A Study on the Effect of the Inter-Sources Distance on the Performance of the SSVEP-Based BCI Systems

Seyed Navid Resalat,Seyed Kamaledin Setarehdan

doi:10.5923/j.ajbe.20120201.04

Seyed Navid Resalat, Seyed Kamaledin Setarehdan

Open Access

https://doi.org/10.5923/j.ajbe.20120201.04

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Abstract

Brain Computer Interfacing (BCI) systems, which are a new communicating channel between humans and the computers are growing rapidly. One such a method is based on the Steady State Visual Evoked Potentials (SSVEP), which can be recorded during visual stimulating of the subject by a twinkling light source with a fixed frequency. An important parameter to be considered is the effect of the inter-sources distance on the accuracy of such BCI systems. In particular inter-sources (LEDs) distances of 4, 14, 24, 44 and 64 cm when the sources plane is located 60 cm away from the subject's eyes (producing inter-sources visual angles of 3.8°, 13.4°, 22.6°, 40.2° and 56° respectively) were examined. In addition, four different sweep lengths of 0.5, 1, 2 and 3 seconds are considered. In addition, due to the usage of the AR models for feature extraction from the SSVEP signals, selection of the best AR model together with the best classifier among the LDA, the SVM and the Naive Bayes are studied. It is showed that the BCI system with D=44 cm, AR order of 13 and either the LDA or the SVM classifiers could produce the best results compared to the other cases.

Highlights

Using the EEG signal as a communication channel was first proposed by Hans Berger in 1929[1]
When the twinkling frequency is below 6 Hz, the resulting potentials are known as Transient visual evoked potentials (VEPs) (TVEPs) otherwise they are called Steady State VEPs (SSVEPs)[5,6]
Our studies showed that for SSVEP sweeps less than 0.5-second length, the accuracy of the classifiers were reduced significantly, the shortest segment length were limited to

Summary

Introduction

Using the EEG signal as a communication channel was first proposed by Hans Berger in 1929[1]. Various BCI systems were developed and used with different levels of success. One such a method is developed based on the visual evoked potentials (VEPs)[3]. Based on the kind of the visual stimulation used, these signals can be divided into three main modes of Pattern Reversal (PR), Pattern Onset/Offset (PO) and Flash (F)[3]. Pattern Reversal Visual Evoked Potentials (PRVEPs) is generated when an external light source with a constant twinkling frequency provoke the visual system[4]. Previous studies have shown that these signals can be effectively recorded at the occipital lobe of the brain having the same fundamental frequency of the twinkling light source together with its 2’nd and occasionally 3’rd harmonics[6,7,8]. By providing multiple light sources with different twinkling frequencies to the subject, it will be possible to produce a

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