Discovering Eye Movement Using Electrooculogram (EOG)

Abstract:

The movement of the eyes can be determined and serve as an indicator of the health of the visual system. This lab experiment was performed by using the BIOPAC program to measure the motion response of the eyes to different stimulations placed along with the course of the electrooculogram. The distinct characteristics of eye movement between different tasks were recorded and compared to the time of moving period and the stationary period. The results found that the response time for moving period is shorter than the stationary period, which indicates the eye spent more time on fixation points. Introduction: The purpose of the various exercises of this experiment were to track eye fixations based on a variety of stimuli and tasks. The eye is modeled as a dipole, with the positive pole at the cornea and the negative pole at the retina. The electrical signal that can be measured from the electric potential field the dipole creates is called the electrooculogram, or EOG.

Eye movements can be tracked by analyzing changes made in the electrical potential field. For example, if the eye moves from center to either left or right, the retina approaches one electrode while the cornea approaches the opposing one (Bulling 2010). Eye fixation is important for environment viewing and maintenance of orientation and equilibrium (Wibbles 2007). Fixation is based primarily on two mechanisms, voluntary and involuntary. Voluntary fixation allows the subject to “lock” and “unlock” visual onto a selected object. In other words, voluntary fixation involves a conscious effort to move the eyes (Uyehara 2008). The unlocking of the eyes is controlled by portions of the frontal lobe, and the locking of the eyes is controlled by the occipital lobe. Refer to Figure 1 for a picture of the visual pathway. EOG 2 Involuntary fixation causes the subject to focus on an object in the field of vision if the subject, or the object moves. Involuntary fixation involves an unconscious effort of eye movement. It is not necessary to move the subject’s eyes in order to compensate for head movement because the eyes and central nervous system do it automatically. Fixation occurs 80-90% of the time. Saccades is another type of eye movement. Saccades are short, jerky movements in response to subject eyes moving from one object to another. For example, when reading, the eyes will make several saccades as the subject reads a line. Eyes can also perform pursuit movements in order to remain fixed on an object. This mechanism allows the subject to detect and predict the course of an object in the visual field (Wibbles 2007).

In table 1, it represents the results of the subject slowly reading 10 to 15 lines of text from a handout, while the computer was recording the subject’s electrooculogram (EOG). The first column labeled line of text shows the first four lines the subject read while hooked up to the EOG. In the second column, the delta T (change over time) was calculated by adding the delta T’s for each period when the eyes were moving for that specific line read. In the third column, the delta T (change over time) was calculated by adding the delta T’s for each period when the eyes were stationary for that specific line read. In the last column, the ratio was calculated by taking the ΔT for when the eyes were stationary for each line and dividing it by ΔT for when the eyes were moving from the same line. For example, when looking at the third line of text read by the subject, the different periods when the eyes were moving for this specific line were added together to get a delta T of 0. 360 seconds.

Conclusion/ Discussion:

The purpose of this experiment was to measure the time changes during the moving period and the stationary period, while the movement of the eyes reacted to different stimulations (Wibbles 2007). The length of the time was recorded by an electrooculogram, where the data was interpreted by blocking off specific time periods. The preciseness and the accuracy of the electrodes around the eyes may be a possible factor contribute to the error in this lab. A solution to this was the use of tape was added around the electrodes to increase the intact with the skin. The program was also calibrated in the beginning of the experiment to reduce the inaccuracy. The results obtained from the horizontal EOG supports the ideal that the electrical difference caused by the anterior part of the eye is more positively charged compared to the posterior part of the eye (Wibbles 2007). Refer to figure 2 and 3 to see an upward peek due to the subject looking to the right, and a downward peek due to the subject looking to the left. The vertical EOG (figure 4 and 5) was performed using the same method, where the upward peaks indicate the eyes were moving up and the downward peaks indicates the eyes were moving down (Uyehara 2008). The third experiment (figure 6) was presented with a tennis ball following a random pattern, where the results shown on the EOG were random with unpredictable peaks (Bulling 2010). This reason for this was because the subject did not have enough time to fixate their eyes on the tennis ball due to it moving at a fast speed. Last, the handout read slowly about 10 to 15 lines (table 1) was used to determine both the horizontal and vertical movement of the eyes. The result suggest that the eyes spent more time on horizontal period (fixation) than the moving period (point to point).