The P300-based brain-computer interface (BCI): effects of stimulus rate.
OBJECTIVE
Brain-computer interface technology can restore communication and control to people who are severely paralyzed. We have developed a non-invasive BCI based on the P300 event-related potential that uses an 8×9 matrix of 72 items that flash in groups of 6. Stimulus presentation rate (i.e., flash rate) is one of several parameters that could affect the speed and accuracy of performance. We studied performance (i.e., accuracy and characters/min) on copy spelling as a function of flash rate.


METHODS
In the first study of six BCI users, stimulus-on and stimulus-off times were equal and flash rate was 4, 8, 16, or 32 Hz. In the second study of five BCI users, flash rate was varied by changing either the stimulus-on or stimulus-off time.


RESULTS
For all users, lower flash rates gave higher accuracy. The flash rate that gave the highest characters/min varied across users, ranging from 8 to 32 Hz. However, variations in stimulus-on and stimulus-off times did not themselves significantly affect accuracy. Providing feedback did not affect results in either study suggesting that offline analyses should readily generalize to online performance. However there do appear to be session-specific effects that can influence the generalizability of classifier results.


CONCLUSIONS
The results show that stimulus presentation (i.e., flash) rate affects the accuracy and speed of P300 BCI performance.


CONCLUSIONS
These results extend the range over which slower flash rates increase the amplitude of the P300. Considering also presentation time, the optimal rate differs among users, and thus should be set empirically for each user. Optimal flash rate might also vary with other parameters such as the number of items in the matrix.
Laboratory of Neural Injury and Repair, Wadsworth Center, New York State Dept. of Health, Albany, NY 12201-0509, USA. mcfarlan@wadsworth.org
Dennis J
DJ
McFarland
William A
WA
Sarnacki
George
G
Townsend
Theresa
T
Vaughan
Jonathan R
JR
Wolpaw
D000328:Adult; D000704:Analysis of Variance; D003143:Communication Devices for People with Disabilities; D016002:Discriminant Analysis; D004569:Electroencephalography; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D030141:Feedback, Psychological / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009862:Online Systems; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology; D014584:User-Computer Interface