1. 3D Space Perception (aka Depth Perception)

2. 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”)

3. 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

4. Failures of Size Constancy
The Moon Illusion

5. Failures of Size Constancy
The Buechet Chair
Click here for more

6. The Ames Room (Iowa State University at Ames, IA)
Failures of Size Constancy
Figure 12.17
Horizontal line at the bottom appears smaller than the one above, even though both are of identical length.
So-called Ponzo illusion arises because the two segments are taken to be at different relative distances by the pictorial cue of the converging lines.
Upper line segment is perceived to be larger in order to satisfy the size-distance relationship.
The Ames Room (Iowa State University at Ames, IA)

7. 3D-Depth Information “Cues”

8. Oculomotor Information
State of Accommodation
State of Vergence

9. 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.

10. 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

11. Static Monocular Sources of 3D Information
Occlusion
Familiar Size (Relative Size)
Texture Gradients
Linear Perspective
Aerial Perspective (Atmospheric extinction)
Shadow Casting

12. Occlusion
Near objects
block visual access to far objects

13. 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.

14. Linear Perspective Figure 12.17
Horizontal line at the bottom appears smaller than the one above, even though both are of identical length.
So-called Ponzo illusion arises because the two segments are taken to be at different relative distances by the pictorial cue of the converging lines.
Upper line segment is perceived to be larger in order to satisfy the size-distance relationship.

15. Linear Perspective in the Service of Art

16. 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?

17. Familiar Size Cue
Novel objects can be psychologically scaled given visual references
of known size. For example…
Easter Island Sculpture
with Familiar Size Cue
Easter Island Sculpture
without Familiar Size Cue

18. 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.

19. 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.

20. 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.

21. Identify the Monocular Depth Cues
A Rainy Day in Paris
Gustav Caillebotte ( )

22. Identify the Monocular Depth Cues
Linear Perspective
Occlusion
Texture Gradient
Aerial Perspective
Shadow Casting
Familiar Size
A Rainy Day in Paris
Gustav Caillebotte ( )

23. Dynamic Monocular Sources of 3D Information
Motion Parallax
Relative Angular Velocity
Radial Expansion/Looming
Moving Shadows

24. 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

25. Optic Flow: Radial Expansion
Optic Flow and Driving Demo

26. Delta Angular Velocity/Angular Size
Lecture Note:
Need for improved Slow Moving Vehicle sign/

27. Binocular Depth Perception

28. 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

29. Binocular Vision (cont.)
Binocular rivalry (Role of the “dominant” eye)
Autokinesis phenomenon

30. 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

31. Retinal Disparity Understanding begins with a consideration of the geometry of the horopter

32. 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

33. “Crossed” and Uncrossed” Retinal Disparity
The corresponding locations for the
“closer” green stimulus exhibits
positive retinal disparity
D = dtemporal – dnasal > 0 (or “crossed” disparity)
“farther” red stimulus exhibits
negative retinal disparity
D = dtemporal – dnasal < 0 (or “uncrossed” disparity)

34. Depth Recovery by Binocular Cortical Cells

35. Panum’s Fusion Area Figure 12.27
Finite range of disparities encoded by binocular neurons means that only a limited range of relative depths can be captured by the visual system.
Panum's fusional area defines the depth range in front of and behind the horopter within which an object is visually fused and capable of generating stereoscopic depth perception.
Objects outside this area are seen as double (diplopic).

36. 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)

37. Support for Nativism
Eleanor Gibson’s Visual Cliff Experiment (and HRD replication studies)
Bela Julesz’s Random Dot Stereogram paradigm

38. 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

39. 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