Comparison of Different Visual Feedback Methods for SSVEP-Based BCIs.

Mihaly Benda,Ivan Volosyak

doi:10.3390/brainsci10040240

Abstract

In this paper we compared different visual feedback methods, informing users about classification progress in a steady-state visual evoked potential (SSVEP)-based brain–computer interface (BCI) speller application. According to results from our previous studies, changes in stimulus size and contrast as online feedback of classification progress have great impact on BCI performance in SSVEP-based spellers. In this experiment we further investigated these effects, and tested a 4-target SSVEP speller interface with a much higher number of subjects. Five different scenarios were used with variations in stimulus size and contrast, “no feedback”, “size increasing”, “size decreasing”, “contrast increasing”, and “contrast decreasing”. With each of the five scenarios, 24 participants had to spell six letter words (at least 18 selections with this three-steps speller). The fastest feedback modalities were different for the users, there was no visual feedback which was generally better than the others. With the used interface, six users achieved significantly better Information Transfer Rates (ITRs) compared to the “no feedback” condition. Their average improvement by using the individually fastest feedback method was 46.52%. This finding is very important for BCI experiments, as by determining the optimal feedback for the user, the speed of the BCI can be improved without impairing the accuracy.

Highlights

Brain–computer interfaces (BCIs) use brain signals to control computer applications or external devices
An online tool for Information Transfer Rates (ITRs) calculation can be found at https://bci-lab.hochschule-rhein-waal.de/en/itr.html
We investigated the effects of different feedback methods on online BCI performance

Summary

Introduction

Brain–computer interfaces (BCIs) use brain signals to control computer applications or external devices. Electrical brain activity can be measured, for example, by electroencephalography (EEG), which is non-invasive and relatively cheap. These facts, combined with the simple setup using an EEG cap allows BCI experiments with larger subject groups; because the procedure does not involve surgery, just simple and easy setup, the used consumables are cheap to replace, and the price of the equipment allows even using multiple recording stations. One of the commonly used methods in BCIs are steady-state visual evoked potentials (SSVEPs) which can be detected from the occipital area of the brain when the users are looking at a light source flickering with a constant frequency between 4 and 90 Hz [2]. Coloured stimuli were tested on multiple occasions [6,7,8]

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