1. Eye Movements, Eye Blinks, and Behavior Nicole Tindall, Kylie Gray, and Sarah Leis

2. Part I: Eye Movements and the EOG Nicole Tindall

3. The Control of Eye Movements Eye movements are used to fixate objects so that they fall on the fovea of the eye Occipital and frontal cortices are involved in eye fixation The eye muscles are innervated by the 3rd (oculomotor), 4th (trochlear), and 6th (abducens) cranial nerves Three sets of muscles are used to move the eyes: Superior and inferior rectus Lateral and medial rectus Superior and inferior obliques

4. Voluntary vs. Involuntary Eye Fixations Voluntary Fixations: when the eye focuses on an object of choice Example: reading Controlled by the prefrontal cortex Involuntary Fixations: constantly occuring Controlled by the occipital cortex

5. Types of Eye Movements Saccadic- movements from one fixation point to the next Saccade variables: Saccade latency- time between presentation of stimulus and fixation Saccade amplitude- distance covered by eye during saccade Direction of movement- whether it is horizontal or vertical movement Velocity- speed of the saccade Fixation pause time- occurs between fixations

6. Types of Eye Movements (Cont�d) Smooth Pursuit- movement the eyes make when following a moving object Example: following a bird in the sky Smooth Compensatory- this movement corrects for differences in head tilt so that the image remains upright

7. Types of Eye Movements (Cont�d) Nystagmoid- abnormal oscillations of the eye Causes: Eye defects Impairment of vestibular (balance) system Impairment of visual or vestibular pathways in the CNS Rapid Eye Movements (REM): Occur during sleep Last anywhere from a few minutes to more than a half-hour Eye Blinks: (3 types)

8. 3 Types of Eye Blinks Voluntary blink: consciously close the eyes Blink Reflex: when the eyes blink to act as a defense mechanism in response to a potentially harmful stimulus Keeps the cornea healthy by keeping the surface moist Occurs about 15,000 times/day (about 15-20 times/min in relaxed state)

9. Recording Eye Movements/Blinks Four methods: Contact-lens method Corneal reflection method Television camera scanning Electrooculogram (EOG)

10. Electrooculogram (EOG) Records the movements (and direction) of the eyes by electrodes placed over the muscles that move the eye Can have binocular or monocular set-up (binocular more reliable) Head must be kept still so the center of the visual field is constant Ideal impedance of the electrodes is under 2,000 ohms (we have been dealing with impedances under 50 Kohms)

11. The EOG Can Record: Saccadic movements Smooth pursuit movements Nystagmus Convergence and divergence of the eye REM during sleep

12. EOG Complications 3 problems to be cautious of: Small magnitude of EOG signal Skin potential that are the same frequency as the EOG signal Slow drift- steady deflection of recording in one direction Caused by unclean electrodes and poor contact with the skin

13. Binocular Electrode Placement Electrodes A & B are used to measure horizontal eye movements Electrodes C & D measure vertical eye movements Electrode E is the ground