Fixation and Visual Attention Flashcards
Eyes are never motionless. Images are held within a discrete area called the ?
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.
3 Types of subconscious movements that are normal
Tremors, drifts, and saccades. All muscles work together to produce this movements.
Tremors. What are they?
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.
Drifts
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.
Microsaccades
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.
What impacts how images are kept within the functional fovea?
Peripheral gaze direction, darkness (poor feedback in dark) and less steady saccades.
What are 4 abnormal movements?
- Slow drift.
- Saccadic intrusion- Square wave jerks, macro saccade jerks, and macro saccadic oscillations.
- Nystagmus
- Aberrant tremor
What is a slow drift? Why is it abnormal?
Slow, irregular, no drop in VA.
Found with functional amblyopia. Usually doesn’t decrease VA, but may cause variability. Can fix with VT.
What is saccadic intrusion? Why is it abnormal? What are the 3 types
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.
What is aberrant tremor?
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.
What two systems promote visual stabilization?
VOR and Optokinetic system OKN.
We tend to look at ___ unless we are given direction that leads us to look elsewhere
Faces
Figure vs ground
Figure- what you put your attention on. Ground- everything else.
Most visual problems are of
Omission, not commission
What is the attention window
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.
Visual Buffer
Ground. Processed via spatial properties, AKA where/relative?
Surrounds figure/attention window.
Attention window and visual buffer are put all together by way of
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?
Proper order of shifting visual attention
Disengage, move, engage. NOT talking about eye movements. Talking about attention.
Which part of shifting visual attention (Disengage, move, engage) do these people have problems with?
- Autism
- Parkinsons
- Myopes
- ADHD
- Difficulty with engage. Attention window is huge.
- Difficulty disengaging. They tend to stare.
- Tendency to lock on, hard to disengage. Reduced blinking, breathing.
- Difficulty with inhibition. Move their attention window often.
Behavioral model of active visual perception. Plays a role in how we plan our eye movements.
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.
When looking at a face, what order do we take?
- Eyes first. Back and forth. Make sure the other eye is where its supposed to be.
- Then move around face based on what ew expect.
- 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.
What did the “Count the F’s” example demonstrate?
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
