The Influence Of Alpha Instantaneous Frequency On Audiovisual Integration

In the field of sensory and perceptual processing,the integration of cross-modal is the core of unified and consistent perception of the external environment,which affects the survival and adaptation of individuals.When external inputs involve multiple sensory modals,temporal proximity between stimulus is a necessary prerequisite for integration to occur,that is,the closer the two stimuli are in time,the more likely they are to be perceived as simultaneous events.The key scientific question this study attempts to answer is: How does the brain temporally correlate information across modalities and perceive it as a meaningful,consistent,and coherent object? Previous visual studies have found that Alpha oscillation provide a temporal framework for visual integration: if two visual stimuli fall within the same Alpha cycle,they are perceived as integration;If it is not within one cycle,it is perceived as separation.Thus,the frequency of Alpha oscillation determines the temporal resolution of perception.In other words,a lower Alpha frequency provides a longer temporal window for perceptual processing,leading to the integration of perception.However,higher Alpha frequency provides a shorter temporal window for perceptual processing,leading to the separation of perception.However,most studies only consider the single modal stimulus.At present,it is not clear whether the perceptual simultaneity of two physically different bimodal audiovisual stimulus can also be predicted by the cycle of Alpha oscillation.Given the temporal characteristics of Alpha oscillation and its close relationship with visual perception,it is reasonable to speculate that Alpha oscillation may provide an important multisensory processing framework in the time-dominated integration of audiovisual information.Therefore,the present study aims to link the continuous oscillation with the temporal organization of perception by modulating the neural oscillation in the brain,and further explores its causal relationship through the induction of lower or higher frequency of Alpha oscillation by modulating the neural oscillation at 8 Hz or 12 Hz.In Experiment 1,the classical audiovisual simultaneity judgment task was used to investigate whether the instantaneous frequency of Alpha oscillation affected the audiovisual integration.Firstly,the point of subjective simultaneity(PSS)of each subject in audio-visual simultaneity judgment was found by psychophysical method.Then,in the EEG experiment,visual and auditory stimuli were presented successively at interval of PSS,and the subjects might judge them as simultaneous or nonsimultaneous.Therefore,Experiment 1 was designed as a single factor experiment,which took simultaneous or non-simultaneous responses of subjects as independent variable and Alpha instantaneous frequency as dependent variable.And the level of Alpha instantaneous frequency under the two judgmental reactions was compared.The results showed that in the 150-960 ms time window after stimulation,the Alpha instantaneous frequency of the "simultaneous" judgment condition was significantly lower than that of the "non simultaneous " judgment condition,and the difference was mainly distributed in the posterior region of the brain.This result suggests that the frequency of Alpha oscillation does affect the audio-visual temporal integration.Experiment 2 used rhythmic visual-auditory stimulation(8/12 Hz)to artificially manipulate the instantaneous frequency of Alpha oscillation and further investigate the causal relationship between Alpha oscillation and audiovisual integration.According to the classic Entrainment effect,rhythmic stimulation at 8 or 12 Hz induces corresponding frequency of neural oscillation in the brain.In Experiment 2,the classical simultaneous judgment task was used again.Alpha instantaneous frequency(8/12 Hz)was used as the independent variable,and the ratio of simultaneous judgment was used as the dependent variable to investigate the difference of simultaneous judgment ratio between high and low frequency conditions.The results showed that the "simultaneous" judgment ratio under the high frequency Alpha condition is significantly lower than that under the low frequency Alpha condition.These results further suggest that there is a causal relationship between cross-modal audiovisual perception and Alpha oscillation,demonstrating the specific function of Alpha oscillation as a temporal framework of audiovisual perception.In summary,this study explores the influence of Alpha oscillation on audiovisual integration through simultaneous judgment tasks.The results show that the instantaneous frequency of Alpha oscillation determines the temporal resolution of multisensory integration and further determines whether multisensory information will be integrated.These results confirm previous findings of single-modal perception and provide a causal mechanism for the temporal framework of the Alpha oscillation for audiovisual integration.