smooth persuit + saccades
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6 Terms
Saccades
Saccades
Eye movement systems
1.Ā Ā Ā Ā Ā Ā Saccade ā fast
2.Ā Ā Ā Ā Ā Ā Smooth pursuit ā slow
3.Ā Ā Ā Ā Ā Ā Vestibular ā slow
4.Ā Ā Ā Ā Ā Ā Vergence ā fast + slow
5.Ā Ā Ā Ā Ā Ā Optokinetic ā fast + slow
Ā
Saccades
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Pulse-step mechanism
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Burst cells - Generates pulse ā high freq to overcome drag of orbital tissue + produce eye movement
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Pause cells- Activate to stop other eye movement
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Neural integrator - Calibrates new eye position
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Tonic cells - Activate to hold new eye position
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Retina error ā diff between target + endpoint ā of eye miss target
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Continuous feedback system to reduce error
Types of saccades
Types of saccades
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Visually guided- eye moves towards stimulus
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Reflexive vs scanning
oĀ Ā Ā Reflexive - appearance of a peripheral stimulus, or by the disappearance of a fixation stimulus
oĀ Ā Ā Scanning ā explores visual scene
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Memory guided ā move towards a remembered target
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Anti-saccade (eye moves away from stimulus)
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Predictive (object is moving in a predictive manner)
Smooth pursuit
Slow eye movement
Continuous input
Input signal is retinal error velocity
Occasionally, saccade required before pursuit movement (āstep-rampā stimuli)
Maximum sustained velocity of 90 degree/sec
Ā
Stimuli
āMotion of image across central retina
āProprioception
āFixation of moving target
Ā
Response after latency of 125msec
Maximum sustained velocity of 90 degree/sec
Vestibular eye system
Continuous feedback system
ā¢Ā Ā Ā Ā Ā Ā Ā Conjugate, smooth eye movements
ā¢Ā Ā Ā Ā Ā Ā Ā Stabilises eyes regarding the environment
ā¢Ā Ā Ā Ā Ā Ā Ā Peak velocity up to 300 400 degree/sec
ā¢Ā Ā Ā Ā Ā Ā Ā Latency between head & eye movement = 15 msec
ā¢Ā Ā Ā Ā Ā Ā Ā Stimulation
ā¢Ā Ā Ā Ā Ā Ā Ā Semicircular canals: type of head movement
ā¢Ā Ā Ā Ā Ā Ā Ā Otolith organs: gravity and acceleration
ā¢Ā Ā Ā Ā Ā Ā Ā Continuous feedback system ā as with saccades
Optokinetic
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Fast & slow
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Velocity builds to equal the surrounding
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Stimuli = sustained head rotation, and combines vestibular response
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Latency of 100 msec
Vergence eye system
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Fast & slow
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Stimuli; target along z-axis
-Ā Ā Ā Ā Ā Ā Ā Ā Ā retinal disparity
-Ā Ā Ā Ā Ā Ā Ā Ā Ā retinal blur
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Synkinesis (with accommodation)
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Continuous feedback system
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Latency of 160 msec
-Ā Ā Ā Ā Ā Ā Ā Ā Ā Maximum velocity of 20 degree/sec
Z axis with eye movement = abduction/adduction (horizontal