Publication Abstracts - 1998

Konrad-Martin, D., Rübsamen, R., Dörrscheidt, G. J., and Rubel, E. W (1998). Development of single- and two-tone responses of anteroventral cochlear nucleus neurons in gerbil. Hear. Res. 121: 35-52.

Department of Speech and Hearing Sciences, University of Washington, Seattle 98195, USA.

Responses of anteroventral cochlear nucleus (AVCN) neurons in developing gerbils were obtained to single-tone stimuli, and two-tone stimuli elicited by best frequency probes presented over a range of intensities. Neurons displayed Type I, Type I/III, and Type III receptive field patterns. Best frequencies ranged from 1.5 to 10.0 kHz. Two-tone suppression (2TS) was first observed in 5 of 16 neurons examined at 14 dab. and in all neurons examined in gerbils aged 15 to 60 dab. Suppression areas grew larger, and discharge rate reductions became greater with age. Features of the two-tone responses that were highly correlated with single-tone responses across age groups include maximum rate reductions and suppression area thresholds. The intensity level of the CF probe-tone also influenced these features of 2TS. Maximum rate reductions to below spontaneous rate levels of activity were common across age groups. Results suggest that the cochlear amplifier is present and fundamentally adult-like by 15 dab for the regions of the cochlea coding the mid frequencies in gerbil. Over the subsequent week, contributions to the developing two-tone responses by the cochlear amplifier increase slightly. Two-tone responses are influenced by central inhibitory mechanisms as early as 14 dab.

Merzenich, MM; Miller, S; Jenkins, WM; Saunders, GH; Protopapas, A; Peterson, B & Tallal, P.  Amelioration of the acoustic deficits underlying language-based learning impairments in Basic Mechanisms in Cognition and Language with Special Reference to Phonological Problems in Dyslexia (Wenner-Gren International Series Vol 70). Von Euler C. Lundberg, I. & Llinas, R. (Eds.) Pergamon.

A large percentage of language-impaired and dyslexic children have abnormal acoustic reception abilities that have been documented in several different classes of psychoacoustic experiements.  Many language-impaired and dyslexic individuals have difficulties sequencing repaidly successive sound inputs because under the right conditions sounds destructively interfere with one another.  Many language-impaired children also have abnormal acoustic masking functions.   Form them, the detection of brief sounds is more strongly suppressed when those sounds are delivered nearby in time and within the same frequency channel as other ('masking') stimuli.  In language-impaired children, these abnormal masking interference effects apply powerfully in the backward direction, that is, the detection of any brief sound is especially strongly suppressed by the occurrence of a rapidly following sound.  At least some language-impaired and dyslexic children also appear to have abnormal frequency discrimination abilities.

There is no dispute that aurally received speech is 'fuzzy' in language-learning impaired and dyslexic children. For these children, the segmental features of speech are not consistently or often appropriately resolved. As is predicted on the basis of abnormal masking interference patterns, language-learning impaired children have difficulty identifying the brief sound parts of words, especially with strong interferences occurring in the backward masking direction for the fine-grained acoustic features of speech that overlap spectrally.  Consistent with this interpretation, just as 'probe tone' in a masking experiment can be made audible by lengthening or amplifying it, so too can the initial or trailing acoustic events of syllables or words be relatively easily rendered more reliably distinguishable or recognizable in impaired children by simply differentially lengthening or strengthening them.

What is the origin of this striking impairment in complex acoustic signal/aural speech reception that so devastatingly limits language abilities in impaired children?  What is actually wrong with the speech processing and learning machinery in the brains of these children? When, where and how does this problem arise? Why is this problem so resistant to change? How do the many other cognitive, pragmatic, emotional and other problems, that are commonly recorded in these children, originate from and relate to this fundamental signal reception/language processing problem? How do the language problems that spring from this acoustic signal reception problem relate to reading impairments? Perhaps most importantly, how can this problem be most effectively remediated in language-impaired children?

In this article, these important questions will be addressed briefly, to the extent that the current state of neuroscience, psychophysics and linguistics can answer them.  The answers to these questions frame a large part of the logic that led us to develop a novel training method for overcoming this problem.  The main principles that underlie this new approach to the remediation of the language-learning problems of these children will be briefly summarized.  Some results from a trial conducted with 500 language-impaired children who were trained using this new methodology will be outlined.  This large trial showed that this problem can be rapidly overcome in many children by a particular form of training.  Finally, several important remaining theoretical and practical questions will be discussed.

Ren, T., & Nuttall, A. L. (1998).  Comment on "Enhancement of the transient-evoked otoacoustic emission produced by the addition of a pure tone in the guinea pig".  Journal of the Acoustical Society of America, 104:344-349.