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| 4.
BCI - Brain–computer interfaces |
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4.1.
Definition and features of a BCI
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4.1.1.
Dependent and independent BCIs |
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Dependent BCI
A dependent BCI does not use the brain’s normal output
pathways to carry the message, but activity in these pathways
is needed to generate the brain activity (e.g. EEG) that does
carry it.
Es:
one
dependent BCI presents the user with a matrix of letters that
flash one at a time, and the user selects a specific letter
by looking directly at it so that the visual evoked potential
(VEP) recorded from the scalp over visual cortex when that letter
flashes is much larger that the VEPs produced when other letters
flash (Sutter, 1992). In this case, the brain’s output
channel is EEG, but the generation of the EEG signal depends
on gaze direction, and therefore on extraocular muscles and
the cranial nerves that activate them. A dependent BCI is essentially
an alternative method for detecting messages carried in the
brain’s normal output pathways: in the present example,
gaze direction is detected by monitoring EEG rather than by
monitoring eye position directly. While a dependent BCI does
not give the brain a new communication channel that is independent
of conventional channels, it can still be useful.
Independent
BCI
An independent BCI does not depend in any way on the brain’s
normal output pathways. The message is not carried by peripheral
nerves and muscles, and, furthermore, activity in these pathways
is not needed to generate the brain activity (e.g. EEG) that
does carry the message.
Es:
One
independent BCI presents the user with a matrix of letters that
flash one at a time, and the user selects a specific letter
by producing a P300 evoked potential when that letter flashes.
In this case, the brain’s output channel is EEG, and the generation
of the EEG signal depends mainly on the user’s intent, not on
the precise orientation of the eyes. The normal output pathways
of peripheral nerves and muscles do not have an essential role
in the operation of an independent BCI. Because independent
BCIs provide the brain with wholly new output pathways, they
are of greater theoretical interest than dependent BCIs. Furthermore,
for people with the most severe neuromuscular disabilities,
who may lack all normal output channels (including extraocular
muscle control), independent BCIs are likely to be more useful.
Source:
Brain–computer
interfaces for communication and control, Clinical Neurophysiology
113 (2002) 767–791, Jonathan R. Wolpaw, Niels Birbaumer, Dennis
J. McFarland, Gert Pfurtscheller, Theresa M. Vaughan |
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