An SSVEP-Actuated Brain Computer Interface Using Phase-Tagged Flickering Sequences: A Cursor System

Abstract

This study presents a new steady-state visual evoked potential (SSVEP)-based brain computer interface (BCI). SSVEPs, induced by phase-tagged flashes in eight light emitting diodes (LEDs), were used to control four cursor movements (up, right, down, and left) and four button functions (on, off, right-, and left-clicks) on a screen menu. EEG signals were measured by one EEG electrode placed at Oz position, referring to the international EEG 10-20 system. Since SSVEPs are time-locked and phase-locked to the onsets of SSVEP flashes, EEG signals were bandpass-filtered and segmented into epochs, and then averaged across a number of epochs to sharpen the recorded SSVEPs. Phase lags between the measured SSVEPs and a reference SSVEP were measured, and targets were recognized based on these phase lags. The current design used eight LEDs to flicker at 31.25 Hz with 45 degrees phase margin between any two adjacent SSVEP flickers. The SSVEP responses were filtered within 29.25-33.25 Hz and then averaged over 60 epochs. Owing to the utilization of high-frequency flickers, the induced SSVEPs were away from low-frequency noises, 60 Hz electricity noise, and eye movement artifacts. As a consequence, we achieved a simple architecture that did not require eye movement monitoring or other artifact detection and removal. The high-frequency design also achieved a flicker fusion effect for better visualization. Seven subjects were recruited in this study to sequentially input a command sequence, consisting of a sequence of eight cursor functions, repeated three times. The accuracy and information transfer rate (mean +/- SD) over the seven subjects were 93.14 +/- 5.73% and 28.29 +/- 12.19 bits/min, respectively. The proposed system can provide a reliable channel for severely disabled patients to communicate with external environments.

EEG Based Brain Computer Interface for Speech Communication: Principles and Applications

“…However, the drawback of this control signal is that the user has to keep his eyes fixed at one point bereft of any random movement. Lee et al [45][46][47] exposed the subjects (participants of the experiment) with a 5 × 5 matrix that contained flashing stimuli of digits, characters, and symbols displayed on the LCD screen. The cells of the matrix flicker in a random sequence.…”

Multi-target stimulator SSVEP using multi-frequency embedded with multi-phase encoding sequence

“…An SSVEP for BCIs has advantages such as short response time, minimal training requirements, and high ITR records of neuroelectric signals from the occipital area as input for communication or device control [3][4][5][6]. Most SSVEPs only use a single-frequency flicker for each selection of flash stimulators [3,4,6]. This Letter proposes a multi-frequency flicker embedded with multi-phase flickering sequences.…”

“…Electrophysiological experiments have shown that neurons in the human visual cortex synchronise their firing to the frequency of flickering light, leading to EEG responses which show the same frequency as the flickering stimulus -namely steady-state visual evoked potentials (SSVEPs) [2]. An SSVEP for BCIs has advantages such as short response time, minimal training requirements, and high ITR records of neuroelectric signals from the occipital area as input for communication or device control [3][4][5][6]. Most SSVEPs only use a single-frequency flicker for each selection of flash stimulators [3,4,6].…”

Combining object detection and brain computer interfacing: Towards a new way of subject-environment interaction

“…Another strategy to handle more targets is not only to incorporate the magnitude of a selection of frequencies but also its phase. For example: in [18], 8 targets where shown, flickering in the same frequency but each with a different phase-shift. Either of the methods or a combination of both can therefore handle an increase in the number of object detectors.…”