Spatial Perception

Question 1

What is spatial perception?

Answer 1

how we perceive the spatial layout of the environment

–> distance, depth, size, etc

Question 2

What are the different classes of depth cues?

Answer 2

kinematic, stereoscopic, oculomotor, pictorial information

Question 3

Depth

Answer 3

Relative position from observer (nearer/farther); qualitative

Question 4

Distance

Answer 4

Absolute position given using some kind of metric or scale; quantitative

note: perception may be “body-scaled” (e.g. arm’s length, steps)

Question 5

Non-metric

Answer 5

depth, qualitative

Question 6

Metric

Answer 6

distance, quantitative

Question 7

Sources of Information for Depth and Distance (motion cues)

Answer 7

Lecture:
Monocular cues
Motion cues
Binocular vision and stereopsis

----
Textbook: 
- Kinematic Information
- Stereoscopic Information 
- Oculomotor Information
- Pictorial Information

Question 8

Kinematic Information

Answer 8

depth cues from motion

Question 9

Motion perspective (aka motion parallax)

Answer 9

when the observer moves, displacement of an object’s image on the eye depends on its distance.

Question 10

Optic flow

Answer 10

a form of motion parallax when the whole visual field is considered in a motion perspective
* pattern of retinal displacement relative to the observer

(demo: watching close tree + far cow on moving train)

Question 11

What is the algorithm for segmenting a retinal image into different objects based on movement

Answer 11

Simple algorithm: get new value at each point by subtracting value there from average of its neighbors

• computation produces a map of significant object and surface edges in visual field; edges are marked by non-zero value (due to discontinuity)

Question 12

Two types of kinematic information

Answer 12

based on movement:

1) Motion perspective (parallax)
2) Optical expansion/contraction
3) Accretion/deletion of texture

Question 13

Optical expansion/contraction

Answer 13

when an object approaches, its image expands; if it is on a “hit” path, the expansion is symmetric

Question 14

Accretion/deletion of texture

Answer 14

when a surface moves relative to another, the nearer surface progressively occludes background texture on the farther surface

Question 15

Stereoscopic Information

Answer 15

depth information gained using the two eyes together

*depends on binocular disparity

Question 16

Binocular disparity

Answer 16

refers to differences in the two eyes’ views of an object

• the amount of binocular disparity depends on the distance of an object from the observer
• depends on how far, and what point you’re looking from SO it can be used as a cue for distance

Question 17

Horopter

Answer 17

sets of points in the world having identical binocular disparities; theoretically arranged in a circle

Question 18

Crossed disparity

Answer 18

“NEARER from us”

– indicates that a point is nearer to the observer than the point being fixated

Question 19

Uncrossed disparity

Answer 19

“FARTHER FROM US”

– indicates that a point is farther from the observer than the point being fixated

Question 20

What are the points of 0 disparity?

Answer 20

• focused on fovea of both eyes

* falling on horopter

Question 21

The farther away the ___er the disparity

Answer 21

bigger

Question 22

Convergence

Answer 22

The ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye)
– Convergence reduces the disparity of that feature to zero (or nearly zero)

Question 23

Divergence

Answer 23

The ability of the two eyes to turn outward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye).
– Divergence reduces the disparity of that feature to zero (or nearly zero)

Question 24

Limitation of accommodation and divergence

Answer 24

Only works on near objects, not far

– eyes are diverged about as much as possible, so neither cue provides much useful information

Question 25

Accommodation

Answer 25

changes in the shape of the lens in each eye to achieve focused images at varying distances
– accommodation may provide distance information via unconscious sensing of the muscular movements (in the ciliary muscles) that produce the lens changes

Question 26

Are retinal images 2D or 3D?

Answer 26

2D
* all retina knows is that photons are hitting photopigments and activating ganglion cells –> do not know anything about how far the photons were

note: how retinal 2D image becomes a 3D image is an ill-posed problem

Question 27

Oculomotor cues

Answer 27

having to do with eye muscles; physical movement of the eyes

*provide metric information; QUANTITATIVE

Question 28

Pictoral Cues

Answer 28

depth cues that can operate in flat pictures; they are all also monocular cues, in that they can operate when you view with only one eye.

– most pictorial cues relate to rules of optics and geometry that govern the projection of the world onto the retina

Question 29

Which cues were originally discovered by artists?

Answer 29

pictoral cues

Question 30

Use of pictorial cues for depth perception involves using…

Answer 30

the rules of projection (law of optics) in reverse

Laws of Optics: Scene
vs.
Retina Inverse Optics: Retina

Question 31

Pictoral cue of texture gradient

Answer 31

density of background texture impacts how close or large we perceive objects to be

Question 32

Pictoral cue of familiar size

Answer 32

for objects we have encountered in the past, our perceptual system has an idea of what size they tend to be
– uses that information for interpreting how FAR they are given their actual size and the image

Question 33

Convergence – metric, non-metric, or relative metric?

Answer 33

metric

Question 34

Accommodation – metric, non-metric, or relative metric?

Answer 34

metric

Question 35

Occlusion – metric, non-metric, or relative metric?

Answer 35

non-metric

Question 36

Familiar size – metric, non-metric, or relative metric?

Answer 36

metric

Question 37

Motion parallax – metric, non-metric, or relative metric?

Answer 37

relative metric

Question 38

Relative size – metric, non-metric, or relative metric?

Answer 38

relative metric

Question 39

Relative height – metric, non-metric, or relative metric?

Answer 39

relative metric

Question 40

Binocular disparity – metric, non-metric, or relative metric?

Answer 40

relative metric

Question 41

Aerial perspective

Answer 41

pictoral cue where far away objects tend to be low contrast/

near objects are high contrast