Accounting for Phase Drifts in SSVEP-Based BCIs by Means of Biphasic Stimulation

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/52026

Title:	Accounting for Phase Drifts in SSVEP-Based BCIs by Means of Biphasic Stimulation
Authors:	Wu,HY;Lee,PL;Chang,HC;Hsieh,JC
Contributors:	電機工程學系
Keywords:	BRAIN-COMPUTER INTERFACE;VISUAL-EVOKED POTENTIALS;COMMUNICATION;TOPOGRAPHY
Date:	2011
Issue Date:	2012-03-28 10:13:36 (UTC+8)
Publisher:	國立中央大學
Abstract:	This study proposes a novel biphasic stimulation technique to solve the issue of phase drifts in steady-state visual evoked potential (SSVEPs) in phase-tagged systems. Phase calibration was embedded in stimulus sequences using a biphasic flicker, which is driven by a sequence with alternating reference and phase-shift states. Nine subjects were recruited to participate in off-line and online tests. Signals were bandpass filtered and segmented by trigger signals into reference and phase-shift epochs. Frequency components of SSVEP in the reference and phase-shift epochs were extracted using the Fourier method with a 50% overlapped sliding window. The real and imaginary parts of the SSVEP frequency components were organized into complex vectors in each epoch. Hotelling's t-square test was used to determine the significances of nonzero mean vectors. The rejection of noisy data segments and the validation of gaze detections were made based on p values. The phase difference between the valid mean vectors of reference and phase-shift epochs was used to identify user's gazed targets in this system. Data showed an average information transfer rate of 44.55 and 38.21 bits/min in off-line and online tests, respectively.
Relation:	IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING
Appears in Collections:	[Department of Electrical Engineering] journal & Dissertation

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