4 - Fusion and Correspondence (Exam 1)

Question 1

What are the 3 possible scenarios that can cause single vision with two eyes?

Answer 1

1. Perceptual merging of two images
2. Monocular viewing
3. Suppression (constant or alternating)

Question 2

What is the alternation/ suppression theory?

Answer 2

The perception of single vision is never the merging or combination of both eyes images

Question 3

What is the fusion theory?

Answer 3

The perception of single vision comes from the merging of each eye’s percept to form one unique percept.

Question 4

What is allelotropia?

Answer 4

The perceptual representation of two disparate directions as one single unique visual direction.

Question 5

What are the 2 types of fusion?

Answer 5

1. Motor fusion

2. Sensory fusion

Question 6

What is the perceptual characteristic of sensory fusion?

Answer 6

Allelotropia

Question 7

What is sensory fusion?

Answer 7

Perceptual process where two similar targets are combined at the neural level without the need for motor fusion.

Question 8

What is motor fusion?

Answer 8

The mechanical movement of both eyes that allows images to fall on the horopter or within Panum’s fusional space.

Question 9

What is the goal of motor fusion?

Answer 9

To change eye position to allow sensory fusion to occur

Question 10

What are 6 factors affecting sensory fusion?

Answer 10

1. Target similarity
2. Target simultaneity
3. Retinal eccentricity
4. Spatial frequency
5. Temporal frequency
6. Spatio-temporal modulation frequency

Question 11

How does target similarity relate to sensory fusion?

Answer 11

Small differences in orientation can be fused

Fused images are averaged

Question 12

What do large differences in orientation result in with regards to target similarity?

Answer 12

Rivalry -

Bi-stable piecemeal alternation between each eyes images

Question 13

What is meant by target simultaneity?

Answer 13

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

Question 14

What is meant by retinal eccentricity?

Answer 14

Relative distance from the fovea

Question 15

How does spatial frequency relate to sensory fusion?

Answer 15

Panum’s fusional area get smaller as spatial frequency increases, and becomes horizontally elliptical at higher that 2.5 cycles per degree

Question 16

How does spatio-temporal modulation frequency relate to sensory fusion?

Answer 16

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.

Question 17

What is the equation for disparity gradient?

Answer 17

n/d

Question 18

With what value of disparity gradient will targets be able to fuse?

Answer 18

Disparity gradient less than 1

Question 19

With what value of disparity gradient will targets not be able to fuse?

Answer 19

Disparity gradient greater than 1

Question 20

What is a major characteristic of disparity gradient?

Answer 20

It creates a forbidden cone-like zone around every fused target in which adjacent targets will not be fused

Question 21

Do changes in CONTRAST and LUMINANCE affect the extent of Panum’s fusional area?

Answer 21

No

Question 22

Can stereoscopic depth be perceived for diplopic targets?

Answer 22

Yes

Question 23

What is fixation disparity?

Answer 23

The angular discrepancy between the point of convergence and the target of interest

Question 24

When are patients with fixation disparity able to perceive targets as single and fused?

Answer 24

When the magnitude of the fixation disparity does not exceed the limit of Panum’s fusional space

Question 25

What is the “normal” fixation disparity seen in patients?

Answer 25

Between 4 arc minutes of eso FD and 6 arc minutes of exo FD

Question 26

What type of fixation disparity do esophores usually have?

Answer 26

Eso fixation disparity

Question 27

What type of fixation disparity do exophores usually have?

Answer 27

Exo fixation disparity

Question 28

What could be a cause of an exophore that has an eso fixation disparity?

Answer 28

A past that involves vision therapy

Question 29

What 2 requirements must a fixation disparity measurement target fulfill?

Answer 29

1. Binocular fusion lock
   target seen by both eyes
2. Monocular targets
   target seen by one eye only

Question 30

What is the angular offset in arc minutes between monocular targets in a fixation disparity target?

Answer 30

The fixation disparity

Question 31

What is the amount of prism required to align monocular fixation targets?

Answer 31

Associated phoria

measure in prism diopters

Question 32

What are Worth’s 3 levels of fusion?

Answer 32

1. 1st degree fusion
2. 2nd degree fusion
3. 3rd degree fusion

Question 33

What is 1st degree fusion?

Answer 33

Simultaneous perception of dissimilar monocular targets

Superimposition is where dissimilar targets are perceived in the same visual direction

Question 34

What is 2nd degree fusion?

Answer 34

Flat fusion

suppression checks in place

Question 35

What is 3rd degree fusion?

Answer 35

Stereopsis

two similar targets with slight differences in visual direction perceived to lie in depth