describe 2 kinds of eye movements and their function
DESCRIPTION
Describe 2 kinds of eye movements and their function. Describe the specialized gaze patterns found by Land in cricket. Describe your results in the ball-catching lab. How do they compare with Land ’ s? What is meant by “ top-down ” and “ bottom-up ” processing? Give examples of both. - PowerPoint PPT PresentationTRANSCRIPT
Describe 2 kinds of eye movements and their function. Describe the specialized gaze patterns found by Land in cricket. Describe your results in the ball-catching lab. How do they compare with Land’s? What is meant by “top-down” and “bottom-up” processing? Give examples of both.
Give some examples that reveal attentional limitations in visual processing. What is “Neuroeconomics”? Explain how the saccadic eye movement circuitry is influenced by reward. Give some examples that eye movements are learned. Describe the Sprague and Ballard theory (Walter) of gaze control. What evidence is there to support the theory. Why is it useful? Draw a sketch of the brain showing the structures involved in the generation of a saccadic eye movement. Specify the function of these structures.
Types of Eye Movement
Information Gathering StabilizingVoluntary (attention) Reflexive
Saccades vestibular ocular reflex (vor)new location, high velocity, ballistic body movements
Smooth pursuit optokinetic nystagmus (okn)object moves, velocity, slow whole field image motion
Vergencechange point of fixation in depthslow, disjunctive (eyes rotate in opposite directions)(all others are conjunctive)Fixation: period when eye is relatively stationary between saccades.
Describe the sequence of eye movements you might make inan everyday task eg making breakfast. Describe the functionof each movement.
Making breakfast:Upon entering the kitchen: saccade to the cupboard on the basis of memory, as I know cereal is located there. Approach cupboard and saccade to door handle to guide hand to open door. Search for cereal with several saccades, maybe landing on boxes of similar size and appearance. When saccade lands on the correct box, stay fixating to guide the grasp of the box. Rotate body and head to exit the cupboard and make a big saccade to the cupboard containing the bowls. Fixate the cupboard while I walk there and make a fixation to the handle to guide opening….
Eye movements in cricket:
Batsman anticipate bounce point
Better batsman arrive earlier
Land & MacLeod, 2001
pursuitsaccade
1) Batsman fixates the bowler’s hand
2) Makes a saccade to the anticipated location of the bounce. 3) This is followed by a smooth pursuit movement after the bounce.
The bounce point gives information about where and when to swing the bat.
Describe your results in the ball-catching lab.Did you find the same basic pattern as Land did?How did your results differ?
Draw a sketch of the brain showing the structures involved in the generation of a saccadic eye movement. Specify the function of these structures (to the extent that this is possible)
(LIP) target selection
signals to muscles
Inhibits SC
saccade decision
Saccade command
monitor/plan movements
Generation of Saccades
V1 (image)
Photoreceptors ganglion cells LGN
Primary visual cortex SEF/FEF, PF Cortex
Basal ganglia (caudate/SNc) SC/mid-brain
brain stem (Reticular formations) oculomotor groups
Retina to Saccade
Photoreceptors ganglion cells LGN
primary visual cortex posterior parietal ctx
pre-motor ctx M1 muscles
Why is prediction necessary?
Components of visuo-motor latency.
Round trip from eye to brain to muscles takes a minumumof 200 msec. Ball (our expt) only takes about 900 msec.Prediction gets around the problem of sensory delays.
What is meant by “top-down” and “bottom-up” processing? Give examples of both.
Bottom up processes are evoked by the visual stimulus.
Top down processes are operations that reflect the subject’s current cognitive goals.
In the case of eye movements, fixations that are for the purpose of getting specificinformation to accomplish a task are said to reflect top down control.
Fixations that are evoked automatically by the occurrence of a stimulus are said tobe under bottom up control.
Examples?
What is “Neuroeconomics”? Explain how the saccadic eye movement circuitry is influenced by reward.
Humans/primates exhibit behaviors that lead to expected reward. Reward is provided by the release of dopamine.
Dopaminergic neurons in basal ganglia signal expected reward. (Schultz, 2000)
Response to unexpected reward
Increased firing for earlier or later reward
Expected reward is absent.
SNpc
Neurons at all levels of saccadic eye movement circuitry
are sensitive to reward.
LIP: lateral intra-parietal cortex. Neurons involved in initiating a
saccade to a particular location have a bigger response if reward is
bigger or more likely
SEF: supplementary eye fields
FEF: frontal eye fields
Caudate nucleus in basal ganglia
This provides the neural substrate for learning gaze patterns in natural behavior, and for modeling these processes using Reinforcement Learning. (eg Sprague, Ballard, Robinson, 2007)
Learning to Adjust Gaze
• Changes in fixation behavior fairly fast, happen over 4-5 encounters (Fixations on Rogue get longer, on Safe shorter)
Time fixatingIntersection.
“Follow the car.”
or“Follow the car and obey
traffic rules.”
Car RoadsideRoad Intersection
Shinoda et al. (2001)
Detection of signs at intersection results from frequent looks.
Top Down strategies: Learn where to look