal feature in the Finnish language context) is different in six-month-old infants who are at genetic risk for developmental dyslexia than in control infants. The results clearly show that the ERP technique can pick up crucial processing differences, which may be detectable well before language disorders are noted. The above studies provide evidence that ATP deficits can serve as a behavioral "marker" of LI. However, direct evidence that deviations in brain activation measured early in development could predict later language related disorders has yet to be found. Although indirect evidence for altered lateralization of brain activity exists, no precise knowledge is as yet available of what neural source locations may contribute to these possible differences. Furthermore, direct evidence of the behavioral consequences of such altered lateralization is also lacking. Our study aims to fill these gaps of knowledge using a combination of brain imaging and behavioral techniques. To date, no comprehensive study has attempted to link these complementary methodologies in order to delineate the underlying basic neurocognitive mechanisms involved in the early onset of LI. In addition, the use of these converging interdisciplinary techniques makes it possible to address a major controversy in the area of developmental language disorders. Specifically, is the processing of basic acoustic properties in early infancy related to subsequent language and cognitive competence, or do temporal processing deficits simply co-occur with the difficulties in phonological decoding seen in children with LI? See also: http://www.hfsp.org/awardees/AbstractsLTB1999/LEPPANEN_311.htm   ERP Lab Photos

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