DESIGN OF PORTABLE LED VISUAL STIMULUS AND SSVEP ANALYSIS FOR VISUAL FATIGUE REDUCTION AND IMPROVED ACCURACY

Brain-computer interface (BCI) applications have emerged as an innovative communication channel between computers and human brain as it circumvents peripheral limbs thereby creating a direct interface between brain thoughts and the external world. This research focuses on non-invasive BCI to improve the design of visual stimuli in eliciting steady-state visual evoked potential (SSVEP) for BCI applications. To evoke SSVEP in the brain, the user needs to focus on a visual stimulus flickering at a constant frequency. Traditionally in research studies, the visual stimulus for SSVEP uses LCD screens where the flicker is generated using black or white patterns, which alternates the colour to produce a flickering effect. However, there are drawbacks for LCD based visual stimuli systems that limit the user acceptance of SSVEP applications. The main limitations are: (i) choice of flicker frequency is limited to the LCDs vertical refresh rate (ii) flickers are mainly limited to black/white patterns (iii) higher visual fatigue for the user due to LCDs background flicker (iv) reduced visual stimulus portability (v) Inaccurate flickers generated and controlled by the software (vi) influence of adjacent flickers causing attention shift when multiple flickers are used for classification and also not being easily adaptable for user requirements. The impediments in eliciting and utilising SSVEP responses for designing a near real-time platform for controlling external applications are addressed from five main perspectives here: (i) design of standalone LED visual stimulus hardware for precise generation of any frequency for replacing the LCD based visual stimulus (ii) eliciting maximal response by choosing most responsive colour, orientation and shape of visual stimulus (iii) identification of the best luminance level for visual stimulus to improve the comfortability of the user and for improved SSVEP response (iv) control of the duration of ON/OFF period for the visual stimulus to reduce eyestrain for the user (i.e. visual fatigue), and (v) hybrid BCI paradigm using SSVEP and P300 to improve the classification accuracy for controlling external applications. The experimental study involved the development of various visual stimulus designs based on LEDs and microcontrollers to minimise the visual fatigue and improve the SSVEP responses. The signal analysis results from the studies with five to ten participants show SSVEP elicitation is influenced by colour, orientation, the shape of stimulus, the luminance level of stimulus and the duration of ON/OFF period for the stimulus. The participants also commented that choosing the correct luminance and ON/OFF periods of the stimulus considerably reduce the eyestrain, improve the attention levels and reduce the visual fatigue. Taken together, these finding leads to more user acceptance in SSVEP based BCI as an assistive mechanism for controlling external applications with improved comfort, portability and reduced visual fatigue

Toward a reliable PWM-based light-emitting diode visual stimulus for improved SSVEP response with minimal visual fatigue

Steady-state visual evoked response (SSVEP) is widely used in visual-based diagnosis and applications such as brain–computer interfacing due to its high information transfer rate and the capability to activate commands through simple gaze control. However, one major impediment in using flashing visual stimulus to obtain SSVEP is eye fatigue that prevents continued long-term use preventing practical deployment. This combined with the difficulty in establishing precise pulse-width modulation (PWM) that results in poorer accuracy warrants the development of appropriate approach to solve these issues. Various studies have suggested the usage of high frequencies of visual stimulus to reduce the visual fatigue for the user but this results in poor response performance. Here, the authors study the use of extremely high duty-cycles in the stimulus in the hope of solving these constraints. Electroencephalogram data was recorded with PWM duty-cycles of 50–95% generated by a precise custom-made light-emitting diode hardware and tested ten subjects responded that increasing duty-cycles had less visual strain for all the frequency values and the SSVEP exhibited a subject-independent peak response for duty-cycle of 85%. This could pave the way for increased usage of SSVEP for practical applications

In-Ear Electrode EEG for Practical SSVEP BCI

Steady State Visual Evoked Potential (SSVEP) methods for brain–computer interfaces (BCI) are popular due to higher information transfer rate and easier setup with minimal training, compared to alternative methods. With precisely generated visual stimulus frequency, it is possible to translate brain signals into external actions or signals. Traditionally, SSVEP data is collected from the occipital region using electrodes with or without gel, normally mounted on a head cap. In this experimental study, we develop an in-ear electrode to collect SSVEP data for four different flicker frequencies and compare against occipital scalp electrode data. Data from five participants demonstrates the feasibility of in-ear electrode based SSVEP, significantly enhancing the practicability of wearable BCI applications

Electroencephalogram Signal Processing For Hybrid Brain Computer Interface Systems

The goal of this research was to evaluate and compare three types of brain computer interface (BCI) systems, P300, steady state visually evoked potentials (SSVEP) and Hybrid as virtual spelling paradigms. Hybrid BCI is an innovative approach to combine the P300 and SSVEP. However, it is challenging to process the resulting hybrid signals to extract both information simultaneously and effectively. The major step executed toward the advancement to modern BCI system was to move the BCI techniques from traditional LED system to electronic LCD monitor. Such a transition allows not only to develop the graphics of interest but also to generate objects flickering at different frequencies. There were pilot experiments performed for designing and tuning the parameters of the spelling paradigms including peak detection for different range of frequencies of SSVEP BCI, placement of objects on LCD monitor, design of the spelling keyboard, and window time for the SSVEP peak detection processing. All the experiments were devised to evaluate the performance in terms of the spelling accuracy, region error, and adjacency error among all of the paradigms: P300, SSVEP and Hybrid. Due to the different nature of P300 and SSVEP, designing a hybrid P300-SSVEP signal processing scheme demands significant amount of research work in this area. Eventually, two critical questions in hybrid BCl are: (1) which signal processing strategy can best measure the user\u27s intent and (2) what a suitable paradigm is to fuse these two techniques in a simple but effective way. In order to answer these questions, this project focused mainly on developing signal processing and classification technique for hybrid BCI. Hybrid BCI was implemented by extracting the specific information from brain signals, selecting optimum features which contain maximum discrimination information about the speller characters of our interest and by efficiently classifying the hybrid signals. The designed spellers were developed with the aim to improve quality of life of patients with disability by utilizing visually controlled BCI paradigms. The paradigms consist of electrodes to record electroencephalogram signal (EEG) during stimulation, a software to analyze the collected data, and a computing device where the subject’s EEG is the input to estimate the spelled character. Signal processing phase included preliminary tasks as preprocessing, feature extraction, and feature selection. Captured EEG data are usually a superposition of the signals of interest with other unwanted signals from muscles, and from non-biological artifacts. The accuracy of each trial and average accuracy for subjects were computed. Overall, the average accuracy of the P300 and SSVEP spelling paradigm was 84% and 68.5 %. P300 spelling paradigms have better accuracy than both the SSVEP and hybrid paradigm. Hybrid paradigm has the average accuracy of 79 %. However, hybrid system is faster in time and more soothing to look than other paradigms. This work is significant because it has great potential for improving the BCI research in design and application of clinically suitable speller paradigm

Exploiting code-modulating, Visually-Evoked Potentials for fast and flexible control via Brain-Computer Interfaces

Riechmann H. Exploiting code-modulating, Visually-Evoked Potentials for fast and flexible control via Brain-Computer Interfaces. Bielefeld: Universität Bielefeld; 2014

Incandescent Bulb and LED Brake Lights:Novel Analysis of Reaction Times

Rear-end collision accounts for around 8% of all vehicle crashes in the UK, with the failure to notice or react to a brake light signal being a major contributory cause. Meanwhile traditional incandescent brake light bulbs on vehicles are increasingly being replaced by a profusion of designs featuring LEDs. In this paper, we investigate the efficacy of brake light design using a novel approach to recording subject reaction times in a simulation setting using physical brake light assemblies. The reaction times of 22 subjects were measured for ten pairs of LED and incandescent bulb brake lights. Three events were investigated for each subject, namely the latency of brake light activation to accelerator release (BrakeAcc), the latency of accelerator release to brake pedal depression (AccPdl), and the cumulative time from light activation to brake pedal depression (BrakePdl). To our knowledge, this is the first study in which reaction times have been split into BrakeAcc and AccPdl. Results indicate that the two brake lights containing incandescent bulbs led to significantly slower reaction times compared to eight tested LED lights. BrakeAcc results also show that experienced subjects were quicker to respond to the activation of brake lights by releasing the accelerator pedal. Interestingly, analysis also revealed that the type of brake light influenced the AccPdl time, although experienced subjects did not always act quicker than inexperienced subjects. Overall, the study found that different designs of brake light can significantly influence driver response times