Mandi A. Kimball and Dr. David L. McPherson, Audiology and Speech Language Pathology

When a person is presented with a tone pip or a click, his or her brain waves, in response to the auditory stimulus can be measured. This response is called the auditory evoked potential (AEP). AEPs can be classified as short-, middle-, or long-latency depending on how long after the stimulus they occur. The P50 wave lies in the middle latency series and occurs approximately 50 ms after the stimulus is presented. Gating is a phenomenon that occurs in the thalamus portion of the brain when identical target stimuli are presented in pairs. The amplitude the P50 wave of the second stimulus in the pair is lower. This reduction in amplitude represents a suppression of non-novel stimuli and is expressed as a percentage amplitude reduction between the pair of stimuli.

This study focused on altering stimulus factors to help determine the limits of the response or change in brain electrical activity associated with changes in stimulus factors. The original plan was to study changes in frequency, intensity, and intra-stimulus factors. It was quickly decided it would be more reasonable to study only one variable a time. This study focused only on intra- stimulus intervals length, (the time between stimulus 1 [S1] and stimulus 2 [S2]) and its effect on the gating phenomenon.

The expected results was that gating would occur when S1 was equal to S2 and the intra- stimulus interval was equal to or shorter than the standard 500 ms. It was also expected that as the intra-stimulus-interval increased to be longer than 500 ms, gating would not occur. Subjects were presented with five pairs of stimuli with a period of 10 seconds (s) between the presentation of each pair. The intra- stimulus time between S1 and S2 in pair one was 0.5 s, 0.25 s in pair two, 1.0 s in pair three, 2.0 s in pair four, and 4.0 s in pair five. Therefore, gating was expected to occur with pair one and two only.

Presently we are in the process of analyzing the data that was collected during the 2000-2001 academic year. We expect to have this completed early Winter Term 2002.

This project has been a wonderful opportunity to learn about research, data collection and analysis. It has also helped prepare me for the research that I will continue to participate in as a graduate student and for the research that I will conduct for my thesis project.