3D Space Perception - PowerPoint Presentation

Slide1

3D Space Perception

(aka Depth Perception)Slide2

3D Space Perception

The flat retinal image problem

:

How do we reconstruct 3D-space from 2D image?

What information is available to support

this process?

Interaction between

Perceived Size

and

Perceived Distance

(both depend upon “scaling”)Slide3

Size Constancy

Perceived size is not slavishly linked to retinal size; otherwise your car would appear to be smaller when observed at increasing distances.

Instead, perceived size tends to remain invariant across observation distance…a phenomenon known as

size constancy

.

Perceived size depends upon the psychological scaling of retinal size relative to perceived distance. Hence, size, distance and 3D visual perception are all based upon a more complex process known as

spatial scaling

.

Corollary

:

Perceived Speed = retinal velocity x scaled distanceSlide4

Failures of Size Constancy

The Moon IllusionSlide5

Failures of Size Constancy

The

Buechet

Chair

Click

here

for moreSlide6

The Ames Room

(Iowa State University at Ames, IA)

Failures of Size ConstancySlide7

3D-Depth Information “Cues”Slide8

Oculomotor

Information

State of Accommodation

State of

VergenceSlide9

Accommodation

In theory, the

efferent

signal driving the

ciliary

muscles (and/or

afferent

feedback from stretch sensors in the

ciliary

muscles) could be used by higher-order visual processes to help scale 3D space and/or visual distance.

There is little evidence to support this hypothetical role of accommodation.Slide10

Vergence

Eye Movements

Support for the role of efferent/afferent 3D information from

vergence

eye movements comes from:

“Tower Speed Illusion

”Slide11

Static Monocular

Sources of 3D Information

Occlusion

Familiar Size (Relative Size)

Texture Gradients

Linear Perspective

Aerial Perspective (Atmospheric extinction)

Shadow CastingSlide12

Occlusion

Near objects

block visual access to far objectsSlide13

Linear Perspective

Parallel lines on the

v

isual plane converge

t

oward the “vanishing

p

oint” with increasing

o

bservation distance

This law of projective

g

eometry provides a

s

trong cue about distance

a

nd 3D space.Slide14

Linear PerspectiveSlide15

Linear Perspective in the Service of ArtSlide16

Familiar Size/Relative Size

Objects of the same physical size

project different size retinal images depending upon the observation distance.

This

knowledge

and prior experience contribute to 3D space perception.

What is the height of this

s

culpture in feet?Slide17

Familiar Size Cue

Easter Island Sculpture

w

ithout Familiar Size Cue

Easter Island Sculpture

w

ith Familiar Size Cue

Novel objects can be psychologically scaled given visual references

o

f known size. For example…Slide18

Texture Gradients

An extended surface

w

ith uniform spatial

t

exture will project a retinal image with a non-uniform texture gradient that increases in spatial frequency as observation distance increases.Slide19

Aerial Perspective

Particulate matter in the atmosphere scatters light; reducing contrast and intensity of the retinal image.

The light from distant objects must pass through more atmosphere than the light from near objects.Slide20

Shadow Casting

Just as occlusion of objects serves as a powerful cue for depth…

occlusion of the illuminant

(sun) forms shadows which provide a powerful source of information for extracting 3D representations from a 2D retinal image.Slide21

Identify the Monocular Depth Cues

A Rainy Day in Paris

Gustav

Caillebotte

(1848-1894) Slide22

Identify the Monocular Depth Cues

A Rainy Day in Paris

Gustav

Caillebotte

(1848-1894)

Linear Perspective

Occlusion

Texture Gradient

Aerial Perspective

Shadow Casting

Familiar SizeSlide23

Dynamic Monocular

Sources of 3D Information

Motion Parallax

Relative Angular Velocity

Radial Expansion/Looming

Moving ShadowsSlide24

Motion Parallax

Motion parallax occurs when an observer fixates a point at intermediate distance and then rotates their head.

Objects in the distance appear to move WITH head motion; while objects closer than the fixation plane appear to move AGAINST the rotation of the head.

Motion Parallax and Dynamic

Shadow Casting

DemoSlide25

Optic Flow: Radial Expansion

Optic Flow and Driving

DemoSlide26

Delta Angular Velocity/Angular Size

Lecture Note

:

Need for improved Slow Moving Vehicle sign/Slide27

Binocular Depth PerceptionSlide28

Advantages of Binocularity

Redundancy (survival value)

Stereopsis

(Predators)

Large Field-of-View (Prey)

Binocular summation improves sensitivity

by √2 (

signal:noise

ratio sampling theory)

Binocular acuity better than monocular;

Same for CSF and many other functionsSlide29

Binocular Vision

(cont.)

Binocular rivalry

(Role of the “dominant” eye)

Autokinesis

phenomenonSlide30

Stereopsis

Ability to use binocular

retinal disparity

information to extract relative depth information from the retinal image pairs

Retinal “mismatch” can be used to reconstruct much of the missing 3

rd

dimension from the flat retinal imagesSlide31

Retinal Disparity

Understanding begins with a consideration of the geometry of the

horopterSlide32

Horopter

(Corresponding Retinal Images)

The

HOROPTER

is an imaginary

s

urface whose points are all at the

s

ame distance as the fixation point.

Points on the

horopter

project to

c

orresponding locations on the temporal and nasal retinas,respectively.These corresponding locationsexhibit zero retinal disparityi.e., D = d

temporal – dnasal = 0Slide33

“Crossed” and Uncrossed” Retinal Disparity

The

corresponding

locations for the

“closer”

green stimulus

exhibits

positive

retinal

disparity

D =

d

temporal

– dnasal > 0(or “crossed” disparity)The corresponding locations for the“farther” red stimulus exhibitsnegative retinal disparity D = dtemporal – dnasal < 0(or “uncrossed” disparity)Slide34

Depth

Recovery

by

Binocular

Cortical

CellsSlide35

Panum’s

Fusion AreaSlide36

Nativists v. Empiricists “Debate”

Nativist position

The CNS is capable of processing many environmental invariants at birth – giving rise to direct perception (e.g., James Gibson)

Empiricist position

Sensory information is too impoverished to explain perceptual experience without recourse to

knowledge

about the world; it is based upon “unconscious inference” (e.g., Bishop Berkeley)Slide37

Support for Nativism

Eleanor Gibson’s

Visual Cliff

Experiment

(and HRD replication studies)

Bela

Julesz’s

Random Dot Stereogram

paradigmSlide38

Random Dot

Stereograms

Bela

Julesz

Can retinal disparity yield perception of depth independent of knowledge about the nature of the world?

Nativist vs. Empiricist DebateSlide39

Red-Blue Anaglyph Technique

(black background)

Anaglyph glasses transmit RED and MAGENTA dots to the left eye; and, the BLUE and MAGENTA dots to the right eye.

Demo stimulus from USD’s PSYC 301 Lab