| |
| |
| 4.
BCI - Brain–computer interfaces |
| |
4.2. Present-day BCIs
| |
4.2.3. P300 evoked potentials
|
|
Infrequent or particularly significant
auditory, visual, or somatosensory stimuli, when interspersed
with frequent or routine stimuli, typically evoke in the EEG
over parietal cortex a positive peak at about 300 ms. Donchin
and his colleagues have used this ‘P300’ in a BCI.
The user faces a 6 x 6 matrix of letters, numbers, and/or other
symbols or commands. Every 125 ms, a single row or column flashes;
and, in a complete trial of 12 flashes, each row or column flashes
twice. The user makes a selection by counting how many times
the row or column containing the desired choice flashes. EEG
over parietal cortex is digitized, the average response to each
row and column is computed, and P300 amplitude for each possible
choice is computed. As the picture shows,
P300 is prominent only in the responses elicited by the desired
choice, and the BCI uses this effect to determine the user’s
intent. The
current P300-based BCI could yield a communication rate of one
word (i.e. 5 letters) per minute.
 |
Picture:
P300 BCI. A matrix of possible choices is presented on
a screen and scalp EEG is recorded over the centroparietal
area while these choices flash in succession. Only the
choice desired by the user evokes a large P300 potential
(i.e. a positive potential about 300 ms after the flash). |
In people with visual impairments, auditory or tactile stimuli
might be used. Single-trial P300 amplitudes might be used for
environmental control in Virtual Realities.
A P300-based BCI has an apparent advantage in that it
requires no initial user training.
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 |
|
|
