emtiyaz (emt) cs, ubc - emtiyaz khan's homepage · pdf filebrain-computer interface...
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Brain-Computer InterfaceOverview, methods and opportunitiesEmtiyaz (Emt)CS, UBC
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Overview• BCI : application, structure, challenges, opportunities• Two examples of BCI : P300 and ERD/ERS• ERD/ERS BCI – Methods• ERD/ERS BCI – Our Work
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Please don’t sleep, we will watch videoshttp://www.youtube.com/watch?v=NIG47YgndP8
http://www.youtube.com/watch?v=qCSSBEXBCbY
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Why a Brain-Computer Interface?1.Use the capabilities of remaining pathways2.Detour around the points of damage (FES)3.Or if you have enough time to kill, use BCI
Military Applications Other Fancy Use
Locked-in SyndromeAmyotrophic Lateral SclerosisMultiple Sclerosis
Image Bayliss’ Thesis, and various webpages
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Why a Brain-Computer Interface?
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A General Brain-Computer Interface (BCI)
Image Pfurtscheller 2006
Evoked Potentials
Operant Conditions
Implanted Methods
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BCI: Challenges and Opportunities
Image Pfurtscheller 2006
Evoked Potentials
Operant Conditions
Implanted Methods
ChallengesHigh Signal VariabilityUnderlying Physics unknownLinear or nonlinear Model?Man-Machine learning dilemma
One obvious opportunityOptimization of Electrode position
P300
ERD/ERS
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P300 BCI
Images from http://ida.first.fraunhofer.de/projects/bci/competition_ii/albany_desc/albany_desc_ii.html
AverageBCI competetion II DatasetTask relevant stimuli
Non-task relevant response
Sequential data, Discrete o/p, Correlation based models
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ERD/ERS BCIAmplitude attenuation/ enhancementin the specific frequency bands
Photographs from Pfurscheller 2002
Sequential data, Continuos o/p,
Strong Spectral charasteristics
C3 C4
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ERD/ERS – Methods
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Inter-trial Variance (IV) Method
Photographs from Pfurtscheller 1998
Only offline
Sensitive to frequency
band selection
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RLS ApproachAdaptive Autoregressive (AAR) Model
Solved with Recursive least square (RLS) algorithms and features classified with Linear Discriminant Analysis (LDA)
observation noise
Photographs from Pfurtscheller 2000
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Our WorkDone at the Indian Institute of Science, Bangalore, Indiain 2002-04
PublishedM. E. Khan and D. N. Dutt, "An Expectation-Maximization Algorithm Based Kalman Smoother Approach for Event-Related Desynchronization(ERD) Estimation from EEG", Vol. 54, No. 7, July 2007, IEEE Transactions on Biomedical Engineering
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Time-varying AR Model
RLS algorithm
Kalman filters
Use EM to get the parameters{A, Q, R, x0, S0)
EMKS
RLS
KS
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Effect of EM Learning on Tracking
Average
Single TrialSignal
Optimization
Improved AR coefficientsTracking, and variance isreduced
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Spectrum EstimationOptimization
Signal
Single Trial
Average
Improved Frequency TrackingVariance is reduced
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Motor Imagery Data: Spectrum estimatesSignal
Single Trial Spectrum Estimate
Right Hand
Left Hand
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Motor Imagery Data : ERD estimation
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Final Comments• BCI datasets provide opportunity to test new
algorithms• Every two year there is a BCI competition. Some free
datasets can be found there (just google BCI competition)
• Do it for fun and blame it on humanity!!