1. Chapter 10: Perceiving Depth and Size

2. Oculomotor Cues
Oculomotor cues are based on sensing the position of the eyes and muscle tension
Convergence - inward movement of the eyes when we focus on nearby objects
Accommodation - change in the shape of the lens when we focus on objects at different distances 2

3. Monocular Cues Monocular cues come from one eye
Pictorial cues - sources of depth information that come from 2-D images, such as pictures
Occlusion - when one object partially covers another
Relative height - objects below the horizon that are higher in the field of vision are more distant
Objects above the horizon lower in the visual field are more distant 3

4. Monocular Cues - continued
Relative size - when objects are equal size, the closer one will take up more of your visual field
Perspective convergence - parallel lines appear to come together in the distance
Familiar size - distance information based on our knowledge of object size 4

5. Figure 10.3 (a) A scene in Tucson, Arizona, containing a number of depth cues: occlusion (the cactus on the right occludes the hill, which occludes the mountain); relative height (the far motorcycle is higher in the field of view than the closer motorcycle); relative size (the far motorcycle and telephone pole are smaller than the near ones); and perspective convergence (the sides of the road converge in the distance). (b) 1, 2, and 3 indicate the increasing height in the field of view of the bases of the motorcycles and the far telephone pole, which reveals that being higher in the field of view causes objects on the ground to appear farther away; 4 and 5 reveal that being lower in the field of view causes objects in the sky to appear farther away.
Figure 10-3 p229

6. Figure 10. 4 Pietro Perugino. Christ Handing the Keys to St
Figure 10.4 Pietro Perugino. Christ Handing the Keys to St. Peter (Sistine Chapel). The convergence of lines on the plaza illustrates perspective convergence. The sizes of the people in the foreground and middle ground illustrate relative size.
Figure 10-4 p230

7. Monocular Cues - continued
Atmospheric perspective - distance objects are fuzzy and have a blue tint
Texture gradient - equally spaced elements are more closely packed as distance increases
Shadows - indicate where objects are located
Enhance 3-D of objects 7

8. Figure 10.6 A scene on the coast of Maine showing the effect of atmospheric perspective.
Figure 10-6 p231

9. Figure 10. 7 Texture gradients created by marathon runners and flowers
Figure 10.7 Texture gradients created by marathon runners and flowers. The increasing fineness of texture as distance increases enhances the perception of depth.
Figure 10-7 p231

10. Figure 10.8 (a) Where are the spheres located in relation to the checkerboard? (b) Adding shadows makes their location clearer.
Figure 10-8 p231

11. Figure 10.9 (a) Early morning shadows emphasize the mountain’s contours. (b) When the sun is overhead, the shadows vanish, and it becomes more difficult to see the mountain’s contours.
Figure 10-9 p232

12. Covering an object is deletion Uncovering an object is accretion
Motion-Produced Cues
Motion parallax - close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly
Deletion and accretion - objects are covered or uncovered as we move relative to them
Covering an object is deletion
Uncovering an object is accretion 12

13. Binocular Depth Information
Stereoscopic depth perception
Differences between 2D and 3D movies
“Stereo Sue”
Strabismus 13

14. Binocular disparity - difference in images from two eyes
Difference can be described by examining corresponding points on the two retinas 14

15. Disparity (Geometrical) Created Stereopsis (Perceptual)
Stereopsis - depth information provided by binocular disparity
Stereoscope uses two pictures from slightly different viewpoints.
Random-dot stereogram has two identical patterns with one shifted in position. 15

16. Figure 10. 19 The two images of a stereoscopic photograph
Figure The two images of a stereoscopic photograph. The difference between the two images, such as the distances between the front cactus and the window in the two views, creates retinal disparity. This creates a perception of depth when the left image is viewed by the left eye and the right image is viewed by the right eye.
Figure p239

17. Disparity (Geometrical) Created Stereopsis (Perceptual) - continued
Three types of 3D TV
Passive – polarized glasses
Active – electronic shutter glasses
Lenticular – mini lenses on screen, no glasses needed 17

18. Figure 10.20 Three types of 3-D TV. See text for details.
Figure p239

19. Figure 10. 21 (a) A random-dot stereogram
Figure (a) A random-dot stereogram. (b) The principle for constructing the stereogram. See text for an explanation.
Figure p240

20. The Correspondence Problem
How does the visual system match images from the two eyes?
Matches may be made by specific features of objects.
This may not work for objects like random-dot stereograms.
A satisfactory answer has not yet been proposed. 20

21. The Physiology of Binocular Depth Perception
Neurons have been found that respond best to binocular disparity.
These are called binocular depth cells or disparity selective cells.
These cells respond best to a specific degree of absolute disparity between images on the right and left retinas.
Disparity tuning curve 21

22. The Physiology of Binocular Depth Perception - continued
Experiment by Blake and Hirsch
Cats were reared by alternating vision between two eyes.
Results showed that they:
had few binocular neurons.
were unable to use binocular disparity to perceive depth. 22

23. The Physiology of Binocular Depth Perception - continued
Experiment by DeAngelis et al.
Monkey trained to indicate depth from disparate images.
Disparity-selective neurons were activated by this process.
Experimenter used microstimulation to activate different disparity-selective neurons.
Monkey shifted judgment to the artificially stimulated disparity. 23

24. Distance and size perception are interrelated
Perceiving Size
Distance and size perception are interrelated
Experiment by Holway and Boring
Observer was at the intersection of two hallways.
A luminous test circle was in the right hallway placed from 10 to 120 feet away.
A luminous comparison circle was in the left hallway at 10 feet away. 24

25. Perceiving Size - continued
Experiment by Holway and Boring
On each trial the observer was to adjust the diameter of the test circle to match the comparison.
Test stimuli all had same visual angle (angle of object relative to the observer’s eye).
Visual angle depends on both the size of the object and the distance from the observer. 25

26. Figure 10. 26 Setup of Holway and Boring’s (1941) experiment
Figure Setup of Holway and Boring’s (1941) experiment. The observer changes the diameter of the comparison circle in the left corridor to match his or her perception of the size of test circles presented in the right corridor. Each test circle has a visual angle of 1 degree and is presented separately. This diagram is not drawn to scale. The actual distance of the far test circle was 100 feet.
Figure p243

27. Perceiving Size - continued
Part 1 of the experiment provided observers with depth cues.
Judgments of size were based on physical size.
Part 2 of the experiment provided no depth information.
Judgments of size were based on size of the retinal images. 27

28. Perception of an object’s size remains relatively constant.
Size Constancy
Perception of an object’s size remains relatively constant.
This effect remains even if the size of the retinal image changes.
The changes in distance and retinal size balance each other 28

29. Nonveridical perception occurs during visual illusions.
Müller-Lyer illusion:
Straight lines with inward fins appear shorter than straight lines with outward fins.
Lines are actually the same length. 29

30. Why does this illusion occur? Misapplied size-constancy scaling:
Müller-Lyer Illusion
Why does this illusion occur?
Misapplied size-constancy scaling:
Size constancy scaling that works in 3-D is misapplied for 2-D objects.
Observers unconsciously perceive the fins as belonging to outside and inside corners.
Outside corners would be closer and inside corners would be further away. 30

31. Figure 10. 36 The Müller-Lyer illusion
Figure The Müller-Lyer illusion. Both lines are actually the same length.
Figure p249

32. Figure According to Gregory (1966), the Müller-Lyer line on the left corresponds to an outside corner, and the line on the right corresponds to an inside corner. Note that the two vertical lines are the same length (measure them!).
Figure p249

33. Müller-Lyer Illusion - continued
Since the retinal images are the same, the lines must be different sizes.
Problems with this explanation:
The “dumbbell” version shows the same perception even though there are no “corners.”
The illusion also occurs for some 3-D displays. 33

34. Figure 10. 38 The “dumbbell” version of the Müller-Lyer illusion
Figure The “dumbbell” version of the Müller-Lyer illusion. As in the original Müller-Lyer illusion, the two straight lines are actually the same length.
Figure p250

35. One possible explanation is misapplied size-constancy scaling.
Ponzo Illusion
Horizontal rectangular objects are placed over railroad tracks in a picture.
The far rectangle appears larger than the closer rectangle but both are the same size.
One possible explanation is misapplied size-constancy scaling. 35

36. Figure 10. 41 The Ponzo (or railroad track) illusion
Figure The Ponzo (or railroad track) illusion. The two animals are the same length on the page (measure them), but the upper one appears larger.
Figure p251

37. Two people of equal size appear very different in size in this room.
The Ames Room
Two people of equal size appear very different in size in this room.
The room is constructed so that:
The shape looks like a normal room when viewed with one eye.
The actual shape has the left corner twice as far away as the right corner. 37

38. Figure The Ames room. Both women are actually the same height, but the woman on the right appears taller because of the distorted shape of the room. (The Exploratorium/S. Schwartzenberg.)
Figure p251

39. Figure 10. 43 The Ames room, showing its true shape
Figure The Ames room, showing its true shape. The person on the left is actually almost twice as far away from the observer as the person on the right; however, when the room is viewed through the peephole, this difference in distance is not seen. In order for the room to look normal when viewed through the peephole, it is necessary to enlarge the left side of the room.
Figure p251

40. The Ames Room - continued
One possible explanation - size-distance scaling
Observer thinks the room is normal.
Women would be at same distance.
Woman on the left has smaller visual angle (R).
Due to the perceived distance (D) being the same her perceived size (S) is smaller 40

41. The Ames Room - continued
Another possible explanation - relative size
Perception of size depends on size relative to other objects.
One woman fills the distance between the top and bottom of the room.
The other woman only fills part of the distance
Thus, the woman on the right appears taller 41

42. One possible explanation:
Moon Illusion
The moon appears larger on the horizon than when it is higher in the sky.
One possible explanation:
Apparent-distance theory - horizon moon is surrounded by depth cues while moon higher in the sky has none.
Horizon is perceived as further away than the sky - called “flattened heavens”. 42

43. Moon Illusion - continued
Since the moon in both cases has the same visual angle, it must appear larger at the horizon.
Another possible explanation:
Angular size-contrast theory - the moon appears smaller when surrounded by larger objects
Thus, the large expanse of the sky makes it appear smaller
Actual explanation may be a combination of a number of cues.
Other factors are: atmospheric perspective, color, and oculomotor cues. 43