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Computational Intelligence and Neuroscience
Volume 2011, Article ID 364385, 5 pages
Research Article

Square or Sine: Finding a Waveform with High Success Rate of Eliciting SSVEP

1Department of Computer and Information Science, University of Mississippi, MS 38677, USA
2Department of Psychology, University of Mississippi, MS 38677, USA
3Department of Health, Exercise Science, and Recreation Management, University of Mississippi, MS 38677, USA

Received 26 March 2011; Accepted 17 July 2011

Academic Editor: Li Yuanqing

Copyright © 2011 Fei Teng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Steady state visual evoked potential (SSVEP) is the brain's natural electrical potential response for visual stimuli at specific frequencies. Using a visual stimulus flashing at some given frequency will entrain the SSVEP at the same frequency, thereby allowing determination of the subject's visual focus. The faster an SSVEP is identified, the higher information transmission rate the system achieves. Thus, an effective stimulus, defined as one with high success rate of eliciting SSVEP and high signal-noise ratio, is desired. Also, researchers observed that harmonic frequencies often appear in the SSVEP at a reduced magnitude. Are the harmonics in the SSVEP elicited by the fundamental stimulating frequency or by the artifacts of the stimuli? In this paper, we compare the SSVEP responses of three periodic stimuli: square wave (with different duty cycles), triangle wave, and sine wave to find an effective stimulus. We also demonstrate the connection between the strength of the harmonics in SSVEP and the type of stimulus.