March 9. Do Now: Explain the Gestalt theory of perception and two examples. EQ- How do we perceive depth and motion?

Transcription

1 March 9 EQ- How do we perceive depth and motion? Agenda: 1. Perception Theories 2. Brain Games Do Now: Explain the Gestalt theory of perception and two examples. Table of Contents: 87. March 9 & Other Perception Theories Notes and Images 89. Perception Practice Q s Homework: Perception Practice Q s Test on Friday!

2 Some fun perceptual illusions

3 Perceptual Illusions Illusions provide good examples in understanding how perception is organized. Studying faulty perception is as important as studying other perceptual phenomena. Line AB is longer than line BC. 3

4 The images are exactly the same except for the thick black area in the right image (an example of the Poggendorff illusion (1860)). In the figure on the right, there appear to be two continuous diagonal lines: a red and a blue line. What occurs in your visual system that could account for the appearance of the continuous diagonal lines? 4

5 Tall Arch In this picture, the vertical dimension of the arch looks longer than the horizontal dimension. However, both are equal. Rick Friedman/ Black Star 5

6 Illusion of a Worm 1981, by permission of Christoph Redies and Lothar Spillmann and Pion Limited, London The figure on the right gives the illusion of a blue hazy worm when it is nothing else but blue lines identical to the figure on the left. 6

7 3-D Illusion Reprinted with kind permission of Elsevier Science-NL. Adapted from Hoffman, D. & Richards, W. Parts of recognition. Cognition, 63, It takes a great deal of effort to perceive this figure in two dimensions. 7

8 Innervisions Depth Perception Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception. Visual Cliff 8

9 How do we judge depth? Binocular Cues- require both eyes Retinal disparity: Images from the two eyes differ (they are 2 ½ inches apart) The brain compares these two images (the differences between them) to determine distance. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a finger sausage as shown in the inset. 9

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11 Real Life Binocular Cues: 3D movies play on Binocular Cues for Depth Perception! They use two cameras that are a few inches apart and overlay the images. The glasses allow you to see one view with the left eye and the other with the right eye- creating the impression of depth!

12 Another Binocular Cue: Convergence: Neuromuscular cues. When two eyes move inward (towards the nose) to see near objects and outward (away from the nose) to see faraway objects. 12

13 Depth Perception Method: Monocular Cues: require only one eye Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away. 13

14 Monocular Cues Interposition: Objects that block other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli. 14

15 Monocular Cues Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower. Image courtesy of Shaun P. Vecera, Ph. D., adapted from stimuli that appered in Vecrera et al.,

16 Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance. The New Yorker Collection, 2002, Jack Ziegler from cartoonbank.com. All rights reserved. 16

17 Monocular Cues Relative Clarity- given two object, the hazier one appears to be further away Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away. From Perceiving Shape From Shading by Vilayaur S. Ramachandran by Scientific American, Inc. All rights reserved. 17

18 Monocular Cues Relative motion: As we move, stable objects appear to move as well! If you fixate on an object while you are moving, objects behind that point (further away) will move in your direction and objects in front of that point (closer) will move in the opposite direction 18

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21 Supplies: 1. Cup 2. Small objects for dropping Binocular Cues and Monocular Cues Lab Steps: 1. Partner 1 sits criss-cross apple sauce against the wall. 2. Partner 2 places the cup two squares in front of the person. 3. Partner 1 closes and covers one eye. 4. Partner 2- slowly move the object above and around the cup. The object should be 1-2 ft above the cup. 5. Partner 1- say drop it when the object appears to be directly over the cup. 6. Partner 2- drop the object. 7. Record the number of times out of 3 when partner 1 gets it right. 8. Move the cup a total of 8-10 squares away. Repeat the lab with one eye closed and covered. 9. Repeat the lab with both eyes open, both 2 squares in front and 8-10 squares in front. 10.Make sure you record the # of times correct for each trial.

22 How do we perceive motion?

23 Motion Perception Motion Perception: Objects traveling towards us grow in size and those moving away shrink in size. The same is true when the observer moves to or from an object. 23

24 Apparent Motion Phi Phenomenon: When lights flash at a certain speed they tend to present illusions of motion. Neon signs use this principle to create motion perception. Two lights flashing one after the other. One light jumping from one point to another: Illusion of motion. 24

25 Perceptual Constancy Perceiving objects as unchanging even as illumination and retinal images change. Perceptual constancies include constancies of shape and size. Shape Constancy 25

26 Size Constancy Stable size perception amid changing size of the stimuli. Size Constancy 26

27 Lightness Constancy The color and brightness of square A and B are the same. 27

28 Color Constancy Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object. Color Constancy 28

29 Optical Illusions can play on our perception of size and distance by using these monocular cues

30 Size-Distance Relationship The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues. Alan Choisnet/ The Image Bank From Shepard,

31 Size-Distance Relationship- Ames Room Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the two corners of the room. Both photos from S. Schwartzenberg/ The Exploratorium 31

32 Ames Room The Ames room is designed to demonstrate the sizedistance illusion. 32

33 Perceptual Interpretation Immanuel Kant ( ) maintained that knowledge comes from our inborn ways of organizing sensory experiences. John Locke ( ) argued that we learn to perceive the world through our experiences. We are born with some basic perception but we learn others as we experience life. 33

34 Restored Vision After cataract surgery, blind adults were able to regain sight. These individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle and a triangle (Von Senden, 1932). 34

35 Facial Recognition After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed. Courtesy of Richard LeGrand 35

36 Perceptual Adaptation Visual ability to adjust to an artificially displaced visual field, e.g., prism glasses. When you get new glasses- it takes a short time before you get used to them Ex: special glasses that made everything appear upside down- took 8 days for eyes to adjust Courtesy of Hubert Dolezal 36

37 Perceptual Set A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures. From Shepard,

38 Perceptual Set Other examples of perceptual set. Dick Ruhl Frank Searle, photo Adams/ Corbis-Sygma (a) Loch ness monster or a tree trunk; (b) Flying saucers or clouds? 38

39 Other examples of perceptual set: 1.In surveys, McDonalds fries are rated as tasting better than fries in a plain white bag even when they are the same fries. 2.Favorite brand soda tastes better than others even when it has been spiked with vinegar Our perception of things is influenced by our past experiences and our emotions. Ex: the distance you have to walk somewhere appears further when you are already tired.

40 Perception Revisited Is perception innate or acquired? 40