Final Material Flashcards
(80 cards)
Pursuit latency for a fast vs slow target motion
Generally, the slower the pursuit, the longer the latency.
Fast target motion= 100ms latency.
Slow target motion= 125 ms latency.
What are the two summing locations in pursuits
- Retina compared target motion vs eye motion.
2. Other sums retinal velocity error with info that you get out of eye velocity positive feedback loop.
What factors are accounted for within the afferent pathways? Their outputs are combined and integrated before we get to the efferent pathway.
RAE- retinal acceleration
RVE- Retinal velocity
RPE- retinal positional errors
As the target gets faster, the eye matches it- up to a point. At what deg/sec can the eye not keep up anymore?
The eye can keep up with an object trailing at 80 deg/sec with approx 1.0 gain. Any faster, and the eye cannot keep up. You would need some saccades to get back on the target.
Why is gaze orientation so important?
Our brain must be capable of visualization and target predictability (sophisticated cortical development) in order to properly track pursuits. Important that the brain can SIMULATE.
2 frames of reference
Egocentric and allocentric. Transition occurs around 18 months of age.
Pursuit sys is slow. Can only travel up to __ deg/sec. Saccade sys is fast. Can travel up to ___ deg/sec
100
800
Prob bc the pursuit sys involves complex pathways and is more neurologically complicated than a saccade. Natures way around this slowness is prediction.
Best way to track a baseball
Track ball over the 1st part of the trajectory w smooth pursuit eye movements. Make a saccadic eye movement to a predicated point ahead of the ball, continue to follow it with peripheral vision. At the end of the balls flight, resume smooth pursuit tracking w the balls image on the fovea.
Movement across retina stimulates
Pursuits and OKN
VOR compensates for:
OKN compensates for:
VOR: Brief, transient head movements
OKN: Compensates for prolonged, sustained movements. Low frequency.
VOR responds to
Acceleration (angular velocity).
As acceleration becomes constant, VOR ____
Declines and OKN sys takes over.
What is OKAN
when rotation is complete, we should get a nystagmus in the opposite direction. Helps to cancel out this post rotational nystagmus that we naturally have.
OKAN is activated by
Rotational acceleration and velocity. It discharges after input as stopped. Tells EOMs “I want you to put in a compensatory action in the opposite direction to counteract what we should expect to happen based on physics”
Otoliths
calcium particles that sit on top of the gelatin in the macula of the saccule. When head is level, otoliths stay in place.
VOR latency
15 ms. Shortest latency for eye movement.
TVOR (Translational)
When head tilts, you get a gravitational force on the otoliths in a particular direction relative to the amt of head tilt.
Displacement needs to be ___ degrees for VOR to kick in
10-20 degrees
VOR stats
Peak head velocity to maintain VOR:
Peak head acceleration to trigger VOR:
100-250 deg/sec
1000-2500 deg/sec
Signal pathway from otoliths to eyes
Otoliths travels via CN 8 to the Vestibular nucleus –> CN 6 –> CN 3 –> eyes
VOR gain of less than one means
Eye movement is less than head movement.
Why does decreased frequency result in decreased VOR gain?
Bc VOR turns off at low freq and OKN turns on.
At close distances, VOR gain _____
Increases.
How does VOR affect myopes in glasses
As if pt is wearing BO prism. Myopes need LESS gain for a given head movement bc the prism contributes to decrease eye movement amount.
