Saccades (M1) Flashcards
What is the stimulus for saccades?
displacement from the fovea
Which model of ocular direction sensing has proprioceptive information from EOMs going into direction centers?
inflow model
Which eye directions are “sensed”? 1. Which are “cortically computed”? 2
- ocular and oculocentric
2. egocentric
What is the normal percent of saccades/fixations that are regressive?
10-15%
What is a saccade that has too long of a pulse called? 1. Too short of a pulse? 2
- hypermetric saccade
2. hypometric saccade
When are saccades slower than normal (don’t follow main sequence)?
- infants
- alcohol use
- voluntary control
- fatigue
- disease: MS, stoke, tumor, aneurysm
What are eye movements that get you where you are supposed to be and make up for inaccurate saccades called?
glissades
What is the percentage of total reading time taken up by eye movements typically?
no greater than 10%
What is an elevation in the visual threshold before, during, and after a saccade called? 1. What does this prevent? 2
- saccadic suppression
2. prevents smearing of retinal image
Do large saccades (greater than 20deg) usually overshoot or undershoot? 1. What corrects for this? 2
- undershoot
2. corrective saccade (not glissade)
What is a large right to left saccadic eye movement that shifts eyes from near the end of one line to near the beginning of the next line of text called? 1. When does it usually begin? 2 .When does it end? 3
- return-sweep saccade
- 6 characters from end of one line
- 6th or so character of next line
What is a saccade directed from right to left (backwards) on the same line of text called?
regressive saccade
What is it called when the patient points to an object that they are receiving visual info from but they cannot see their hand? 1. How does this present during an EOM paresis? 2
- pastpointing
2. when only using paretic eye, overshoot location with point
During forced duction of the eye does the image appear to move in the positive, negative or neither direction? 1. Does this provide evidence for the outflow or inflow model of ocular direction sensing? 2
- negative direction
2. outflow bc if inflow then would appear to be no movement
What is responsible for the lack of blurring during a saccade?
saccadic omission
When should abnormal saccades be referred?
- suspect brain lesion (imaging)
2. kids (eye movement training)
What is the length of time (usually in ms) that the eye pauses or remains fixated on a word called? 1. What is the numerical average? 2
- fixation duration
2. 225ms (depends on text)
For reading, when does the number of fixations per portion of text increase?
- increased difficulty of material
2. poor readers
What causes the greatest changes in latency period?
providing subjects with prior info about movement of the target (decreases it)
What are the movements that are done intentionally that is a saccade to the opposite side that the target moved to? 1. When are these poor? 2
- antisaccades
2. schizophrenia and other frontal lobe problems
What are possible causes of abnormal saccades?
- lesion in brain pathway (MS, stroke, tumor, aneurysm)
- poor attention
- poor coordination
What is the fixation that occurs after a regressive saccade called?
regression
What part of the saccade keeps the eye in position? 1. What does the neural pulse overcome to occur? 2. What is the neural pulse created from? 3
- step
- “elastic” forces tending to pull eye back to original position
- neural integrator
When are changes in egocentric location important clinically?
post TBI (especially parietal lobe damage)
What part of the saccade drives the eye to a new position? 1. What does the neural pulse overcome to occur? 2
- pulse
2. viscous resistance of the globe and orbital contents
What is the saccadic main sequence used for? 1. What is the equation for this? 2
- see if motion was saccade and whether it was normal
2. duration = (2.2msec/deg)*(amplitude) + 21msec
What does drug induced ocular paralysis with curare cause?
- pastpointing
2. illusion of movement
What is oculocentric direction sensed with?
retinotopic information
Which model of ocular direction sensing has innervation to the eye to move and the same info is sent to the direction centers?
outflow model
For large amplitude saccades, what is the peak velocity?
700deg/sec
During resisted forced ocular duction of the eye does the image appear to move in the positive, negative or neither direction? 1. Does this provide evidence for the outflow or inflow model of ocular direction sensing? 2
- negative
2. outflow bc image does not move (inflow) but appears to move for the person
What is the average magnitude of movement of eyes across the page while reading? 1. Range? 2
- 1.5deg or 8 characters
2. 0.5-4deg or 1-18 characters
What are the issues to the saccadic movement that are common in abnormal saccades?
- look slower
- longer latency
- inaccurate
If a flash occurs in the middle of a saccade, what is the relative blur perception?
blurry percept of the room
If a flash begins before a saccade and ends after, what is the relative blur perception?
total absence of blur perception
What is the amount of print (words) one can perceive and process with each fixation called?
average span of recognition
What are saccades where there is a really short latency due to a warning period called?
express saccades
What is the visual direction of an object specified with respect to the straight ahead (and associated greek letter)?
egocentric direction (χ)
What is the typical latency period length average for a saccade? 1. Range? 2
- 200ms
2. 120-350ms
What is the number of words read per unit time called? 1. What is average for college students? 2
- reading rate
2. 200 to 350 words per minute
What is the duration of response?
from when the eye starts to move to when it is actually pointed at the target
What is ocular direction sensed with?
extraretinal information
What is the equation that can be used to compute the egocentric direction?
χ = α + β
What is the visual direction of an object specified relative to the “line of fixation” called (and associated greek letter)?
oculocentric direction (β)
What is the direction of the line of fixation measured from the straight ahead position called (and associated greek letter)?
ocular direction (α)
In what range are most naturally occurring saccades? 1. What is required if a saccade greater than this occurs? 2
- less the 15deg
2. eye movement combined with head movement
Which provides for faster saccades: toward or away from straight ahead?
toward
What are the two plots that make up the main sequence?
- duration vs amplitude
2. peak velocity vs amplitude
