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 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.

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 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….

Describe the specialized gaze patterns found by Land in cricket.

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?

Catching: Gaze Patterns

CatcherThrower

saccade X

X

smooth pursuit

X

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)

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)

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

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.