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Brain-Computer Interfaces for Communication in Paralysis: A Clinical Experimental Approach

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Brain-Computer Interfaces for Communication in Paralysis: A Clinical Experimental Approach. By Adil Mehmood Khan. Contents ● Introduction ● BCI for communication in paralysis ● BCI software ● Self-regulation of SCPs and training ● Spelling through brain-cmputer communication. - PowerPoint PPT Presentation
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Brain-Computer Interfaces for Communication in Paralysis: A Clinical Experimental Approach By Adil Mehmood Khan
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  • Brain-Computer Interfaces for Communication in Paralysis: A Clinical Experimental ApproachByAdil Mehmood Khan

  • Contents

    Introduction

    BCI for communication in paralysis

    BCI software

    Self-regulation of SCPs and training

    Spelling through brain-cmputer communication

  • Brain-Computer-Interface (BCI) ? A system for controlling a device e.g. computer, wheelchair or a neuroprothesis by human intention which does not depend on the brains normal output pathways of peripheral nerves and muscles [Wolpaw et al., 2002].HCI Human Computer InterfaceDBI Direct Brain Interface (University of Michigan)TTD Thought Translation Device (University of Tbingen)

  • Some examples of BCI applications

    BCILeeb et al., Computational Intelligence and Neuroscience, 2007 (doi:10.1155/2007/79642)

  • Brain Computer Interfaces

    Allow patients to control a computer by concious changes of brain activity

    Provide a means of communication to completeley paralysed patients: amyotrophic lateral sclerosis (ALS), cerebral palsy, locked in syndrome

    Can be used to control a cursor, select symbols, control external devices like orthesis / prothesis (depending on type of BCI)

    Have a very low data rate, typical a few bit per second or less

    First results in the 1970ies (Vidal, visual evoked potentials, VEP-BCI)

  • Brain Computer Interfaces Principles of operation:

  • Brain Computer Interfaces Electrophysilogical Activities used

    SCP Slow Cortical Potentials Mu Movement Imagination P300, SSVEP ERP-Analysis

    cortical neurons, direct brain interfaces

    http://www.wired.com/news/images/full/thoughtlock1_f.jpgThe control informationis extracted from thereal time EEG-recording

  • Brain Computer Interfaces SSVEP

    Steady State Visual Evoked Potentials derived from the visual (occipital) cortex

    focussing attention to visual stimuli of different frequency shows up in the EEG freqeuncy bands

    relibable and high transfer rate, but some prerequisites (eyes)http://www.iua.upf.es/activitats/ semirec/semi-Reilly/

  • Brain Computer Interfaces SCP BCIs

    detection of slow cortical potentials (SCPs)

    needs DC EEG Amplifiers

    first successful device end 1990s: Niels Birbaumers Thought translation device intensive training was necessary to gain control over the SCP waves

    Patinet using TTD to write a letter http://www.heise.de/ct/06/18/088/bild1.jpgSCPs:

    DC-shifts, slow negativation of cortical areas

    Preparation of movement and cognitive tasks,

    Several hundert milliseconds before the task

  • Brain Computer Interfaces - -rhythm BCIs

    rhythm is the idle-rhythm of the motor cortex

    frequencies around 10 and 18 Hz.

    ERD / ERS event related desynchronisation / synchronisation movements or imagination of movements inhibit the rhythm

    Berlin-BCI, http://www.fraunhofer.de/

  • Brain Computer Interfaces - P300 BCIs

    P300 wave posivite component in the event related potential, 300ms after a stimulus natural response to events considered as important

    selection of a symbol: count the flashes, algorithm averages trails and finds a P300

    P300 runtime user interface

  • Brain Computer Interfaces - / P300 comparison

    - BCIs P300 BCIs

    Require training do not require training2d-control possible 1D control only movement imagination concentration / decision affected by movement affected by distraction

  • BCI for Communication in ParalysisAn overview of different approaches to BCIs developed at Institute of Medical Psychology and Behavioral Neurobiology.Thought-Translation Device (TTD).Brain-Controlled Web Browser.Visual and Auditory feedback modes.Oscillatory Features based Classification.

  • SCPs: A Brief HistoryAn initial application: Epileptic SeizuresDown regulation of brain potentials towardsa positive amplitude.

    BCI for locked-in syndromeCommunication through self-regulation of SCPsAlso known as TTD

  • BCI SoftwareThought Translation Device: ComponentsEEG AmplifierEEG8 systemG.tec amplifiersBrainAmp systemTwo MonitorsOne for operator (supervise the training)One for patient (feedback)Sampling frequency: 256HzDigitized with 16 bits/sampleAmplitude range: +(-) 1mVLow frequency cutoff: 0.01 HzHigh frequency cutoff:: 40-70 Hz

  • TTD Feedback and Communication SystemThe current version of TTD software is derived from BCI2000 standard

  • TTD Feedback and Communication System

  • Data acquisition and storageOnline signal processingClassificationFeedback and application interfaceTTD Software

  • Research Platform for BCI Systems Written by Gerwin Schalk, Wadsworth Center, Albany (NY) Modular structure: Signal Aquisition, Signal Processing and User Application communicatie via TCP/IP Operator module used for configuration of the other modules various user tasks availbale: 1D/2D cursor, Speller, P300, SCP free for academic use driver for OpenEEG availablehttp://www.bci2000.org/Brain Computer Interfaces - BCI2000

  • BCI2000: ComponentsFiltersSpatial, temporal, and spectralOnline artifact detection and correctionClassificationLinear Discriminant Analysis (LDA)Simple Threshold ClassificationSupport Vector Machine (SVM)MATLAB interfaces.

  • Self-Regulation of SCPs Slow event-related direct-current shifts of the EEG. They last from 0.3 seconds up to several seconds. Occur as a result of external or internal events. Negative shift is related to excitability of neurons. Positive shifts are measured during the execution of cognitive tasks Healthy subjects as well as patients can learn to produce positive or negative SCPs Training requires feedbackVisualAuditory

  • Self-Regulation of SCPs Recording site for feedback signal is usually Cz. EEG is usually recorded from 3-7 Ag/AgCI-electrodes placed at Cz, C3, C4, Fz, and Pz. vEOG is recorded using a bipolar channel for online and offline artifact correction. A fixed percentage of vEOG signal is subtracted from the SCP signal at Cz for EOG correction. SCPs are calculated by applying a 500ms moving average to EEG signal.

  • Self-Regulation of SCPs With the visual feedback modality:Subjects viewed the course of their SCPs as the vertical movement of feedback cursor.Vertical cursor movement corresponded to the SCP amplitude.Task was to move the cursor towards the modality indicated by a red rectangle.

  • Self-Regulation of SCPs: Training Process

  • Self-Regulation of SCPs: Training Process First 2-4 sec of the trial. Target is illuminated in red. Allows the subject to prepare for the corresponding SCP regulation.

  • Self-Regulation of SCPs: Training Process Feedback is provided by the vertical position of the steady horizontally moving cursor. Cortical negativity moved the cursor up. Positivity moved the cursor down. Center of the screen corresponded to the baseline. Task is to move the cursor to the red area.

  • Self-Regulation of SCPs: Training Process A response is classified as correct if:Average potential carried the correct polarity.Or is inside the target boundaries of the required goal. Classification methods, such as LDA or SVM can be used for improvement of the correct response rate.

  • Self-Regulation of SCPs: Performance PerformancePercentage of correct responses in valid trials.After a rate of 75% correct responses, subjects were trained to select letters and write messages Subjects typically reach this level after 1 to 5 months of training, with 1 to 2 training days per week. A training day comprises 7 to 12 runs, and a run comprises 70 to 100 trials.

  • ApplicationsSpelling by Brain-Computer Communication:

    A program driven by yes or no responses, which serve as select or reject commands.Requires three intervals in one trial.Allows user to select letters from a language alphabet and to combine letters into words and sentences.

  • ApplicationsPresentation of the letter set.Displayed in target rectangles on the screen.Spelling by Brain-Computer Communication:

    A program driven by yes or no responses, which serve as select or reject commands.Requires three intervals in one trial.Allows user to select letters from a language alphabet and to combine letters into words and sentences.

  • ApplicationsFeedback is provided.Self regulation of SCP amplitudes is used to select or reject the letter set.Spelling by Brain-Computer Communication:

    A program driven by yes or no responses, which serve as select or reject commands.Requires three intervals in one trial.Allows user to select letters from a language alphabet and to combine letters into words and sentences.

  • ApplicationsResponse interval indicating to user the result of the selection.Error correction is done using a go-back option.Spelling by Brain-Computer Communication:

    A program driven by yes or no responses, which serve as select or reject commands.Requires three intervals in one trial.Allows user to select letters from a language alphabet and to combine letters into words and sentences.

  • Spelling by Brain-Computer Communication

  • Spelling by Brain-Computer CommunicationPerformance:

    Writing the most conveniently situated letter , E, takes 5 trials.

    Writing the most remote sign requires 9 trials, i.e. 36 45 sec.

    Improvement

    A simple personal dictionary to make free spelling less time consuming.

    Contains words that are frequently used by patients.

    A complete word is suggested after at least two letters have been written.

    This word can then be chosen with a single selection response.


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