Vlab Manual Ch05

8/10/2019 Vlab Manual Ch05

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Chapter 5: Perceiving Objects and Scenes

1. Robotic Vehicle Navigation: DARPA Urban Challenge

2. Apparent Movement

3. Linear and Curved Illusory Contours

4. Enhancing Illusory Contours

5. Context and Perception: The Hering Illusion

6. Context and Perception: The Poggendorf Illusion

7. Ambiguous Reversible Cube

8. Perceptual Organization: The Dalmatian Dog

9. Law of Simplicity or Good Figure

10. Law of Similarity

11. Law of Good Continuation

12. Law of Closure

13. Law of Proximity

14. Law of Common Fate15. Real-World FigureGround Ambiguity

16. FigureGround Ambiguity

17. Perceiving Rapidly Flashed Stimuli

18. Rotating Mask 1

19. Rotating Mask 2

20. Rotating Mask 3

21. Global Precedence


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Virtual Lab Manual 135

1. Robotic Vehicle Navigation: DARPA Urban Challenge

Scene perception and object recognition seem to come so easily to humans that we often

take for granted what an amazing feat this is for the human visual system. It has beendifficult for scientists to create a machine with the object perception capabilities of

humans. Some research scientists have taken on the great task of creating automobiles

with object recognition capabilities that allow them to be autonomous vehicles that cannavigate and drive entirely on their own without a human driver or remote control. The

Defense Advanced Research Projects Agency (DARPA) Urban Challenge is an

autonomous vehicle research and development program with the goal of developing

technology that will keep warfighters off the battlefield and out of harms way.

This film shows the robotic car Boss, which was developed by General Motors and

Carnegie-Mellon University, as it navigates the course during a qualifying event held betweenOctober 27 and 30, 2007 that preceded the actual race, which was held on November 3.

Eleven vehicles qualified for the finals. Boss finished first, followed by cars from Stanford,

Virginia Tech, M.I.T., University of Pennsylvania/Lehigh, and Cornell. It is important to

realize as you watch this film that there is no driver and no one is controlling the car remotely.All driving decisions are made by Boss onboard computers, aided by visual information

from its many sensors.

Film courtesy of Tartan Racing, Carnegie-Mellon University.

RESULTS & DISCUSSION

1. How does Boss respond to street signs? To other traffic?

2. Do you think the vehicles navigation would be different if a human driver werebehind the wheel? What advantage would the human have over the robotic navigation

system? What advantage might a robotic system have over a human driver?


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2. Apparent Movement (Phi Phenomena, Space and Time)

In this demonstration of apparent movement, two spheres are flashed in two different

locations, one after the other. Vary the separation and interframe interval with the slidersbelow the display.


1. Adjust the separation to match the values in the left column below, and then adjust the

interframe interval until you see (a) smooth movement between the dots (enter data in

center column), and (b) no movement between the dots (enter data in far rightcolumn).

Separation Interframe Interval Interframe interval

(smooth movement) (no movement)600

500

400

300

200

100

2. What can you conclude about the influence of separation and interframe interval onthe perception of apparent movement?

3. How could you compare your perception of movement when there is a large

separation and small separation between the spheres? (Set interframe interval so you

perceive movement for both small and large separations. Then, describe whether themovement is the same or different in the two cases.)

4. What do you think a Gestalt psychologist would have to say about this effect?


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3. Linear and Curved Illusory Contours

This exercise provides examples of illusory contours and demonstrates how the

characteristics of the display influence the contours. Examples of both straight andcurved illusory contours are presented. Note how the contours change as objects are

modified.


1. Describe the illusory contours in the basic figure, without apparent occlusion, and

without the spheres. Did the brightness of the illusory figure differ from the rest ofthe field, and was it constant across the different conditions?

2. What happens physically when you click on remove outline?

3. What happens perceptually? (Click reset to view again, if necessary.)

4. How does the result in #3 relate to (a) the structuralists idea that perception is causedby sensations, and (b) the Gestalt psychologists ideas about perception?

5. What happens to your perception when you delete the sphere? Based on this

observation, what is the crucial stimulus characteristic for creating illusory contours?

6. Describe what you saw when you moved the slider in the curved contour figure.

Based on this observation, what is the crucial stimulus characteristic for creatingcurved illusory contours?


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4. Enhancing Illusory Contours

The strength of illusory contours is dependent on the specific characteristics of the

stimulus display. Adding appropriate information can significantly enhance theappearance of the illusory contours or change the perceived characteristics of the illusory

surface. In this demonstration, add each extra component separately, and note the impact

on the illusory contours. Pay attention to the strength of the illusory contours and theappearance of the illusory surface. Try to determine the principles behind the

enhancement effect.


1. What was the effect of adding new elements to the display?

2. What variation in the display caused the illusory surface to appear transparent, rather

than solid?


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5. Context and Perception: The Hering Illusion

The Hering illusion involves a distortion of lines when the lines appear in the context of a

radiating pattern. The lines appear to be bent even though they are perfectly straight.After reading the description click on Done to see the illusion.


1. Describe how the lines appeared in the Hering figure and what happens when the

background is eliminated.

2. How would the Gestalt psychologists use this result to support their ideas about

perception?


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6. Context and Perception: The Poggendorf Illusion

The Poggendorf illusion involves the apparent misalignment of two short diagonal lines

when two parallel lines are placed between them. This exercise presents the classicPoggendorf Illusion as well as a variation in which the width occluding rectangles can be

varied or made partially transparent. Note whether you perceive the basic illusion on the

left. Place your mouse over the left image to prove to yourself that the diagonal lines arenot misaligned. Vary the width of the lines from thin to thick while they are opaque.

Then click on the transparent icon and do the same.

Demonstration courtesy of Michael Bach.


1. Describe how the lines appeared in the classic Poggendorf Illusion on the left.

2. Describe how the size of the illusion changed as you varied the width of the yellow

stripes. What happened to your perception of the illusion when you clicked ontransparent ?


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7. Ambiguous Reversible Cube

The moving cube presented in this demonstration is not a typical cube, but is missing a

corner (gray faces). The cube is ambiguous because the viewer can experience a numberof perceptions. The following two are easiest to perceive:

a) A small grey cube cut out of one corner of the large colored cube.

b) A small grey cube jutting out from the corner of the large colored cube.

Click on the arrow under the display to activate the movie. You can stop the movie atany point and move the slider below the movie yourself. (Note that you cannot control

the two white sliders in side the picture.)



1. Describe what happens when your perception flips from a to b (see above). How

does the grey cube move when you perceive it as jutting out from the colored cube?

2. Could you perceive a third perception? If so, describe it.

3. What happens to movement of the large cube beginning about one minute into the

movie? How does that affect your perception?

4. How does your perception of this display support the idea that the stimulus on theretina is ambiguous?


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8. Perceptual Organization: The Dalmation Dog

The Gestalt laws of perceptual organization describe how the visual system utilizes

certain cues for perceptual organization. This demonstration shows how our visualsystem can also use motion information as a cue to group the many elements of an image

to create the perception of larger objects.

First, view the image containing black patches on a white background and decide if you

recognize any object(s). Stop here and do this now before reading further. If you do not

recognize an object, try viewing it again after reading this hint: dog. Next, click on the

help me 1 button. Last, click on the help me 1 off and then the help me 2 button.



1. Describe your initial perception of the display. Did you perceive an object initially?

If so, did you have experience with this image before? If not, did the hint word dogsignificantly help you?

2. Explain what you perceived after clicking on help me 1. After clicking on help me1 off, was your perception the same as it was before you clicked?

3. Describe what you saw when clicking on help me 2. What did clicking on this

button demonstrate to you with regards to the power of motion as a cue for perceptual

organization?


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9. Law of Simplicity or Good Figure

A central idea in the Gestalt approach to perceptual organization is that we tend to

organize our perceptual world so that figures are simple or good. This demonstrationillustrates one case in which your interpretation in terms of a good figure does not match

what is actually present.


1. What did you perceive in the original display? What was revealed when the

components of the display were separated?

2. Why is this display unlikely to occur in the environment?

3. We certainly can construct stimulus displays in which the Gestalt laws will result inincorrect perceptions. If these laws are fallible, why is our perception in the real

world as accurate as it tends to be? (Hint: See #2 above). When are we most likely to

be led astray by the Gestalt laws? Give an example, if possible.


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10. Law of Similarity

One of the Gestalt laws of perceptual organization is the law of similaritysimilar

patterns tend to be grouped together or perceived to be part of the same, larger object. Inthis exercise you will see how the organization of a stimulus array is affected by the

similarity of the arrays individual components. Note the organization of the array prior

to adding a similarity component, and then see how the organization changes as youintroduce two colors or other characteristics.


1. Describe your perception of the array prior to adding color. How did your perception

change when some spheres were red and others were blue?

2. What do you think would happen if the balls were randomly colored red or blue,rather than using rows or columns to assign color? Would grouping still occur?

3. Describe a real-world situation in which the law of similarity contributed to yourperception.


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11. Law of Good Continuation

The law of good continuation states that a figure is organized so that its lines are straight

or smoothly curved and follow the smoothest path. If the stimulus is composed of points,rather than lines, the points are organized so that if connected, the lines created will be

straight or smoothly curved and follow the smoothest path.

This demonstration illustrates the impact of the law of good continuation. Before doing

anything to change the display, note how you organize the complex pattern into parts.

Then, move the slider to the right to separate the pattern into two components. Click on

GOOD CONTINUATION and separate the parts again. Note your reaction to thisorganization.


1. How did you perceptually organize the original figure? Did the first separation

confirm your expectations?

2. Describe how the pattern was organized in the GOOD CONTINUATION condition.

How is this organization consistent with the law of good continuation?

3. Describe a real-world situation that is influenced by the law of good continuation.


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12. Law of Closure

The law of closure states that figures tend to be perceived as complete, unbroken patterns.

Small gaps or other missing parts often are ignored, and the figure is organized as itwould be without those gaps. This is a very similar concept to the law of good

continuation.

This exercise illustrates the law of closure. Click on the figures to create small gaps in

the figures. Note whether your perception of the figures shape changes.


1. Describe your perception of the figures before and after the gaps were introduced.

Did anything change? What do you think would happen if the gaps were morenumerous or larger?

2. Describe a real-world situation in which the law of closure is at work.


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13. Law of Proximity

The law of proximity states that stimuli that are close to one another tend to be grouped

together. This exercise illustrates how the law of proximity works. Note how you woulddescribe the stimulus array prior to making any adjustments. Next, vary the distance

between the spheres and note how the organization of the array changes.


1. Report how the initial arrangement appeared. What happened when you varied the

separation between the spheres?

2. Describe a situation in the real world in which the law of proximity operates to

determine our perception.

3. Why are we usually able to determine where one object begins and another ends, even

if the objects are touching one another?


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14. Law of Common Fate

The law of common fate introduces movement as a cue for perceptual organization.

According to this Gestalt law, stimuli that move together tend to be grouped together.Stimuli that do not move in the same direction or at the same speed as others tend to be

grouped separately.

This exercise illustrates how perceptual grouping is influenced by common fate. Note

how the objects are organized when in motion. (Note that the strawberries may move

very rapidly. To slow them down, exit the demonstration and then start it up again.) Click

on CHANGE GROUPING to see different arrangements. Note whether the law ofcommon fate overrides other Gestalt principles.


1. Why does the information provided with the demonstration suggest that the law of

common fate overrides the law of proximity in this demonstration? Describe the

situation that illustrates this idea.

2. Describe a real-world situation in which the law of common fate determines

perception.


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15. Real-World Figure-Ground Ambiguity

Rubins reversible face-vase figure is a classic example of ambiguous figure-ground

perception.

Figure-ground ambiguity is most common in artificial, scantily-detailed patterns. In most

real-world situations, there is enough information to prevent figure-ground ambiguity andreversals, but occasionally there are situations in which cues are in conflict and reversals

occur. Such is the case of the Kaiser Porcelain Limited vase created for a wedding

present for Queen Elizabeth II and the Duke of Edinburgh. Even though the object is the

vase, the reversed perspective does occur under proper conditions.

This exercise demonstrates how figure-ground segregation can shift as information

changes. Note your dominant perception when the initial high-contrast version is viewed.Move the cursor to change the contrast and details available in the different regions of the

scene. Note how your perception changes and what seems to determine that change.

Note whether you observe any figure-ground reversals when the vase is shown in detail.


1. What was the dominant figure-ground orientation of the initial version of the figure?Describe how this changed as the characteristics of the scene changed.

2. What features did you find most important in allowing the vase to be perceived as anobject with little ambiguity? Why were reversals still possible?

3. Do you think you would have noticed the alternative figure-ground orientation for the

version showing the picture of the wedding present if you were not primed to look for

it?


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16. Figure-Ground Ambiguity

Perception of a scene first requires a determination of what parts of the stimulus array

represent background, or ground, and what parts represent objects, or figures.

This demonstration uses a painting by Bev Doolittle to investigate the effect of contrast

on figure-ground perception. Slide the cursor to adjust the scenes contrast, and notewhether lowering the contrast changes figure-ground perception. Evaluate the cues you

use to identify figure and ground in this picture. To get a better feel for how differences

in contrast influence figure-ground segregation, manipulate the contrast of only the

background.


1. How did contrast influence figure-ground perception? What happened when the

contrast of only the ground was adjusted?

2. What cues allowed you to identify the figures in this ambiguous stimulus? Explain.

3. What real-world situation corresponds to the very low contrast conditions possible in

this demonstration?


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17. Perceiving Rapidly Flashed Stimuli

Visual scene perception takes place very rapidly. In order to study the time it takes to perceive

scenes, researchers such as Li Fei-Fei and colleagues have presented pictures to observers veryrapidly and asked them to describe what they could perceive at different stimulus presentation

durations. Mask stimuli are usually presented immediately after each brief picture

presentation to ensure that observers see the pictures for exactly the desired duration.

This exercise shows some rapidly flashed pictures followed by textured masks like the ones

used in Fei Fei and colleagues experiments, in which they investigated what people can takein from briefly presented stimuli.

Demonstration Courtesy of Li Fei-Fei.


1. Click on the right arrow to view the film. What did you perceive when pictures were

flashed? (Note that you may not perceive anything on some trials, either becausenothing was presented, or the picture was presented too quickly.)

2. Watch the film a second time. Could you perceive any more pictures the second time

than the first time? Why do you think this might be?

3. Move the slider manually to reveal some of the pictures. Then view the film, looking

specifically for one or two particular pictures. Does your perception differ from yourinitial viewing? If you saw more (even though the exposure time was still the same),

why does this occur?


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18. Rotating Mask 1

We often make unconscious perceptual assumptions that influence visual perception

based on our experience with the world. This demonstration shows how our assumptionabout the three-dimensional shape of a face can create an error of perception.

This demonstration shows a film of a computer-generated face mask that is rotating.View the mask as it rotates and note your perception of the mask as you view the hollow

side. Then, take your mouse and use it to slow down the rotation to examine the mask,

and stop the rotation of the mask at various points.



1. What do you perceive when viewing the hollow side of the mask?

2. When you moved the mask slowly with your slider, what happened to your perceptionof the face at the point when you were just able to see some of the faces features on

the hollow side? Explain why this occurred.


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19. Rotating Mask 2

This demonstration is a rotating Charlie Chaplin mask. Repeat the observations you

made in the other rotating mask demonstration (#18).



1. Compare your perception of this hollow mask to your perception of the mask in the

previous demonstration.

2. If there were differences between this demonstration and the previous one, what

characteristics of the stimulus might be involved?


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20. Rotating Mask 3

This is yet another rotating mask, but this one has a nose-ring on both sides of the mask.

Demonstration courtesy of George Papathomas.


1. What do you perceive when viewing the hollow side of the mask? Which direction do

the eyes rotate when you are viewing the hollow side of the face?

2. Can you explain your perception of the nose ring relative to the mouth when viewing

the hollow side of the mask?

3. Do you perceive the illusion when the face mask is laid on its side? What happens tothe appearance of the eyes in this position as opposed to when the face mask was

upright?


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21. Global Precedence

Global precedence refers to the issue of whether information about the more global

aspects of a stimulus such as its overall shape is processed faster than information aboutthe local characteristics (details) of the stimulus. Some researchers suggest that a global

precedence effect might occur because global information is carried in a faster pathway

than local information.

In this experiment you will replicate an experiment originally conducted by Navon in

which large letters are created from a number of smaller letters. In some conditions that

response is made in reference to the large letters (global condition), and in otherconditions the response is to the small letters (local condition). The letters that are

irrelevant are often varied so that in some cases global and local information is consistent

(both S) and in some cases inconsistent (small S arranged in an H). This variable allowsthe idea of faster global processing to be tested.

The experiment uses reaction times to examine the difference in global and local

processing. You should carefully read the instructions before beginning. Also,remember to respond as rapidly as possible, without making too many mistakes.

Complete the practice trials so that you are familiar with the stimuli and procedures.


1. Report your data for both global and local processing conditions. How does globalprocessing compare to local processing overall?

2. What can you conclude from your data regarding the relative speed of local and global

processing?

3. Reaction time data is very useful, but it must be interpreted carefully. If you wereslower responding to one letter, what conclusions are possible? If you were faster in

one condition than another, but you also made more errors in that condition, what

problem does this create in interpreting your data?


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Vlab Manual Ch05