Binocular Vision: Lecture 14: Stereopsis 1

Question 1

1. What is the main benefit of having Binocular Vision?
2. The relationship b/w Distance form the Horopter and Horizontal Disparity is a very orderly one, and the brain is able to detect what?
   a. What does the brain convert this to?

Answer 1

1. Gives us Precise Distance Info.
2. Interocular Differences in Position (HD)
   a. Converts it into a Perception of RELATIVE DEPTH! (this is Stereopsis)

Question 2

Cues to Depth Perception

1. What are the 2 Binocular Cues?

Answer 2

1. Retinal Disparity and Convergence

Question 3

Cues to Depth Perception

1. What are the 4 Major MONOCULAR CUES?
   a. Pictoral leads to what?

Answer 3

1. Accommodation, Angular Declination, Motion Parallax, and PICTORAL
   a. Linear Perspective, which is influenced by Lighting and Shadow, Relative Size, and Familiar Size. (Relative Size and Linear Perspective are influenced by Clarity, Texture, and Interposition)

Question 4

Distance of an Object as a Cue (1)

1. When size is the ONLY distance cue available, the Larger Object will appear where?
   a. Why?
2. Is the Interaction of Size and Distance always straightforward?
3. Under natural Viewing conditions, unfamiliar shapes seen for the first time that produce a large retinal image size may be interpreted by the visual system as being what?

Answer 4

1. It will appear Closer
   a. Because it’s size on the Retina (retinal Image) is Larger
2. No
3. as being Physically Close

Question 5

Size of an Object as a Cue

1. What is it: The perceived size of the object producing a Retinal Image of a given fixed size is PROPORTIONAL to its PERCEIVED DISTANCE?
   a. If the Observer looks at a wall, the Afterimage of a Flash will be seen how?
   b. IF the wall is close to the Observer, the Afterimage will seem what?

Answer 5

1. EMMERT’s LAW
   a. will be seen PROJECTED onto the wall.
   b. will seem SMALL

Question 6

Size Constancy

1. For 2 physical objects that produce retinal images of different sizes to be perceived as being the same physical size if these objects are judged to be at what?
2. Size Constancy is MAINTAINED by what?
3. Smaller Objects appear to be the same size even though what is different?

Answer 6

1. at Different Distances
2. by a Perceptual Scaling of the Perceived Size of an Object according to its estimated distance
3. even though their angular subtense is different

Question 7

Familiar Size

1. In natural settings with Familiar Objects, we can readily interpret the relative sizes of the Familiar Objects from what?

Answer 7

1. From our past experience, and use this info to help us estimate the distance of the objects from us.

Question 8

Linear Perspective

1. What is it?
   a. Example?

Answer 8

1. the Perception of parallel lines or edges Converging Toward a Distant Vanishing Point at the Horizon.
   a. Railroad tracks receding into the distance. More distant tracks look to be CONVERGING towards one another, and the ties b/w the tracks are seen as Narrower

Question 9

Texture Gradient

1. Distant Objects are seen not only as Smaller but also more what?
2. Simply reducing what of an Object can Make it appear as if it’s Farther Away?

Answer 9

1. More DENSELY PACKED than near Objects (This is Texture gradient)
2. Reducing the Contrast

Question 10

Interposition

1. What is it?

Answer 10

1. The Obstruction of the View of a distant object by a closer object. Distant objects can’t occlude the view of near objects. (Ex: Parents house obstructing part of the view of the mountains behind it)

Question 11

Shading of an Object

1. The Direction of Lighting and Shading of an Object can tell us about the Object’s what?
   a. The shading is interpreted as the Shadows formed from what?

Answer 11

1. Depth

a. from Illuminated Convex or Concave shapes

Question 12

Accommodation

1. The level of innervation for accommodation could provide what info?
   a. Kind of like what?
2. Studies have shown that accommodation is not utilized much in judging what?

Answer 12

1. Distance information
   a. Like an Autofocus Camera
2. in judging distance

Question 13

Motion Parallax

1. An Object at the same distance as an observer’s fixation point will appear to be STATIONARY when the Observer (or just the observer’s Head) is in what?
2. However, objects that are either in FRONT of or BEHIND the Fixation point will appear to move how?
   a. The direction of motion is determined by whether the object is closer of farther from what?
3. MOTION PARALLAX helps animals with limited BINOCULAR VF’s to see what?

Answer 13

1. is in MOTION
2. to Move Laterally relative to the fixation point if the Observer Moves
   a. than the Fixation Point (Farther..it moves with motion, Closer, it moves against motion)
3. to See DEPTH

Question 14

Stereopsis

1. Stereopsis GREATLY ENHANCES our ability to judge what?
   a. It allows us to be much better at what 3 things?
2. Stereopsis is the Visual System’s ONLY DIRECT MEANS of SEEING what?
3. Stereopsis allows for Extremely Accurate what?

Answer 14

1. Depth
   a. FIGURE-GROUND SEGREGATION (picking out camouflaged objects from their surrounds), AVOIDING COLLISIONS WITH LOOMING OBJECTS, and Accurately navigating thru our environment than we would be with one eye alone.
2. of Seeing DEPTH!
3. Hand-Eye Coordination

Question 15

Convergence

1. The Closer the Object, the GREATER degree of what is REQUIRED for CONVERGENCE?
2. A Subject fixates a target at a fixed distance thru BASE-OUT Prisms: As increasingly strong base-out prisms are introduced, the subject will be forced to do what?

Answer 15

1. of INNERVATION
2. to increase his convergence to keep the target single; and the target will be perceived as getting closer to the observer.

Question 16

Requirements for Stereopsis

1. Stereopsis occurs most accurately when images in EACH eye are formed on what?
2. The 2 images will still be fused because they lie where?
   a. Instead of being perceived as lying on the horopter, the visual system assigns the object what?
3. It’s the difference in LATERAL SEPARATION b/w the Half-Views of the Fixated and Nonfixated Objects (HORIZONTAL DISPARITY) that allows the visual system to estimate to what degree the object is Displaced from what?

Answer 16

1. Non Corresponding Retinal Points that are CLOSE TOGETHER (i.e., w/in Panum’s Fusional AREA)
2. w/in Panum’s Area
   a. a Perceived Depth RELATIVE to the HOROPTER
3. from the Horopter

Question 17

Requirements for Stereopsis (2)

1. The direction or sign of the depth is determined by the direction of what?
   a. If the object is in front of the Fixation point, the object produces retinal images that are formed on each eye’s what? THIS IS CALLED?
   b. Conversely, if Object is Farther away than the fixation point, it will produce Retinal images on what of each eye? This is called?

Answer 17

1. of Relative displacement of the images in the two eyes
   a. TEMPORAL RETINA; this is called CROSSED DISPARITY
   b. Nasal Retina; UNCROSSED DISPARITY

Question 18

Requirements for Stereopsis (3)

1. What is it: The Distance of a Given Single Object from the EGOCENTER of the OBSERVER.
2. What is it: The Difference in the EXTERNAL LONGITUDINAL ANGLES SUBTENDED by a SINGLE OBJECT at EACH EYE.

Answer 18

1. ABSOLUTE DEPTH

2. ABSOLUTE DISPARITY

Question 19

Requirements for Stereopsis (4)

1. Vergence is used to process what?
   a. what do we use Stereopsis for?
2. Once vergence Eye movements are used to bifoveally fixate one object, RELATIVE DEPTH b/w that object and its neighbors is encoded by what?
   a. Stereopsis is thus a RELATIVE MEASUREMENT in which the perceived depth is relative to what?

Answer 19

1. LARGE ABSOLUTE DISPARITIES
   a. Smaller Disparities
2. by RELATIVE DISPARITY (the difference b/w the absolute disparities of the two objects)
   a. to the Fixation Distance

Question 20

Requirements for Stereopsis (5)

1. The Binocular Visual System Processes what?
2. Binocular Disparity tells us an Object’s what in sPace?
3. However, Binocular disparity Does not tell us what?

Answer 20

1. Relative Disparity, not absolute disparity
2. Relative Position in Space (if it’s closer to us or father away from us compared to other objects)
3. the Absolute position of any particular Object

Question 21

What happens to the Retinal Images of 2 Eyes when one Experiences the Pulfrich Effect?

1. Neutral density filter darkens the image in one eye, in turn slowing what?
   a. If the pendulum moves, it will produce an image at what
2. The image falling on the Unfiltered eye’s retina will be what?
   a. however, the filtered eye’s image will do what?
3. The Neutral density filter therefore introduces what?
   a. This disparity is interpreted by the visual system as an equivalent what?

Answer 21

1. the processing of that eye’s image.
   a. at the Same locus on each eye’s retina
2. will be processed and transmitted to the Visual Cortex Quickly
   a. will take a longer time to reach the cortex
3. a Temporal Disparity b/w the processing speed of the Left eye and right eye.
   a. an equivalent Spatial Binocular Disparity, and therefore an Illusory Depth is Seen.

Question 22

Pulfrich Effect: Can be caused by what four things?

Answer 22

1. Anisocoria
2. Corneal Scars
3. Monocular Cataracts
4. Optic Neuritis

Question 23

Howard Dolman Apparatus

1. The magnitude of displacement needed to see depth, that is, the difference threshold for depth, is what?
2. What is available to the observer?

Answer 23

1. Stereoacuity

2. Monocular Cues

Question 24

1. Stereoacuity depends on what?

2. The Larger the PD, the LARGER what?

Answer 24

1. Interpupillary Distance (PD)

2. the larger the disparity seen w/a given test rod displacement.