Fixation and Visual Attention

Question 1

Eyes are never motionless. Images are held within a discrete area called the ?

Answer 1

Functional Fovea. +/- 30 min of arc. The longer a fixation is held with intent, the larger the area gets.

The goal is to keep the image within the functional fovea.

Question 2

3 Types of subconscious movements that are normal

Answer 2

Tremors, drifts, and saccades. All muscles work together to produce this movements.

Question 3

Tremors. What are they?

Answer 3

Constant shake. Fast. High frequency, small amplitude of only 1 cone diameter. Below threshold for Yoked muscles, so they are not correlated between eyes. No adverse effect on vision. Noise.

Question 4

Drifts

Answer 4

Error producing.
Slow velocity, amp of 15 cones.
Most of “Fixation” time. Pt spends 95% of the time in drift.
Not correlated between the eyes because it is because it is below the threshold for yoked muscles.
Irregular movements.

Question 5

Microsaccades

Answer 5

Error correcting.
1-2 per second as they correct for drifts.
Amp is 5 min per arc. These movements are binocular, under central control. Muscles are yoked.

Question 6

What impacts how images are kept within the functional fovea?

Answer 6

Peripheral gaze direction, darkness (poor feedback in dark) and less steady saccades.

Question 7

What are 4 abnormal movements?

Answer 7

1. Slow drift.
2. Saccadic intrusion- Square wave jerks, macro saccade jerks, and macro saccadic oscillations.
3. Nystagmus
4. Aberrant tremor

Question 8

What is a slow drift? Why is it abnormal?

Answer 8

Slow, irregular, no drop in VA.

Found with functional amblyopia. Usually doesn’t decrease VA, but may cause variability. Can fix with VT.

Question 9

What is saccadic intrusion? Why is it abnormal? What are the 3 types

Answer 9

Saccadic intrusion: Large fixational saccades that interrupts attempts at fixation.

Square wave jerks: Jerk eye away from target, then back to target 200 ms later.

Macrosaccade jerks: Larger than square wave jerks. Easier to see. More frequent. Only 100 ms in between jerks.

Macrosaccadic oscillations- Pattern of saccades away and back towards the center. Increases after each movement. Common in cerebellar disease.

Question 10

What is aberrant tremor?

Answer 10

Less common. Usually, normal eye movements such as tremors, drifts, and micro saccades cover up this. It is abnormal to see this movement, since that indicates that the normal movements are no longer occurring. See in states of unconsciosness.

Question 11

What two systems promote visual stabilization?

Answer 11

VOR and Optokinetic system OKN.

Question 12

We tend to look at ___ unless we are given direction that leads us to look elsewhere

Answer 12

Faces

Question 13

Figure vs ground

Answer 13

Figure- what you put your attention on. Ground- everything else.

Question 14

Most visual problems are of

Answer 14

Omission, not commission

Question 15

What is the attention window

Answer 15

Figure. Processed via object properties, AKA what is it?
The area on which we place our attention.
Can change size
Can change with or without an eye movement. Ex: Someone walking in door while you are studying.

Question 16

Visual Buffer

Answer 16

Ground. Processed via spatial properties, AKA where/relative?
Surrounds figure/attention window.

Question 17

Attention window and visual buffer are put all together by way of

Answer 17

Associative memory, which accesses previous info. This gives CONTEXT to the attended object. Information lookup- Is this object familiar? If not, how can I make an educated guess? Have I seen anything similar before?

Question 18

Proper order of shifting visual attention

Answer 18

Disengage, move, engage. NOT talking about eye movements. Talking about attention.

Question 19

Which part of shifting visual attention (Disengage, move, engage) do these people have problems with?

1. Autism
2. Parkinsons
3. Myopes
4. ADHD

Answer 19

1. Difficulty with engage. Attention window is huge.
2. Difficulty disengaging. They tend to stare.
3. Tendency to lock on, hard to disengage. Reduced blinking, breathing.
4. Difficulty with inhibition. Move their attention window often.

Question 20

Behavioral model of active visual perception. Plays a role in how we plan our eye movements.

Answer 20

Ex: Attention window. Look at the scene. Through the “what” system, a hypothesis is made. Compared and either recognized or not. Yes? Move on. No? make further comparisons. After done, can shift attention window and move eyes.

Object recognition is separate processing and represents the “What” and “Where” information at high levels of the visual system. Lots of back and forth communication. Here is where we determine what the object is.

Question 21

When looking at a face, what order do we take?

Answer 21

1. Eyes first. Back and forth. Make sure the other eye is where its supposed to be.
2. Then move around face based on what ew expect.
3. If it matches expectation, yes its a face! If not, make further comparisons.

People follow predictable patterns IF you know what you’re looking at. Can even depict image based on scan path.

Question 22

What did the “Count the F’s” example demonstrate?

Answer 22

That we are so used to processing without having to study each detail that we miss things.

Ex: the “V” sound produced by the letter “F” in “OF”
Other senses and automaticity can confuse