Transcript Brain-Computer Interfaces for Communication in Paralysis
Brain-Computer Interfaces for Communication in Paralysis: A Clinical Experimental Approach By Adil Mehmood Khan
TTD Feedback and Communication System
• The current version of TTD software is derived from BCI2000 standard
TTD Software
Data acquisition and storage Online signal processing Classification Feedback and application interface
Spelling by Brain-Computer Communication
Contents
● Web surfing with BCI ● Auditory-controlled BCI ● Visual and auditory feedback comparison ● BCI using ECoG ● Comparison of non-invasive BCI approaches
Brain Controlled Web Surfing ● Allow patients to surf the web by concious changes of brain activity ● Enables a completely paralyzed patient to participate in the broad portion of life reflected by the WWW.
● History of providing WWW access to ALS patients dates back to 1999
•
TTD was used to operate a standard web browser, i.e.
Descartes
● Descartes was controlled by binary decisions ● Services provided
•
Writing letters, writing emails, and surfing the web.
Setup of EEG-controlled web brwoser “Descartes“
Web surfing with “Descartes“ - A ● ●
Patient views a list of predefined WebPages.
Each webpage is offered successively at the bottom of the screen for selection.
●
Page selection through positive SCPs whereas page rejection by negative SCPs.
Web surfing with “Descartes“ - B ●
Page loaded after its selection and shown for a predefined period of time.
Web surfing with “Descartes“ - C ●
The links on the previous page are offered alphabetically as a dichotomous tree .
●
Subject will select or reject each item by regulating SCPs
“Nessi“ – An Improved Graphical Brain-Controllable Browser
BCI-software communication with Nessi
Nessi‘s email interface
Nessi‘s virtual keyboard
An Auditory–Controlled BCI ● Feedback:
•
Visual
•
Auditory
•
High pitch tones indicate cortical negativity
•
Low pitch tones indicate cortical positivity
•
Hybrid (Visual and Auditory)
Auditory–Stimulation in EEG
Auditory–Stimulation in EEG
Auditory–Stimulation in EEG
Auditory–Stimulation in EEG
An Auditory–Controlled BCI: Paradigms
Comparison between Visual and Auditory Feedback
Functional MRI and BCI ● BCI combined with FMRI to uncover relevant areas of brain activation during regulation of SCPs.
● EEG from 12 healthy subjects was recorded inside an MRI scanner while they regulate their SCPs.
● Successful positive SCP shift was related to an increase of blood oxygen level dependent (BOLD) in the anterior basal ganglia .
● While negativity was related to an increased BOLD in the thalamus .
SVM Classification of Autoregressive Coefficients: ● In contrast to SCPs:
•
Frequency range below 1Hz
•
Classified according to their time domain representation ● EEG correlates of an imagined-movement as best represented by oscillatory features of higher frequencies, i.e. 8-15 and 20-30 Hz
•
Desynchronization of μ–rhythm over motor areas.
● Coefficients of a fitted autoregressive (AR) model were used to realize this phenomena. ● SVM was them employed for the classification of these AR coefficients.
SVM Classification of Autoregressive Coefficients:
BCI using ECoG signals: ● EEG:
•
Limited signal-to-noise ratio
•
Low frequency range ● Invasive ECoG signals:
•
Broader frequency range (0.016 to 300 Hz)
•
Increased signal-to-noise ratio
•
3 out of 5 epilepsy patients were able to spell their names within only one or two training sessions.
● ECoG signals were derived from a 64-electrode grid placed over motor-related areas.
● Imagery of finger or tongue movements was classified with SVM classification of AR coefficients.
BCI using ECoG signals:
Comparison of Noninvasive Input Signals for BCI ● Noninvasive BCI:
•
Sensorimotor rhythms (SMR)
•
Slow cortical potentials (SCPs)
•
P300 ● Extensively studied in healthy participants and to a lesser extent in patients.
● For this reason SCP-, SMR-, and P300-based BCIs were compared for free spelling.
Background Information for All Patients
Comparison Study ● SCPs:
•
None of the seven patients showed sufficient performance after 20 sessions.
● SMR
•
Half the patients showed an accuracy ranging from 71 to 81 %. ● P300
•
Performance ranged from 31.7 to 86.3 %