Eog & Emg Based Virtual

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AMIT KUMARB080540EC

S7- ECE


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What Is BCI ?BCI - communication channel through EOG& EMG signals.In situation of disease, there may beinability to communicate with othersthrough means such as speech/typing .Eye movement tends to be one of the last

remaining active muscle capability forpeople with neurodegenerative disorders,such as ALS. So, there is a need for eyemovement based system to enable

communication.


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EEG SIGNAL :-

*Technical artifacts :- noise from electricpower source.

* biological artifacts :- (eye artifacts , ECG

, EEG etc..).Eye blink is not an artifacts and is a controlsignal to select the block /char in the virtualkeyboard .The kurtosis coefficient and amplitudecharacteristics are used to detect the controlsignal.


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Armen R developed an EOG based systemfor computer control.

This system is created to allow user tointeract with a computer only by movingtheir eyes.


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Ternary keyboard for electro--cular spelling interface.

Each successive eye movement command left , right andcentre command .In this system, eye gaze direction is used to navigate aparticular letter on the virtual screen keyboard & EMGsignal click to navigated letter.Eye gaze direction is obtained from EOG signal & theEMG signal is recorded from the eyebrow of the user .We got this idea from who developed EMG basedHANDS-FREE WHEELCHAIR control with EOGattention shift detection.They used the EOG signal for speed control of thewheelchair and the EMG to select a particular direction.


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BCI A communication channelMental activities leads to change of electrophysio -

-logical signals like the EEG.The BCI detects such changes and transforms it into acontrol signal which can be used to control a simple videogame , motion of a wheelchair.The first step in developing an effective BCI paradigm is todetermine suitable control signals from the EEG.A suitable control signal has the following attributes.* it can be precisely characterized .

*it can be readily modulated /translated to express theintention.*It can be detect and tracked consistently& reliably.The EEG eye blink signals have all the above 3 attributes &hence can be used as a control signal .


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EOG is a method for sensing eye movement and isbased on recording the standing corneal-retinalpotential arising from hyperpolarisations &depolarization existing b/w cornea & retina.

The potential considered as steady electrical dipolewith a ive pole at retina & +ive pole at cornea.Human eye is like a spherical battery that the centre

of cornea is +ive & the retina isive.The micro-current flow radially from the +ive pole to

ive pole of the battery.


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EOG RECORDING

The EOG is captured by 5electrodes placed arround theeye.The EOG signals are obtained by

placed 2 electrodes to the R &L ofthe eye(d-e) to detect horizontalmovement & another pair aboveand below the eye(b-c) to detectvertical movement. A ref.electrode is placed on the forhead.EOG changes 20mV for each

degree of eye movement.


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EOG signal is a result of a number of factors,including -eyeball rotation & movement, eyelidmovement, head movement.To design a ideal system , an high gain differentialamp(1000-5000) is used , with HPF (Fc- 0.05Hz) & aLPF (Fc-35Hz)

Ag-AgCl electrode (high impedence). & Si-rubberelectrode (of impedence below 10K ohm).Low impedence range 40-200 ohm , the Si-rubber

electrode is more suitable to sense the very lowamplitude bio-signals as compared to otherelectrodes (Ag-AgCl).


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It is a technique for evaluating and recordingthe electrical activity of eye brow muscleactivity.

EMG is recorded by using a small wearabledevice that acquires signal from the sensors onthe headband .EMG IS detected b/w 70-1000KHz ,amplitude

range is 10-100microV and freq range of DC -100Hz.EMG signals can be easily separated from theEOG signals using BPF


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Eye blinks are characterized by peaks withrelatively strong voltages .Eye blink classification based on duration

-- Short blink

blink duration < 200ms.-- Long blink blink duration >=200ms.Eye blink classified into 3 types: REFLEXIVE-the eyeblink reflexive is simplest

response & doesnot require the involvement ofcortical structures.VOLUNTARY- blinking due to predetermined

condition.


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SPONTANEOUS eye blinks occur without externalstimuli specified & they are associated with psycho-physiological state of the person .

The kurtosis & amplitude characteristics of the eyeblinks are used to detect the control signals .


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The eye related signal will be predominent inthe frontal & prefrontal regions of the brain .Peak in -ive regions shows an eye open event.

& positive peak shows an eye close event.

An eyeblink signal can be detected by its +ive

&-ive peak occourance.


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The EEG signal is stochastic & set of samples iscalled realizations/samples function x(t) .The expectation is mean of realisation & is c/d

1st order central momentum.2nd order cental momentum is the variance .The sqrt of variance is the S.D, which measure

the spread/dispersion arround the mean.The kurtosis , c/d 4 th order central momentum,characterize the relative flatness & peakness ofthe signal disturbance.


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The kurtosis coefficient of an

event is high when there is aneye blink.

eye event can be detected bykurtosis coefficient.


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the process of selection of a letter from VSK.1st of all the EOG signal is measured using EOGrecording method .

Then , the eye gaze angle is calculated from the EOGsignal using an algorithm . When the curser reachesto the reqd letter , EMG signal is used to make clickon the selected letter .EMG signal is used to make a click because itsaccuracy& clearance.


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Eyeblink are used as input/control signal in thisBCI .the user has to produce an eyeblink in 5s timeinterval . The BCI detects in this 5s intervalwhether eyeblink is present or not.

A single selection can be done in 20 s . In every 5sinterval user should make an eyeblink . So in effectat the end of 20s interval BCI will detect one of thefollowing event .Single eyeblink occurredTwo eyeblink occurredThree eyeblink occurred

Th i l h b (A Z)& h


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The entire alphabet(A-Z)& space characters areavialable in the VK. The total 27 character aredivided into 3 blocks.


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labVIEW is a powerfull GDE for signal acquisition, measurement analysis, & data presentation givingthe flexibilty of a programming lang. without

complexity of traditional development tools.2 process - * front panel

* block diagram code .

Front panel :- the front panel consist of 27 LEDs, onefor each character. When the block/char is selectedthese LEDs glow .


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The actual programming in labVIEW is thedevelopment of the block diagram. The blockdigram code describe the utility of a front panel

object .In the block diagram various loop & structurere used to develop complex algorithms.A while loop in combination with a for loop &other functins calculates the kurtosis value .


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This system is aimed towards development of ausable and low cost brain-computer interface fordisabled and aged persons.

The BCI developed can be used for communicationpurposes, which use eye blinks as control signals,especially for patients those suffering fromAmyotrophic lateral sclerosis (ALS).

The Virtual Keyboard developed obtained a correctspelling rate of 1.00 character/min which is excellent.The spelling rate can be improved by reducing the

time given to produce the eye blink.


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Hari Singh Dhillon, Rajesh Singla, NavleenSingh Rekhi, Rameshwar Jha , EOG and EMG

Based Virtual Keyboard: A Brain-ComputerInterface , Dec 2009, pp 259-262.

Brijil Chambayil and Rajesh Singla,

VirtualKeyboard BCI using Eye blinks in EEG, Nov2010,pp 466-470.


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Eog & Emg Based Virtual

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