2. Introduction
Some neurological
conditions, such as
amyotrophic lateral sclerosis
(ALS),epilepsy can lead to
severe motor disability.
Such patients are referred to
as “locked-in”.
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Many patients cannot use conventional devices
made for patients with severe motor disability,
because these require consistent control over at
least one muscle group.
3. Recent studies indicate that humans can
learn to control certain components of
their EEG and can use them as a new
communication channel.
EEG-based communication methods
requires no neuromuscular control.
In order to enable such patients to
communicate, a technique was developed
where subjects learn to control their slow
cortical potential producing signal
according to the task requirement.
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4. What is SCP?
SCP(slow cortical potential)—one of the EEG signal
Compared with other EEG signals, SCPs have two
important advantages:
First, they are present
in the brain activity of
every person.
Second, the the control
of SCP was found to be
highly specific.
Therefore, a SCP self regulatory method has been
developed for communication purposes.
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5. 3 Requirements 4 Communication
First, the learning ability of completely
paralyzed patients must be proven.
Second, the EEG must be analyzed on-line
for immediate reinforcement.
The on-line analysis must include all the
transformations necessary to extract the
to-be-controlled signal.
Third, the software has to be flexible in
order to adjust it to the individual shaping
procedure.
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6. Technology used in TTD
In its present form, the core of
the TTD consists of a single
computer program that runs
under all MS-Windows versions.
This software contains the
functions of
electroencephalogram (EEG)-
acquisition storage , signal
processing, classification ,and
various applications for brain-
computer - communication
such as spelling.
It was written in C++ for
windows and uses the BCI-2000
common standard .
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7. Block Diagram
•The EEG is recorded from Cz, C3, and C4 of the 10-20 leads. SCP
shifts from Cz (vertex) serve as the primary signal, which has to
be controlled and used for operating the thought-translation
device (TTD).
•The signals are amplified with an EEG amplifier set to a low-pass
filter of 30 Hz and a time constant of 8 s and then digitized with a
sampling rate of 100 Hz.
•EEG amplifier with a long time constant is essential.
•Thus we get many kind of signals i.e. signals for all the
component s of EEG including background noise.
•We use filters to remove the background noise and again
perform signal transformation to get the required signal and to
perform cursor movement on the computer screen.
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8. Procedure
Patients sit in wheelchairs or beds and
viewed a color PC screen .
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9. two rectangles (goals) and a small moving
object (ball) are displayed.
viewing distance is about 140 cm.
If the second (C3–C4) channel used, two
more goals (on the right and the left
frame of the screen) are displayed.
Two alternating tones of different pitch,
which followed each other in an interval
of 2 s, held the patient to the rhythm of
the program.
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10. The ball move during the low-pitch tone
and the high-pitch tone (active phase) and
remained in the center of the screen
between the high-pitch tone and the low-
pitch tone (baseline phase).
The patient’s task is to move the ball in a
specified direction toward one of the goals
during the active phase.
The minimum SCP amplitude difference
between baseline and active phase
necessary to move the ball from the
center of the screen into a goal.
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11. If a negative potential has to be produced in
the active phase, compared with the baseline
interval, the ball moves upwards, and vice-versa
(“positivity”), is true when the ball moves
downwards.
If there was no difference between the baseline
interval and the SCP amplitude in the active
phase, the ball remained in the center of the
screen.
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12. Production of Language
Goals used presented a word or letter sequence
(the lower goal) and a space for the patient’s own
text (the upper goal).
In the case depicted, the patient has to select the
letter “M”. In order to do this, the patient has to
move the ball into the bottom goal. If the
characters shown should not be selected (if it
doesn’t contain the required letter), the patient’s
task would be to keep the ball away from this goal.
HUMAN
HU
M
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13. When EEG responses reach an accuracy of 80–85%,
the method of choice is a dichotomic LSP structure.
At the first level, the alphabet is divided in two parts,
at the second level each half is divided into two
quartiles, etc., up to the last level containing only
one letter.
In training condition, learning to use LSP proceeds
from easy to more difficult task. It starts with two-
level dichotomic structure to three, four and so on.
Any of the above two methods can be used for
selecting text.
A B E H N P S T
A B E H N P S T
A B E H N P S T
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14. Merits
TTD can achieve an
accuracy level of 65–85%.
The present software
can easily be used for
control of patient’s
environment (e.g., call attendant, switch a light
on or off, etc.) by means of short task sequences
being linked with corresponding technical
devices.
Studies shows a reduction of epileptic seizures by
teaching patients to voluntarily produce positive
SCP shifts.
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15. Demerits
SCP is the necessity of a low time constant
and, hence, contamination by
Electrooculogram (EOG) artifacts.
It requires more time for communication.
It is costly.
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16. Improvements
Reliable techniques for on-line EOG
artifact control during self regulation have
developed.
To achieve higher speed :-
1.Error rate should be reduced.
2.We should reduce the time necessary for
each single response.
3.Complexity of the alphabet and language
structure of LSP should be reduced.
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