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. 2017 Jul 26;11:391. doi: 10.3389/fnhum.2017.00391

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Copyright © 2017 Dreyer, Herrmann and Rieger.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Stimulation device and signal overview. (A) Custom stimulation shield with a small central fixation light-emitting diode (LED) and four stimulation LEDs at 10 cm (5.72° visual angle at 1 m distance) radial distance. One specific Steady-state visual evoked potential (SSVEP) frequency was assigned to each stimulation LED throughout the experiment. (B) A 20 Hz sine wave which was used to drive one LED, and the respective frequency spectrum. (C) A frequency modulated (FM) signal (100 Hz carrier, 80 Hz modulation frequency and a modulation index of 0.5) and its frequency spectrum. (D) A signal with the same parameters as in (C) except that the modulation index is increased to 2. This leads to an increased peak in the spectra at 20 Hz.