Yu-Yi Chien

Polychromatic SSVEP stimuli with subtle flickering adapted to brain-display interactions

OBJECTIVE Interactive displays armed with natural user interfaces (NUIs) will likely lead the next breakthrough in consumer electronics, and brain-computer interfaces (BCIs) are often regarded as the ultimate NUI-enabling machines to respond to human emotions and mental states. Steady-state visual evoked potentials (SSVEPs) are a commonly used BCI modality due to the ease of detection and high information transfer rates. However, the presence of flickering stimuli may cause user discomfort and can even induce migraines and seizures. With the aim of designing visual stimuli that can be embedded into video images, this study developed a novel approach to induce detectable SSVEPs using a composition of red/green/blue flickering lights. APPROACH Based on the opponent theory of colour vision, this study used 32 Hz/40 Hz rectangular red-green or red-blue LED light pulses with a 50% duty cycle, balanced/equal luminance and 0°/180° phase shifts as the stimulating light sources and tested their efficacy in producing SSVEP responses with high signal-to-noise ratios (SNRs) while reducing the perceived flickering sensation. MAIN RESULTS The empirical results from ten healthy subjects showed that dual-colour lights flickering at 32 Hz/40 Hz with a 50% duty cycle and 180° phase shift achieved a greater than 90% detection accuracy with little or no flickering sensation. SIGNIFICANCE As a first step in developing an embedded SSVEP stimulus in commercial displays, this study provides a foundation for developing a combination of three primary colour flickering backlights with adjustable luminance proportions to create a subtle flickering polychromatic light that can elicit SSVEPs at the basic flickering frequency.

Augmenting VR/AR Applications with EEG/EOG Monitoring and Oculo-Vestibular Recoupling

Head-mounted virtual reality and augmented reality displays a.k.a. VR/AR goggles created a revolutionary multimedia genre that is seeking ever-broadening applications and novel natural human interfaces. Adding neuromonitoring and neurofeedback to this genre is expected to introduce a new dimension to user interaction with the cyber-world. This study presents the development of a Neuromonitoring VR/AR Goggle armed with electroence-phalo-gram and electrooculogram sensors, programmable milli-Ampere current stimulators and wireless fog/cloud computing support. Beside of its potential use in mitigating cybersickness, this device may have potential applications in augmented cognition ranging from feedback-controlled perceptual training to on-line learning and virtual social interactions. A prototype of the device has been made from a Samsung Gear VR for S6. This study explains its technical design to ensure precision data sampling, synchronous event marking, real-time signal processing and big data cloud computing support. This study also demonstrates the effective-ness in measuring the event-related potentials during a visual oddball experiment.

High-frequency polychromatic visual stimuli for new interactive display systems

Brain–computer interfaces (BCIs) are intuitive operation modes that use electrical brain activity to communicate with external electronic devices. Over the past decade, BCI systems have been used for assistive living applications.1 In addition, 3D technologies are now widely available and are frequently used for virtual reality and augmented reality applications. As vision is the most dominant sense for humans, it is thought that BCI-enabled interactive displays (especially 3D displays) will also have a broad range of applications in gaming and e-learning. The steady state visual evoked potential (SSVEP) is an example of a BCI modality that can be induced by visual stimuli. The SSVEP is the natural response of the brain to repetitive stimuli that are modulated at a constant frequency. It is thought that the SSVEP may be the most suitable modality in brain–display interactions (BDIs) because of its non-intrusive, easy detection, and high information transfer rates.2 The functional architecture of BDI systems is illustrated in Figure 1. SSVEP-based BCI systems have been developed in recent years because of their attractive features. To induce strong SSVEP responses, however, most of these systems use visual stimuli in a low-frequency band (less than 20Hz).3 Unfortunately, bright lights that flicker in this frequency range can be distracting to viewers, and they can cause visual fatigue, migraine headaches, and even photosensitive epilepsy attacks. Our group is making the first steps in the development of a display-embedded SSVEP stimulus. As part of this work, we have proposed using a combination of flickering red-green lights to create an imperceptible flickering visual stimulus that can elicit an SSVEP at a basic flickering frequency.4 We have thus conducted a series of experiments to investigate whether the Figure 1. Architecture of a typical brain–display interactive system. SSVEP: Steady-state visual evoked potential.

Research on steady-state visual evoked potentials in 3D displays

Brain-computer interfaces (BCIs) are intuitive systems for users to communicate with outer electronic devices. Steady state visual evoked potential (SSVEP) is one of the common inputs for BCI systems due to its easy detection and high information transfer rates. An advanced interactive platform integrated with liquid crystal displays is leading a trend to provide an alternative option not only for the handicapped but also for the public to make our lives more convenient. Many SSVEP-based BCI systems have been studied in a 2D environment; however there is only little literature about SSVEP-based BCI systems using 3D stimuli. 3D displays have potentials in SSVEP-based BCI systems because they can offer vivid images, good quality in presentation, various stimuli and more entertainment. The purpose of this study was to investigate the effect of two important 3D factors (disparity and crosstalk) on SSVEPs. Twelve participants participated in the experiment with a patterned retarder 3D display. The results show that there is a significant difference (p-value<0.05) between large and small disparity angle, and the signal-to-noise ratios (SNRs) of small disparity angles is higher than those of large disparity angles. The 3D stimuli with smaller disparity and lower crosstalk are more suitable for applications based on the results of 3D perception and SSVEP responses (SNR). Furthermore, we can infer the 3D perception of users by SSVEP responses, and modify the proper disparity of 3D images automatically in the future.

Brain-display interactive system by using steady-state visual evoke potential(SSVEP) stimulation

Steady-state visual evoked potential (SSVEP) is one of the most effective modalities for brain-computer interaction. However, its flickering visual stimuli may cause discomfort, even induce migraine and seizure attacks among its viewers. This paper presents a novel approach to induce SSVEP with high signal-to-noise ratios (SNRs) using composite color lights flickering near or above its critical flicker fusion (CFF) thresholds. Different combinations of frequencies, relative phases and pulse widths of the stimuli waveforms were tested for their effectiveness to produce high SNR values among their SSVEP responses. Results of our experiments were analyzed and studied. The rationale behind the special design of high-frequency polychromatic stimuli and the implications towards the development of an effective brain-display interaction (BDI) system were also discussed.