The Study Of Influence Of Inter-Stimulus Interval (ISI) On Brain Evoked Potentials

Over the last years more and more research was focused on the exploration of the brain and its function. This research is about the brain evoked potentials (EP) response to sequential stimuli. With paired-stimuli paradigm, the influence of a preceding stimulus on the brain evoked potentials(EP) to the succeeding stimulus was studied in this research, under three kinds of stimuli as follows: (1) the preceding stimulus and the succeeding stimulus were both auditory stimuli; (2) the preceding stimulus and the succeeding stimulus were both visual stimuli; (3) the preceding stimulus and the succeeding stimulus were cross-sensory stimuli, in which two situation were included; the first situation was auditory-visual cross-modal stimuli in which the preceding stimulus was auditory stimulus and the succeeding stimulus was visual stimulus, the second situation was visual-auditory cross-modal stimuli in which the preceding stimulus was visual stimulus and the succeeding stimulus was auditory stimulus. It is important in theory to study the mechanism of prepulse inhibition or sensory gating. We can have a good understanding of the brain functions in its information processing, by exploring the brain electrophysiological characteristics in response to sequential stimuli, and by identifying the locations of the structures which contribute to the sensory gating process. The characteristics of influence of preceding stimulus S1 on the brain evoked potentials (EP) to the succeeding stimulus S2 are demonstrated, through analysis of EP waveforms, EP amplitude and EP latency, through plotting the amplitude response curves, through plotting peak-peak response curves and through plotting energy response curves. The experiment data demonstrated that the preceding stimulus S1 had a significant and robust influence on the mid-latency evoked potentials (EP) of the succeeding stimulus S2, although mid-latency evoked potentials (EP) are influenced by attention. It was found that EP of the succeeding stimulus S2 was inhibited by the preceding stimulus S1, and the inhibition level was dependent on inter-stimulus interval (ISI) of the two stimuli, the shorter the ISI the stronger the inhibition level would be. Evoked potential of the succeeding stimulus S2 was inhibited completely by the preceding stimulus S1, as the inter-stimulus interval (ISI) was shorter than a threshold value. The inhibition effect reflected the characteristics of the brain EP response to continuous stimuli with certain time interval. The theory of physiological refractory effect was put forward to explain about the inhibition effect, i.e., there is a refractory effect on brain EP response to continuous stimuli as ISI being shortened to a threshold. It demonstrated that there is a certain threshold in brain EP response when brain continuously receiving the outer stimuli. The inhibitory influence of the preceding stimulus might be caused by the neural refractory effect. Prepulse inhibition phenomena suggest that the principle of time priority encoding and time weighting encoding is followed in brain information processing. The data of visual and auditory cross-modal stimulating experiments made contribute to the electrophysiological explanation of McGurk effect and the visual illusion caused by auditory stimuli.