Page 94 - Handbook of Biomechatronics

Sensors and Transducers 89

6.5 Eye Movement
Where a person is looking is another potentially useful signal. Eye tracking
can be done through three main ways: tracking the movement of something
attached to an eye, generally a special contact lens, visual observation, or
electrooculogram (EOG) (eye muscle electrodes) (PASCO, n.d.).
A special contact lens can be fit with electrical coils. As the coils move,
they disturb the electrical field. These disturbances can be measured and
converted to movement profiles.
Video cameras with tracking algorithms can be setup to record and track
the position of the eye. Postprocessing of the video data is performed for eye
movement analysis and interpretation.
EOG electrodes perform a similar function as EMG. The muscles
contract which release a voltage. Through precise placement of the EOG
electrodes, the orientation of the eye can be sensed (Fig. 31).
Another measure of prosthesis performance is mental load. You decide
to measure the mental load Jacob experiences while using his old prosthesis
compared with his new prosthesis. To do so, you setup a screen in front of
the test treadmill. As Jacob is using the treadmill at various speeds, you show
an image on the screen and measure the time it takes for Jacob to notice the
image. Using EOG electrodes, you are able to measure a precise time
between the appearance of the image and Jacob noticing it. You hope that
the new prosthesis will require less mental load, or a smaller time difference
between displaying the image and Jacob’s eyes moving toward the image.

Fig. 31 Placement of electrooculogram (EOG) electrodes.