Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Speech-Language Pathology

Department or School/College

School of Speech, Language, Hearing and Occupational Sciences

Committee Chair

Al Yonovitz

Commitee Members

Nancy Dold, Allen Szalda-Petree, Daniel Denis, Catherine Off


Auditory Processing Disorder, Backward Masking, Lead Toxicity


University of Montana


Objective: Past research documents the ototoxicity of inorganic lead (Pb), which in children may include associated auditory processing and learning disabilities. The present investigation aims to explore in computer modelled rats, as a laboratory animal model, the persistent effects of Pb-contaminated drinking water on measures. i.e., wave latency and amplitude, of auditory brainstem function and specifically the response to a known evoked-potential assessment of Backward Masking (BM) as a marker of Auditory Processing Disorder (APD). BM refers to the disruption of an animal's response to a stimulus when succeeded by a later stimulus temporally.

Methods and Study Design: In order to assess the neuro-ototoxic effects and changes in auditory threshold induced from Pb, the early auditory brainstem response (ABR) is typically obtained in anesthetized rats. Unlike the ABR, the middle and late evoked auditory response is modulated by the state of the organism and is not available in anesthetized subjects. It is the middle and late evoked auditory responses that would elucidate a BM effect.

For the software modelling male and female Sprague-Dawley rats will be randomized on the basis of body weight either to 0.0% (Control), 0.2% Pb acetate drinking-water exposures based on findings of an initial Pb dose range-finding trial. All response measures will be modelled with Simulink (MATLAB, Mathworks) and also with a hardware body worn unit. Assessments of ABR and middle-late responses (MID-LATE) will be obtained after 30 days of simulated chronic Pb exposure.

Apparatus: A specially built apparatus has been designed to allow novel methodologies that allow for simultaneous measurement of early, middle and late Evoked Potentials (EPs). The EPs will be measured in active, un-sedated, un-restrained virtual rats. Chronically implanted dural electrodes will be used to obtain data. To accomplish this active measurement, data will be transferred wirelessly from a portable unit to a computer. Specially designed stimuli will yield a clinically applicable method to test for APDs in children. Currently, there are only subjective perceptual tests that are prone to significant error.



© Copyright 2020 Silas Brewer Smith