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Motivation

Motivation. Increase bandwidth of BCI. Reduce training time Use non invasive technique. Methods: underlying phenomenon. Steady State visually evoked potential (SSVEP) Exact multiples of stimulus frequency in EEG data . Instantaneous FFT. 7 Hz flicker. Average FFT.

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Motivation

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  1. Motivation • Increase bandwidth of BCI. • Reduce training time • Use non invasive technique

  2. Methods: underlying phenomenon • Steady State visually evoked potential (SSVEP) • Exact multiples of stimulus frequency in EEG data Instantaneous FFT 7 Hz flicker Average FFT Are harmonics due to physiology or signal processing?

  3. Methods: experiment setup • Each bottom flicker at different frequency (6 to 14 Hz) • User gazes at one bottom to select it. • Signals at 01 and 02 electrodes, ear lobes reference and ground. 10-20 system

  4. Methods: signal processing • Bandpass filter 4 to 35 Hz • Calculate FFT every 0.3 sec • 1024 point FFT on 512 points of data, rest are zeros • Determine the sum of fundamental frequency and second harmonic • Threshold is twice the mean of the spectrum • Same fundamental has to be detected in 4 consecutive FFTs

  5. ResultsTask 1: inputting a phone number 6 subjects no errors 2 subjects some errors 5 subjects couldn’t input number

  6. ResultsTask 2: transfer speed

  7. ResultsTask 3: buttons spacing

  8. Conclusion • Subjects respond differently, no statistically significant results obtained. • Up to 55 bits /min transfer rate • Requires no training • Input accuracy decreases when subject is listening to conversations • Advanced signal processing to remove brain background activity can be used in a future.

  9. Discussion • Strengths • Simple and straightforward experimental approach. • Presents convincing evidence for effectiveness of SSVEP BCI. • Weaknesses • SSVEP based BCI doesn’t work for everyone. • Inconsistent result (ex. bandwidth from 1 bit/sec to 55 bit/sec) • Crude signal processing. • No control of eye and face movements

  10. Questions • What are some practical application of this system beyond paralyzed patients? • How does the performance (bandwidth, accuracy, training) of this BCI system compare to invasive methods?

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