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| 4.
BCI - Brain–computer interfaces |
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4.2. Present-day BCIs
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4.2.2.
Slow cortical potentials |
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Among
the lowest frequency features of the scalprecorded EEG are slow
voltage changes generated in cortex. These potential shifts
occur over 0.5–10.0 s and are called slow cortical potentials
(SCPs).
Negative SCPs are typically associated with movement while positive
SCPs are usually associated with reduced cortical activation.
People can learn to control SCPs and thereby control movement
of an object on a computer screen. This demonstration is the
basis for a BCI referred to as a 'thought translation
device' (TTD).
SCPs are extracted by appropriate filtering, corrected for EOG
activity, and fed back to the user via visual feedback from
a computer screen that shows one choice at the top and one at
the bottom. Selection takes 4s.
During a 2s baseline period, the system measures the user’s
initial voltage level. In the next 2 s, the user selects the
top or bottom choice by decreasing or increasing the voltage
level by a criterion amount. The voltage is displayed as vertical
movement of a cursor and final selection is indicated in a variety
of ways. The BCI can also operate in a mode that gives auditory
or tactile feedback. Users train in several 1–2 h sessions/week
over weeks or months. When they consistently achieve accuracies
of about 75%, they are switched to a language
support program (LSP).
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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