EEG-Based Communication and Control:Short-Term Role Feedback

Present by: Yu Yuan-Chu 2003.12.24

  Dennis J. Mcfarland, Lynn M. McCane, and J. R. Wolpaw

IEEE Transactions on Rehabilitation Engineering, VOL. 6, NO. 1, JUNE 1998

NCTU BCI Group 2

MotiveIn 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 Group 3

Short-Term Role of Feedback

EEG based communication systemEight 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 feedbackCursor movement

Event at the end of the trial: hit/miss

Proved which one remain essential

NCTU BCI Group 4

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 Group 5

Procedure64 channels EEGAmplification 20000, band pass 1-60 HzDigitized at 196 Hz on line, 128 Hz off lineThree kind derivation

Bipolar derivationCommon average reference derivationLaplacian derivation

Every 100ms, the most recent 200 ms segment was analyzed by an autoregressive algorithmAmplitude in a 3 Hz wide frequency band188 cursor steps, 94 steps from the top and bottom

NCTU BCI Group 6

Evaluation of the FeedbackThree 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 valueTotal variance of the EEG amplitudes for the top and bottom targets

The difference between the mean amplitudes for top and bottom targets

NCTU BCI Group 7

Accuracies Comparison

High accuracy usually takes several monthsNo significant effect of feedbackSessions 11 and 12 was significantly correlated with accuracy for sessions 9 and 10, but not for NCM

NCTU BCI Group 8

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 Group 9

DiscussionFeedback 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 Group 10

DiscussionMight be distracted by the cursor

Close attention might impede maintenanceRelaxed 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 Group 11

Practical ImplicationsReduced 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