Flashcards in Eye Movements Deck (21)
What are the four types of eye movements?
1. smooth pursuit
to keep an object on the fovea)
1. rapid, ballistic “jumps” to bring an object onto the fovea
2. There is suppression of visual information during a saccade
3. Why you don’t see a blur of the visual world during a saccade
4. Average of 3 saccades per minute during the day!
1. neither is monosynaptic
2. VOR: Vestibular ocular reflex (vestibular system)
3. OKN: optokinetic nystagmus (visual object movement)
moving the fovea to an object closer (convergence) or farther away (divergence)
Conjugate eye movements:
1. both eyes move in the same direction.
2. Initiated by a variety of sensory inputs, visual and vestibular inputs most important
Vergence eye movements:
1. eyes movie in opposite directions
2. Example – both eyes turn nasally (“cross-eyed”) during the near reflex
1. the combination of changes our eyes undergo when we attempt to focus on a near object.
2. Both medial recti contract, pulling the eyes nasally.
3. Pupils constrict to increase the depth of field
4. Ciliary muscles contract, allowing lens to become fatter and thus focus on a near object.
near reflex is driven by
visual input to association areas of the visual cortex
saccade is a
a rapid movement that brings the eyes to a predetermined target or position at a rate of up to 700˚/second
(contrast to smooth pursuit, which tops out at 50˚/second).
Saccades can be used to
1. restore the eye toward the center of orbit during some tracking tasks, whether it was visually or vestibularly evoked.
2. used in voluntary way to rapidly foveate an interesting peripheral stimulus, moving the eye away from the center of orbit.
Visually-evoked saccades are ballistic in character
1. Programmed to foveate a particular target, even if the target moves after the saccade is initiated.
2. A very high frequency burst is needed for initial acceleration
3. A carefully calculated steady rate is required to maintain the new eye position
Rhythmic pattern of saccades and tracking movements elicited by a simple stimulus like a rotating striped drum
Saccades control centers are in the ____
cortex and the superior colliculus.
Motor neurons and pattern generators for saccades are located in the ___
midbrain and pons.
Vertical saccades –
pattern generator located near the oculomotor nuclei (midbrain)
Horizontal saccades –
pattern generator located in the reticular formation near the abducens nucleus
(in the paramedian pontine reticular formation (PPRF))
motor neurons for vertical eye movements are in the _____, while motor neurons for horizontal eye movements involve the ______.
Horizontal saccades are driven ____
E.g. saccade to the left is driven by activity in the right frontal eye field.
The frontal eye field in the frontal lobes of the cortex can activate saccades by two pathways:
1. Direct to the reticular formation
2. Via the superior colliculus and then to the reticular formation