**Real–Time Low–Latency Estimation of the Blinking and EOG Signals**

Robert Krupi ´nski and Przemysław Mazurek *Department of Signal Processing and Multimedia Engineering West Pomeranian University of Technology, Szczecin Poland*

### **1. Introduction**

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optimization of a broadband mini exposure chamber for studying catecholamine release from Chromaffin cells exposed to microwave radiation: Finite-difference time-domain technique. *IEEE Transactions Plasma Science*, Vol. 34, No. 4, (August Electrooculography biosignals (EOG) are very important for the eye orientation and eyelid movements (blinking) estimation. There are many applications of the EOG signals. Most important applications are related to the medical applications [Duchowski (2007)]. The EOG signal is used for the analysis of eye movement in the selected medical test of the eye related health problems. It is also important for the sleep analysis. The EOG signal has much higher level than the important EEG (electroencephalography) signals and should be removed from the EEG measurements [Duchowski (2007); Shayegh & Erfanian (2006)]. The reduction of the EOG artifacts from EEG is considered by many researchers and it is also important for the practical applications of the EEG–based Human–Computer Interfaces.

The EOG and blinking signals are used in Human–Computer Interfaces in: the ergonomics, the advertisement analysis [Poole & Ball (2005)], the human–computer interaction (HCI) systems (e.g. a virtual keyboard [Usakli at al. (2010)], the vehicle control [Barea et al. (2002); Firoozabadi (2008)], the wearable computers [Bulling et al. (2009)]), and the video compression driven by eye–interest [Khan & Komogortsev (2004)].

Many alternative oculography techniques are available. The applications of the EOG signals for the HCI applications should be considered as one of the available techniques. The most important disadvantage is the long–time stability of the measurements and the influences of the other factors like light sources. The video–oculography (VOG) is interesting alternative, but the long–time influence of the infrared illuminators usually used on the eye has not been well tested. The infrared oculography (IROG) applies a small set of the illuminators (IR LEDs) and IR sensors for the estimation of eye movements.

The recent application of the EOG signal is the computer animation. The estimated orientation and blinking signals are used for the control of eye and eyelid of the human–generated avatar [Deng et al. (2008)]. This is specific for the motion capture technique [Duchowski (2007); Krupi ´nski & Mazurek (2009)] that, for instance, was used successfully in Beowulf movie [Sony et al. (2006); Warner Brothers (2008)]. Such a motion capture technique is alternative to the video–based motion capture systems fixed to the human head.

A measured biosignal has two important subsignals: electrooculography and blinking. Both of them should be separated and the interesting parameters should be estimated. The

**LEFT RIGHT UP**

a DC signal.

**REF**

Fig. 2. Different measurement systems: 3/4, 4/5, and 7/8

**L R**

Real–Time Low–Latency Estimation of the Blinking and EOG Signals 315

is important especially for the medical purposes. The configuration 4/5 is the compromise between both mentioned configurations. The large number of electrodes reduces the long time reliability due to the degradation of skin contact. The reduced number of electrodes is preferred for the applications where the touching of the human face is possible. The wires located especially below eyes in the 4/5 and 7/8 configuration is one of disadvantage. The

The number of electrodes depends on the acquisition systems. The first number represents the number of active electrodes used for measurements and the second number is the total number of electrodes. The additional electrode (the number 4 in the 3/4 configuration) is the reference electrode (REF). The acquisition systems typically use differential inputs. Such input type is preferred due to better SNR. Two channels are used and the first one is the LEFT–UP and the second one is the RIGHT–UP. The example signals are shown in Fig. 3. High impedance inputs are necessary due to the high resistance of the voltage source. The additional suppression of the 50/60 Hz interference is necessary [Prutchi & Norris (2005)], because the power lines are the source of the biosignal disturbances for the EOG signal, which has bandwidth about 200 Hz. Filtering techniques and appropriate wiring are used for the reduction of power lines interference. High frequency power line interference is omitted if a measurement system has the low–pass properties. The main source of high frequency interference is an incandescent light source. The power line interference is additive to a biosignal, especially, if the measurement systems wires are not shielded. Some portion of

The long time stability of the skin contact is obtained using the adhesive electrodes or an electrogel. The Ag/Ag–Cl electrodes are used typically. Such electrode types are conductive, but the other types (e.g. capacitance–based) are also used. The conductive electrodes support

The EOG biosignal needs a much higher sampling rate in comparison to other biosignal measurement systems. The sampling rate should be about a few hundreds samples per second. The low–pass filtering property of the measurement system is necessary. The AC coupling application used for the suppression of the DC signal is not correct. The DC level and low–frequency components corresponds to the eye orientation. The band–pass filtering in some measurement systems makes the differentiation of signals and the correction of

**REF**

**L R**

**C**

**LD RD**

**RU**

**REF**

**LU**

**LU**

**LD**

3/4 configuration allows the placement of electrodes in less visible parts of a face.

the power line interference occurs between electrodes on the human body.

**2.3 Measurements settings and signal processing**

measurements very hard or not possible.

possibilities of application of the HCI system based on EOG depend on the biosignal measurement system and digital signal processing techniques applied to the obtained signals.
