Brain Interface Design for Asynchronous Control

Event Related Potentials Event Related Potentials (ERP) - ERP is any measured brain response that is directly the result of a thought or perception. - ERPs can be reliably measured using electroencephalography (EEG). Schematic depiction of the measurement and averaging of event-related potentials. Singular "waves" temporally associated with a specific experimental event are usually labeled according to their polarity and latency from the triggering event. (e.g. N100 = negatively poled ERP with peak latency at roughly 100 milliseconds; P300 = positively poled ERP with peak latency at roughly 300 milliseconds). Negative potential deflections are often presented facing upwards. ASSUME : TIME DELAY TO DETECT ERPs, AVERAGING TECH. USED//////// will enhance the signal-to-noise ratio A wave showing several ERP components, including the N100 and P300

What is the Outlier Processing Method(OPM) OPM is the method that extract the outlier which mean the event-related potentials(ERPs) yi = xi + vi - Yi is the measured value of the observed process at time i. - Xi is the value of the ongoing process - Vi is the value of the outlier process which is assumed independent xi

What is the Outlier Processing Method(OPM) Stimulated outlier extraction using GM2, LSQ, GM, and GM1 Parameter Estimates The results indicated that the extraction process preformed better GM2 than with GM, LSQ estimates while the performance with GM1 and GM2 were similar

Event Related (De)synchronization Event Related (De)synchronization (ERD/ ERS) - Certain events can block or desynchronize the ongoing alpha activity. - These type of changes can be detected by frequency analysis. - Decrease or increase of power in specific frequency bands. ERD and ERS is defined as the percentage of power decrease or increase - the power within the specific frequency band in the period after the event: PB - the power in the baseline : Pref

Method of Detecting IC and NC OPM This method estimates ERPs using the AR model and various parameter estimators. Using estimated ERPs, the original signal separated by IC and NC ERD This method detected ERD by decreasing of power in specific frequency bands. Using ERD, the signal is separated by IC and NC

Method of Detecting IC and NC LF-ASD They find the feature that VMRPs has higher relative power than NC state in 1-4Hz bandwidth via time-frequency analysis of EEG pattern. Feature extractor Analysis of 1-4Hz bandwidth with bi-scale wavelet: w(a, b) The robustness of feature prediction was improved by pairing elemental features by correlation After this procedure, Bi-scale wavelet. When b is zero, the strongest features were observed. So analysis was implemented at zero value of b. Where di represents the time shift : This vector was equally weighted with each dimension reflecting the value of and aggregate feature.

Method of Detecting IC and NC LF-ASD Feature classifier: Using this feature, they has developed the low-frequency asynchronous switch design(LF-ASD) Output of the classifier was turned on: value = 1 Output of the classifier was turned off: value = 0 Classification Method: 1-NN Feature Space Modeling: LVQ3 12-bit ADC Classification Method: 1-NN Feature Space Modeling: LVQ3

Data Glove. Data glove is a sensing device for hand motion using motion sensors such as accelerometer, gyroscope, bend sensor, and so on. Data glove based on bend sensor is used for training finger movement.

Training Section The desired movement was explained to the subject and the subject was allowed to practice while investigator watched and corrected the subject`s motion. A nonstandard finger flexion was selected as the target movement because it was assumed to be new to all subjects. The investigator used visual inspection of averaged finger movement to maintain similarly. After training, the subject was allowed to practice until at least 60% of movements were recognized.

Electrode placement for Experiments Region of the motor cortex They chose to limit the features to the top six primarily because these features were the minimal set that provided uniform coverage of the motor areas (SMA, MI) of the cortex. The strongest discriminatory features were found in autocorrelations within six electrode pairs F1-FC1, Fz-FCz, F2-FC2, FC1-C1, FCz-Cz, and FC2-C2 on the 10-20 system for electrode placement. Electrode placement for LF-ASD

Data Collection The center ball moved through a visual angle of 2 degree up to down or side to side. The second ball marked 2 moved randomly throughout the space. The boundary labeled as 3 was either a single-lined or a double-lined rectangle Experimental Display

Data Collection When the single-line boundary box was displayed, the subject was instructed not to move, but to keep monitoring for possible collisions between the outer and center ball. When the boundary of the box is changed from a single line to double line, the subject was instructed to try to time their movements for changing the movement direction of the center ball Data collection continued until 50 successful movements and 10 idle trial were recorded within monitor. Experimental Display

Data Collection When the single-line boundary box was displayed, the subject was instructed not to move, but to keep monitoring for possible collisions between the outer and center ball. When the boundary of the box is changed from a single line to double line, the subject was instructed to try to time their movements for changing the movement direction of the center ball Data collection continued until 50 successful movements and 10 idle trial were recorded within monitor. Experimental Display

Method of Evaluating Asynchronous Control method of evaluating asynchronous control that considers both TP and FP rates is the use of receiver operating characteristic curves.

Receiver Operating Characteristic In signal detection theory, receiver operating characteristic is a graph of the sensitivity for binary classifier system. Define an experiment from positive and negative. The four outcomes can be formulated in a 2x2 confusion matrix Actual value Prediction outcome P n Total P` True Positive False Positive N` False Negative True Negative P = 100 N = 100 Confusion matrix

Receiver Operating Characteristic To draw a ROC, only TP rate and FP rate are needed. A ROC is defined by FP rate and TP rate as x and y respectively. TPR : sensitivity, FPR : 1-sensitivity ※ Terminology and derivations from a confusion matrix … Equation 1 … Equation 2 … Equation 3

Receiver Operating Characteristic Example of ROC

Results ROCC of the three method

Conclusion Asynchronous control is the most natural and user-friendly mode of device control. LF-ASD works with high accuracies of more than 97 percent under low FP. These brain-switches could be used in devices such as environmental controllers or virtual keyboards

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