Brain Interface Design for Asynchronous Control

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What is Neil Squire Society The long-term objective of the brain interface project is to create a multi-position, brain-controlled switch that is activated by brain signals measured directly from the scalp of an individual. They believe that such a switch will allow an individual with a severe disability to have effective control of devices such as assistive appliances, computers Project Background The Neil Squire Society is the organization in Canada that for the past 20 years has used technology, knowledge and passion to empower Canadians with physical disabilities

Introduction(i) design specifically for self-paced or asynchronous control environmentsWithin the context of general brain interface (BI) technology research, The Nail Squire Brain lab has focused on BI system design specifically for self-paced or asynchronous control environments. more naturalThis asynchronous mode of device is more natural than the more commonly studied synchronized control mode whereby the system dictates the control of the user

Introduction(ii) Schemes of Presentation – Presentation about an overview of asynchronous control. –Summary of Neil Squire Society`s effort to develop asynchronous BI system. – Discussion of several major issues that have arisen from asynchronous BI development.

Which feature is used in BCI systems? In typical BCI based on EEG, the operator generates a “control signal” by consciously changing his cognitive state when he wants to control device. temporal patterns, and signal power levelThe change in cognitive state is measured as specific temporal patterns, and signal power level in the operator`s EEG activity Temporal patterns signal power time

Asynchronous Vs. Synchronous

Synchronous Vs. Asynchronous

What is the Synchronous mode? Synchronous mode –In this system, the system initiates the period of control, not the user, and user is expected to be consciously controlling the interface during the control periods likely fig.

What is the Synchronous mode? Drawbacks of the synchronous –BI transducer will make a control signal regardless of whether the person is actually intending control. –User cannot make control signal until system polling period to occur in order to engage BI transducer.

What is the Asynchronous mode? Asynchronous mode alternating periods of attentive idleness and active control –In this system, which we will call asynchronous control applications, are characterized by alternating periods of attentive idleness and active control as illustrated in Fig. require constant users attention and irregular –In this system, there are applications that require constant users attention and irregular, user-initiated control. This system is usually not communications applications but control applications.

Asynchronous Control (i) when control is intended.Asynchronous control refer to the type of control where output signals are changed or commands are issued only when control is intended. remain neutral or unchanged.During the no control(NC) state, one would expect the system output to remain neutral or unchanged. EEG Signal Intentional control No Control When user is intended When user is talking, daydreaming, and thinking

Asynchronous Control (ii) Examples of asynchronous control –turning on lights, changing television channels, and interacting with a computer. –When you remove your hand from your computer mouse, you enter an NC state and the mouse output remains stable and unchanged-that is, the mouse pointer does not continue to move on the computer screen. In other word, The mouse is then available for control simply by replacing your hand. asynchronous control allows the user to define when things happen.In short, asynchronous control allows the user to define when things happen. According to these points, asynchronous control is more characteristic of most real-world control applications than synchronous control.

Asynchronous Control (iii) System idling : The neutral or unchanging system output response desired during periods of NC –For effective system, we should use the idling system to be realized. –This system is analogous to car engine. –Using FP(false positive) rate measures how well BI transducers idle for more complete measure of asynchronous control.

Classification of EEG Device Idle support indicates if the interface device will support idling Available define when the interface device allows user control

Classification of EEG Device Idle support : If control paradigms not support the idling, the system produce an unintended action if and when the user enters the NC state. (Midas touch problem)

Control Paradigm Availability Idle support No idle supportIdle support PeriodicallySynchronousSystem-paced ContinuouslyConstantly engagedAsynchronous Constantly engaged mode is impractical operation where the user is continuously controlling the interface without a break and any NC activity will cause an error.

EEG-Based Asynchronous Brain-Switches

Obtaining the EEG signal related movement Obtain the EEG signals when spinal cord injury (SCI) people and able- bodied people move their finger. –The only difference between the people with (SCI) and those without are the actual physical movements that may or may not occur during their attempted finger movement System of Electrode Placement The international system of electrode placement is the most widely used method to describe the placement of electrodes at specific intervals along the head. Even numbers refer to the right hemisphere and odd numbers refer to the left hemisphere

Electrode placement for LF-ASD Region of the motor cortex Electrode placement for Experiments Motor cortex : The anatomical region of the brain known as Area 4 was given the name primary motor cortex (symbol: M1) after Penfield showed that focal stimulations in this region elicited highly localized muscle contractions at various locations in the body. Penfield

Electrode placement for Experiments Electrode placement for LF-ASD provided uniform coverage of the motor areas (SMA, MI) of the 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. F1-FC1, Fz-FCz, F2-FC2, FC1-C1, FCz-Cz, and FC2-C2 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 system for electrode placement. Region of the motor cortex

Asynchronous Brain-Switches For asynchronous control application Idle support * Idle support * Low FP rates * Low FP rates Specific signal processing algorithm

Classify NC state and IC state Problems in State Classification. i) This needs an indication of intent in order to process the data. ii) It is not case for synchronous applications because user intent is assumed during the control periods.

Classify NC state and IC state Method 1. –Subjects to self-report intent during the data recordingDisadvantage i) Self-report complicates the signal analysis because one does not know exactly when the movement was made. ii) It is hard to provide the user with any form of feedback during these sessions.

Classify NC state and IC state What is the Outlier Processing Method? outlier processing method (OPM) - The outlier processing method (OPM) is the only BCI technique that has been designed specifically to differentiate idle from active EEG in an asynchronous control applications outlier processing method (OPM) - They use the outlier processing method (OPM) for extracting single-trial voluntary movement-related potentials(VMRPs) from EEG related to finger movement.

Classify NC state and IC state Method 2. –Separate the VMRP state from NC state via OPM in the obtained signal. VMRPs has higher relative power than NC state in 1-4Hz bandwidthThey find the feature that VMRPs has higher relative power than NC state in 1-4Hz bandwidth via time-frequency analysis of EEG pattern. low-frequency asynchronous switch design(LF-ASD) Using this feature, they has developed the low-frequency asynchronous switch design(LF-ASD) Feature Space t power

Classify NC state and IC state SCI people and able-bodied people are sameThe BI experiments results by SCI people and able-bodied people are same. In other words, results by actual physical movements and imagery of movements are same. LF-ASD demonstrated TP rates of percent during IC states in combination with low FP rates of percent during NC. The result is independent subjects. When the FP rate is high, the LF-ASD system is frustrating to use. Thus, they intentionally operated the system in this case.

Thank You.

Feature Extraction Methodology First, signals prefiltered between 1-4Hz and the compound feature described by (1)