title: An SSVEP-based BCI using high duty-cycle visual flicker.
abstract: Steady-state visual-evoked potential (SSVEP)-based brain-computer interfaces (BCIs) have generated significant interest due to their high information transfer rate (ITR). Due to the amplitude-frequency characteristic of the SSVEP, the flickering frequency of an SSVEP-based BCI is typically lower than 20  Hz to achieve a high SNR. However, a visual flicker with a flashing frequency below the critical flicker-fusion frequency often makes subjects feel flicker jerky and causes visual discomfort. This study presents a novel technique using high duty-cycle visual flicker to decrease user's visual discomfort. The proposed design uses LEDs flashing at 13.16  Hz, driven by flickering sequences consisting of repetitive stimulus cycles with a duration T (T = 76 ms). Each stimulus cycle included an ON state with a duration T(ON) and an OFF state with a duration T(OFF) (T = T(ON) + T(OFF)), and the duty cycle, defined as T(ON)/T, varied from 10.5% to 89.5%. This study also includes a questionnaire survey and analyzes the SSVEPs induced by different duty-cycle flickers. An 89.5% duty-cycle flicker, reported as a comfortable flicker, was adopted in a phase-tagged SSVEP system. Six subjects were asked to sequentially input a sequence of cursor commands with the 25.08-bits/min ITR.
authors.affiliation: Department of Electrical Engineering, National Central University, Jhongli 32001, Taiwan. pllee@ee.ncu.edu.tw
authors.forename: Po-Lei
authors.initials: PL
authors.lastname: Lee
authors.forename: Chia-Lung
authors.initials: CL
authors.lastname: Yeh
authors.forename: John Yung-Sung
authors.initials: JY
authors.lastname: Cheng
authors.forename: Chia-Yen
authors.initials: CY
authors.lastname: Yang
authors.forename: Gong-Yau
authors.initials: GY
authors.lastname: Lan
mesh_terms: D000328:Adult; D003143:Communication Devices for People with Disabilities; D004569:Electroencephalography / Q000379:methods* / Q000523:psychology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008328:Man-Machine Systems; D010775:Photic Stimulation / Q000379:methods*; D012815:Signal Processing, Computer-Assisted; D011795:Surveys and Questionnaires; D014584:User-Computer Interface