Theoretical Basis And Application Of SSVEP As Attention Tag

Steady-state visual evoked potential(SSVEP)is a periodic response to a repetitive visual stimulus with a specific frequency.It consists of the fundamental frequency of the stimulus as well as its harmonics.Currently,SSVEP is widely used in cognitive research and Brain Computer Interface(BCI)design.In cognitive research,SSVEP as attention 'tag',can simultaneously and implicitly quantify the distribution or deployment of attention on multiple stimuli.In BCIs,SSVEPs as signal inputs,had high signal-to-noise ratio,little user training.high Information Transfer Rate(ITR)and other advantages.However,there are still many controversies regarding SSVEP and its basis as attention 'tag' or BCI signal source.In addition,the influence of many factors on SSVEPs and its mechanism needed to be further examined.Therefore,this study explored the modulation of SSVEPs on attention and the interaction of SSVEPs at different frequencies,so that SSVEPs can be better used in cognitive research and BCI development.The present study included three parts as follows:Experiment 1 was conducted to examine the difference between the first(fundamental)and second harmonics of SSVEPs at different frequencies,and clearify the confusion between stimulus frequency and response frequency.The results indicated that compared with the stimulus frequency,the response frequency was the key factor of the amplitude and SNR of SSVEP.When the response frequency was the same,there was no significant difference between the first and second harmonics.The discussion about the dissociation of the first and second harmonics in previous studies needed to further exclude the effect of response frequency;Experiment 2 explored the modulation effect of attention on the first and second harmonics of SSVEPs at different response frequencies.The results showed that there was no significant difference between the first and second harmonics,but there was a significant difference in the modulation of SSVEPs with different response frequencies,and the maximum modulation effect was observed at alpha band.When determining stimuli frequency for BCIs based on SSVEPs,theta band can be considered in addition to the alpha band;Experiment 3 wanted to analyze the interaction of SSVEPs at different frequencies.Experiment 3a examined the interaction of SSVEPs with different frequencies in the case of two stimuli;Experiment 3b examined the differences in SSVEPs with different frequencies and the corresponding BCI performances in the case of more stimuli.The results indicated that SSVEPs of different frequencies was independent;in BCIs,the number of stimulus and the layout of frequencies had no effects on SSVEPs but affected the accuracy and performance of BCIs.It was concluded that response frequency was a potential confounding factor and had an important influence on the validity of the study based on the dissociation of the first and second harmonics,while stimulus frequency had an important influence on the effect size and statistical power of studies in cognitive research based on attentional modulation of SSVEPs.Stimulus frequency,the number of stimulus and the layout of frequencies had effects on performances of BCIs.Stimulus frequency mainly affected the attentional modulation of SSVEPs,while the number of stimulus and the layout of frequencies mainly impacted the performances of the recognition algorithm in BCIs.