Binocular Vision: Lecture 6: Fusion and Corresponding Retinal Points

Question 1

3 Big requirements for Binocular Vision

Answer 1

1. Stimulation of CRP
2. Identical Visual Info
3. Stimulation of CRP w/in 100 ms

Question 2

1. CRP
2. Binocular Disparity
3. Confusion

Answer 2

1. VM Circle
2. Diplopia
3. ARC
   * Not sure if that’s what he was trying to say. Maybe listen to his lecture here….

Question 3

Worth’s Classification (3 things)

Answer 3

1. Simultaneous Perception
2. Flat Fusion
3. Stereopsis

Question 4

How do we Combine the Info from our 2 eyes into a Single Percept (is he trying to say perception)?

1. Motor Fusion: What is it?
2. Sensory Fusion: What is it?

Answer 4

1. Vergence Eye Movements position the eyes so Corresponding points (similar Contours in each retinal image) are Superimposed
2. Neurophysiological and Psychological Process where the Visual Cortex combines the superimposed views obtained INDEPENDENTLY by the 2 eyes into 1 unified Perception of Visual Space

Question 5

1. What will disrupt Sensory fusion? (multiple things…just think about it)
2. When will a STRABISMIC Patient have inadequate MOTOR AND SENSORY FUSION?
3. When will a STRABISMIC patient have inadequate MOTOR FUSION, but Normal SENSORY FUSION?

Answer 5

1. major dissimilarities b/w the 2 retinal images (size differences due to Anisometropia), VISUAL DIFFERENCES (due to Amblyopia), or Lack of Motor Fusion
2. When they SUPPRESS
3. When they COMPENSATE by using ARC

Question 6

2 Possible Theories of Sensory Fusion

1. ALTERNATION or SUPPRESSION THEORY: What is it?
2. BINOCULAR RIVALRY: What is it?

Answer 6

1. the 2 monocular VIEWS inhibit each other. This prevents us from seeing both at once. So there’s NO SIMULTANEOUS BINOCULAR PERCEPT
2. Grossly dissimilar Images are presented to each Eye (Donkey and Rose)

Question 7

1. Under natural Viewing conditions, with SIMILAR IMAGES, what can be perceived w/Brief Presentations of BINOCULAR STIMULUS?
2. What if the 2 images are in slightly different visual directions, what will the visual system do?

Answer 7

1. Stereopsis

2. It switches from one eye’s input to the other eye’s input, and the OBJECT seems to MOVE back and forth.

Question 8

1. Fusion Theory: What does it tell us that we can do in both eyes?
   a. How are these images processed? (Simultaneously or Successively)
   b. Has this theory been proven true?

Answer 8

1. tells us that we are able to get SIMILAR IMAGES in BOTH EYES at the SAME TIME
   a. SIMULTANEOUSLY instead of successively (postulated by Suppression theory)
   b. YES. Under NORMAL, NATURAL, VIEWING CONDITIONS

Question 9

1. Under Rivalrous Stimulus Conditions, is everything in Both Monocular Visual stimuli seen Simultaneously by the 2 eyes?
   a. How does the visual system process info in this situation?
   b. Fusion is the RULE for what type of images?
   c. Rivalry is the RULE for what type of images?

Answer 9

1. NO!
   a. It Alternatively processes info from each eye in sequence
   b. for SIMILAR MONOCULAR IMAGES
   c. for DISSIMILAR IMAGES

Question 10

1. So our eyes combine info from the 2 eyes in the Visual System. Can it still access to the Uncombined Monocular Info?
   a. Why?
   b. What does this provide?

Answer 10

1. YES
   a. So it can detect small differences b/w the 2 eyes images.
   b. Binocular Disparity and Stereopsis

Question 11

The Limits of Fusion

1. Images formed on corresponding retinal points are seen as SINGLE. What does this suggest in regards to the RETINA?
2. What will produce a SINGLE BINOCULAR PERCEPTION?

Answer 11

1. a Point-to-point Correspondence b/w the 2 retinas
2. An area on one eye’s retina, when stimulated together w/a given single retinal point in the other eye will produce this.

Question 12

Limits of Fusion (2)

1. Images w/in Panum’s Area can be fused and seen as single, but still have what?
2. Why is Panum’s Area useful in Binocular Fusion?
3. What does Panum’s Area Reduce?

Answer 12

1. slightly different visual directions in the 2 eyes
2. Because it allows for some imprecision or DRIFT in Eye movements w/o the introduction of Diplopia
3. It reduces the potentially Adverse effects of Fixation Disparity (this is a small binocular misalignment of the eyes in which fusion and single vision are achievable)

Question 13

Limits of Fusion (3)

1. How does PANUM’s Limiting Case work?
   a. 1 Pair of targets is FOVEATED and FUSED, while what happens to the Third Target?

Answer 13

1. Targets are presented to each eye separately.

a. It’s along the Visual Axis of One eye, but on a NONFOVEAL POINT in that eye. It CAUSES BINOCULAR DISPARITY

Question 14

Limits of Fusion (4)

1. Measurements of the VERTICAL LIMITS of PANUM’s AREA requires what?
   a. Why…what does it do?
2. Panum’s Area is what shape?
   a. Which way is 3-6 times larger: Horizontally or Vertically?

Answer 14

1. a POLAROID FILTER
   a. It separates the images of the 2 eyes, then moves the 2 targets apart vertically until they are first seen as diplopic.
2. Elliptical
   a. Horizontally

Question 15

Limits of Fusion (5)

1. Is our reduced ability to tolerate Vertical Disparities due to a smaller vertical extent of Panum’s Area?

Answer 15

1. NO. It’s due to a DECREASED ABILITY to make VERTICAL FUSIONAL EYE MOVEMENTS

Question 16

Limits of Fusion (6)

1. Fovea: Extent of Panum’s Fusional Area?
2. As you move farther into the retinal Periphery, the size of the Fusional Area INCREASES how?
   a. What %?
3. In the periphery, what can a patient tolerate?
   a. However, a Similar Size difference will result in what if STIMULI are SMALL and RESTRICTED to the CENTRAL AREA?

Answer 16

1. 5’ and 20’ of ARC
2. in DIRECT PROPORTION to the ECCENTRICITY
   a. at 6-7% of the ANGLE of ECCENTRICITY. DUE to INCREASE in the SIZE of the RECEPTIVE FIELD
3. 6-7% INTEROCULAR IMAGE SIZE DIFFERENCE (ANISEIKONIA)
   a. loss of BINOCULAR FUSION

Question 17

Limits of Fusion (7)

1. The rate of change of the size of Panum’s Area was consistent w/Predictions of the Limitations on Panum’s Area imposed by what?
2. A Single target, w/a given Binocular Disparity, may fuse EASILY, however, what happend when a 2nd Disparate Target is Introduced Nearby?

Answer 17

1. by GRATING RESOLUTION
2. the first target may fail to FUSE (similar to Crowding effect). (Larger rate of change in disparity as a function of target separation for closely spaced targets)

Question 18

Limits of Fusion (8)

1. Can Panum’s Fusional Area change?
   a. If so, How?
   b. How do Spatial Limits of Panum’s AREA INCREASE?
2. Does change in Luminance w/in a Range of 3 Log Units above threshold have any effect on Panum’s Area?
3. What about INCREASING CONTRAST for Targets over a wide spatial frequency Range?

Answer 18

1. YES
   a. Depends on EXPOSURE DURATION of the TARGET during MEASUREMENT
   b. w/LONGER TARGET EXPOSURE DURATIONS due to FUSIONAL EYE MOVEMENTS
2. Has LITTLE EFFECT
3. Has almost NO EFFECT on the EXTENT of PANUM’s AREA

Question 19

Vision therapy

1. Purpose?
2. Size of Panum’s Fusional Area may be affected by the presence of what ocular condition?

Answer 19

1. to Improve Fusion. Start w/targets that have LARGEST Panum’s FUSIONAL AREA (using larger targets)
2. Strabismus