Chapter 17 Optokinetic Eye Movements Flashcards
Name the three kinds of optic flow, and give a practical example of each.
- linear: caused by head pitch and yaw yield, i.e. looking to the left and walking forward
- radial: moving quickly toward an object (think about running toward a door straight in front of you)
- rotatory: caused by head roll, i.e. watching a rotating Ferris wheel
Which types of optic flow provides a stimulus to the optokinetic system?
linear and rotatory
*radial optic flow cannot be compensated by eye movements in humans
What is circularvection? When would you perceive circularvection? Have you ever had this experience before?
Circularvection is a large rotating field that induces a pronounced illusion of self-motion in the opposite direction
- when you’re parked on the highway and two large semi trucks start moving forward at the same seed at the same time and you feel like you’re moving backward
- when you’re placed inside a large stripped drum spinning rightward, you will have the sensation that your body is spinning left
What is the purpose of optokinetic eye movements?
maintain a stable gaze for the environment despite head movements
How does the function of the optokinetic response differ from that of pursuit?
Optokinetic eye movements help to stabilize the environment while the body is moving through it, where pursuit eye movements are for following a moving environmental object
*the optokinetic response must be suppressed during smooth pursuits (think bird flying though the forest)
Which two phases of the optokinetic response are observed in ‘railroad nystagmus’? In which direction are these two components in relation to the relative motion of the world outside the train?
- slow phase: linear-negative feedback mechanism (i.e. following an object with your eyes while looking out of the train), with the motion of the world outside
- fast phase: resetting saccade (i.e. a quick reset back to the center when your eyes can no longer follow the object), opposed to the motion of the world outside
In the previous question, the person on the train was moving, and the world was stationary. Can you give an example from daily life where you are stationary but a large external stimulus is moving, and so produces an optokinetic response?
(previous question for reference: Which two phases of the optokinetic response are observed in ‘railroad nystagmus’? In which direction are these two components in relation to the relative motion of the world outside the train?)
When you are standing on the sidewalk and a large truck drives by in addition to other cars
Describe an experiment you could preform to demonstrate the phenomenon of optokinetic afternystagmus.
When an observer watches a large moving field for some time and then is placed in darkness, the optokinetic nystagmus continues to occur, decaying in amplitude with time for ~20 seconds. This is called optokinetic afternystagmus.
You could put someone in a large moving drum and after watching for a while, turn off the lights.
You could be sitting on a train, looking out the window, while you pass though a pitch black tunnel.
What role does velocity storage play in the observed eye movements in your experiment of the previous question?
(previous question for reference: Describe an experiment you could preform to demonstrate the phenomenon of optokinetic afternystagmus.)
The optokinetic afternystagmus is due to velocity storage, an adaptive component that ‘stores’ object velocity and then releases it when the stimulus motion stops. This storage of the object’s velocity allows optokinetic afternystagmus to occur even after motion has stopped.
What role does the development of cortical pathways during infancy have on the observed characteristics of the monocular optokinetic response during infancy?
Because the cortical pathways develop during infancy, there are expected and observed asymmetries in monocular optokinetic responses during this time because the second stream is immature until about 12 weeks of age.
What are the main centers in the sub-cortical and cortical pathways serving the optokinetic response?
Sub-cortical pathways:
- AOS - accessory optic system
- NOT - nucleus of the optic tract
Cortical pathways:
- V1 - visual cortex
- LGN - lateral geniculate nucleus
- MT - middle temporal area
- MST - medial superior temporal area
The right nucleus of the optic tract responds to __(a)__-ward target motion viewed by the __(b)__ eye. This direction is __(c)__-al to __(d)__-al.
The right nucleus of the optic tract responds to (a) RIGHTWARD target motion viewed by the (b) LEFT eye. This direction is (c) TEMPORAL to (d) NASAL.
