Movements of the Eyes EOG

The fovea, a small area in the retina, has the highest number of cones (which are sensitive to color), giving us sharp vision.
Our brain tries to keep important visual details focused in the fovea when there’s enough light.

To focus on things we're interested in, we need to move our head and/or eyes. This is called visual tracking.
Small, quick eye movements called microsaccades happen automatically.
We can also control our eye muscles willingly.

There are six muscles that move the eyeball:
- Lateral rectus (controlled by cranial nerve VI)
- Superior oblique (controlled by cranial nerve IV)
- The other four are controlled by cranial nerve III.
Eye movements need to work together for us to perceive depth by comparing images from each eye.

The human eyeball acts like a battery, with a voltage between the front (cornea) and the back (retina).
Moving the eyeball creates voltage changes that can be measured:
- Electrodes are placed next to the eyes for horizontal movements and above/below them for vertical movements.
- The measurement is close to zero when the eyeball is in the center; moving the eye causes a positive voltage change.
- The signal from EOG directly relates to how much we move our eyes (approximately 20 mV for each degree), helping to find where we are looking.
- Typical accuracy is 1.5-2 degrees, and we can measure ranges of ±70 degrees both vertically and horizontally.

The EOG signal usually ranges from 0.05 to 3.50 mV, and it measures activity from 0 to 15 Hz.
After focusing on something for a while, the signal returns to its original level.
Movements in the face or jaw can add noise and errors to the EOG signal.

EOG is used less often now for tracking gaze direction; more commonly, cameras are used in experiments.

Measures changes in pupil size controlled by the autonomic nervous system:
- The sympathetic system causes the pupils to dilate (controlled by cranial nerve V).
- The parasympathetic system causes them to constrict (controlled by cranial nerve III).
The pupillary response reacts to tasks, indicating changes in pupil size due to stimuli.
Pupil size can show emotional responses:
- Dilation can indicate attraction, while constriction can signal unappealing stimuli.
It also relates to cognitive effort and emotional states like sadness or fear.

Eye-blinking in response to sudden stimuli can indicate emotional arousal when assessed through EMG (electromyography).

EOG helps track where we look and how long in experiments about thinking processes.
It's important in sleep studies to identify rapid eye movement (REM) phases.
It is also used to investigate how visual stimuli affect attention and laterality.

Movements of the Eyes (Electrooculography, EOG)

Importance of Visual Processing: Vision is crucial for understanding our environment, involving complex processing steps.
Retina Structure: The fovea in the retina has the most cones for sharp, color-sensitive vision.
Eye and Head Movement: Visual tracking requires moving our head and eyes, with small, involuntary movements (microsaccades) occurring as well.
Eye Muscles: Six muscles move the eyeball; lateral rectus (cranial nerve VI), superior oblique (cranial nerve IV), and four others (cranial nerve III). Coordinated movements help perceive depth.
Electrooculography (EOG) Mechanism: The eyeball has a battery-like voltage. Movements create measurable voltage changes using electrodes. Typical accuracy is 1.5-2 degrees.
EOG Signal Characteristics: Ranges from 0.05 to 3.50 mV, measuring eye activity up to 15 Hz.
Limitations of EOG: Less commonly used today; cameras are preferred for tracking gaze direction.
Pupillography: Measures pupil size changes, indicating emotional responses and cognitive effort, controlled by the autonomic nervous system.
Startle Reflex Measurement: Eye-blinking in response to stimuli signifies emotional arousal, measured through EMG.
Applications: EOG is used in experiments about attention and in sleep studies to monitor REM phases.