Pursuit Eye Movements Flashcards
Ocular pursuit of the eye appeared late in the course of evolution and followed appearance of ___ which exists in primates (and reptiles)
the fovea
Which species have two fovea?
birds
Which species have an area centralis with more cones but more rods overall
cats/dogs (night vision)
T/F we can track an object without a fovea
false
How do species without a fovea track movement?
saccades
What is the negative feedback in pursuits?
inhibitory closed loop, uses image motion as central command to efferent pathway
T/F pursuits can modify themselves while movement is still going on
true
Which has more complex neurology, pursuits or saccades?
pursuits
How does negative pursuit feedback correct for too fast or too slow?
too fast– slow eye movement, too slow–put in corrective saccade to keep up
How does the visual system know if the pursuit is accurate?
compare target motion and image motion on the retina
What are the solid and dashed lines on the pursuit model diagram?
solid–flow of neural signals
dashed–physical events
What is the positive feedback in pursuits?
eye velocity; helps get a sense of the degree of error
Where does the afferent pathway info go?
summative area, like neural integrator
When does the efferent pathway of a pursuit begin?
once target velocity has been reconstructed following eye velocity positive feedback
When does pursuit command happen?
After positive feedback and efferent pathway
What are the 3 afferent pathways?
retinal acceleration error, retinal velocity error, and retinal position error
How long is the delay between target motion and afferent pathways?
90 msec
T/F afferent pathways need to be summed before going to efferent pathways?
true
As target velocity increases, pursuit gain…
decreases; especially in older population
Where do young people start to see a decrease in pursuit gain?
40-50 deg/sec drops to gain of .9-.8
When do older people decrease pursuit gain to 0.8
target velocity of 10 deg/sec
What is pursuit latency?
time take from the decision to move to the beginning of the actual movement
What is pursuit latency for fast targets?
100 milliseconds +/- 5 msec
What is pursuit latency for slow targets (less than 5 degrees per second)?
up to 125 msec
In general, the slower the pursuit, the longer the…
latency
Rank the latency of eye movements from lowest to highest
VOR, pursuit, vergence, saccades
Rank the velocity of eye movements from fastest to slowest
saccades, VOR, pursuit, vergence
What is the latency of a smooth pursuit?
100-125 msec
What is the velocity of a pursuit?
80 deg/sec
What is the latency of a saccade?
200 msec
What is the velocity of a saccade?
1000 deg/sec
What is the velocity of VOR?
300 deg/sec
What is the latency of VOR?
15 msec
What is the latency of vergence?
160 msec
What is the velocity of vergence?
10 deg/sec
How long can eye velocity match stimulus velocity?
to 80 deg/sec
Gaze orientation was one of the first functions that required the development of a brain that could…
predict, be curious, and simulate action
What two things allow for pursuits?
cortical development and precise foveal function
What is taxis?
orientation towards a sensory source ex: phototaxis, heliotaxis, thermotaxis, etc
What four things does gaze orientation encompass?
projection, questioning, visualization, and prediction
Berthoz says gaze orientation is
stationary locomotion
What are the two frames of reference?
egocentric and allocentric
What is egocentric?
reference is relative to self
What is allocentric?
reference is relative to objects in the environment
Which frame of reference develops first?
egocentric
How does a baby direct its gaze?
using the body and turning head and eyes about its body axis
Before 18 months babies fixate on
a landmark to which they anchor their progression around the room
What is the first sign a baby is constructing allocentric relationships?
locating an object in the environment
What happens if an baby’s anchor point is hidden?
reverts back to egocentric strategy
After 18 months an infant can…
mentally update his position in the room while he is walking, employing mechanism of mental rotation and translation
T/F the intervention of high-level cognitive mechanisms in adaptation to sensory conflicts is really a problem of frames of reference
true
What is one of the most important aspects of adaptation?
ability to move from one frame of reference to another and to combine them
What do patients need to relearn after VOR lesion?
how to move from one frame of reference to another
What is maximum eye velocity for pursuits?
80 degrees/sec
What happens if target motion is faster than 80 degrees/sec?
need saccades to get back on target; older=more catch-up saccades
What is natures way around the slowness of pursuits?
prediction
Why is batter unable to maintain tracing when ball is at close distance?
high angular velocity
The faster the pitch…
the farther away from home plate your eyes can accurately track the ball
What are 3 strategies batters use to track a ball?
track w/ eye movements only and fall behind the last 10 feet; track with head movements and pursuits and fall behind in last 5 feet; use pursuits, then saccade to predicted point, continue to follow with peripheral vision, and resume smooth pursuit tracking at end with ball’s image on fovea
T/F batters use vergence eye movements
false
Describe the flight of the baseball in thirds
1/3 batter forms mental model of trajectory, 2/3 observe difference b/w actual and mental, update mental and finalize swing, 3/3 observe errors in mental model to better track the next pitch
Superstars have success because:
faster pursuit, ability to suppress VOR, anticipatory saccades, prediction
How do we quantify quickness?
latency of saccadic eye movement system and eye-hand reaction time– lab only not clinic
What is zero-latency tracking?
overcoming time delay and tracking predictable targets with no delay provided the target position waveform is smooth and predictable with frequency b/w 0.1 and 1.0 Hz with small accelerations
What does the time to collision concept relate
T=relation b/w observed diameter of the car in front which you are approaching and the speed with which this diameter expands
If movement proceeds at constant velocity, time to collision can be evaluated by…
speed with which the retinal image of the object expands
Time to contact is given solely by…
retinal cues
How does our hand adapt its shape to the apparent shape of an object before contact?
we sample, calculate, and open change then change shape without conscious thought
T/F the muscular activity of the arm is always initiated at the same time (before contact), no matter what the velocity of the target
true
T/F the hand always take the shape of the object we are about to catch at the same distance from the hand
false– just happens at the same time before catching no at the same distance from the hand
How does tennis relate to time to collision?
the movement of the racket is constant and independent of the approach velocity, thus the beginning of the movement may in fact be adjusted by the value of the T margin– adjust based on calculation of retinal slip made internally
How much time is needed to estimate distance/time to contact?
need 240-300 msec to catch a ball
To catch a ball traveling at 10 meters per second, the athlete has a temporal window of ___ during which his hand can remain closed
50 msec
Catching a ball is preceded by __ that prepares for impact and is followed by a ___ induced by the impact
anticipatory muscular activity, reflex activity
Subjects seem to base their response, whether anticipation or reflex on…
prediction of the dynamic properties of the ball under the influence of gravity
