EEG-Based Communication and Control: Short-Term Role Feedback Present by: Yu Yuan-Chu Dennis J. Mcfarland, Lynn M. McCane, and J. R. Wolpaw IEEE Transactions on Rehabilitation Engineering, VOL. 6, NO. 1, JUNE 1998

NCTU BCI Group2 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

NCTU BCI Group3 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: Hz Two forms of feedback Cursor movement Event at the end of the trial: hit/miss Proved which one remain essential

NCTU BCI Group4 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

NCTU BCI Group5 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

NCTU BCI Group6 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 r 2 value Total variance of the EEG amplitudes for the top and bottom targets The difference between the mean amplitudes for top and bottom targets

NCTU BCI Group7 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

NCTU BCI Group8 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

NCTU BCI Group9 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

NCTU BCI Group10 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

NCTU BCI Group11 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