A N SSVEP-A CTUATED B RAIN C OMPUTER I NTERFACE U SING P HASE -T AGGED F LICKERING S EQUENCES : A C URSOR S YSTEM Chairman ： Dr. Hung-Chi Yang Presenter ： HSUAN-CHIA KUO Adviser ： Dr. Shih-Chung Chen Date ： 2013/12/25 PO-LEI LEE, JYUN-JIE SIE, YU-JU LIU, CHI-HSUN WU, MING-HUAN LEE, CHIH-HUNG SHU,PO-HUNG LI, CHIA-WEI SUN, and KUO-KAI SHYU Annals of Biomedical Engineering, Vol. 38, No. 7, July 2010 (© 2010) pp. 2383–2397

O UTLINE INTRODUCTION MATERIALS AND METHODS RESULTS CONCLUSIONS REFERENCES

INTRODUCTION Patients suffering from severe motor disabilities, such as amyotrophic lateral scleroses (ALS) Novel techniques allow users to control external devices or express their intentions independent of peripheral neuromuscular functions

INTRODUCTION Among those proposed solutions, one promising technique, called brain computer interface (BCI) This paper proposes a new SSVEP uses only one Oz EEG channel for SSVEP recordings and employs a simple architecture for SSVEP extraction.

MATERIALS AND METHODS Seven volunteers (Six males and one female), ages from 24 to 32 years.

MATERIALS AND METHODS Application study I Control StudyApplication Study

MATERIALS AND METHODS Application study I Came back6 months later

MATERIALS AND METHODS Application study II More complicated application study !

C ONTROL S TUDY Phase difference the predicted phase delay the detected phase lags In the induced SSVEPs using averages of different epoch lengths.

APPLICATION STUDIES Aimed to demonstrate the feasibility of the proposed system by inputting command sequences.

MATERIALS AND METHODS Subject I 1-h experience Visual stimulation Other Naïve subjects

MATERIALS AND METHODS Six months later…

MATERIALS AND METHODS Subject I and II 1.5-h experience Other 0.5-h experience

MATERIALS AND METHODS Pic 1. The schematic diagram of the proposed SSVEP-actuated BCI system

APPLICATION TASK I Produce a sequence of eight cursor commands ON BLBR OFF Pic 2. Flickering LEDs

APPLICATION TASK II ON BLBR OFF Pic 3. Flickering LEDs

EEG R ECORDINGS Used only one bipolar EEG channel One electrode (oz(+)) and (oz(−)) A ground electrode Bandpass, 0.5–50 hz Pic 4. Electrode Position

V ISUAL S TIMULI Square wave Oscillating at Hz (32 ms duration for each ON–OFF cycle) ON BLBR OFF Pic 5. Flickering LEDs

V ISUAL S TIMULI The ith LED flicker (LEDi) was set as ： θi = (i − 1) * 45° Full-phase cycle (360°) with a ±22.5° phase margin.

V ISUAL S TIMULI The flickering frequency is known as Hz The phase delay can be controlled by setting a time delay on the square wave generation:

V ISUAL S TIMULI Pic 6. Visual Stimuli

S IGNAL P ROCESSING OF SSVEP SSVEP-based BCI The flickering sequences ： Set at Hz Tagged with distinct phases The Oz EEG signals ： Band-Pass-Filtered between and Hz

S IGNAL P ROCESSING OF SSVEP LED1 ： Estimate the subject-specific phase lag SSVEP ref The induced SSVEP from LED1 Averaging the epochs in the 1-min recording for each subject SSVEP gaze Epochs induced from each LED flicker Excluding LED1 Were averaged over 60 epochs No overlaps

S IGNAL P ROCESSING OF SSVEP Tref The latency of the maximum amplitude peak Accomplished recognition of user’s gazed-target by ： The phase lag between SSVEPgaze and the SSVEPref

GAZED - TARGET IDENTIFICATION Tpeak The latency of maximum amplitude peak in SSVEPgaze Time lag (td) ： Td = t peak − t ref Θ detected ： Θ d ：

GAZED - TARGET IDENTIFICATION Di ： The ith LED (flicker LEDi) with minimum angle distance Di is recognized as the gazed-target.

Pic 7. Oz EEG RECORDINGS

RESULTS Pic 8. SSVEP-Based BCI Suing Phase Encoded Flickering Sequences

Pic 9. LEE

Pic 9. LEE et al

CONCLUSIONS This work proposes a SSVEP-based BCI using phase-tagged flickering sequence to produce cursor commands for communication purposes. Subjects shift their gazes at different LED flickers and phase information of the induced SSVEP is extracted for recognizing the gazed- targets.

CONCLUSIONS- FEATURES SSVEP ： Stable Reliable Noise can be removed by simply Bandpass Filter Only one flickering frequency Avoid interferences from low-frequency noise A more comfortable visualization.

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