The dynamics effect of stimulus parameters on EEG

Aim and Hypotesis: A method (dichotic test) which is based on EEG, with high temporal resolution about information processing of brain hemispheric asymmetry, constitutes the main area of this thesis. For interpretion of electrophysiological data and behavioral results, effects of stimulus parameters were examined in sensorial (intensity, timbre, and location of voice, voice onset time, etc.) and cognitive (attention shift, conflict detection, etc.) axes.Method: In this study, 60 healthy volunteers whose native language was Turkish (mean age 23.38) were studied for behavioural data. As a subgroup, 60 individuals whose mean age 21.65 was were studied for electrophysiological assessment. For the evaluation of the effects of the stimulus parameters dichotic test was utilized.Results: The general behavioral data indicated high right ear advantage. The stimulus parameters such as voice onset time, the property of the voice (women/men voice), directed attention to one of the ears, the presentation way of the syllables (homonym, heteronym) were shown to have an effect on the ear preference. In electrophysiological evaluations; the amplitude, latency differences and the activations of the different brain areas for early and late responses were displayed.Conclusion:The stimulus parameters affect both behavioural and electrophysiological results. While acoustical characteristics of voice causes the main effects, early and late components were prominent in electrophysiological results. These effects can be controlled by using standart groups, the appropriate stimulus and experimental design/patterns.While the early stage electrophysiological results occured in central region and were associated with sensorial processing, late stage responses were observed in frontal region and were interpreted as cognitive processing (conflict detection, etc.). Shorter LN latencies in REA condition were consistent with structural model of Kimura. This result makes it likely that the overall REA is a time-bound effect.The results indicate that the stimulus parameters have impact on the brain function and also dynamically influence the EEG which is an observatory tool of the brain. The current results may provide a support for highlighting the psychophysiological experimental design, for the assessment of the electrophysiological recording and analysis methods, for selecting the proper methods related to the short and long term processing of the brain functions, for constructing an interpretation for psychophysiological to pathological cases and for paving a road to advanced analysis methods.