THRESHOLD DETERMINATION WITH AUDITORY BRAINSTEM RESPONSE

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The long-term goal of this project is to increase the accuracy and efficiency of the Auditory Brainstem Response (ARB) in predicting auditory thresholds in hearing-impaired infants and young children. This will be accomplished by determining the optimal stimulus and recording parameters to use for ABR audiometry. An objective technique known as Fsp' which evaluates the strength of the recorded auditory neural potential relative to the background noise will be used as a measure of the effects of recording and stimulus manipulations. Subjects will be selected from two categories: 1. Hearing-impaired adults 2. Infants. Adult subjects will be further divided into hearing-loss groups based on severity and audiogram configuration and infants will be grouped into categories based on age. Two types of stimuli will be evaluated: 1. Clicks 2. Tone bursts in notched noise. The following experimental parameters will be manipulated: 1. Recording filter bandpass 2. Electrode placement 3. Stimulus rate 4. Stimulus polarity. Stimulus levels for each experiment have been chosen to evaluate a range of responses just above and below expected threshold. In all cases, 10,000 sweeps will be averaged to optimize the signal-to-noise ratio of the recordings. Recording bandpass effects on ABR threshold will be evaluated first and the bandpass which produces a significant improvement in the ABR signal-to-noise ratio will be used in subsequent experiments. Simultaneous recordings will be made from three, orthogonal electrode channels and a forth standard clinical channel to evaluate electrode placement effects while stimulus rate and polarity are manipulated. The dependant variable in all experiments will be the Fsp value associated with each response. The Fsp by stimulus level functions can also be used to determine the threshold of the ARB for any given set of parameters. Experiments are designed to evaluate stimulus and recording effects individually as well as interactions between experimental parameters, stimulus type and subject factors of hearing impairment and developmental stage.