PPT

Report
3D Space Perception
(aka Depth Perception)
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”)
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 distance
Failures of Size Constancy
The Moon Illusion
Failures of Size Constancy
The Buechet Chair
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Failures of Size Constancy
The Ames Room
(Iowa State University at Ames, IA)
3D-Depth Information “Cues”
Oculomotor Information
• State of Accommodation
• State of Vergence
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.
Vergence Eye Movements
Support for the role of
efferent/afferent 3D
information from
vergence eye
movements comes
from:
“Tower Speed Illusion”
and
Botox Treatment of
Rectus Muscles in
Strabismus Surgery
Static Monocular
Sources of 3D Information
•
•
•
•
•
•
Occlusion
Familiar Size (Relative Size)
Texture Gradients
Linear Perspective
Aerial Perspective (Atmospheric extinction)
Shadow Casting
Occlusion
Near objects
block visual access to far objects
Linear Perspective
Parallel lines on the
visual plane converge
toward the “vanishing
point” with increasing
observation distance
This law of projective
geometry provides a
strong cue about distance
and 3D space.
Linear Perspective
Linear Perspective in the Service of Art
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
sculpture in feet?
Familiar Size Cue
Novel objects can be psychologically scaled given visual references
of known size. For example…
Easter Island Sculpture
without Familiar Size Cue
Easter Island Sculpture
with Familiar Size Cue
Texture Gradients
An extended surface
with uniform spatial
texture will project a
retinal image with a
non-uniform texture
gradient that
increases in spatial
frequency as
observation
distance increases.
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.
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.
Identify the Monocular Depth Cues
A Rainy Day in Paris
Gustav Caillebotte (1848-1894)
Identify the Monocular Depth Cues
Linear Perspective
Occlusion
Texture Gradient
Aerial Perspective
Shadow Casting
Familiar Size
A Rainy Day in Paris
Gustav Caillebotte (1848-1894)
Dynamic Monocular
Sources of 3D Information
•
•
•
•
Motion Parallax
Relative Angular Velocity
Radial Expansion/Looming
Moving Shadows
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 Demo
Optic Flow: Radial Expansion
Optic Flow and Driving Demo
Delta Angular Velocity/Angular Size
Lecture Note:
Need for improved Slow Moving
Vehicle sign/
Binocular Depth Perception
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 functions
Binocular Vision (cont.)
• Binocular rivalry
(Role of the “dominant” eye)
• Autokinesis phenomenon
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 3rd dimension from the
flat retinal images
Retinal Disparity
Understanding begins with a consideration of the
geometry of the horopter
Horopter
(Corresponding Retinal Images)
The HOROPTER is an imaginary
surface whose points are all at the
same distance as the fixation point.
Points on the horopter project to
corresponding locations on the
temporal and nasal retinas,
respectively.
These corresponding locations
exhibit zero retinal disparity
i.e.,
D = dtemporal – dnasal = 0
“Crossed” and Uncrossed” Retinal Disparity
The corresponding locations for the
“closer” green stimulus exhibits
positive retinal disparity
D = dtemporal – dnasal > 0
(or “crossed” disparity)
The corresponding locations for the
“farther” red stimulus exhibits
negative retinal disparity
D = dtemporal – dnasal < 0
(or “uncrossed” disparity)
Depth
Recovery
by
Binocular
Cortical
Cells
Panum’s Fusion Area
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)
Support for Nativism
• Eleanor Gibson’s Visual Cliff Experiment
(and HRD replication studies)
• Bela Julesz’s Random Dot Stereogram
paradigm
Random Dot
Stereograms
Can retinal disparity yield perception
of depth independent of knowledge
about the nature of the world?
Nativist vs. Empiricist Debate
Bela Julesz
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

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