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.
Describe 2 kinds of eye movements and their function.
Types of Eye Movement
Information Gathering
Voluntary (attention)
Stabilizing
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
Vergence
change point of fixation in depth
slow, disjunctive (eyes rotate in opposite directions)
(all others are conjunctive)
Fixation: period when eye is relatively stationary between saccades.
Why do we move our eyes?
High density of cone photoreceptors in central fovea - also high acuity
Describe the sequence of eye movements you might make in
an everyday task eg making breakfast. Describe the function
of 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….
Describe the specialized gaze patterns found
by Land in cricket.
Eye movements in cricket:
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.
Batsman anticipate bounce
point
Better batsman arrive earlier
Land & MacLeod, 2001
saccade
pursuit
Describe your results in the ball-catching lab.
Did you find the same basic pattern as Land did?
How did your results differ?
Catching: Gaze Patterns
X
X
saccade
Thrower
X
smooth pursuit
Catcher
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)
Generation of Saccades
monitor/plan
movements
(LIP) target selection
saccade decision
Inhibits SC
V1 (image)
Saccade command
signals to muscles
Retina to Saccade
Photoreceptors
ganglion cells
Primary visual cortex
LGN
SEF/FEF, PF Cortex
Basal ganglia (caudate/SNc)
SC/mid-brain
brain stem (Reticular formations)
oculomotor groups
Why is prediction necessary?
Components of visuo-motor latency.
Photoreceptors
ganglion cells
primary visual cortex
pre-motor ctx
M1
LGN
posterior parietal ctx
muscles
Round trip from eye to brain to muscles takes a minumum
of 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 specific
information to accomplish a task are said to reflect top down control.
Fixations that are evoked automatically by the occurrence of a stimulus are said to
be 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)
SNpc
Response to unexpected
reward
Increased firing for earlier or
later reward
Expected reward is
absent.
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)
Give some examples that eye movements are learned.
Jovancevic & Hayhoe 2009 Real Walking
Learning to Adjust Gaze
• Changes in fixation behavior fairly fast, happen over 4-5
encounters (Fixations on Rogue get longer, on Safe shorter)
Top Down strategies: Learn where to look
Shinoda et al. (2001)
“Follow the car.”
or
“Follow the car and obey
traffic rules.”
Time fixating
Intersection.
Road
Car
Roadside
Intersection
Detection of signs at intersection results from frequent looks.
Give some examples that reveal attentional limitations in visual
processing
1. Difficult to detect color change in one of 8 colored squares.
2. Invisible gorilla
1. Color-changing card trick
What are these examples called?
What conclusions has been drawn from these experiments.