EEG-Based Communication and Control:
Short-Term Role Feedback
Dennis J. Mcfarland, Lynn M. McCane, and J. R. Wolpaw
IEEE Transactions on Rehabilitation Engineering, VOL. 6, NO. 1, JUNE 1998
Present by: Yu Yuan-Chu
2003.12.24
Motive
In the short-term, µ rhythms control is not
dependent on the sensory input provided by
the cursor movement
Feedback can have inhibitory as well as
facilitory effects on EEG control
The effects vary across subjects
Find the implications for the design of the
training procedure
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Short-Term Role of Feedback
EEG based communication system
Eight 3-min runs, and each run consists of about
30 trials
Cursor moves as a linear function of EEG
amplitude in specific frequency bands
µ rhythms: 8-12 Hz, ß rhythms: 20-24 Hz
Two forms of feedback
Cursor movement
Event at the end of the trial: hit/miss
Proved which one remain essential
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Methods
Ten adults, 6-18 years prior to participation
No prior experience with EEG-based
communication
After an initial evaluation defined the frequencies
and scalp locations of rhythm activity
12 training sessions at a rate of 1-3 sessions per
week
First ten were standard training, final two were special
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Procedure
64 channels EEG
Amplification 20000, band pass 1-60 Hz
Digitized at 196 Hz on line, 128 Hz off line
Three kind derivation
Bipolar derivation
Common average reference derivation
Laplacian derivation
Every 100ms, the most recent 200 ms segment was
analyzed by an autoregressive algorithm
Amplitude in a 3 Hz wide frequency band
188 cursor steps, 94 steps from the top and bottom
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Evaluation of the Feedback
Three trial formats
STD: STANDARD
NCM: NO CURSOR MOVEMENT
NFB: no feedback
Procedure:
Sessions 11 and 12:STD
Sessions 13 and 14: random
Compare the in accuracy and r2 value
Total variance of the EEG amplitudes for
the top and bottom targets
The difference between the mean
amplitudes for top and bottom targets
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Accuracies Comparison
High accuracy usually takes several months
No significant effect of feedback
Sessions 11 and 12 was significantly correlated with accuracy
for sessions 9 and 10, but not for NCM
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Mean accuracies : STD and NCM
Feedback did not have a
significant effect on the
overall level
Sessions 11 and 12 did not
show a similar correlation
Performances for sessions 9
and 10
composed only of STD runs
predicted performance on the
STD runs, but not NCM
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Discussion
Feedback effects:
Lasting: affect learning
Transient: affect performance
Ideal human-machine systems should provide
instantaneous feedback, Smith said
Not possible for EEG
finite sample of EEG 200ms
additional 20 ms for computation and display
Serve to maintain the subject’s interest
Rapid reaction to cursor movements when in the
wrong direction
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Discussion
Might be distracted by the cursor
Close attention might impede maintenance
Relaxed state that facilitates µ rhythms activity
Wrong direction can generalized EEG desynchroniztion
Hit might be associated with EEG synchronization or
desynchronization
Visual stimulus might affect the visual alpha rhythm
which is similar in frequency to the µ rhythms
Removal of cursors movement is good for some subject
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Practical Implications
Reduced by decreasing the brightness and
size of the cursor
Probably not impair the guidance
Reduce the distraction
Analogous to motor control tasks
The prominent visual stimulation of the
moving cursor was not essential for the
maintenance of performance
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