| Mismatch Negativity(MMN)is an event-related potential component that reflects the brain's ability to automatically detect deviant stimuli.MMN has been recognized as one of the biomarkers of schizophrenia with important application value.However,due to the flexibility of the experimental paradigm,the selection of the types of stimuli and the setting of parameters are various in clinical research.The main index to evaluate the paradigm in clinical research is effect size.Meta-analysis shows that the effect size is positively correlated with the amplitude,and the effect size was larger when the time processing was involved.Therefore,improving the amplitude of MMN in the dimension of time processing will be conducive to the optimization of the paradigm.In this study,three time processing related paradigms with relatively larger effect sizes were selected to conduct a preliminary exploration of this problem by examining the relationship between amplitude and stimulus parametersIn the first study,the long-duration deviant paradigm was chosen to investigate the relationship between the amplitude of MMN and the stimuli differences.The duration of the standard stimulus in this experiment was 50 ms,and that of the deviant stimulus was 100 ms,150 ms,200 ms and 250 ms respectively.The statistical results showed that the amplitude was not significantly different between 150 ms,200 ms and 250ms(P>0.05),but the amplitude of the three were all significantly greater than that of 100 ms(P<0.05)The results indicate that the amplitude of the long-duration deviant MMN mounts up with the increase of the stimuli differences within a certain range and then plateaus out.When the duration of the deviant stimulus is 3 times that of the standard stimulus,the amplitude reaches the maximum and the duration is relatively short,which maybe the optimal parameter setting for the long-duration deviant paradigmIn the second study,the interaural phase difference(IPD)paradigm was chosen to examine the relationship between the amplitude and the stimuli differences.In this experiment,the IPD of the standard stimulus was O°and that of the deviant stimulus was 2.63",45",90",135°,and 180"respectively.As a result,MMN was not induced when the IPD is 2.63".And compared with 90°,135°and 180°,the amplitude of 45°was significantly lower(P<0.05).After 90°,there was an upward trend,but the difference was not significant(P>0.05).The results show that the amplitude of the IPD MMN mounts up with the increase of the stimuli difference within a certain range,and then plateaus out.When the IPD is 180°,the amplitude is the largest,which is considered to be the optimal parameter setting of the paradigmIn the third study,the gestalt paradigm was chosen to examine the relationship between the amplitude and the stimulus structure.Three gestalts was examined in this experiment,and the number of the stimuli which constitute the gestalts was 2,3 and 6.The statistical results showed that when the number of the stimuli was 2 and 3,the amplitude was not statistically different(P>0.05),but compared with 6,it shows an increasing trend(P<0.1),and the data recording time is more shortened.When the number of the stimuli was 2,recording time is shortened by 40%.This result indicates that when the number of stimuli in the gestalt is reduced,the amplitude of the MMN is likely to be higher and time costs is lower,and when the number of the stimuli was 2,time costs is more lower,which is more suitable for clinical applicationIn summary,this study selected three time processing related MMN paradigms from simple to complex in the dimension of time processing for improvement,and finally improved the amplitude or reduced the time cost to different degrees.This study provides a good paradigm reference for the clinical application of MMN,and also has a certain theoretical significance for improving its effect size in the study of schizophrenia. |
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