Development of a Brain-Computer Interface using Steady State Visual Evoked Potential
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Visual Evoked Potential (VEP) is a damped oscillation-like reaction brain wave obtained from a cerebrum vision field by visual stimulation lasting almost one second. VEP is divided into two categories. One is a transient VEP (t-VEP) observed with low stimulation cycle, and the other is a steady-state VEP (ss-VEP) observed with high stimulation cycle. The former is the reaction wave for every stimulus, while the latter is the fused waveform of t-VEPs, and observed as sinusoid. Since ss-VEP is known to synchronize with the stimulation wave, from the brain wave we can decide the illumination frequency. This study aims the development of a device, which can recognize the LED at which patient gazes, when several light emitting diodes (LEDs) illuminating with different driving frequencies. By assigning the LEDs to specific functions, such as calling caregivers, opening/closing a curtain, ON/OFF of TV set, our device can work as an input part of an environment control system for quadriplegic patients. Our device records brain wave from electrodes mounted on ear pads and nose pads of an eyeglass frame, rather than from electrodes on vision cortex, while the SNR was much smaller than vision cortex lead. In order to overcome the less SNR signal processing was employed. The measured brain wave with eyeglass frame electrodes was analyzed with FFT and Autoregressive-model estimate, and we could identify the light source that the patients stared.
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