M O Perceptual Organization 13 D U L E

OUTLINE OF RESOURCES I. Introducing Perceptual Organization Lecture/Discussion Topics: Object Recognition (p. 3) (p. 4) Classroom Exercise: Perceptual Illusions and Principles (p. 3) Classroom Exercise/Student Project: The Wundt-Jastrow Illusion (p. 2) Student Projects: Playing Cards and Illusions (p. 4) Instant Object Recognition (p. 4) Video: Scientific American Frontiers, 2nd ed., Segment 10: Lights, Camera, Magic!* PsychSim 5: Visual Illusions (p. 2) ActivePsych: Digital Media Archive, 2nd ed.: A Variety of Visual Illusions* (Also appropriate for the section on the size-distance relationship) NEW II. Form Perception Classroom Exercises: Form Perception (p. 5) An Auditory Analogue of the Visual Reversible Figure (p. 6) The Ganzfeld (p. 6) III. Depth Perception Lecture/Discussion Topic: Autostereograms (p. 8) Classroom Exercise: Binocular Vision (p. 8) Classroom Exercises/Student Projects: A Kinetic Depth Illusion (p. 7) (also appropriate with the other activi- ties suggested under Introducing Perceptual Organization) Binocular Vision Versus Monocular Vision (p. 8) ActivePsych: Digital Media Archive, 2nd ed.: The Visual Cliff* NEW IV. Perceptual Constancy Lecture/Discussion Topic: Auditory Organization (p. 10) NEW Classroom Exercises: Variation in the Size of the Retinal Image (p. 8) Perceived Distance and Perceived Size (p. 9) Brightness Contrast (p. 10) UPDATED Classroom Exercise/Student Project: Perceived Lunar Size (p. 9) Videos: Digital Media Archive, 1st ed.: Psychology, Video Clip 5: Depth Cues* Digital Media Archive, 1st ed.: Psychology, Video Clip 4: Müller-Lyer Illusion*

*Video titles followed by an asterisk are not repeated within the core resource module. They are listed, with running times, in the Preface of these resources and described in detail in their Faculty Guides, which are available at www.worthpublishers.com/mediaroom.

1 2 Module 13 Perceptual Organization

MODULE OBJECTIVES After completing their study of this module, students should be able to: 1. Discuss Gestalt psychology’s contribution to our understanding of perception. 2. Explain the figure-ground relationship, and identify principles of perceptual grouping in form perception. 3. Discuss research on depth perception involving the use of the visual cliff, and describe the binocular and monocular cues in depth perception. 4. Describe the perceptual constancies, and show how the perceived size-distance relationship operates in visual illusions.

MODULE OUTLINE

I. Introducing Perceptual Organization (p. 171) Illusions reveal the ways we normally organize and interpret our sensations, so a discussion of illusions, with some fun demonstrations, might be a good way to introduce the basics of perception. Following are sever- al suggestions for such a discussion.

PsychSim 5: Visual Illusions With this program, students see how the Müller-Lyer, Ponzo, and horizontal-vertical illusions work by trying to guess the length of a line or the size of objects at varying distances. The results of their performance are graphed. You may prefer to use this in conjunction with the explanation of the illusions in the latter part of this module.

Classroom Exercise/Student Project: The Wundt-Jastrow Illusion David Pick suggests use of the Wundt-Jastrow illusion to highlight the distinction between sensation and per- ception. This compelling and reliable illusion is easy to demonstrate and is a wonderful opener to class discus- sion of perception. In the right column is the template for constructing the illusion. Enlarge it approximately 300 percent, using an 11” x 17” sheet of paper and then trace two copies onto poster board. Cut out the two seg- ments for presentation in class. Initially, present them nineteenth century, when psychology was emerging as a side by side, curving in the same direction, and ask if discipline, perceptual illusions such as this one had one appears larger. This is truly a dramatic illusion with already begun to fascinate scientists. Illusions mislead the segment on the inside curve appearing undeniably us by playing on the ways we organize and interpret our larger. Reverse the position of the two segments and sensations. Understanding illusions can sometimes pro- your class will be astonished to find that the apparently vide valuable clues to the ordinary mechanisms of per- smaller segment now appears to be the larger. Then ception. place one over the other to convince your audience that Pick suggests making the illusion the basis for a they are indeed the same. Finally, present the segments project in which students attempt to discover its under- curving away from each other and they will also appear lying explanation. He suggests that they begin by equivalent. Emphasize that while the same sensation is searching the literature. It is variously referred to as the produced by the two stimuli, under certain conditions Wundt-Jastrow illusion, the Jastrow illusion, the Ring the perception of them is very different. By the late Segment illusion, and the Concentric Arc illusion. Pick Module 13 Perceptual Organization 3 notes that J. O. Robinson’s work contains the most receding in space. If this were true, the line should extensive discussion of the illusion but offers no final reappear from behind the figure at a place several explanation of it. Students might also formulate their millimeters lower than it does. own hypotheses and design appropriate experimental 2. The Gestalt Law of Pragnanz tests to be presented in class. Have students look at the figures for just a Pick, D. (1992, August). The Wundt-Jastrow illusion as moment, turn the page over, and reproduce them on demonstration of the discrepancy between sensation and another sheet. Then have them compare their draw- perception. Paper presented at the Annual Convention of ings with the originals. Did they draw a circle the American Psychological Association, Washington, instead of a tilted ellipse, a square with 90° angles, DC. a complete triangle without rounded corners, and an “X” without curved lines? If so, they have Classroom Exercise: Perceptual Illusions and demonstrated the Gestalt law of Pragnanz, which Principles states that our perceptions will always be as “good” An illusion that is easy to demonstrate and will involve as prevailing conditions allow. Literally, the entire class is the horizontal-vertical illusion (see “Pragnanz” refers to “conveying the essence of also PsychSim 5). Before students arrive, draw a 3-foot something.” We tend to simplify and perfect figures horizontal line on the chalkboard. When class begins, in our perceptions. slowly bisect it with a vertical line, asking students to raise their hands when they believe the vertical equals 3. Context Effects the horizontal. Mark the point at which half the class In the series of letters and numbers, “B” and “13” believe the lines are equal. Continue the vertical line are identical. The handwritten statements are clear- until every student agrees it equals the horizontal. Then ly legible, but did students notice that “is” and “15” measure the two lines and extend the vertical until the are identical, as are “h” in “phone” and “b” in two lines are equal. The class median will usually be 30 “number,” and “d” in “code” and “l” in “Please”? percent or so short, and rarely will a single student have In each case context determined their perception of requested a vertical line sufficiently long. While verti- the script. cal lines generally look longer than horizontal lines, the 4. The Oblique Effect effect is accentuated by the bisection. When one line is The oblique effect demonstrates the impact of liv- interrupted by another, we estimate the interrupted line ing in a carpentered world. Our visual sensitivity is as being shorter. If you draw an “L” so that the two better for horizontal and vertical stimuli than for lines are equal in length, students will be more accurate. obliquely oriented stimuli. Students need to stand Handout 13–1 can be used to introduce the text dis- back from the three stimuli (you might tape this cussion of perception. one to the wall) until they can no longer resolve 1. The Poggendorf Illusion clearly the oblique lines in the center circle. It will In the Poggendorf illusion a straight line disappears appear uniformly gray. However, they will still see at an angle behind a solid figure and reappears at a the lines in the left and right circles. People who do position that seems wrong. For each figure, have not live in a carpentered world are able to see all students indicate which line represents the continu- three equally well. ation of the diagonal line on the left. Then have Lecture/Discussion Topic: Object Recognition them use a straight edge to determine whether they As you begin your discussion of perception, remind are correct. students of the distinction between bottom-up process- Architects need to be concerned with this illu- ing (starting with entry-level sensory analysis) and top- sion. Lines hidden behind a column will look dis- down processing (using our experiences and expecta- placed when they emerge on the other side. A plane tions to interpret those sensations). Modern theories of collision in which 4 people died and another 49 object recognition make a closely related distinction were injured has also been attributed to this puz- between data-driven and conceptually driven process- zling perception. Two airplanes were preparing to ing. Stanley Coren and his colleagues use the top figure land in the New York City area in 1965 when a in Handout 13–2 to illustrate. What do students see? cloud formation between them created the Poggen- For those having difficulty, suggest that it is a drawing dorf illusion. Both pilots thought they were going of an animal they have seen many times before. If they to collide, so they each changed course—and then still can’t figure it out, sketch the drawing on the next they collided. One explanation for this illusion is page on the chalkboard or project it as an overhead. that the lower left end of the line appears nearer (Once they see the cow, they wonder how they missed it than the upper right; that is, the line is seen as initially.) 4 Module 13 Perceptual Organization

In our first look at a figure, data-driven processes Student Project: Instant Object Recognition extract shapes of various sizes and features. In the sub- Given the complexity, limits, and even predictable sequent conceptual driven process, we match the collec- errors of the perceptual process, you may want to assign tion of features with objects in our long-term memory. students a simple homework assignment that will help Organizational strategies and expectations based on our them to appreciate the counterpoint, namely, that per- knowledge of the world guide our search for patterns in ception is effective and efficient. Suggested by both sensory input. Irving Biederman and Margaret Matlin, the project Data-driven processing tends to emphasize the highlights how we recognize objects instantly. local features in object recognition. Local features are Tell students that the next time they watch televi- the detailed aspects of a figure. In contrast, the overall sion, they should adjust the sound to “mute.” With their or global aspects give the entire figure its meaningful eyes closed, they should change channels, then open shape. The bottom figure in Handout 13–2 illustrates their eyes and immediately shut them again. They the distinction between local and global processing and should repeat the exercise several times. In the fraction highlights how local features can interfere with a more of a second they have to view a channel, they will easily global percept. The figure is a computer-processed identify and interpret the images, even though they have block representation of a photograph, produced by never seen them before and do not know what to locally averaging brightness information so that the expect. Biederman indicates that most people can usual- brightness value in each of the squares is an average of ly interpret the meaning of a new scene in one-tenth of a number of brightness samples taken in the same area a second. This also explains, as Matlin notes, why view- of the picture. The strategy seeks to determine whether ers can recognize the rapidly presented images on MTV local brightness information can elicit the perception of even when they are shown at a rate of five per second. the original photograph. Squinting or looking at the photograph from a greater distance typically helps. It is, Biederman, I. (1995). Visual object recognition. In S. F. of course, a picture of Abraham Lincoln. Kosslyn & D. N. Osherson (Eds.), An invitation to cogni- tive science (2nd ed., pp. 121–165). Cambridge, MA: Coren, S., Ward, L. M., & Enns, J. T. (2003). Sensation MIT Press. and perception (6th ed.). New York: Wiley. Matlin, M. W. (2005). Cognition (6th ed.) New York: Student Project: Playing Cards and Illusions Wiley. Psychologists Jules Block and Harold Yuker have pre- pared two standard decks of playing cards with each Lecture/Discussion Topic: Visual Agnosia card containing a separate illusion. The cards (stock A discussion of visual agnosia, defined by Stanley number CR30396–35), which are accompanied by a Coren and his colleagues as “a syndrome in which brochure that explains the illusions, are available for all parts of the visual field are seen, but the objects $8.95 from Edmund Scientific Company, 60 Pearce seen are without meaning,” provides an excellent intro- Ave., Tonawanda, NY 14150–6711 (1-800-728-6999). duction to a discussion of perception. Module 13 Perceptual Organization 5

Oliver Sacks’ opening tale in The Man Who ary areas associated with complex Mistook His Wife for a Hat provides the interesting case visual analysis. study of Dr. P., a distinguished musician and teacher Coren, S., Ward, L. M., & Enns, J. T. (2003). Sensation who could see but not recognize familiar faces. and perception (6th ed.). New York: Wiley. Likewise, he saw faces where there were none and acted accordingly—for example, patting the heads of Sacks, O. (1987). The man who mistook his wife for a parking meters and addressing carved knobs on furni- hat. New York: Summit. ture. When Dr. P. was examined and asked to describe II. Form Perception (pp. 171–173) the pictures in a National Geographic magazine, his eyes would dart across the page picking up only tiny Classroom Exercise: Form Perception details. A striking color or shape might catch his atten- Handout 13–3 can be used to reinforce and extend the tion and elicit comment but in no case did he perceive text discussion of form perception. the scene as a whole. After his examination, the patient Figure 1 reveals what Stanley Coren calls the “urge looked around for his hat. He reached out and took hold to organize.” The various small elements can be organ- of his wife’s head and tried to lift it up to put it on. He ized in a variety of ways, which continually change as had mistaken his wife for a hat! we shift from one organization to another—in a sense, Coren describes several other forms of agnosia, reversible figure-ground. Have students stare at the fig- including the following. In visual object agnosia, peo- ure, identifying the various patterns they see. Our ple who have no damage to the visual apparatus are organization of elements into various patterns demon- unable to recognize familiar objects. For example, one strates that perception is an active, constructive process. patient given a line drawing of a pair of eyeglasses In the mid-1970s, psychologist Bernard Karmel delight- admitted confusion and started to guess: “There is a cir- fully demonstrated this with a string of blinking cle . . . and another circle . . . a cross bar . . . Why, it Christmas lights and a Beatles recording. Although the must be a bicycle.” Such patients also have trouble sep- lights had no real pattern, they were perceived as pulsat- arating the parts of a figure from their overall context. ing in rhythm with the music; the observers simply fil- Shown a picture of a clock they may identify it. tered out the lights that did not fit the beat and ampli- However, if the clock is crossed out with a couple of fied those that did. straight lines, recognition is lost. Figures 2a and 2b, provided by Roger Shepard, are simultagnosia, the individual cannot pay atten- In additional examples of reversible figure and ground. tion to more than one stimulus at a time. For example, Shepard notes that the figure-ground ambiguity is par- the person may not be able to place a dot inside a circle ticularly strong for the first two letters in 2a, thanks to a because that would require paying attention to both the fortuitous complementarity of shape between the “F” of dot and the circle simultaneously. Visual object agnosia “Figure” and “G” of “Ground” and between the “i” of and simultagnosia often appear in the same patients and “Figure” and “r” of “Ground.” These letters tend to be the disorders are sometimes grouped together as visual seen as “F” or “G” and “i” or “r” but not fully as both integrative agnosia. at once. Other agnosia effects are more general and may Figures 3a and 3b, provided by J. Richard Block involve more than one sense. People with these prob- and Harold Yuker, are examples of “ambiguous figures” lems may be just as impaired using, say, their tactile or in which reorganizations of the figures create totally kinesthetic sense as with their visual sense. For exam- new perceptions. 3a is called the Wilson figure and is ple, those suffering spatial agnosia have difficulty both an Eskimo (the dark area is an igloo and the negotiating their way through the world. Even in famil- Eskimo is facing toward it) and an Indian head (the iar settings they make wrong turns. They become lost in dark area is the Indian’s headdress). In the second fig- their own homes. Strangely, such patients also often ure, the bird can be seen as either a goose or a hawk show a tendency to ignore one side of an object in depending on the direction it’s flying. Although we space. So when asked to draw symmetrical objects, they know both pictures are there, we cannot see them simul- produce an imperfection on one side. taneously. At the same time, it is difficult to maintain Agnosia seems to be a result of physiological dam- focus on only one without the other reappearing. age, typically to the higher brain centers involved in the Figure 4 from Coren provides additional examples interpretation of stimuli. Although the damaged areas of the Gestalt principles described in the text. The 12 may be quite specific, they are not the primary receiv- circles in 4A are organized into two groups, illustrating ing areas of the cortex. For example, visual agnosias are the principle of proximity. In 4B, a triangle of black often associated with damage to the more forward por- dots appears against a background of Xs, and in 4C, the tions of the occipital cortex, which are the secondary two halves of the circular field appear quite separate, visual areas and to the temporal lobes, which are terti- 6 Module 13 Perceptual Organization both illustrating the principle of similarity. Figure 4D is lect their written responses, and place them on the typically seen as a spiral of dots with one dot outside, board. Although there will be many common responses, illustrating the principle of continuity. Figure 4E is seen there will also be evidence of unique perspectives. as a diamond between two vertical lines, and 4F is seen as a triangle; both illustrate the principle of closure. Warren, R., & Gregory, R. (1958). An auditory analogue of the visual reversible figure. American Journal of Were it not for the principle of closure, 4E could be Psychology, 71, 612–613. seen as a letter W stacked on a letter M (or as a letter K faced by a mirror image K), and 4F could be seen as Classroom Exercise: The Ganzfeld three separate acute angles. Finally, Coren suggests that Figures G and H show how Gestalt principles can be so The perception of contours—locations in which there is powerful they produce visual illusions. Distances a sudden change of brightness—is basic to form per- between parts of a pattern that are organized into the ception. Without them there is no perception of shape. same group (proximity principle) are underestimated A simple contour, and certainly one of the simplest relative to the same distances when the parts belong to visual forms, is a black line drawn on a white sheet of different groups. paper. Eliminate contours and you effectively eliminate . Block, J. R., & Yuker, H. (1989). Can you believe your Gestalt psychologists call a field that contains no eyes? New York: Gardner Press. visible contours a Ganzfeld (“whole field”). In a series Coren, S., Ward, L. M., & Enns, J. T. (2003). Sensation of studies they showed that perception in a Ganzfeld is and perception (6th ed.). New York: Wiley. very unusual. Subjects generally report that they see only a “shapeless fog that goes on forever.” Even when Shepard, R. N. (1990). Mind sights. New York: Freeman. colored light is introduced, the hue of the light fades quickly and the gray fog returns. Classroom Exercise: An Auditory Analogue of the Visual Students can experience the Ganzfeld for them- Reversible Figure selves by cutting Ping-Pong balls in half along the Because of visual capture, as noted on page 3 of seam. The halves that bear the manufacturer’s stamp resource Module 12, visual illusions tend to dominate should be discarded. Although not essential, gluing those of the other senses. However, auditory and other some cotton around the rims that are saved will facili- sensory illusions also occur. For example, the steady tate a comfortable fit. Students should then cover each beat of a metronome or clock is heard as if it were a eye with half a Ping-Pong ball. Have them direct their repeating rhythm of two, three, or four beats—not as an toward a light source so that their view will be unaccented click-click-click. Similarly, as suggested by flooded with diffuse, contourless light. Have students Richard Warren and Richard Gregory, when speech reflect on their experience. Any color will soon fade sounds—either words or short phrases—are repeated into gray. Eventually they will experience a perceptual without pause, the verbal organization undergoes abrupt “blank out,” the impression that all sense of vision has transitions into other words and phrases, sometimes been lost. In the absence of contours we actually experi- accompanied by apparent changes in the component ence a feeling of blindness. If someone passes an object sounds. Students may discover this for themselves by across the field, say a pencil, vision will immediately simply repeating aloud a word such as say. It will shift return. Often those experiencing the Ganzfeld will fran- abruptly to ace and back again. Warren and Gregory tically search for something to focus upon, simply in suggest that there are dozens of such reversible words order to orient themselves. Students can experiment and that this verbal effect of alteration seems similar in with their “Ping-Pong” Ganzfelds by painting halves principle to the reversal of the figure-ground relation- different colors—say, green, red, and blue. They can ship in visual figures. then place a different colored half over each eye and This verbal alteration is studied best with a record- determine how the brain handles this unique situation. ing of a word repeated continuously. In the Preface to Some will see only one color, some will report seeing these resources we suggest precisely such a demonstra- half one color and half the other, still others will alter- tion using the word cogitate. Warren and Gregory sug- nate in seeing one and then the other. gest the word rest. After making a tape of 3 to 5 min- In a laboratory, where Ganzfeld situations are pro- utes, have students listen carefully and write down duced with more elaborate equipment and are experi- every word or phrase they hear. As rest is repeated, stu- enced for a longer time, many observers become dents are likely to hear it shift to tress, stress, or even extremely fatigued and report that their bodies feel Esther. Like visual perception, our perception of audito- light. Motor coordination, balance, and time judgment ry stimuli is organized by the meanings our minds may also be disrupted. Dizziness is not uncommon. A impose. Have students volunteer their responses, or col- few observers seem to lose their sight completely for a Module 13 Perceptual Organization 7 period of time after being in the Ganzfeld for 15 min- 10 FOR T = 9 TO 13 utes. 40 FOR T = 13 TO 9 STEP –1 “Blank outs” may also occur in natural environ- —or— ments. For example, in the snow-covered Arctic where 10 FOR T = 3 TO 13 there is often little sensory change, observers may com- 40 FOR T = 13 TO 3 STEP –1 plain of “snow blindness.” The Ganzfeld experience clearly demonstrates that vision requires temporal and The second involves slowing the rate at which the spatial change to function normally. figures are generated by introducing delay loops:

III. Depth Perception (pp. 173–175) 25 FOR A = 1 TO 5: NEXT A 55 FOR A = 1 TO 5: NEXT A Classroom Exercise/Student Project: A Kinetic Depth —or— Illusion 25 FOR A = 1 TO 10: NEXT A To introduce depth perception, you might want to use 55 FOR A = 1 TO 10: NEXT A Steven Gilbert’s BASIC program for generating a kinet- ic depth illusion on a personal computer (or you might The third alteration eliminates one strand of the double use this as part of your introduction to perception). Its helix to test whether a single rotating helix emerges (it simplicity and insensitivity to variations in viewing con- does): ditions, i.e., size of monitor, viewing distance or angle, make it ideal for classroom demonstration. If provided Single helix the program, students can also generate and work with 20 PRINT TAB(T)“–” it on their own. 50 PRINT TAB(T)“–” The following BASIC program generates the Source: Reprinted by permission of Lawrence Erlbaum Double Helix illusion. Associates, Inc. and the author from Gilbert, S. (1991). A new kinetic depth illusion for introductory psychology 10 FOR T = 7 TO 13 and sensation and perception courses. Teaching of 20 PRINT TAB(T)”–”TAB(27–T)”–” Psychology, 18, 55–56. 30 NEXT T 40 FOR T = 13 TO 7 STEP –1 With all these alterations, the illusion of rotation re- 50 PRINT TAB (T)”–”TAB(27–T)”–” mains robust, whereas the timing and frequency of 60 NEXT T reversals in the direction of the spin are strongly 70 GOTO 10 affected. 80 END Gilbert suggests that the Double Helix illusion Program output initially appears as a single contin- illustrates features of other more familiar illusions. For uous stream of two-dimensional diamond figures, each example, the perception of moving strands of a helix 14 rows high and 14 columns wide. Connected end-to- emerging from successive exposures of stimuli dis- end like strung beads, the figures float upward at a con- placed in space resembles the (the illu- stant rate. Before long, however, the floating diamonds sion of movement created when two or more adjacent stop rising and become a double helix spinning on a lights blink on and off in succession). The periodic vertical axis. For most observers the direction of spin reversing of the direction of spin of the helix resembles spontaneously reverses every few seconds. The change the reversals of the and the Goblet-Faces from one direction of rotation to the other sometimes illusions. And, as with the Müller-Lyer illusion, percep- occurs instantaneously; sometimes the figure reverts to tion of the essence of the illusion (three-dimensional the original floating diamonds configuration before spinning helixes) may depend on particular kinds of reversing its spin. experience (for example, familiarity with helix-like Observers are typically amazed that the apparent stimuli or spinning objects). three-dimensional spinning and rotational reversals of Finally, as an independent project, students can the helix are not “real” events written into the program. investigate a number of questions regarding the illusion. Presenting the seven-line program convinces even the For example: Does the illusion require binocular input? computer-naive student that a few simple commands Is it influenced by practice, fatigue, fixation point, or could not produce the complex and irregular three- head and eye movements? Is it sensitive to physical dimensional movements. context or social cues—for example, can observers be Gilbert provides three possible alterations in the induced to see more or fewer reversals by instructions program for changing its parameters. The first involves or by reports from confederates? Are individual differ- changing the relative height and width of the diamonds ences in the perception of the Double Helix related to by altering the range for the FOR-NEXT loops: differences in the perception of other illusions—for 8 Module 13 Perceptual Organization example, do students who see more reversals in the sented at the 68th Annual Meeting of the Midwestern Goblet-Faces illusion also see more reversals in the Psychological Association, Chicago, IL. Double Helix illusion? Lecture/Discussion Topic: Autostereograms Gilbert, S. (1991). A new kinetic depth illusion for intro- The text cites retinal disparity as an important binocular ductory psychology and sensation and perception cours- es. Teaching of Psychology, 18, 55–56. cue to depth and notes that the creators of 3-D movies simulate retinal disparity by photographing a scene with Classroom Exercise: Binocular Vision two cameras placed a few inches apart. When viewed through spectacles that allow the left eye to see only the The importance of binocular cues to depth perception is image from the left camera and the right eye the image easily demonstrated. Have students close one eye, point from the right camera, the 3-D effect mimics normal their two forefingers toward each other, then bring them retinal disparity. together quickly. They are likely to miss. An even more By now many, if not all, of your students will have difficult test is to have them hold a pencil in each hand encountered the “hidden pictures” (called Magic Eye™) and bring the points together. It is important, of course, that have appeared in newspapers and in malls and spe- that their hands not be at arm’s length. If they repeat cialty shops throughout the country. At first glance, either test, they ought to drop their arms out of view these pictures appear to form repetitive and meaningless before they try again. This will eliminate the perception patterns. However, as the observer fixates on something of any depth cues from the position of the hands and at a different distance (often instructions suggest the arms. reflection in the glass covering the hidden picture or Binocular vision is also responsible for an illusion viewing the picture cross-eyed), an enchanting 3-D in which we see a hole in our hand. Have students roll a image springs to life. Like the old stereograms viewed sheet of paper into a tube and raise it to their right eye through spectacles, these autostereograms rely on reti- like a telescope. Tell them to look through it, focusing nal disparity to produce their effect. Rather than using on a blank wall in front of them. Now have them hold two separate images, however, they use repeating col- their open left hand beside the tube and continue to umns that potentially present a slightly different image focus ahead. The images received by the two eyes will to each eye. When one views the picture directly, there fuse and the hole in the tube will appear to be in the is no retinal disparity. However, if one focuses through student’s hand. They may need to slide the hand along- the image so that the fixation point is behind the plane side the tube until they find the precise spot where the of the picture, retinal disparity produces a rather star- hole appears to go through the very center of the palm. tling 3-D image. Handout 13–5a provides an example to Fisher, J. (1979). Body magic. New York: Stein and Day. use in class. The figure is a rat pressing a bar. Handout 13–5b displays the specific figure. For those students Classroom Exercise/Student Project: Binocular Vision having difficulty seeing the 3-D images, suggest the Versus Monocular Vision following: Look cross-eyed at the stereogram, or hold Larry Boehm suggests a useful classroom exercise that, the figure close to the eyes and then gradually move it in just a few minutes, demonstrates the value of binocu- back while maintaining the same focus. Still a third lar cues (it also makes a good student project for an strategy is to place glass or clear plastic over the image. out-of-class assignment). After discussing depth cues If a person focuses on his or her own reflection in the and depth perception, distribute a copy of Handout glass, the image should start to appear in the back- 13–4 to each student. Divide your class into groups of ground. In addition to illustrating the effects of retinal three. Tell your students they will take turns in filling disparity, it is a wonderful example of how perception is the roles of pitcher, catcher (the research participant), an active process involving organization that occurs in and data recorder. The pitcher, standing about 10 feet the brain after the eyes’ images have been fused. from the catcher, is to toss a tennis ball 20 times to the Students can learn more about stereograms and even catcher. The catcher’s job is to catch as many throws as download a program for creating their own at possible with one hand, first by using both eyes, then W. A. Steer’s stereogram page at www.techmind.org. only one eye (with appropriate counterbalancing). The recorder keeps track of the number of successful catch- IV. Perceptual Constancy (pp. 176–179) es. In using this demonstration, Boehm found students Classroom Exercise: Variation in the Size of the Retinal were significantly better at catching the tennis ball with Image two eyes (mean = 9.8) than with one eye (mean = 6.8). As distance between the eye and an object increases, the Boehm, L. (1996, May). An inexpensive and reliable size of the retinal image decreases. Normally, we com- demonstration of monocular and binocular depth percep- pensate for the size changes related to distance changes, tion for sensation and perception or statistics. Paper pre- Module 13 Perceptual Organization 9 and the perceived sizes of objects remain constant. Stu- windows and estimate the size of a distant object, say a dents can experience the relationship between retinal lamppost. They should return to their seats and draw a image size, distance, and size constancy through a line the length of which produces the same-size retinal simple demonstration. image that the post did. Then, have them go to the win- Have students hold a hand in front of them at arm’s dow, hold up a thumb to measure the post, and, return- length and move it toward their head, then away; they ing to their seats, measure their lines with their thumbs. will perceive no change in size. The size of the retinal Most will have drawn a line that is much too long. image is, of course, changing. Is there a way to detect Coren, S., Ward, L., & Enns, J. T. (2003). Sensation and this change? Have students hold the forefinger of their perception (6th ed.). New York: Wiley. left hand about 8 inches in front of their face and focus on it. They should then position their right hand at arm’s LaVoie, A. (1987). Emmert’s law. In V. P. Makosky, length past their left forefinger. While maintaining fixa- C. C. Sileo, L. G. Whittemore, C. P. Landry, & M. L. tion on their left fingertip, they should move their right Skutley (Eds.), Activities handbook for the teaching of psychology (Vol. 2, pp. 46–48). Washington, DC: hand toward and away from their face. Although their American Psychological Association. focus should be on the finger, they should also notice the image of the hand as it moves. It will change dra- Classroom Exercise/Student Project: Perceived Lunar matically in size. Size Coren, S., Ward, L., & Enns, J. T. (2003). Sensation and Both Gordon Hodge and Mark Kunkel have suggested perception (6th ed.). New York: Wiley. student projects or classroom activities that involve judgments of lunar size. They provide a useful strategy Classroom Exercise: Perceived Distance and Perceived for introducing the important distinction between distal Size and proximal stimuli as well as the Moon illusion. The close connection between an object’s perceived dis- Handout 13–6, designed by Kunkel, asks students to tance and perceived size is readily demonstrated. imagine themselves outside on a clear evening with a Distribute a copy of the figure below to each student in bright full Moon and then to mentally select from a class. Under reasonably good light, have students focus group of items one that will occlude or cover up the full on the “X” in the white rectangle. After a minute or so Moon when held in the outstretched hand. (The list of they will form an . That is, gazing at a blank objects was chosen based on previous investigations of piece of paper on their desk, they will see a floating estimated lunar size.) If you use the handout to intro- dark rectangle. If they now transfer their gaze to a more duce the Moon illusion you will, of course, want to distant, light-colored wall, they will see a much larger have students make two judgments: one of the “zenith” dark rectangle. As the afterimage is projected against Moon, the other of the “horizon” Moon. Hodge reports surfaces of varying distances, its apparent size changes. that, as one might expect, average judgments are quite This vividly illustrates how size and distance interact by different. means of the size constancy mechanism. If you use the handout as a classroom activity, you Allan LaVoie suggests another simple way of can compile students’ responses. Then ask for raised demonstrating how we automatically correct for dis- hands for each item choice. Alternatively, responses tance with an increase in perceived size. He notes that may be written on small slips of paper and passed for- an artist sometimes uses an independent standard, such ward. Create a frequency histogram of estimates. (This as holding up a thumb, to judge accurately the size of a is also a good demonstration for highlighting basic sta- distant object. Have your students go to the classroom tistical concepts, including measures of central tenden-

X 10 Module 13 Perceptual Organization cy and variation.) Kunkel reports that students typically Ninio, J. (2001). The science of illusions. Ithaca, NY: overestimate lunar size, with the modal responses being Cornell University Press. between a quarter and a softball. While students can check their estimates during the next full Moon, the full Lecture/Discussion Topic: Auditory Organization Moon actually occupies one degree (or 1/180th) of the The text notes that perceptual organization applies to night sky, regardless of its altitude or the time of year, other senses as well as vision. Jacques Ninio notes how and can be occluded by a pea held at arm’s length. this applies to hearing. For example, different lines of The exercise typically leads to a lively discussion research indicate that we hear a sound signal as com- of the Moon illusion, as well as the more general task plete even though we may receive only fragments of it. of perception. It provides a good opportunity to review He quotes Radau’s L’Acoustique, published in 1867: the fundamental question posed in introducing Modules 11–14: How does the world out there get in? How do A very odd phenomenon is the one that Mr. Willis we construct our representations of the external world? referred to by the name of paracousis. Here is what it To begin with, we must clearly distinguish between two consists of. Certain hard-of-hearing persons who usually do not hear faint sound, suddenly do hear them when general classes of stimuli: A distal stimulus is an actual they are accompanied by a loud noise. Mr. Willis knew a object “out there” in the world, and a proximal stimulus woman who was always attended by a servant with the is the representation of objects in contact with a sense job of beating a drum when somebody was talking to organ, in this case the visual image on the . her; she then heard very clearly. Another person heard Hodge, G. (1990, January). The moon illusion as a stim- only when bells were ringing. Mr. Holder cites two other ulus for critical thinking: A demonstration. Paper pre- similar cases: that of a man who was deaf when one did sented at the 12th annual National Institute on the not beat a nearby bass drum, and that of another person Teaching of Psychology, St. Petersburg, FL. who heard best when he was in a carriage that was jolt- ing over the cobblestones. Kunkel, M. (1993). A teaching demonstration involving perceived lunar size. Teaching of Psychology, 20, The explanation of this intriguing phenomenon is 178–180. that the noise, adding to the words, communicates parts of the speech above the hearing threshold. Having the Classroom Exercise: Brightness Contrast illusion of hearing continuously, the hearing impaired Handout 13–7a provides two startling illusions that reconstruct the whole of the communication. illustrate the phenomenon of brightness contrast. You More contemporary research studies also demon- might also use this phenomenon to introduce context strate the principle of closure or completion when effects that are covered in Module 14. applied to hearing. Research participants with normal They are Dr. Edward H. Adelson’s argyle and snake hearing are asked to lip-read someone they know, first illusions. In both illusions the diamond-shaped regions when the speech is inaudible, then when the acoustic are identical gray. So powerful are these illusions that speech signal is replaced by a signal without meaning most students will need to block out the context to be but with the same timbre as the voice of the person convinced. Alternatively, they may cut out the relevant being lip-read. In the latter situation, they show greatly figures and place them side by side. increased understanding of the message. As the text explains, perceived lightness stays In a laboratory experiment, R. M. Warren recorded roughly constant, given an unchanging context. What the word legislature and then erased one syllable so that happens when the surrounding context changes? As one could hear only the remaining fragments. When he both illusions dramatically illustrate, the replaced the missing syllable with a very loud noise, the computes brightness and color relative to surrounding audience heard the whole word. Apparently, notes objects. Thus, perceived lightness changes with context. Ninio, the brain interprets the loud noise superimposed Handout 13–7b is Gaetono Kanizsa’s remarkable on a syllable as masking it. We assume that the whole fluctuating gray. In this case, the perceiver alters the word was pronounced, and our brain completes the sig- context to produce lightness changes. Students can see nal by automatically forming a hypothesis about the the gray figure as a transparent rectangle floating above missing part. the white rectangle, the black circles being part of the Giovanni Vicario performed musical experiments white sheet. In this case, the gray looks relatively light. showing that if a note in a rising scale is replaced by However, they can also see a white rectangle with cir- some white noise 20 decibels louder, the listener hears a cles revealing the black rectangle beneath and the gray note of an intermediate pitch between the ones that have rectangle being inserted between the two sheets. The been retained on both sides of the noise. People always gray then looks noticeably darker. Remarkable! This is perceive the natural note that is missing from the scale. also a very good example of the active interpretation Ninio, J. (2001). The science of illusions. Ithaca, NY: and organization of top-down processing. Cornell University Press. Module 13 Perceptual Organization 11

HANDOUT 13–1

1.

2.

3.

4.

Source: Part 1: From Matlin, M. SENSATION AND PERCEPTION © 1998 Published by Allyn & Bacon, Boston, MA. Copyright © 1988 by Pearson Education. Reprinted by permission of the publisher. Parts 2, 3, 4: Figures from Stanley Coren, Lawrence M. Ward, and James T. Enns, SENSATION AND PERCEPTION, 6/e. Copyright © 2003. Reprinted with permission of John Wiley & Sons, Inc. 12 Module 13 Perceptual Organization

HANDOUT 13–2

Source: Stanley Coren, Lawrence M. Ward, and James T. Enns, SENSATION AND PER- CEPTION, 6/e. Copyright © 2003. Reprinted with permis- sion of John Wiley & Sons, Inc. Module 13 Perceptual Organization 13

HANDOUT 13–3

1.

2.

(a)

(b) 14 Module 13 Perceptual Organization

HANDOUT 13–3 (continued)

3.

(a) (b)

4.

Sources: Figures 1 and 4: From Stanley Coren, Lawrence M. Ward, and James T. Enns, SENSATION AND PERCEPTION, 6/e. Copyright © 2003. Reprinted with permission of John Wiley & Sons, Inc. Figure 2: From Mind Sights by Roger N. Shepard, Figures 69 and 73. © 1990 by Roger N. Shepard. Used with permission of W. H. Freeman and Company. Figures 3A and B: Block, J. R. & Yuker, H. (1969). Can You Believe Your Eyes? p. 16. Gardner Press, Inc., 19 Union Square West, New York, NY 10003. Module 13 Perceptual Organization 15

HANDOUT 13–4

Depth Perception: Binocular Vision Versus Monocular Vision

Each eye sees objects from two slightly different angles. The brain is able to use retinal disparity and the information about the position of each eye to judge the distance of the object. This demonstration is designed to give you an appreciation of binocular depth cues.

Work in groups of three. One person will be the catcher, one the pitcher, and one the data recorder.

Procedure 1. The pitcher throws the ball to the catcher 10 times. The catcher has both eyes open, but to make it more diffi- cult the catcher uses one hand only to catch the ball. Record the number of balls caught. 2. The pitcher throws the ball to the catcher 10 times but this time the catcher uses one eye only. Record the number of balls caught.

Repeat the procedure with each person serving as the catcher.

Observations

My Data Class Data One Eye Two Eyes One Eye Two Eyes

Number caught

Source: Adapted from a demonstration in Blood and guts: A working guide to your own insides by Linda Allison. Copyright © 1976 by Yolla & Bolly Press. By permission of Little, Brown and Company. 16 Module 13 Perceptual Organization

HANDOUT 13–5a Module 13 Perceptual Organization 17

HANDOUT 13–5b 18 Module 13 Perceptual Organization

HANDOUT 13–6

Imagine that you are outside on a clear night in which there are no clouds, and there is a bright full moon. Pretend that on a table in front of you are objects that range in size from a BB to a beach ball as follows:

1.BB 2. Pea 3. Dime 4. Penny 5. Nickel 6. Quarter 7. Golf ball 8. Baseball 9. Softball 10. Small salad plate 11. Large dinner plate 12. Frisbee 13. Basketball 14. Beach ball

Please pretend that you are going to pick one of these things that WHEN HELD AT ARM’S LENGTH JUST COVERS UP THE MOON. Imagine that you are picking one that when you hold it in your hand will JUST BARELY COVER UP THE MOON so that you can no longer see it.

_____ Put the number of the object you chose here.

Source: Reprinted by permission of Lawrence Erlbaum Associates, Inc., and the author from Kunkel, M. (1993). A teach- ing demonstration involving perceived lunar size. Teaching of Psychology, 20, 179–180. Module 13 Perceptual Organization 19

HANDOUT 13–7a

Source: Dr. Edward H. Adelson, Department of Brain and Cognitive Science, MIT, Cambridge, MA. Reprinted by permission. 20 Module 13 Perceptual Organization

HANDOUT 13–7b

Source: Reprinted from Jacques Ninio, Franklin Philip (trans.), The science of illusions. Copyright © 1998 by Editions Odile Jacob. Used by permission of the publisher, Cornell University Press.