4 - Fusion and Correspondence (Exam 1) Flashcards
What are the 3 possible scenarios that can cause single vision with two eyes?
- Perceptual merging of two images
- Monocular viewing
- Suppression (constant or alternating)
What is the alternation/ suppression theory?
The perception of single vision is never the merging or combination of both eyes images
What is the fusion theory?
The perception of single vision comes from the merging of each eye’s percept to form one unique percept.
What is allelotropia?
The perceptual representation of two disparate directions as one single unique visual direction.
What are the 2 types of fusion?
- Motor fusion
2. Sensory fusion
What is the perceptual characteristic of sensory fusion?
Allelotropia
What is sensory fusion?
Perceptual process where two similar targets are combined at the neural level without the need for motor fusion.
What is motor fusion?
The mechanical movement of both eyes that allows images to fall on the horopter or within Panum’s fusional space.
What is the goal of motor fusion?
To change eye position to allow sensory fusion to occur
What are 6 factors affecting sensory fusion?
- Target similarity
- Target simultaneity
- Retinal eccentricity
- Spatial frequency
- Temporal frequency
- Spatio-temporal modulation frequency
How does target similarity relate to sensory fusion?
Small differences in orientation can be fused
Fused images are averaged
What do large differences in orientation result in with regards to target similarity?
Rivalry -
Bi-stable piecemeal alternation between each eyes images
What is meant by target simultaneity?
If L and R images are presented at the same time, they are presented in perfect temporal synchrony
If one image is presented a short time after the other, temporal asynchrony is created
What is meant by retinal eccentricity?
Relative distance from the fovea
How does spatial frequency relate to sensory fusion?
Panum’s fusional area get smaller as spatial frequency increases, and becomes horizontally elliptical at higher that 2.5 cycles per degree
How does spatio-temporal modulation frequency relate to sensory fusion?
Subject experiences 3D corrugated wave only with horizontal disparity modulation
Panum’s fusional area becomes more circular as temporal frequency increases, horizontal has dramatic change.
What is the equation for disparity gradient?
n/d
With what value of disparity gradient will targets be able to fuse?
Disparity gradient less than 1
With what value of disparity gradient will targets not be able to fuse?
Disparity gradient greater than 1
What is a major characteristic of disparity gradient?
It creates a forbidden cone-like zone around every fused target in which adjacent targets will not be fused
Do changes in CONTRAST and LUMINANCE affect the extent of Panum’s fusional area?
No
Can stereoscopic depth be perceived for diplopic targets?
Yes
What is fixation disparity?
The angular discrepancy between the point of convergence and the target of interest
When are patients with fixation disparity able to perceive targets as single and fused?
When the magnitude of the fixation disparity does not exceed the limit of Panum’s fusional space
What is the “normal” fixation disparity seen in patients?
Between 4 arc minutes of eso FD and 6 arc minutes of exo FD
What type of fixation disparity do esophores usually have?
Eso fixation disparity
What type of fixation disparity do exophores usually have?
Exo fixation disparity
What could be a cause of an exophore that has an eso fixation disparity?
A past that involves vision therapy
What 2 requirements must a fixation disparity measurement target fulfill?
- Binocular fusion lock
target seen by both eyes - Monocular targets
target seen by one eye only
What is the angular offset in arc minutes between monocular targets in a fixation disparity target?
The fixation disparity
What is the amount of prism required to align monocular fixation targets?
Associated phoria
measure in prism diopters
What are Worth’s 3 levels of fusion?
- 1st degree fusion
- 2nd degree fusion
- 3rd degree fusion
What is 1st degree fusion?
Simultaneous perception of dissimilar monocular targets
Superimposition is where dissimilar targets are perceived in the same visual direction
What is 2nd degree fusion?
Flat fusion
suppression checks in place
What is 3rd degree fusion?
Stereopsis
two similar targets with slight differences in visual direction perceived to lie in depth
