Space

2. Space/Depth Perception Lecture Outline Cue Approach A. Oculomotor Cues B. Pictoral Cues C. Motion-produced Cues D. Binocluar Disparity *stereoscope 1. Corresponding Retinal Points 2. Disparity Information and the Brain Perception of Size A. Visual Angle, Retinal Size, and Distance B. Perceiving Size as Visual Angle Changes *Law of Size Constancy C. Size Constancy and Depth Perception *Law of Visual Angle *Emmert’s Law D. Illusions of Size

3. I. Cue Approach The cue approach postulates connections between stimuli in the environment, the images these stimuli present to the retina, and perceived depth We will discuss four groups of depth cues Oculomotor Cues Pictoral Cues Motion-produced Cues Binocular Disparity

4. Oculomotor Cues These are cues that depend on our ability to sense the position of our eyes and tension in our eye muscles Convergence/Divergence Convergence – eyes move inward to focus close up objects Divergence – eyes move away from each other to focus an object farther away.

5. Oculomotor Cues Accommodation – the shape of the lens changes shape to focus objects Lens bulges to focus near objects Lens flattens to focus objects farther away

6. Pictoral Cues Cues that can be depicted in a still picture or from the picture formed on the retina. Overlap (Interposition or Occlusion) – objects that are closer to us block our view of objects that are farther away

7. Relative Size Larger objects appear to be closer (person who is farther away appears smaller)

8. Relative Height Objects closer to the horizon appear to be farther away

9. Atmospheric/Aerial Perspective Distant objects appear less sharp because the observer must look through air and particles between them and the object.

10. Linear Perspective Convergence of parallel lines.

11. Texture Gradient Can see more detail in close objects. Lose detailed texture information for farther objects.

12. Shading/Relative Brightness Surfaces facing a light source are brighter and surfaces facing away are darker.

13. Shading/Relative Brightness

14. Shading/Relative Brightness

15. Motion-Produced Cues These are cues that rely on movement to the observer, or movement of objects in the environment Motion Parallax Deletion and Accretion Kinetic Depth Effect

16. Motion Parallax The direction and speed of motion is different for objects due to their position relative to the observer’s fixation point.

17. Deletion and Accretion Deletion – observer moves and closer object covers more of an object farther away. Accretion – observer moves and closer object covers less of an object farther away.

18. Kinetic Depth Effect A 2-dimensional picture is seen in 3-D becaued of motion. kinetic depth

19. Binocular Disparity Binocular means it depends on both eyes. Relates to the fact that we have two eyes that see the world from slightly different positions.

20. Binocular Disparity That the position of our eyes is related to depth perception has been illustrated by the use of a stereoscope.

21. Stereoscope The stereoscope uses slightly offset pictures to produce the illusion of depth.

22. Binocular Disparity Because the eyes present us with two different images of the visual scene, we must combine the disparate images to form a single percept of the scene. This is called fusion. To enable us to merge the disparate images, we have corresponding retinal points.

23. Corresponding Retinal Points For every point on one retina, there is a corresponding point on the other retina. These corresponding points on each retina would overlap if one retina could be slid on top of the other.

24. Retinal Disparity

25. Handouts

26. Disparity Information and the Brain Barlow, Blakemore, & Pettigrew (1967) found cells in the cortex of the cat that respond best to stimuli that fall on points which are separated by a specific degree on the retina. Hubel & Weisel (1970) found these cells in the visual cortex of monkeys and they identified them as binocular depth cells.

27. Binocular Depth Cells

28. III. Perception of Size Visual Angle, Retinal Size, and Distance Perceiving Size as Visual Angle Changes -Law of Size Constancy Size Constancy and Depth Perception -Law of Visual Angle -Emmert’s Law Illusions of Size

29. Visual Angle, Retinal Size, and Distance The distance of an object from an observer affects the size of the object on the retina (affects visual angle). Visual Angle – a description of the amount of space taken up on the retina by an object.

30. Perception of Size Perceiving Size as Visual Angle Changes Law of Size Constancy Size Constancy and Depth Perception Holway & Boring (1941)

31. Holway & Boring Study At the beginning of each trial the test and comparison circles are 1o of visual angle. On each trial the observer’s task is to adjust the diameter of the comparison circle to match the actual diameter of the test circle.

32. Holway & Boring Study 4 Phases Phase 1 – the observer has all depth cues so judgments were based on the physical sizes of the circles Results supported the Law of Size Constancy

33. Holway & Boring Study

34. Holway & Boring Study Holway and Boring began removing depth cues Phase 2 – Observer’s performed the task monocularly What depth cues were removed?

35. Holway & Boring Study

36. Holway & Boring Study Phase 3 – Observers looked through a peephole Observers begin to see the circles as the same size – not as much adjustment

37. Holway & Boring Study

38. Holway & Boring Study Phase 4 – the hallway was draped with black drapes. Minimal adjustment of the comparison stimuli by observers. With the elimination of depth cues the perception of size follows the law of visual angle more closely.

39. Holway & Boring Study

40. Holway & Boring Study The results of the Holway & Boring study suggest that depth information, as well as visual angle are important for size constancy Gregory (1966) proposed that we have a constancy scaling mechanism Size-distance scaling Emmert’s Law

41. Illusions of SizeAmes Room

42. Illusions of SizeAmes Room

43. Illusions of SizeMüller-Lyer Illusion

44. Illusions of SizePonzo Illusion

45. Illusions of SizeMonsters