The effects of stimulus intensity on the cognitive P3 evoked response
Dille, Marilyn Louise Farnsworth
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Short-term memory problems are a normal part of aging but they can also indicate early signs of dementing diseases such as Alzheimer's. The P3 cognitive evoked response is a technique thought to directly assess short-term memory function. However, it has not been shown to be sensitive to mild short-term memory disorders. The P3 procedure is not standardized and this lack of sensitivity can be attributed, in part, to stimulus related factors used to generate the response.The purpose of Experiment 1 was to investigate the effect of increasing stimulus intensity on the P3 response. Many clincial populations cannot be counted upon to actively listen during the P3 discrimination task. It was hypothesized that the alerting effects of high stimulus intensity would cause a passive listener to generate a P3 response that was identical to an active listener. High intensity stimuli increased the prevalence of the P3 response. Additionally, the P3 latency shortened and the P3 amplitude was increased using high level stimuli. However, the P3 response obtained during passive listening was significantly different from the P3 response during active listening in young adults from the general population. P3 responses obtained from these two listening strategies should not be compared, especially at low stimulus intensities.The purpose of Experiment 2 was to compare equal and unequal relative toneburst intensities on the P3 measures. Hearing loss is a common finding among clinical populations with memory problems and can make the oddball tone unequal in loudness to the standard tone. It was hypothesized that changes in the salience of the discrimination task resulting from changes in the relative loudness of the tone pairs would change the P3 measures. It was found that the P3 response were less prevalent and longer in latency when subjects listened passively and the tonebursts were unequally intense, a listening condition common for individuals with dementia and hearing loss. Since a significant finding among clinical populations on whom the P3 might be applied is a prolonged or absent response, it is very important that the discrimination task be done at high intensity levels with the tones equally loud. If comparison are to be made between groups, both groups should be using the same listening strategy.
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