Perception

Jump down page to:

Ambiguous Figures
Figure vs. Ground
Depth Cues
The Gestalt
Motion Perception
Context and Constancy
Illusions
Change Blindness
Auditory Perception and ESP

Ambiguous Figures

Ambiguous Spinning Wheel [Demonstration]
Description: An example of ambiguous motion. Much like ambiguous figures, the motion of the wheel in this demonstration may be reversed at will, depending on how the viewer looks at it.

Instructions: Click 'The Spinning Wheel' in the frame on the left. Allow the applet to load. You should see a sphere with a wheel spinning on the outside of it. Which way is the wheel spinning? Can you change the direction of the wheel by concentrating on it?

Animated Necker Cube [Demonstration]
Description: An animated example of the classic Necker cube. The orientation of the cube is ambiguous and can be seen from two perspectives. Objects are passed through the cube in order to aid the viewer in seeing both perspectives.

Instructions: Allow the applet to load. Objects will automatically appear and pass through the cube. Scroll down for further information on Necker cubes.

Husband/Father-in-Law Ambiguous Figure [Demonstration]
Description: Initially, the viewer sees a young man. When the picture is inverted, the viewer sees an older man.

Instructions: Click 'Husband/Father-in-Law' in the frame on the left. Allow the applet to load. Look at the drawing. Can you see elderly man hidden in the young man? If not, click on the image. It will invert, thereby making it much easier to see the alternate figure.

King's College of London's 10 Illusions and 2 Stereograms [Demonstration]
Description: This site contains 10 'quick and dirty' illusions/illustrations and 2 stereograms (that actually work from an electronic source!!). Demonstrations include the Old/Young Lady, Duck/Rabbit, and Old Man/Lovers ambiguous figures.

Missing Corner Cube [Demonstration]
Description: Unlike the ambiguous figures that only have two interpretations, this interactive demonstration presents an ambiguous 3D figure with three interpretations.

Instructions: Click '3-in-1 Animation' in the frame on the left. Allow the applet to load. Focus on the image. Can you see a cube with its bottom corner cut out of it? Can you see a room with a cube sitting in the corner of it? Can you see a large cube with a smaller cube floating in front of it? You can click on the image and drag the mouse to the left or the right to change perspective. Can you still see all three of the interpretations?

Necker Cube and Subjective Contours [Demonstration]
Description: This demonstration shows a Necker cube. When you press 'play' animations help people to see how the cube can be perceived 2 ways.

Instructions: Select 'Simulations and Demonstrations' from the left side of the screen. Make sure that people see at least 1 of the 2 possible 3D cubes. Although you can select 'play' to enact animations designed to help people to see the figure both ways. We didn't find this very helpful (but did find the Animated Necker Cube demonstration helpful). Once people can see at least on 3D cube consistently and clearly, ask them why. The image is made up of nothing more than blue circles with missing pieces. In this way, people can experience a sense of 'gestalt'.

Cautions: The image will take a minute or so to load. Shockwave player required.

Postcard Exhibits [Demonstration]
Description: This site contains 4 'quick and dirty' exhibits on various aspects of perception.

Exhibit 1: This is an image of the 'Old lady vs. Young lady' ambiguous figure.

Exhibit 2: This is an image of Stroop words - the names of colors are shown in conflicting colors (e.g., the word red is in green).

Seeing is Believing [Demonstration]
Description: Here you will find a collection of ambiguous figures (e.g., vases/faces, old woman/young woman, duck/rabbit, and Eskimo/Indian chief)

Instructions: To activate the exercise, select 'Seeing is Believing' and follow the instructions.

Cautions: You must use the NETLAB navigation tools (Back/Continue) to work within the NETLAB frame. Using your browser's navigation tools (e.g., Netscape's Back button) will help you navigate within the parent site, but not the NETLAB exercise. Shockwave player required.

Saxophonist or Woman's Face? [Demonstration]
Description: This site shows a figure that looks like a saxophonist or a woman's face.

Instructions: Select 'Simulations and Demonstrations' from the left side of the screen. After the screen loads (you will see a Necker cube), continue to click on the 'next' located in the upper right corner of the screen until the page indicator above the images reads '7 of 7'.

Cautions: The image will take a minute or so to load. Shockwave player required.

Believing is Seeing! [Demonstration]
Description: Here you will find the Camouflaged Dalmatian demonstration.

Instructions: To activate the exercise, select 'Believing is Seeing' and follow the instructions. If you continue through the demonstration, the Dalmation is revealed.

Cautions: You must use the NETLAB navigation tools (Back/Continue) to work within the NETLAB frame. Using your browser's navigation tools (e.g., Netscape's Back button) will help you navigate within the parent website, but not the NETLAB exercise. Shockwave player required.

King's College of London's 10 Illusions and 2 Stereograms [Demonstration]
Description: This site contains the Rows/Columns of dots demonstration. The perception continually shifts from rows to columns as the viewer tries to determine what is the figure and what is the ground.

M.C. Esher Gallery [Display]
Description: This site contains the works of M.C. Esher, a world-famous artist renown for his clever use of monocular depth cues and Gestalt grouping principles to create artistic ambiguity and illusion.

Instructions: Select the picture of interest. Use the picture to support a discussion of Gestalt grouping principles or pictorial depth cues.

Perceptual Transparency Illusion [Demonstration]
Description: Is the spinning triangle opaque and behind the axes or is it transparent and in front of the axes? The perception changes depending on what the viewer determines to be the figure and the ground.

Instructions: Click on 'Transparency Illusion' in the frame on the left. Allow the applet to load.

Vase or Faces? [Demonstration]
Description: This image shows a white vase against a black background. The contours of the vase create silhouettes of faces.

Instructions: Select 'Simulation and Demonstrations' from the left side of the screen. After the screen loads (you will see a Necker cube), continue to click on the 'next' located in the upper right corner of the screen until the page indicator above the images reads '6 of 7'. Ask students what they see. Show that the contours create silhouettes of faces. Note that when we focus on the faces, the vase seems to fade into the background, and that when we focus on the vase the faces seem to fade into the background. Also note that we must pick one point of focus (the vase or faces) so that we can organize sensory information properly and that we cannot really focus on both the faces and vases simultaneously.

Cautions: The image will take a minute or so to load. Shockwave player required.

Instructions: Allow the applet to load. Objects will automatically appear and pass through the cube. Further information on Necker cubes is listed below.

Convergence [Demonstration]
Description: This site contains an excellent and interactive demonstration of convergence.

Instructions: Use this site to demonstrate convergence, which students often misunderstand. Use the arrow button at the bottom of the image to move the apple closer to, or farther from the eyes (arrow buttons with vertical lines move the apple as close, or as far from the eyes as possible). The eyes will move and the image will show an adjusted angle of convergence.

Cautions: The initial images may take a minute or two to load. Microsoft Internet Explorer browser required. When you scroll down the image may become disjoint. Scroll up to correct the problem.

Hans Irtel's Vision Demonstrations [Demonstrations]
Description: Here you will find a collection of static visual demonstrations (Hermann Grid, Hermann Grid with white circles, color and context effects, shading and context effects, etc.). Because it is likely that people will use this site in many different ways, we do not review the entire collection of images.

Instructions: Use this demonstration as you discuss various aspects of perception. Use the hot links to navigate the site. For people in a hurry, try 'Context Effects I' first.

Instructions: Select the picture of interest. Use the picture to support a discussion of Gestalt grouping principles or pictorial depth cues.

Instructions: Click '3-in-1 Animation' in the frame on the left. Use this site to demonstrate shading as a depth cue.

Instructions: Scroll down and select a music video or movie trailer of your choice.

Cautions: Windows Media Player required. Video clips may take a little while to load.

Motion Parallax [Demonstration]
Description: This site contains an excellent and interactive demonstration of motion parallax.

Instructions: Click 'play' to make the scene move as if you were in a car traveling to the left. Click 'stop' to pause the action. Notice that objects tend to move in the opposite direction and than closer objects appear to move faster than farther objects.

Cautions: The initial image may take a minute or two to load. Flash 4.0 player required.

Motion Parallax in Outer Space [Activity]
Description: An interactive activity places the viewer in a spaceship in an alternate universe. Using knowledge of the 'normal' universe, the viewer attempts to return home by identifying motion cues that are realistic rather than those that are not.

Instructions: Read the introduction and press 'begin' when you are ready. You should see two window views with stars passing by. Choose the window that appears to have the most realistic motion. Two new views will appear. Choose the more realistic one. Two more views will appear. Choose again. If you have been correct the entire time, you should be returned to a 'normal' universe with an explanation of what happened.

Mummy Figure [Display]
Description: The page contains several pictures of an ancient mummy's mask. When the concave side of the mask is examined, the lack of visual cues creates ambiguity in the perception of the face as concave or convex. This may be an interesting example to use in a discussion of depth cues, shadowing, ambiguous figures, or perception in general.

Perception Jeopardy [Activity]
Description: This site contains an online Jeopardy game with answers about sensation and perception (Categories: visual system, visual receptors, color vision, hearing, other senses, perceptual processes, depth perception). Can you come up with the correct question?

Instructions: Use this site for an in-class review of sensation and perception. Use the mouse to select a question (denoted by point values like 100, 200, etc.). Click on 'Question' to see if you are correct.

Shadows and Depth (from Mississippi State) [Demonstration]
Description: This site demonstrates the effects of different types of shadows on depth perception. Change the object's shadow to change the apparent depth of the object (although the motion of the object is not altered in any way).

Instructions: On the bar at the top of the page, select 'demos.' Next, scroll down and select 'Ball and Shadow Illusion.' A page should come up with a red ball moving back and forth across a square plane. Select 'show me the magic' to continue. A new page will come up with the ball still moving back and forth, but with a new shadow. Select 'show me more magic' to see how the ball's apparent motion is affected by another different shadow. Finally, select 'show me the magic secret' for an explanation.

Stereograms [Display]
Description: This page has a collection of stereograms, or seemingly random patterns which, when looked at with the proper focus, reveal three-dimensional pictures.

Instructions: Allow the images to load. Click on an image to enlarge it. Try to focus at a point behind the plane of the monitor. When a three-dimensional image begins to take form, focus on it. Use this site to support a discussion on accomodation and convergence.

World of Escher [Display]
Description: This site contains numerous images of M. C. Escher's work.

Instructions: Use this demonstration to support a discussion on monocular depth cues. Click on the desired image to enlarge it.

Distorted Mona Lisa [Demonstration or Video]
Description: This site shows normal and distorted pictured of the Mona Lisa upside-down. Both pictures look normal. The site also shows the same picture right side-up. Now, one of the pictures looks grotesque. At the bottom of the page are links to very short video clips showing the same thing.

Instructions: Use this site to demonstrate that people perceive the whole before the individual pieces of a scene..

Cautions: Quicktime or Windows Media player required to show the video clips. Pictures are dark and potentially hard to see.

Illusory Contour Pictures [Display]
Description: Shows examples of Illusory contour pictures that can be copied and used in class.

Instructions: To use in the classroom as an overhead or power point slide, copy and paste any of the pictures shown.

Implicit Figure Motion [Demonstration]
Description: An animated extrapolation of implied figures. When the movie is started, the eight dots alternate between having or not having a pie slice taken out of them. As a result, the implied square appears to rotate. Could be a useful addition to a discussion of perception, implied figures and motion, and Gestalt principles.

Instructions: Allow the page to load. Select 'demonstrations' from the frame at the left. A new page will come up. Select 'motion perception.' A new page will come up with a new frame to its left. From the list in the frame to the left, select 'implicit figure motion.' The movie should load and begin playing automatically.

Instructions: After loading the image, let students look at the picture for a few moments and then ask them to describe what they see ('What's this?'). Discuss the Gestalt idea and ask student how many noticed the picture's details ('What are the desks made of? What about the easel?). Can your students find the watch? How many everyday objects can your students find? Now, ask them why they didn't see the picture as a collection of these objects right away.

Kanizsa Illusion (from Sandlot Science) [Demonstration]
Description: In this interactive demonstration, three circles with wedges cut out of them are situated such that they imply the existence of a triangle. Serves as a good example of the Gestalt idea that the whole is more than the sum of its parts.

Instructions: Click on 'The Kanizsa Illusion' in the frame on the left. Allow the applet to load. Stare at the three semi-circles. Can you see a white triangle overlaying them? Adjust the 'mouths' of the pac-man figures by moving the sliding bar to the left or to the right. Can you 'see' the shape of the triangle change as well?

Kanizsa Illusion II (from Sandlot Science) [Demonstration]
Description: In this interactive demonstration, eight circles with wedges cut out of them are situated such that they imply the existence of a sun-shaped and square objects. Serves as a good example of the Gestalt idea that the whole is more than the sum of its parts.

Instructions: Click 'The Kanizsa Illusion II' in the frame on the left. Allow the applet to load. Stare at the eight semi-circles. Can you see a white sun-shape overlaying them? Adjust the 'mouths' of the pac-man figures by moving the sliding bar to the left or to the right. Can you 'see' the shape of the sun change as well?

Motion Perception Warehouse [Demonstrations]
Description: This site contains a number of demonstrations on motion perception including 'Plaid Motion'. When superimposed, the two gratings appear to form a single plaid pattern, drifting rigidly.

Instructions: Select the 'Plaid Motion' demonstration from the frame on the left side of the screen.

Moiré Pattern Generator [Demonstration]
Description: Animated moiré patterns develop when you move one transparent pattern over another. The apparent motion and the patterns created serve as a clear example of the gestalt principle.

Instructions: Click 'Moiré Pattern Gen. I' in the frame on the left. Allow the applet to load. You will see a kaleidoscopic image. By clicking on 'A' or 'B' you may see the two different patterns that are rotating in different directions. Clicking the arrows at the top will change the respective directions of the patterns. Click 'Moiré Pattern Gen. II' for a similar demonstration.

Necker Cube and Subjective Contours [Demonstration]
Description: This demonstration shows a Necker cube. When you press 'play' animations help people to see how the cube can be perceived 2 ways.

Instructions: Use this activity to demonstrate the Gestalt idea that 'the whole is more than the some of its parts.' Select 'Simulations and Demonstrations' from the left side of the screen. Make sure that people see at least 1 of the 2 possible 3D cubes. Although you can select 'play' to enact animations designed to help people to see the figure both ways, I didn't find it very helpful (but see the Animated Necker Cube). Once people can see at least on 3D cube consistently and clearly, ask them why. The image is made up of nothing more than blue circles with missing pieces. In this way, people can experience a sense of 'gestalt'.

Cautions: The image will take a minute or so to load. Shockwave player required.

Photomosaics [Display]
Description: This site contains photomosaics - bigger pictures made up of many small related pictures (e.g., a picture of a dollar made of many smaller pictures of foreign currency).

Instructions: Select either 'Screen Savers' or 'Posters'. Select a photomosaic to show and click on the picture to enlarge it. After loading the image, let students look at the picture for a few moments and then ask them to describe what they see ('What's this?'). Discuss the Gestalt idea and ask student how many noticed that the picture is made up of many smaller related pictures (e.g., the one dollar bill is made up of smaller pictures of other foreign bills).

Motion Perception

Instructions: Allow the applet to load. Objects will automatically appear and pass through the cube. Further information on Necker cubes is listed below.

Apparent Motion [Demonstration]
Description: An example of how we often perceive motion where there really is none. By shifting a pattern of illumination from one location to another, we perceive the shift as motion. As such, we perceive motion in televisions, computer screens, films, and other areas of our everyday lives.

Instructions: Allow the applet to load. You should see a box filled with 76 small 'lights.' Each vertical column lights up as a whole in a sequence of colors, such that it appears that different colors are 'moving' horizontally across the box. You may speed up or slow down the rate of motion by using the buttons underneath the box. You may also space the columns closer or further apart by using the other buttons underneath the box.

Instructions: Ask students to guess what the dots represent. Now press the 'Run!' button. The dots will move in what should be a familiar motion. If students are still uncertain as to what the dots represent, select 'lines.' The character will continue to move, but now with lines added in. If you'd like to see if your student's are correct, click 'the whole.'

Biological Motion Defines Form (from Vision Science) [Demonstration]
Description: An animated example of biological motion. When the movie is paused, the dots appear to be random. When the movie is unpaused, it becomes apparent that the dots are moving in a common biological motion. An excellent example that could be used in discussions of perception, motion cues, or Gestalt principles.

Instructions: Allow the page to load. Select 'demonstrations' from the frame at the left. A new page will come up. Select 'motion perception.' A new page will come up with a new frame to its left. From the list in the frame to the left, select 'biological motion.' The demonstration should load and begin playing automatically.

Breathing Square Illusion (from Caltech) [Demonstration]
Description: This interactive demonstration/illusion is based on the perceptual system's inability to resolve ambiguous information about a rotating square's true direction of movement when it is occluded. You can control the level of occlusion and see how this alters the illusion - the extent to which the square appears to expand and contract quickly.

Instructions: Wait for the applet to load. You will see a rotating square partially obscured by four stationary squares. Using the sliding bar on the bottom, adjust the size of the stationary squares. You may also click on the square's image to alternate between four stationary squares or one stationary cross.

Concentricity Distorted by Motion [Demonstration]
Description: In this interactive exercise, the viewer is asked to center a rotating triangle over a rotating square. The difference in shape, size, and constant movement makes it difficult for the viewer to perform this task accurately.

Instructions: Click 'Concentricity' in the frame on the left. Allow the applet to load. You should see a red triangle rotating over a blue square. By clicking on the triangle, you may move it around. Try to place the triangle such that it is centered on the square. When you are satisfied that you have done this, press the 'show grid' button to see how close you came to centering the triangle on the square.

Induced Motion [Demonstration]
Description: This site contains a several pictures of vertical lines moving uniformly in front of a static blue dot to demonstrate induced motion.

Cautions: The initial images may take a minute or two to load. This demonstration works better on Microsoft Internet Explorer than on Netscape.

Kinetic Depth [Demonstration]
Description: An example of how motion can imply depth. When the demonstration is paused, the viewer sees a two-dimensional circle of dots. When the demonstration is unpaused, the motion of the dots implies the presence of a three-dimensional sphere.

Instructions: Allow the page to load. Select 'demonstrations' from the frame at the left. A new page will come up. Select 'motion perception.' A new page will come up with a new frame to its left. From the list in the frame to the left, select 'kinetic depth.' The movie should load and begin playing automatically.

Motion As A Grouping Principle: Moving Box [Demonstration]
Description: This site contains an excellent demonstration of how we use motion to assist object recognition. The site shows how a box patterned to match a background disappears when it is still, but is clearly identifiable when it is moving.

Instructions: Click and hold on 'Freeze Motion' to stop the box's movement. Watch it blend into the background. Release to regain motion.

Motion As A Grouping: Moving Disc of Dots [Demonstration]
Description: This site shows a section of dots move together across the background dot pattern. When you pause the movie, the 'disc' of dots becomes imperceptible as it blends into the background. When you play the movie, the section of dots move together showing that motion serves as a grouping principle.

Instructions: Click on the pause button (| |) to pause the movie and watch the disc fade away. Click on the arrow button to play the movie again watch the disc reappear.

Cautions: The image will take a minute or so to load. Quicktime player required.

Instructions: Click 'Hidden Dog Illusion' in the frame on the left. Allow the applet to load. Study the image. Can you see the hidden dog? If not, press 'show' to make the background disappear, or 'run' to make the dog run. Either way, the location of the dog will become apparent.

Motion As A Grouping Principle: Moving Psi of Dots [Demonstration]
Description: This site shows a section of dots shaped like a Psi move together across the background dot pattern. Before the Psi moves, it is impossible to see. When it moves, it is impossible to miss. The demonstration repeats automatically.

Cautions: The image will take a minute or so to load. Java-enabled browser required.

Motion As A Grouping Principle: Moving Shapes [Demonstration]
Description: This site contains an excellent demonstration of how we use motion to assist object recognition. The site shows how various shapes patterned to match various backgrounds seem to disappear when they are still, but are clearly identifiable when moving.

Instructions: Use this image to support a discussion on perception, gestalt ideas, and motion as a grouping principle and object recognition aid. Click on 'select shape' to select either a triangle, circle, or star as the moving object. Click on 'reveal shape' at any time to show the shape's location. Click on 'animate shape' to start the shape in motion or to pause motion. You can alter the path of the shape by clicking on it and dragging it into the desired path. Click on one of the other background patterns to change the background pattern (and the shape's as well).

Motion Parallax [Demonstration]
Description: This site contains an excellent and interactive demonstration of motion parallax.

Instructions: Click 'play' to make the scene move as if you were in a car traveling to the left. Click 'stop' to pause the action. Notice that object tend to move in the opposite direction and than closer objects appear to move faster than farther objects.

Cautions: The initial image may take a minute or two to load. This demonstration works on Microsoft Internet Explorer much better than it does on Netscape. Flash 4.0 player required.

Motion Parallax in Outer Space [Demonstration]
Description: An interactive exercise/demonstration which places the viewer in a spaceship in an alternate universe. Using his or her knowledge of what a 'normal' universe should look like, the viewer attempts to get back to his or her home universe by distinguishing between motion cues which are realistic and those that are false. The demonstration could be an interesting addition to a discussion of motion parallax, depth cues, motion, and perception.

Motion Perception Warehouse [Demonstrations]
Description: This site contains a number of demonstrations on motion perception. Useful ones include:

Four-Stroke Apparent Motion: This animation shows a repeating cycle of four different frames (hence 'four-stroke') that gives the impression of continuous forward motion.

Second-Order Motion: As the movie advances, each successive column reverses contrast in sequence creating apparent motion.

Plaid Motion: When superimposed, the two gratings appear to form a single 'plaid' pattern, drifting rigidly.

Direction Repulsion Animation: A direction repulsion animation that shows two fields of drifting dots that appear to move over each other transparently and affect the perception of the other.

Kinetic Depth: A demonstration that shows the visual system can construct complex 3-D shape representations from motion information.

Stereokinetic Depth: A rotary movement demonstration that creates an impression of 3-D structure by producing apparent distortion in the shape of concentric patterns

Implicit Figure: There are no continuous contours defining the central square, but instead occlusion cues in the form of missing segments in the circles 'imply' the presence of the shape.

Instructions: Select demonstration from the frame on the left side of the screen.

Paradoxical Rest [Demonstration]
Description: An animated example in which a rotating square appears to stand still due to an occluding cross in front of it. Could be a useful addition to a discussion of perception or motion cues.

Instructions: Allow the page to load. From the frame on the left, select 'demonstrations.' A new page will come up in the right frame. Scroll down and select 'motion integration.' A new page will come up with a list of demonstrations. Select 'paradoxical rest.' The movie should automatically load and begin playing.

Phi Phenomenon and Apparent Motion [Demonstration]
Description: This site contains an interactive activity designed to show the Phi Phenomenon. It also allows the viewer to manipulate the physical, spatial, and temporal characteristics of the demonstration to change the perception.

Instructions: Use this experiment to support a discussion of apparent motion. To begin the demonstration, click on 'Start Here' and then on 'Try It'. Adjust the characteristics of the flashing lights by using the on-screen control panel. Click-and-drag the corresponding gray button to adjust the lights' size, distance from each other, temporal interval between flashes, and flash duration. Click on a different color to change either the left or right light's color. To go to the next demonstration click 'Next'. Here you can use a similar control panel to adjust the characteristics of a virtual baseball that is thrown by a player. After you are done with the control panel (you don't have to adjust anything) click 'Next' to watch the ball travel (apparent motion).

Stereokinetic Motion [Demonstration]
Description: An animated example of stereokinectic motion. The rotary motion produces an apparent distortion in concentric circles, thus creating an illusion of 3D. Depending on how the viewer looks at it, the image could be construed as a protrusion or a tunnel. Could be an interesting addition to a discussion of perception, motion cues, and depth cues.

Instructions: Allow the page to load. Select 'demonstrations' from the frame at the left. A new page will come up. Select 'motion perception.' A new page will come up with a new frame to its left. From the list in the frame to the left, select 'stereokinetic motion.' The movie should load and begin playing automatically.

13 and Top Down Perception [Demonstration]
Description: This demonstration shows a 13. When you click on the image, the screen asks you 'What's this?' When you click the screen again, the 13 is situated between a 12 and a 14, prompting the perception of the object as a thirteen. When you click the image again, the 13 is situated between an A and a C, prompting the perception of the object as the letter B.

Instructions: Use this demonstration to support a discussion of top-down processing. Ask students what the object is. Click on the object to get the numbers to appear and ask again. Click on the object to get the letters to appear and ask again. Ask or discuss why is the same object perceived differently in each case?

Cautions: The initial images may take a minute or two to load. Microsoft Internet Explorer browser required. When you scroll down the image may become disjoint. Scroll up to correct the problem.

Color and Context (from Grand Illusions) [Demonstration]
Description: The illusion demonstrates the contextual effects of color. An 'X' comprised of pink squares is drawn on a filed of white and green checkers. The pink squares that fall next to white squares appear pink, and the pink squares that fall next to green squares appear red.

Instructions: Open the website and allow for the page to load. Have the students answer the question at the top before scrolling down for the explanation.

Cautions: The illusion is based on pink and green colors and may not be useful for colorblind students.

Color and Context (From John Kranz) [Demonstration]
Description: This demonstrations shows 2 green squares. When you click on the image, the squares are embedded in yellow and blue backgrounds. Each time you click the image, it changes. Although the green squares are the same color (demonstrated by the first image), they appear to be different when they are embedded in different colors.

Instructions: Click on the image (repeatedly) to change the background colors and eventually to change the shape of the green object(s). Use this site to show that our perception of color depends on context. But wait, aren't sensation and perception separate? How can context alter the way our brain interprets light energies? An interesting discussion for sure.

Cautions: The initial images may take a minute or two to load. Microsoft Internet Explorer browser required. When you scroll down the image may become disjoint. Scroll up to correct the problem.

Color and Context (from Worth Publishers) [Demonstration]
Description: This demonstration shows 2 gray X's embedded in different colors. Although the X's are the same color, they appear to be different colors. When you press 'play' the background colors change pronouncing the effect.

Instructions: Select 'Simulations and Demonstrations' from the left side of the screen. Select 'play' to make the background colors change. They will continue to change until you leave the simulation site.

Cautions: The image will take a minute or so to load. Shockwave player required.

Droodles [Activity]
Description: 'Droodles' is an interactive exercise in memory. Nonsense drawings are presented with nonsense names and the viewer is asked to remember both. Nonsense drawings are then presented with clever, descriptive titles and the viewer is again asked to remember both. The activity demonstrates that the meaningful names facilitate the recall of seemingly nonsensical drawings and the perceptual organization of information.

Instructions: Ask students to study the droodles for a minute, paying attention to both the drawing itself and its respective name. Press 'begin.' The droodles will disappear. Ask students to redraw the droodles (whose positions have been moved around) in their notebooks. When students are ready, click on each of the dots beneath the drawings. The actual droodle will appear to the left side of the screen. Next, click 'try more droodles' and repeat the process. This time the droodles are given meaningful labels. An explanation will be presented when you are finished.

Cautions: Images will take a minute or so to load. Shockwave player required.

Exploratorium's 5 Interactive Illusions [Demonstration]
Description: This site contains 5 interactive illusions that demonstrate how judgements of size, distance, continuity, and linearity are context dependent.

Illusion 1: Use the mouse to move the virtual dial (click-and-drag). As the dial moves the size of the yellow circle on the right (the one surrounded by smaller circles) will change size. Change the size of the circle until your students believe that it matches the yellow circle on the left (the one surrounded by larger circles). Click on the black button labeled 'reveal illusion' to see how close the judgement is. Click on the button labeled 'next illusion' to continue on.

Illusion 2: This is a version of the Muller-Lyer Illusion. Use the mouse to move the virtual dial (click-and-drag). As the dial moves the white circle will move. Move the circle until your students think it is in the center of the horizontal yellow line (the middle of the arrow). Click on the black button labeled 'reveal illusion' to see how close the judgement is. Click on the button labeled 'next illusion' to continue on.

Illusion 3: Use the mouse to move the virtual dial (click-and-drag). As the dial moves the size of the red circle on the right will change size. Change the size of the circle until your students believe that the red circles are the same size. Click on the black button labeled 'reveal illusion' to see how close the judgement is. Click on the button labeled 'next illusion' to continue on.

Illusion 4: This is a version of the Poggendorf Illusion. Use the mouse to move the virtual dial (click-and-drag). As the dial moves the green line segment below the bar will move. Move the line segment until your students think that it will line up with the top line segment. Click on the black button labeled 'reveal illusion' to see how close the judgement is. Click on the button labeled 'next illusion' to continue on.

Illusion 5: Use the mouse to move the virtual dial (click-and-drag). As the dial moves the size parallel nature of the two lines will change. Change these lines until your students believe that they are parallel. Click on the black button labeled 'reveal illusion' to see how close the judgement is. NOTE: The graphic nature of the lines provide alternative cues about the angles of the lines potentially ruining the demonstration.

Gray Contrast and Context (from The Exploratotium) [Demonstration]
Description: This site provides an interactive figure of gray and black vertical bars. Although the gray bars are identical, they seem to change shade as you move them.

Instructions: Use this demonstration as you discuss the role of context in perception. First, click on the bars under the gray circle and hold the mouse button down. The black bars will disappear showing that all of the gray bars are identical. Next, click on the arrows to move the gray bars to the left or right. Notice that the gray bars that end up on top of the black bars look lighter while the gray bars that end up in between the black bars look darker. You can also click on the gray circle to center the gray bars.

Gray Contrast and Context (from Worth Publishers) [Demonstration]
Description: This animated clip shows 2 gray bars embedded in different colors (black or white). Although the bars are the same shade, they appear to be different shades.

Instructions: Use this activity to demonstrate that our perception of brightness is context dependent. Select 'Simulations and Demonstrations' from the left side of the screen. After the screen loads (you will see a Necker cube), continue to click on the 'next' located in the upper right corner of the screen until the page indicator above the images reads '5 of 7'. Ask students which gray bar is brighter. You can 'click and drag' the black background to show that the shades are the same, and to swap backgrounds and changes the perception of the shades.

Cautions: The image will take a minute or so to load. Shockwave player required.

Illusions Reveal the Brain's Assumptions [Demonstration]
Description: This site demonstrates how context influences our perceptions of features. The site includes a nice demonstration of subjective contours (Kanizsa's Triangle), the use of shading as a grouping principle, and the effect of perspective on length judgement.

King's College of London's 10 Illusions and 2 Stereograms [Demonstration]
Description: This site contains 10 quick and dirty illusion/illustration demonstrations and 2 stereograms (that actually work from an electronic source!!). Demonstrations include: Hermann Grid, Find the Dalmatian, Impossible Triangle, Rows/columns of dots, Old/Young lady, Duck/Rabbit, and Old man/Lovers ambiguous figure, Moller-Franz Illusion, Distorted Skull figure, Shimmering image, and Shark and Saturn Stereograms.

Instructions: Use this demonstration to show how size and depth cues facilitate visual illusions. Select 'Simulations and Demonstrations' from the left side of the screen. After the screen loads (you will see a necker cube), continue to click on the 'next' located in the upper right corner of the screen until the page indicator above the images reads '3 of 7'. Ask students which monster/red bar is bigger. If the illusions work, the will tell you the top monster/bar is bigger. Select 'play a' or 'play b' to have the computer show that the monsters/red bars are identical. Discuss distance and depth cues and why this illusions occurs.

Cautions: The image will take a minute or so to load. Shockwave player required.

Rabbit/Duck Ambiguous Figure [Demonstration]
Description: People rely on context or expectations to help interpret ambiguous information. This site shows a duck/rabbit figure.

Instructions: Ask half of your students to close their eye. Present the other half with the words 'quack quack.' Now repeat the process for the other half of your students and show them the words 'carrot eater.' Tell your students that you are going to load a picture to the screen. Ask them to remember the first thing that comes to mind when they look at the loaded image. Select 'Simulations and Demonstrations' from the left side of the screen (you may want to pre-load this image). The image will load. Ask each side of the room to look at the image and note what comes to mind. If you press play, the figure's features are modified to show how the figure could be either a duck or a rabbit. Use this demonstration to support your discussion on context, expectations, perception, and top-down processing.

Cautions: The image will take a minute or so to load. Shockwave player required.

Size Constancy in a Photograph [Demonstration]
Description: This site contains an interesting and effective and interactive way of demonstrating size constancy and relative height issues.

Instructions: Show students that the scene is a normal, everyday photograph. Next, select ' When you are ready, go to the next page'. Point out the little guy at the bottom of the screen. Ask them what is wrong with the picture and then point out that the little guy is the exact same person walking along the trail higher in the photo. Why does he look normal on the trail, but little at the bottom of the screen? For fun you can select 'Version with several copies of the walker' to have many 'little guys' appear across the photo, 'An animated version' to show the little guy rapidly moving along the trail, or 'Interactive Figure' to show the move the guy in the red hat and the trail walker in the white shirt to a different room. In this room you can add or remove various relative size, relative height, and texture gradient cues.

Cautions: The 'An animated version' option may not work on older versions of Netscape. Images may take a minute or two to load.

Stroop Effect: Discovery City [Demonstration]
Description: This site contains an interactive demonstration of the Stroop effect.

Instructions: Follow on-screen instructions. Use this site to support discussions of various aspects of perception and context.

Visual Search Experiment [Demonstration]
Description: This site contains an interesting and useful setup for either demonstrating basic (find a T among Ls) and complex (find a red T among red Ls) visual search tasks or demonstrating a short visual search experiment. The site also provides competing hypotheses and a testable prediction.

Instructions: Use this demonstration to support a discussion on perception, cognition, or research methods (What is the independent/dependent variable? How are variables operationally defined, What does RT indicate about mental processes, Are there potential confounds, etc.). Click on 'Click here to test theories' to begin. Use the mouse to select your target (T or red T), distracters (Ls or red Ls), display size, and number of trials. When you select the number of trials, the experiment will begin. Click on the 'X' to start each trial.

Illusions

Café Wall Illusion (from the Exploratorium) [Demonstration]
Description: This site provides an interactive illusion based on the brickwork of a café in Bristol. Although the horizontal lines in the wall are straight, they appear curved.

Instructions: Use this demonstration as you discuss the perception of contours. You can move the bricks back and forth by clicking on the arrow buttons. Notice that the effect disappears when the bricks are either aligned or in a checkerboard pattern. You can also change the brightness of the mortar by clicking on the top or bottom of the brightness arrow.

Impossible Figures Image [Demonstration]
Description: This site shows multiple pictures of impossible figures - figure that look normal at first glance, but are architecturally impossible.

Instructions: Use this image to support a discussion on perception or gestalt ideas.

Müller-Lyer Experiment (from John C. Hay) [Activity/Demonstrations]
Description: This site contains an interesting and useful setup for either demonstrating the Muller-Lyer Illusion or demonstrating a short Muller-Lyer Experiment.

Instructions: Use this demonstration to support a discussion on perception, cognition, or research methods (What is the independent/dependent variable? How are variables operationally defined, What does RT indicate about mental processes, Are there potential confounds, etc.). Follow the on-screen instructions. Use the first trial to demonstrate the illusion. At the end of the trial, you can manipulate the lines' color, the length, angle, and type of fins (point in or out), and the number of trials. Subjects will press the spacebar to begin each trial.

Müller-Lyer Illusion (from Sandlot Science) [Demonstration]
Description: An interactive version of the classic illusion. The extended or retracted end pieces on the lines cause the lines to look longer or shorter in relation to each other.

Instructions: Click on 'Müller-Lyer Illusion' in the frame on the left. Allow the applet to load. Using the mouse, click on the left line to extend the top or the bottom such that the left line is equally as long as the right line. When you feel they are the same length, press the 'show measure' button to see how close you were.

Instructions: Use this activity to demonstrate the illusion and spur discussion about its explanation. Select 'Simulations and Demonstrations' from the left side of the screen. After the screen loads (you will see a necker cube), continue to click on the 'next' located in the upper right corner of the screen until the page indicator above the images reads '4 of 7'. Ask students which vertical red line is longer. Select 'play' to show that they are the same lengths. Select 'next' to go to a similar demonstration using circles. Select 'play' to show that the line lengths are similar.

Cautions: The image will take a minute or so to load. Shockwave player required.

Ouchi Illusion (from Sandlot Science) [Demonstration]
Description: The site provides a still image of the Ouchi illusion. Interestingly, the illusion is not well understood - though it could be based in perceptual ambiguities caused by the juxtaposition of curved and straight lines.

Instructions: Ask students to move your eyes around the image while keeping the center circle in the periphery of view. The center circle appears to separate itself from the rest of the image and move. You can scroll down for further explanation.

Poggendorf Illusion (from Dave Landrigan) [Demonstration]
Description: This site shows 2 pictures: the illusion (2 apparently continuous diagonal lines passing through a vertical black bar) and the same image without the bar (revealing 3 lines that are not in fact continuous).

Instructions: Use this image to support a discussion of perception, occlusion, and visual illusions.

Poggendorff Illusion Experiment (from John C. Hay) [Activity/Demonstration]
Description: This site contains an interesting and useful setup for demonstrating the Poggendorff Illusion or for demonstrating a short Poggendorff Experiment.

Instructions: Use this demonstration to support a discussion on perception, cognition, or research methods (What is the independent/dependent variable? How are variables operationally defined, What does RT indicate about mental processes, Are there potential confounds, etc.). Follow the on-screen instructions. Use the first trial to demonstrate the illusion. At the end of the trial, you can manipulate variable attributes. Press the spacebar to begin each trial.

Poggendorf's Illusion (from Sandlot Science) [Demonstration]
Description: An interactive version of the classic illusion. The obstructing bar causes the line to look disconnected.

Instructions: Click on 'Poggendorf's Illusion' in the frame on the left. Allow the applet to load. Using the mouse, click on the top part of the line to move the top part such that it matches up with the bottom part of the line. When you feel they are matched, press the 'show' button to see how close you were.

Ponzo Illusion (Sandlot Science) [Demonstration]
Description: An interactive version of the classic illusion. The converging railroad tracks cause the lines to look longer or shorter in relation to each other.

Instructions: Click on 'Ponzo Illusion' in the frame on the left. Allow the applet to load. Using the mouse, click on the bottom line to extend the right or left sides such that the bottom line is equally as long as the top line. When students feel they are the same length, press the 'show measure' button to see how close they are.

Cautions: The image will take a minute or so to load. Shockwave player required.

Temple Illusion [Video]
Description: This site provides an image of what appears to be a model of a temple, an image of a person interacting with the model in what should be an impossible way, and a video clip at the bottom of the page to show what is going on.

Instructions: Use this demonstration as you discuss the monocular depth cues and perceptual constancy. First, discuss the images at the top of the page. See if students have an explanation to the question 'What's going on?' Next, scroll to the bottom of the page and watch the 5-second video clip that shows the answer.

Twisted Cord Illusion: (from Sandlot Science) [Demonstration]
Description: The twisted cord illusion is one of the most powerful illusions available. This interactive demonstration allows the viewer to contrast the effects of the twisted lines with lack of effect associated with the solid lines

Instructions: Wait for the applet to load. You will see a series of parallel lines with black and white twists that are shifting from side to side.

World of Escher [Display]
Description: This site contains numerous images of M. C. Escher's work.

Instructions: Use this demonstration to support a discussion on monocular depth cues. Click on the desired image to enlarge it. Click on the image again to enlarge it again.

Zöllner Illusion [Demonstration]
Description: An interactive version of the classic illusion. The parallel lines appear distorted once an overlay of fine lines is added.

Instructions: Click ' Zöllner Illusion' in the frame on the left. Allow the applet to load. You will see a yellow background with black stripes. Notice how the fine lines in the center appear to distort the parallel black lines. If you wish, you may reverse the fine lines or make them disappear entirely by clicking on the image once or twice.

Change Blindness

Change Across Scenes (the conversation) [Video]
Description: In this short (15 second) video a number of features change each time the camera cuts to a different position (clothing, the objects on the table, and the positions of the actors' arms). Out of 9 possible detections, only 1 subject noticed a change in the corresponding experiment. Even when people intentionally search for changes in this video, they tend to notice fewer than 2 of the 9 changes on average.

Instructions: Allow for the movie to load. It should begin to play on its own. If not, press the play button underneath the movie screen. For another similar demonstrations (smaller clip) see http://www.wjh.harvard.edu/~viscog/grafs/demos/personchange.mov.

Gradual Changes to Colors in Scenes [Video]
Description: A series of 12 second movie clips which demonstrate tendency not to perceive gradual change. In each of the clips, an object's color is gradually changed into a new, different color. If the viewer does not know specifically where to look, it is likely that the change in color will be missed. Could be a useful addition to a discussion of perception, attention, or border cues.

Gradual Change to Objects in Scenes [Video]
Description: A series of 12 second movie clips which demonstrate tendency not to perceive gradual change. In each of the clips, an object is gradually faded into or out of the picture. If the viewer does not know specifically where to look, it is likely that the change will be missed. Could be a useful addition to a discussion of perception, attention, or border cues.

Person Change Event [Video]
Description: In this short (20 second) and amusing video clip, a confederate walks up to an unsuspecting pedestrian and asks for directions. While the subject is explaining the directions, two other confederates carrying a door rudely pass in between the subject and the confederate. While this is happening, the confederate joins in carrying the door and the confederate originally holding the tail end of the door replaces the first confederate in the conversation. Despite the new, different confederate, only 50% of subjects noticed the change.

Instructions: Allow for the movie to load. It should begin to play on its own. If not, press the play button underneath the movie screen. For another similar demonstrations (this time with a construction worker) see http://www.wjh.harvard.edu/~viscog/grafs/demos/construction.mov.

Sustained Inattentional Blindness [Video]
Description: An interesting movie clip demonstrating inattentional blindness, or humans' tendency to fail to perceive certain information while concentrating on something else. The viewer is asked to count the ball passes made by a certain team or player on a video. In this clip, a transparent woman with an umbrella walks through the middle of the ball game. Because they aren't looking for her, many viewers tend to fail to see her entirely. Could be an interesting addition to a discussion of attention and perception. The clip is about 18 seconds long.

Auditory Perception: The Verbal Transformation Effect [Demonstration]
Description: This site contains a recording of a man saying 'tress' over and over again. We, of course, hear 'stress' as our perceptual system organizes auditory information into useful units.

Instructions: Click on 'Tress Test.' Use this demonstration to support a discussion on auditory perception. After the program loads, the voice will begin automatically. Click on 'Stop' to pause the sound.

Psi, ESP, and Parapsychology [Video]
Description: This site contains 7 video clips [2:00 - 5:00 long] on various topics associated with Psi and ESP. The clips are pro ESP.

Do you have comments? Concerns? Suggestions? Do you know of something we should include? Email Andrew Peck.