Motion Artifact During Surface EMG/EOG Collection

There are several sources of motion artifact that can interrupt the EOG signal that is being acquired. The main ones that must be filtered out or taken account of are those created by neck movements (see figure 17), blinking of the eyes (see figure 16), or EMG signals from surrounding muscles of the eyes. Another cause of motion artifacts can be the involuntary movement of the electrodes on the subject’s face as well as the movement of the subject himself. In order to account for these artifacts in the signal reading, their frequency range must be filtered out. The frequency range of these motion artifacts are small however, not that much smaller than that of the EOG signal. Therefore to stop the crossing over of the two frequencies the artifacts must all be filtered out. Below are images of the eye blinking and neck movement signals that will be filtered out using the MATLAB software [9].

Figure 16: Effect of eye blinks on EOG signal [9]

Figure 17: Effect of neck movement on EOG signal [9]

Some other sources of noise that can obstruct the EOG from being ideal are involuntary blinks and variations in the characteristics of skin-electrode interface. Both of these sources of noise can affect even a filtered signal.

Figure 18: EOG signals for various actions that include the eye motions and involuntary blinking

As shown (see figure 18), the involuntary blinking has about half the amplitude of the voluntary blinking, roughly 1.75V. The frequencies that the bandpass filters accepted ranged from 10 Hz to 150 Hz.