The Effect of SOA on An Asynchronous ERP and VEP-Based BCI

Abstract

Our previous study established an asynchronous BCI system by using the oddball paradigm to simultaneously induce event-related potentials (ERPs) and visual evoked potentials (VEPs) (E-V BCIs). We found that stimulus onset asynchrony (SOA) is an important factor for performance since it significantly affects the ERP and VEP. Increasing the SOA increases the ERP, which improves the accuracy of detecting target stimuli. However, a larger SOA leads to a lower VEP frequency, which causes the VEP to have poor accuracy when discriminating between the brain states. How to balance the two potentials and accuracies is a problem. This study established eight SOAs from 100 ms to 375 ms that were composed of different interstimulus intervals and the same stimulus duration of 80 ms. We used a probability-based Fisher linear discriminant analysis (P-FLDA) classifier to calculate the classification accuracies of the ERP-based visual speller, VEP-based brain state discrimination, and E-V BCI. The results show that as the SOA increases, the amplitudes of N200 and P300 increase, and the accuracy also shows an increasing trend. However, the frequency of the VEP and the accuracies of state discrimination show downward trends. The change in accuracies of the E-V BCI system combining these two parts is nonlinear, and the SOA optimal value is 125 ms. The SOA of 125 ms yields the best accuracies of 95.83% and practical bit rate of 57.17 bits/min in the E-V BCI system, which provides a guideline for selecting the SOA to improve the performance.

Comparison of Two Paradigms Based on Stimulation with Images in a Spelling Brain–Computer Interface

“…The positivity found at around 350–600 ms, which was generalized across the entire scalp surface, was probably a P300 signal, the component that gives its name to this type of BCI system (i.e., a P300 speller). This positivity has been also reported at similar temporal intervals in several other studies (e.g., by Kellicut-Jones and Sellers [ 15 ] and M. Li et al [ 32 ]). The negativity found for the occipital areas (PO7, PO8, and Oz) at around 280 ms could be an N170 signal (e.g., Kaufmann et al [ 16 ], Q. Li et al [ 17 ], and Lu et al [ 33 ]).…”

The Effect of Jittered Stimulus Onset Interval on Electrophysiological Markers of Attention in a Brain–Computer Interface Rapid Serial Visual Presentation Paradigm

“…Additionally, compared to relevant discussion in [17] which assumed equal target and non-target likelihoods, the present RSVP design possessed unequal classes. As well, while previous reports described changes to ERP attention effects with increasing SOI durations, the present study used dramatically shorter latencies overall than [18], and another comparison of different SOA values on ERPs and VEPs did so using a block design [26]. Increasing N200 and P300 amplitudes observed in that study and a lack of such effects in the present study might be explained by our use of uniform random distributions, which result in an unchanging mean SOI value across conditions.…”

“…In the context of this investigation, "attention" is defined as selective visual attention to the presentation of a target letter stimulus. Likewise, SOI refers to the time elapsed between the onset of two sequential stimuli, which some groups refer to instead as stimulus onset asynchrony (SOA) [11,26]. Our study analyzed three EEG-based signals known to be evident during RSVP: N200, P300, and alpha attenuation [11,19].…”

Evaluation of Different Types of Stimuli in an Event-Related Potential-Based Brain–Computer Interface Speller under Rapid Serial Visual Presentation

“…Specifically, our results regarding the amplitude difference showed that the distinguishing potentials between target and non-target stimuli are N200 and P300. Both potentials have previously been employed in the literature for ERP-BCI applications and have been manipulated—using different stimuli or SOA—to enhance system performance [ 41 , 42 ]. In our study, the differences in the ERP waveform related to amplitude difference were more affected in terms of latency rather amplitude.…”