Brain response to luminance-based and motion-based stimulation using inter-modulation frequencies

<div><p>Steady state visual evoked potential (SSVEP)-based brain computer interface (BCI) has advantages of high information transfer rate (ITR), less electrodes and little training. So it has been widely investigated. However, the available stimulus frequencies are limited by brain responses. Simultaneous modulation of stimulus luminance is a novel method to resolve this problem. In this study, three experiments were devised to gain a deeper understanding of the brain response to the stimulation using inter-modulation frequencies. First, luminance-based stimulation using one to five inter-modulation frequencies was analyzed for the first time. The characteristics of the brain responses to the proposed stimulation were reported. Second, the motion-based stimulation with equal luminance using inter-modulation frequencies was also proposed for the first time. The response of the brain under these conditions were similar to that of luminance-based stimulation which can induce combination frequencies. And an elementary analysis was conducted to explain the reason of the occurrence of combination frequencies. Finally, the online test demonstrated the efficacy of our proposed two stimulation methods for BCI. The average ITRs reached 34.7836 bits/min and 39.2856 bits/min for luminance-based and motion-based stimulation respectively. This study demonstrated that the simultaneous modulation of stimulus luminance could extend to at least five frequencies to induce SSVEP and the brain response to the stimulus still maintained a certain positive correlation with luminance. And not only luminance-based stimulation, but also motion-based stimulation with equal luminance can elicit inter-modulation frequencies to effectively increase the number of targets for multi-class SSVEP.</p></div

Motion-based stimulation.

<p>Motion-based stimulation.</p

The sum of peak values at 15 Hz in the PSD among all the participants and peak values at 16 Hz in the PSD among all the participants.

<p>The sum of peak values at 15 Hz in the PSD among all the participants and peak values at 16 Hz in the PSD among all the participants.</p

Experimental design.

<p>Experimental design.</p

The time domain waveforms, power spectrum density and time-frequency maps acquired while a participant was staring at the equal amplitude stimulations.

<p>(a) The time domain waveforms. (b) Power spectrum density. (c) Time-frequency maps.</p

Online classification accuracy of luminance-based stimulation according to stimulation duration.

<p>Online classification accuracy of luminance-based stimulation according to stimulation duration.</p

Online classification accuracy with motion-based stimulation according to stimulation duration.

<p>Online classification accuracy with motion-based stimulation according to stimulation duration.</p

Frequency spectrum of EEG data for a single trial at the Oz site with luminance-based and motion-based stimulation using dual inter-modulation frequencies.

<p>(a) Frequency spectra of EEG data for a single trial at the Oz site with luminance-based stimulation using dual inter-modulation frequencies. (b) Frequency spectra of EEG data for a single trial at the Oz site with motion-based stimulation using dual inter-modulation frequencies.</p

Mean of ITR of all the subjects with different stimulation duration.

<p>Mean of ITR of all the subjects with different stimulation duration.</p

NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion

New pincer–Pt complexes coordinated by (nitronyl nitroxide)-2-ide radical anion were prepared as stable compounds in high yields. The structures of these Pt complexes and the oxidized complexes were unequivocally determined by spectral and crystal structure analyses. The oxidation potential of the nitronyl nitroxide moiety in these complexes was shifted in the negative direction by ∼0.6 V as a result of coordination to the Pt­(II) atom