graz-brain-computer interface: state of research
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Graz-Brain-Computer Interface: State of Research. By Hyun Sang Suh. Overview: BCI systems. The user performs a certain task, which has a distinct EEG signature. The specific features are extracted from the EEG. - PowerPoint PPT PresentationTRANSCRIPT
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Graz-Brain-Computer Interface: Graz-Brain-Computer Interface: State of ResearchState of Research
ByHyun Sang Suh
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Overview: BCI systemsOverview: BCI systems
The user performs a certain task, which has a distinct EEG signature
The specific features are extracted from the EEG
A pattern classification system uses these EEG features to determine which task the user performed
The BCI presents feedback to the user, and forms a message or command
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Motor execution vs. Movement imaginationMotor execution vs. Movement imagination
Imagination
Execution
ERD ERS
500mstime
Subject 1, g3 Subject 2, f4
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How can we discriminate four motor How can we discriminate four motor imagery tasks?imagery tasks?
Tongue
Left Hand
Right hand
Foot
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The mu-wave BCIThe mu-wave BCI Mu wave activity occurs around roughly 12 Hz.
Alpha waves are strongest over the visual areas in the occipital lobe, But mu waves are strongest over the motor areas in the frontal lobe.
Mu activity changes as people perform or imagine movement. You have ERD/ ERS patterns depending on the motor imagery tasks
Time
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Subjects and experimental paradigmSubjects and experimental paradigm
Participants: Six female and three male healthy right-handed subjects.
Remain relaxed and avoid any motion during experiment. Imagine the experience of movement (kinesthetic, MIK). The arrow pointing represent one of the four different
tasks (left hand, right hand, both feet and tongue). EEG signal were recorded from 60 electrodes referenced
to the left mastoid.
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Quantification of ERD/ ERSQuantification of ERD/ ERS
First, band-pass filtering of each trial. Second, squaring of samples (with smoothing) Third, averaging of N trials.
The ERD/ ERS pattern is defined as the percentage power decrease (ERD) or power increase (ERS) comparison to one-second reference interval (0.5-1.5 sec).
( )( ) B ref
ref
P t PERD t
P
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Kappa coefficient and ITVKappa coefficient and ITV
Kappa coefficient - To measure distinctiveness
1
11acc n
n
Where acc is the accuracy derived by confusion matrix, n is the number of classes
Intertask variability (ITV) - standard deviation of averaged ERD/ ERS
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Frequencies and band power changesFrequencies and band power changes
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Time-frequency maps displaying ERD/ ERSTime-frequency maps displaying ERD/ ERS
time
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Maps displaying the topographical Maps displaying the topographical distribution of averaged band powerdistribution of averaged band power
High ITV
Low ITV
Intertask variability: ITV
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Brainloop Interface for GoogleBrainloop Interface for Google
R. Scherer, G. Pfurtscheller. The self-paced Graz brain-computer interface: methods and applications. Computational Intelligence and Neuroscience 2007, 79825, 2007.
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Mu vs. P300 BCIsMu vs. P300 BCIs
Requiring training
Work in real-time
2D control possible
Continuous control
Affected by movement
Requiring no training
Require averaging
1D control only
Discrete control
Affected by distraction
Mu BCI P300 BCI
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Phase Synchronization FeaturesPhase Synchronization Features Currently, BCIs system is not considered the relationships
between EEG signals measure at different electrode recording. We can obtain the additional information from this
relationships.
Phase Locking value (PLV) is one of the method to quantify such relationships.
The PLV can measure the level of phase synchronization between pairs of EEG signals.
The PLV value of 1 means that the two channels are highly synchronized, whereas a value of 0 means no phase synchronization.
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Phase Synchronization FeaturesPhase Synchronization Features
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BCI Applications BCI Applications
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Patient with Spinal Cord InjuryPatient with Spinal Cord Injury Spinal Cord Injury (SCI) - Damage or trauma to the spinal
cord that result in a loss or impaired function
- The effects of SCI depend on type of injury (i.e, a car accident, falls, sports injuries, or a disease)
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Restoration of hand movement in SCI patientRestoration of hand movement in SCI patient
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Functional Electrical StimulationFunctional Electrical Stimulation
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BCI controlled FESBCI controlled FES
G. Pfurtscheller, G. R. Müller, J. Pfurtscheller, H. J. Gerner, Rüdiger Rupp. 'Thought'-control of functional electrical stimulation to restore hand grasp in a patient with tetraplegia. Neuroscience Letters 351, 33-36, 2003. .
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What is the Neuroprosthese?What is the Neuroprosthese? It is a device which replaces nerve function lost as a result of
disease or injury.
The neuroprosthetics can act as a bridge between functioning elements of the nervous system and damaged nerves.
It can be used in the spinal cord to allow standing in paraplegics.
Hand prostheses
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AUDITORY PROSTHETICSAUDITORY PROSTHETICS most successful example of sensory prosthetic is the cochlear
implant. lack the cochlear hair cells that transduce sound into neural
activity. Extended to direct stimulation of the brainstem for those with
dysfunctional cochlear nerves.
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VISUAL PROSTHETICSVISUAL PROSTHETICS The device uses electrical signals to bypass dead photoreceptors
and stimulate remaining viable cells of the retina. Images come from the external video camera worn behind the
patient’s glasses. The images are transmitted through a computer to electrodes
attached to the retina Reproduce the visual image in the occipital lobe.
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BCI controlled NeuroprostheseBCI controlled Neuroprosthese The BCI system is implanted
his right hand and arm
Detect brain pattern (ERD/ ERS) of left hand foot imagery movement
Provide two graps patterns
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BCI controlled NeuroprosthesisBCI controlled Neuroprosthesis
G. R. Müller-Putz, R. Scherer, G. Pfurtscheller, R. Rupp. EEG-based neuroprosthesis control: a step towards clinical practice. Neuroscience Letters 382, 169-174, 2005.
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BCI controlled GameBCI controlled Game
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