Stereopsis Part 1, 2 & 3

Front 1

What does Stereopsis provide?

Back 1

precise depth preception at near and enhances our space perception

Front 2

How does Stereopsis arise?

Back 2

From binocular cues and horizontal disparity.

Front 3

What is Depth Perception?

Back 3

Discrimination of relative distance between objects in space.

Front 4

What is Binocular Disparity?

Back 4

Based on the fact that the two eyes are separated horizontally and view the world from different vantages.

Front 5

How does Absolute Disparity occur?

Back 5

An object whose image falls on NON-CORRESPONDING retinal points has absoltue disparity with respect to the horopter.

Front 6

What is the equation for Absolute Disparity?

Back 6

n= binocular parallax - vergence angle

Front 7

What does Absolute Disparity do to eye movement?

Back 7

Guides vergences eye movement in order to bifoveally fixate an object.

Front 8

What does the signal from vergence provide?

Back 8

Information about target distance to the visual system.

Front 9

How does Relative Disparity occur?

Back 9

Two or more objects that are not on the same horopter have a relative disparity with respect to each other

Front 10

What is Relative Disparity?

Back 10

The difference between the absolute disparities of two points.

Front 11

Does Relative Disparity change with fixation distances?

Back 11

NO!!!

Front 12

What is Disparity Gradient?

Back 12

Linear Change in Horizontal disparity of near by objects across space.

Front 13

How is Disparity Gradient calculated?

Back 13

Difference of nearby objects disparities divided by average separation.

Front 14

What is Disparity Curvature?

Back 14

Describes changes of disparity gradient over visual angle.

Front 15

What is Vertical Disparity?

Back 15

The difference between the angle of elevation measured in the two eyes for an object.

Front 16

What can cuase Vertical Disparity?

Back 16

1. Ocular Misalignment(Fixation Disparity, strabismus)
2. Objects nearer to one eye
3. Vertical Magnification in aniseikonia

Front 17

What is Diffrequency?

Back 17

depth tilt from interocular spatial frequency differences.

Ex: Vertical Sine Wave Low SF presented to OS and High SF presented to OD simultaneously, then the brain fuses them and we perceive a depth tilt.

Front 18

What is Chromostereopsis?

Back 18

Surface areas of different colors in the same vertical plane appears to be at different distances from the eyes to some observers.

Front 19

What does Chromosteropsis result from?

Back 19

Transverse Chromatic Abberation

Front 20

Is Chromosteropsis a TRUE stereoscopic effect and disappears when one eye is covered?

Back 20

YES!!!

Front 21

What is the Pulfrich Phenomenon?

Back 21

An object swinging in the frontoparallel plance appears to be traveling in an elliptical pattern toward and away from the observer in depth when there is a lower luminance contrast in one of the observer's eyes.

Front 22

What is the Classical Explanation of the Pulfrich Effect?

Back 22

An illusion of depth resulting from a temporal delay of the image from one eye.

Front 23

Is temporal delay geometrically equivalent to spatial disparity?

Back 23

YES!

Front 24

Does the Pulfrich stimulus activate mechanisms which usually process spatial disparity?

Back 24

Yes!

Front 25

Name Four Other Depth Perceptual Phenomena and which one is the True Binocular Effect?

Back 25

1. Motion Parallax(Mono)
2. Shapes from Motion
3. Diffrequency
4. Chromostereopsis(True Binocular effect)

Front 26

What does Stereoacuity measure?

Back 26

The intactness of Binocular Vision.

Front 27

How is Stereoacuity defined?

Back 27

It's the smallest binocular disparity that can be detected. i.e. it is the minimum disparity beyond which no stereoscopic effect is produced.

Front 28

T/F: Better stereoscuity does not translate to better stereopsis.

Back 28

TRUE, b/c of...
1) Depth Perception Bias
2) Asymmetries in the ability to see crossed vs. uncrossed disparities.

Front 29

By what factor is the use of disparity for depth judgments better than using only monocular cues?

Back 29

By a factor of 20

Front 30

Is Stereoacuity for humans better than predicted by photoreceptor sampling?

Back 30

Yes!

Front 31

95-98% of the population achieves stereoacuity of better than__________.

Back 31

40 arc SEC

Front 32

Stereoacuity for humans can reach the level of _______.

Back 32

4-5 arc SEC

Front 33

When measuring stereoacuity by the Method of constant Stimuli, two stimuli are used, the reference stimulus has _____, the test stimulus has _________.

Back 33

1. Reference Stimulus has
Zero disparity
Test Stimulus has
Crossed or uncrossed disparity

Front 34

When measuring stereoacuity by the Method of Constant Stimuli what is the subject asked to judge?

Back 34

the depth direction of the test stimuli

Front 35

Measuring stereoacuity with Real Depth test uses...

Back 35

3D objects that are separated in space by a certain amount to stimulate a specified amount of retinal disparity.

Front 36

What is an example of a
Real-depth test?

Back 36

Howard-Dolman Stereoacuity Test

Front 37

How is the Howard-Dolman Test Set Up?

Back 37

1. Two rods, ea. 1 cm diameter
2. 6 sm separation bt rods
3. One Rod fixed, one movable
4. Subject views rods through aperature.

Front 38

What test distance is used for the Howard-Dolman Test?

Back 38

6 meters

Front 39

What is the traditional procedure used for the Howard -Dolman test?

Back 39

Method of Adjustment

Front 40

What is the subject ask to do during the Howard-Dolman Test?

Back 40

The subject moves the adjustable rod until a difference in depth bt rods is first noticed.

Front 41

What is the formula for the Disparity & Depth relationship?

Back 41

n=(PD/viewing distance sq.) x (separation bt rods)

n= angular disparity in radians

Front 42

The greater the separation bt the rods, angular disparity is ________.

Back 42

Larger

Front 43

The shorter the viewing distance, angular disparity is.

Back 43

Larger

Front 44

The Smaller the PD, angular disparity is_______.

Back 44

Smaller

Front 45

To maintain a valid perceptual constancy between depth & disparity, an observer must scale the __________ with ________.

Back 45

Horizontal disparity with viewing distance.

Front 46

Measuring Stereoacuity with Projected-depth tests uses

Back 46

separated 2D objects presented to each of the two eyes in a stereoscope or with polarizer.

Front 47

2 examples of Projected-depth tests are

Back 47

1. Randot Stereo Test
2. Wheatstone's Mirror Stereoscope

Front 48

How is stereoacuity derived when using the Projected-depth tests?

Back 48

directly from the detected angular differences in positions of common objects in the two half views of the stereogram.

Front 49

Name 9 Factors that affect Stereoacuity.

Back 49

P-R-O-C-E-S, T-L-C

1. Practice
2. Retinal Eccentricity
3. Optical Blur/defocus
4. Color
5. Exposure Duration
6. Stimulus Motion
7. Target Separation(Crowding)
8. Luminance
9. Contrast

Front 50

Luminance

Back 50

Dimmer= less sensitivity to disparity & depth percpt

Front 51

Exposure Duration

Back 51

Shorter exposure= threshold elevated, but we can see depth

Front 52

How many msec of exposure to the target achieves the best stereothreshold?

Back 52

100 msec

Front 53

Contrast

Back 53

Low contrast = stereothreshold are elevated

Front 54

Color

Back 54

Blue= Stereothreshold worse

Front 55

Optical Blur

Back 55

Stereoacuity reduced

Front 56

Which causes worse Stereoacuity, Monocular blur or Binocular Blur?

Back 56

Monocular Blur

(Monovision decreases stereoacuity, don't recommend to Pilots)

Front 57

Target Separation

Back 57

Stereoscopic threshold are lowest when Reference & test targets are laterally separated by 15-50arc min.

Front 58

When Reference & Test Targets are separated >50 arcmin

Back 58

it's difficult to discriminate & stereoscopic thresholds elevate

Front 59

When Reference & Test Targets are separated <15 arcmin

Back 59

Stereoacuity is degraded

Front 60

Stimulus Location

Back 60

Stereoacuity max at fovea & diminishes exponentially w/ increasing eccentricity

Front 61

During Stimulus location what is the standing or Pedestal disparity

Back 61

The disparity of the nearer target.

Front 62

Practice

Back 62

1. Stereoacuity improves with practice= Perceptual learning

2. exist inVernier Acuity

3. Practice in one VF location does not transfer to other VF location

Front 63

Stimulus Motion

Back 63

1. Stereoacuity remains if lateral 2D retinal Image motion is < 2-3 deg/sec.

2. Microsaccades & Drifting does not degrade stereoacuity

Front 64

What is Motion-in-Depth?

Back 64

Stereomotion= a visual percept in a dynamic 3D world. The images of the left & right eyes move in horizontally opposed directions on the two retinas.

Front 65

Are we sensitive to stereomotion?

Back 65

No, observers w/normal visual acuity & stereopsis may show stereomotion scotoma.

Front 66

Strabismic Patients

Back 66

Thresholds elevate in both Static & Dynamic threshold

(Dynamic is better than static)

Front 67

What are threshold findings from Clinical/Lab Exams.

Back 67

Good= 15-30 arc sec
Highly Skilled Subjects= low as 2-7 arc secs.

Front 68

Patent Stereopsis is aka?

Back 68

Quantitative

Front 69

What is Patent "Quantitative" Stereopsis?

Back 69

Stereopsis from disparities w/in & slightly beyond Panum's Fusional Range.

Direction & mag of depth is accurately perceived.

Degree of depth is proportional to the mag of Binocular disparity

Front 70

Latent Stereopsis is aka?

Back 70

Qualitative

Front 71

What is Latent Qualitative Stereopsis?

Back 71

Stereopsis from a range of DIPLOPIC disparities(greater than Panum's Area) where DIRECTION of depth is accurately perceived but NOT mag of depth.

Front 72

Stereogram

Back 72

Two flat, 2D objects presented to ea. eye independently. Each image mimics the effect of having two eyed separated by IPD distance.

The complete figures viewed binocularly are called stereogram.

Front 73

Stereoscopic half-view

Back 73

target independently presented to ONE eye.

Front 74

Stereo Pair

Back 74

TWO stereoscopic half-views, one presented to OD and other presented to OS.

Front 75

What is a Stereoscope?

Back 75

an instrument that alters the relationship bt distance & disparity by lenses, mirrors or prisms so that an independent image is presented to each eye.

Front 76

What are two Stereoscopes that have Mirrors.

Back 76

1. Wheatstone
2. Amblyscope

Front 77

Which Stereoscope has Prism?

Back 77

1. Brewster(Refracting)

Front 78

What is an Anaglyph?

Back 78

Objects of complementary colors are viewed through colored filters to obtain independent control of binocular objects.

Front 79

What is a Vectogram?

Back 79

Each half view is polarized with one view's polarization 90 degrees away from other eye's polarixzation. Filter's are worn.

Front 80

What is an example of a Vectogram?

Back 80

Titmus Stereo Test

Front 81

Liquid Crystal Shutter Goggles

Back 81

Lenses are darkened with electric current.

Front 82

Autostereograms

Back 82

monocular views for BOTH eyes are contained in the same figure as repeated patterns.

Magnitude of depth perceived depends on convergence of observer & which of the patterns are fused.

Front 83

Wallpaper Illusion

Back 83

If one converges at a position in front of a repetitive pattern, the pattern shift forward in depth to a plane near the convergence plane

Front 84

Classes of Stereoscopic Targets

Back 84

1. Line/Contour Stereograms
2. Stereogram with stimulus which is invisible monocularly but visible by disparity processing.(RANDOM DOt Stereograms= RDS)

Front 85

Local Stereopsis

Back 85

1. No Ambiguity about corresponding contours.

2. Disparity of contours in one region is processed w/out reference to disparities in other regions.

3. Similar contours in the two monocular images are matched and ea. locus is assigned a disparity to elcit stereopsis.

Front 86

Global Stereopsis

Back 86

1. Have Ambiguities in correct correspondence of retinal images,

2. Global neighborhood of ea. matching pair of dots or lines that provide the stimulus for stereopsis must be taken into account.

3. Large areas of binocular view are matched by finding patches w/similar disparity & combining them to see an overall shape in depth.

Front 87

Contour Stereogram

Back 87

1. Monocular Contours
2. Only require LOCAL stereopsis

Front 88

Random DOT Stereogram

Back 88

1. NO monocular contours

2. Require both LOCAL & GLOBAL

3. Longer time to perceive depth, but w/practice time needed deceases.

Front 89

Stereo Corresponding Problems

Back 89

Visual System must determine what portion of one eye's image corresponds to a portion of the other eye's image.

Front 90

Stereo Corresponding Problem Solution

Back 90

1. The Visual sytem seeks out the image matching that yields the most unambiguous depth with a solid appearance & sharpest edges.

2. The visual system does not perform an element by element matching, but a GLOBAL perception over a large spatial scale.

Front 91

Suggested Image Matching Scheme

Back 91

1. Unique-matching rule, one to one
2. Matching of Similar Features
3. Surface smoothness constraint
4. Depth avg. (disparity pooling)

Front 92

How are Fine disparities proccessed?

Back 92

By neurons with small receptive fields(HSF)

Front 93

How are Coarse Disparities processed?

Back 93

By neurons with Large receptive fields(LSF).

Front 94

Fine Stereopsis

Back 94

1. Parvocellular Sytem
2. Operates w/small retinal disparities & static or slowly moving targets.

Front 95

Coarse Stereopsis

Back 95

1. Magnocellular system
2. Operates w/Large retinal disparities & moving objects.

Front 96

Three Disparity Channels

Back 96

1. Zero
2. Crossed
3. Uncrossed

Front 97

Stereoblindness

Back 97

Observers with NORMAL vision may exhibit...
1. Crossed disparities Alone
2. Uncrossed disparities Alone
3. Disparity direction

Front 98

Central Stereopsis

Back 98

1. +/- 0.5 degrees at the fovea

2. Detects small disparities at fixation point

Front 99

Peripheral Stereopsis

Back 99

1. +/-7-10 degrees
2. Selective for Large diparities
3. May still be intact when central stereopsis is absent

Front 100

Stereoperimetry

Back 100

Testing stereoacuity at differnt locations w/in the VF.