EOG Signals

Raw EOG signals measure the electric signal from the user’s eyes, that measures all of electric signalling of the electrodes. Raw EOG signals capture both the voluntary and involuntary muscle contractions. The difference between raw EOG signals and ideal EOG signals is that ideal EOG signals filter out involuntary muscle contractions. Below are graphs comparing raw signals to filtered signals:

Figure 13: Graphs comparing raw EOG signals to filtered EOG signals (NEEDS REFERENCE)

The top two graphs (see figure 13) are raw signals that capture all signals with noise and involuntary contractions, while the bottom two graphs represent the positive data without the scattered, erratic noise.

By examining the ideal EOG signal shown below, we can determine the direction of an individual's eyes (see figure 14). When the patient looks either up or right, the wave gradually increases in the positive direction until it reaches about .1 mV (depending on the person), and then the wave drops back to the base line. When the individual looks either down or to the left, the wave gradually decreases in the negative direction until it reaches about -.1 mV and then rises again back to the base line. This ideal EOG signal is rarely obtained due to motion and noise artifacts (discussed in previous posts), however the general shape can be used to determine direction in any scenario (10).

Figure 14: Ideal EOG signal collected from left and right or up and down movement of eyes (10)