Steady State Visual Evoked Potentials

In this chapter, several decoding methods for the Steady State Visual Evoked Potential (SSVEP) paradigm are discussed, as well as their use in Brain Computer Interfaces (BCIs). The chapter starts with the concept of BCI, the different categories and their relevance for speech- and motor disabled patients. The SSVEP paradigm is explained in detail. The discussed processing and decoding methods employ either time-domain or spectral domain features. Finally, to show the usability of these methods and of SSVEP-based BCIs in general, three applications are described: a spelling system, the ``Maze'' game and the ``Tower Defense'' game. We conclude the chapter by addressing some challenges for future research.

The sustained periodic modulation of a stimulus induces an entrainment of cortical neurons responding to the stimulus, appearing as a steady-state evoked potential (SS-EP) in the EEG frequency spectrum. Here, we used frequency tagging of SS-EPs to study the crossmodal links in spatial attention between touch and vision. We hypothesized that a visual stimulus approaching the left or right hand orients spatial attention toward the approached hand, and thereby enhances the processing of vibrotactile input originating from that hand. Twenty-five subjects took part in the experiment: 16-s trains of vibrotactile stimuli (4.2 and 7.2 Hz) were applied simultaneously to the left and right hand, concomitantly with a punctate visual stimulus blinking at 9.8 Hz. The visual stimulus was approached toward the left or right hand. The hands were either uncrossed (left and right hands to the left and right of the participant) or crossed (left and right hands to the right and left of the participant). The vibrotactile stimuli elicited two distinct SS-EPs with scalp topographies compatible with activity in the contralateral primary somatosensory cortex. The visual stimulus elicited a third SS-EP with a topography compatible with activity in visual areas. When the visual stimulus was over one of the hands, the amplitude of the vibrotactile SS-EP elicited by stimulation of that hand was enhanced, regardless of whether the hands were uncrossed or crossed. This demonstrates a crossmodal effect of spatial attention between vision and touch, integrating proprioceptive and/or visual information to map the position of the limbs in external space.

Background

Intracortical electrode arrays that can record extracellular action potentials from small, targeted groups of neurons are critical for basic neuroscience research and emerging clinical applications. In general, these electrode devices suffer from reliability and variability issues, which have led to comparative studies of existing and emerging electrode designs to optimize performance. Comparisons of different chronic recording devices have been limited to single-unit (SU) activity and employed a bulk averaging approach treating brain architecture as homogeneous with respect to electrode distribution.
New method

In this study, we optimize the methods and parameters to quantify evoked multi-unit (MU) and local field potential (LFP) recordings in eight mice visual cortices.
Results

These findings quantify the large recording differences stemming from anatomical differences in depth and the layer dependent relative changes to SU and MU recording performance over 6-months. For example, performance metrics in Layer V and stratum pyramidale were initially higher than Layer II/III, but decrease more rapidly. On the other hand, Layer II/III maintained recording metrics longer. In addition, chronic changes at the level of layer IV are evaluated using visually evoked current source density.
Comparison with existing method(s)

The use of MU and LFP activity for evaluation and tracking biological depth provides a more comprehensive characterization of the electrophysiological performance landscape of microelectrodes.
Conclusions

A more extensive spatial and temporal insight into the chronic electrophysiological performance over time will help uncover the biological and mechanical failure mechanisms of the neural electrodes and direct future research toward the elucidation of design optimization for specific applications.
Keywords

    Electrophysiology; Microelectrode arrays; Gamma oscillations; Firing rate; Power density spectra; Electrochemical impedance spectroscopy; Signal-to-noise; Visual evoked activity; Visual cortex

This study confirmed the hypothesis that it is possible to elicit SSVEPs through closed eyelids during NREM sleep. To test this hypothesis, SSVEP amplitudes were measured in eight subjects across two conditions of stimulation (stimulation on and stimulation off) and three brain states (waking, light sleep, and deep sleep). Results showed a significant interaction between stimulation and brain state. In particular, EEG activity at the frequency of stimulation was higher during both light sleep and deep sleep in the stimulation on condition than in the stimulation off condition. The fact that it is possible to elicit SSVEPs during sleep may provide a new way to study how SSVEPs are generated in the brain—one that might help resolve open questions such as identifying the SSVEP activation sequence or deciding if SSVEPs derive from evoked or oscillatory neural processes.

This article presents a summary of research conducted between 2014 and 2018 regarding the possibility of a distant mental interaction between pairs of sensorially isolated subjects. A total of 85 experimental sessions were completed, during which the EEGs of each subject of the pair were recorded (respectively called "Sender" and "Receiver"), all while the Sender was given a series of light and auditory stimuli of one second duration. Members of the pairs knew each other well and were also experienced in relaxation and meditation techniques. The cerebral response to a series of stimuli is well known and is called the ERP (Event Related Potential), but the aim of this study was to look for a possible-presumably weak-response also in the Receiver. Specifically, we studied the possibility of applying a frequency modulated stimulus (from 10 to 18 Hz) in accordance with the Steady-State method and observing any possible distant response to the same frequency. The over...

Objective. The performance and usability of brain–computer interfaces (BCIs) can be improved by new paradigms, stimulation methods, decoding strategies, sensor technology etc. In this study we introduce new stimulation and decoding methods for electroencephalogram (EEG)-based BCIs that have targets flickering at the same frequency but with different phases. Approach. The phase information is estimated from the EEG data, and used for target command decoding. All visual stimulation is done on a conventional (60-Hz) LCD screen. Instead of the 'on/off' visual stimulation, commonly used in phase-coded BCI, we propose one based on a sampled sinusoidal intensity profile. In order to fully exploit the circular nature of the evoked phase response, we introduce a filter feature selection procedure based on circular statistics and propose a fuzzy logic classifier designed to cope with circular information from multiple channels jointly. Main results. We show that the proposed visual stimulation enables us not only to encode more commands under the same conditions, but also to obtain EEG responses with a more stable phase. We also demonstrate that the proposed decoding approach outperforms existing ones, especially for the short time windows used. Significance. The work presented here shows how to overcome some of the limitations of screen-based visual stimulation. The superiority of the proposed decoding approach demonstrates the importance of preserving the circularity of the data during the decoding stage.

The electrical response of the retina was examined as a function of retinal region, using stimuli of various spatial frequencies in the first experiment. In the second experiment, the regional response of the retina to defocus at high and low spatial frequencies was investigated. Twenty three subjects were recruited for global flash multifocal electroretinogram (mfERG) in experiment 1. Black and white gratings (printed on plastic transparent sheets) of four spatial frequencies (SF), 0.24, 1.2, 2.4 and 4.8 cycle per degree were presented in front of the mfERG stimulation. The amplitudes and implicit times of the direct (DC) and induced (IC) components of mfERG responses were pooled into six concentric rings for analysis. There was low amplitude DC at low SF, which increased with increasing SF, and which decreased with increasing eccentricity. The IC was high in amplitude at all SF and reduced in amplitude with increasing eccentricity. Our findings suggested that outer and inner retin...

Abstract—This paper presents an implementation of an effective synchronization between a registration and a stimulation module that form part of a steady state visual evoked potential (SSVEP)-based Brain Computer Interface (BCI). Each of the synchronized modules were created and designed in two different platforms as well as in two different workstations, so a particular objective of this work consisted in finding the best platforms to stimulate and register the EEG in order to create a communication channel and protocol between the ...

Brain Computer Interface (BCI) is system that established a direct connection between the human brain and computer thus providing an additional communication channel. Nowadays, they are used in a broad filed of application. In the current application, a SSVEP is used to control a robotic hand through a BCI system. This paper present the preliminary results from two subjects which indicate the characteristics of SSVEP harmonics amplitude differ from one subject to another.

This paper introduces novel detection features for the steady-state visually evoked potential (SSVEP) based brain computer interfaces. The coefficient of variation and variation speed features were developed using the stability of SSVEP response. The developed features were tested on 13 subjects. On this dataset, for which the chance level is 12.5%, about 70% detection accuracy was obtained. Based on these results, it is considered that the coefficient of variation and the variation speed can be used as discriminative features for SSVEP. By using familiar SSVEP features and developed features together, higher SSVEP detection accuracy can be obtained. By this procedure the performance of single channel SSVEP based BCI systems can be improved.

This paper presents the development of a real-time brain computer interface (BCI) system based on the detection of steady-state visual evoked potential (SSVEP). The system includes a frequency-programmable visual stimulator, EEG-band amplifier and filter, 16-bit data acquisition card, and signal processing and classification algorithms. Three visual stimuli flickering at varying frequencies were shown to the subject, and the system is able to identify the desired target that the subject was focusing on. Experiments on ten healthy subjects using the designed system yielded an average detection accuracy of 86.15%.

We introduce a game in which the player navigates an avatar through a maze by using a brain-computer interface (BCI) that analyzes the steady-state visual evoked potential (SSVEP) responses recorded with electroencephalography (EEG) on the player's scalp. The four command control game, called ``The Maze'' was specifically designed around a SSVEP BCI and validated in several EEG set-ups when using a traditional electrode cap with relocatable electrodes and a consumer-grade headset with fixed electrodes (Emotiv EPOC). We experimentally derive the parameter values that provide an acceptable trade-off between accuracy of game control and interactivity, and evaluate the control provided by the BCI during gameplay. As a final step in the validation of the game, a population study on a broad audience was conducted with the EPOC headset in a real-world setting. The study revealed that the majority (85%) of the players enjoyed the game despite of its intricate control (mean accuracy 80.37%, mean mission time ratio 0.90). We also discuss what to take into account while designing BCI-based games.

Pure alexia (PA) has been associated with visual deficits or a failure to activate the visual word form area (VWFA). We report a patient with pure alexia due to posterior cortical atrophy, in whom event-related potentials revealed a delay in the P100 component and an absent N170 compared with controls. Furthermore, there was a tendency for a larger delay in P100 latencies associated with incorrectly read words. This suggests that some cases of PA might result from deficits in visual perception, signaled by the P100 early potential which could lead to an inability to consistently activate the VWFA, marked by the absent N170.

The phenomenon of paracontrast documented by means of psychophysical techniques has not been readily demonstrable using electrophysiological responses as an index of masking. We have analyzed averaged cortical potentials during presentation of visual stimuli that produce psychophysical masking. Differences in the masking profiles obtained from the two experimental conditions are apparent. However, both electrophysiological and psychophysical data do indicate an interaction between responses to an annulus and a disc which varies with the time interval between the stimuli. Both sets of data also reflect differences in masking between right and left eyes. We conclude that the cortical potentials evoked by temporally disparate stimuli do interact, but that the masking profile is not identical to the profile obtained by psychophysical methods.

Bursts of oscillatory neural activity have been hypothesized to be a core mechanism by which remote brain regions can communicate. Such a hypothesis raises the question to what extent oscillations are coherent across spatially distant neural populations. To address this question, we obtained local field potential (LFP) and membrane potential recordings from the visual cortex of turtle in response to visual stimulation of the retina. The time-frequency analysis of these recordings revealed pronounced bursts of oscillatory neural activity and a large trial-to-trial variability in the spectral and temporal properties of the observed oscillations. First, local bursts of oscillations varied from trial to trial in both burst duration and peak frequency. Second, oscillations of a given recording site were not autocoherent; i.e., the phase did not progress linearly in time. Third, LFP oscillations at spatially separate locations within the visual cortex were more phase coherent in the prese...

Previous studies have demonstrated that as little as 18 hours of sleep deprivation can cause deleterious effects on performance. It has also been suggested that sleep deprivation can cause a "tunnel-vision" effect, in which attention is restricted to the center of the visual field. The current study aimed to replicate these behavioral effects and to examine the electrophysiological underpinnings of these changes. Repeated-measures experimental study. University laboratory. Nineteen professional drivers (1 woman; mean age = 45.3 +/- 9.1 years). Two experimental sessions were performed; one following 27 hours of sleep deprivation and the other following a normal night of sleep, with control for circadian effects. A tunnel-vision task (central versus peripheral visual discrimination) and a standard checkerboard-viewing task were performed while 32-channel EEG was recorded. For the tunnel-vision task, sleep deprivation resulted in an overall slowing of reaction times and incre...

then shared between different persons. This allows some kind of Plug&Play interaction. Furthermore, by modelling rest/idle periods with the confidence indicator, it is possible to detect active control periods and separate them from "background activity": this is capital for real-time, self-paced operation. Finally, the indicator also allows to dynamically choose the most appropriate observation window length, improving system's responsiveness and user's comfort. Good results are achieved under such operating conditions, achieving, for instance, a false positive rate of 0.16 min −1 , which outperform current literature findings.