Visual Perception: I. What is perception? II. Gestalt Laws of Grouping A. Proximity B. Similarity C. Continuity D. Closure E. Common Fate F. Simplicity G. Review of Gestalt Groupings III. Figure and Ground IV. Perceptual Constancy A. Lightness Constancy B. Color Constancy C. Shape Constancy D. Size Constancy E. Review of Constancy V. Depth Perception A. Monocular Cues 1. Interposition 2. Atmospheric Perspective 3. Texture Gradient 4. Linear Perspective 5. Motion Parallax B. Binocular Cues VI. Illusions A. Illusions of Length 1. Poggendorff Illusion 2. Muller-Lyer Illusion 3. Ponzo Illusion B. Illusions of Shape: Zollner Illusion c. Illusions of Size: Aims Room D. Illusions of Contours E. Impossible Figures F. Reversible Figures VII. Class Game show: Peril VIII. Conclusion
What is perception? The book Psychology: An Introduction defines perception as ―The process of creating meaningful patterns from raw sensory information‖ More specifically Hugh Foley Associate professor of Psychology at Skidmore College defines perception as ―process by which organisms interpret and organize sensation to produce meaningful experience of the world.‖
Perceptual organization Arranging sensory stimulus into meaningful experience involves thinking, understanding and remembering. Attempt to read the following sentence Can you read this text upside down? 1. Easier to read right side up 2. Knowledge of letters and shapes helps us to read the sentence - For example, look at this Chinese character. Without knowledge of Chinese characters this symbol is meaningless but to someone with knowledge of Chinese it is the symbol for love. 3. Read as whole words and phrases – You didn’t read each letter 4. Context is key – Since the word upside is often followed by down for this reason one may overlook that each letter in down is also reversible. U.M.O.P
Gestalt Groupings • Proximity • Similarity • Continuity • Closure • Common Fate Proximity The closer objects are to one another, the more likely we are to mentally group them together. (Foley, 2005) Proximal Random This random grouping of boxes helps us to perceive them as separate objects. Proximal Unity When the squares are close, unity occurs. While they continue to be separate shapes, they are now perceived as one group. Something else is happening here notice the black circles that are appearing between the squares. We will explain this phenomenon in more detail
Similarity Linking together parts of the visual field that are similar in color, lightness, texture, shape, etc. (Foley, 2005) This is why despite the likeness in shape of the circles to on the right we perceive them in two groups because of their size.
Similarity The law of similarity is the reason why we perceive rows instead of columns with these circles and triangles. Continuity Leads us to see a line as continuing in a particular direction rather than making an abrupt turn. (Foley, 2005) The viewers eye will naturally follow a line or a curve. The crossbar of the ―h‖ leads the eye to the maple leaf.
Continuity Continuation occurs when the eye is compelled to move through one object and continue to another object. Gestalt psychologists use this term to describe our tendency to see lines as continuing, without breaks. In the drawing on the left below, we see a straight line with a curved line running through it. Notice that we do not see the drawing as consisting of the two pieces in the drawing on the right. Closure We are inclined to overlook incompleteness in sensory information and to perceive a whole object even where none really exist. (Morris and Maisto, 1993) On the right we complete the lines on the object so we can observe the panda. Closure We prefer complete forms to incomplete ones which is why in the image below we mentally close the lines to perceive a duck. Common fate The law of common fate leads us to group together objects that move in the same direction. (Foley, 2005) Imaging if three of the circles are moving in one direction and the two other circles are moving in the other we would mental group the circles that moved in the same direction. Simplicity The law of simplicity encompasses all the other Gestalt laws of perception. People prefer the simplest possible organization. According to the principle of simplicity, we likely to describe this as a spiral rather than nine vertical rows of dots (the spiral is simpler).
Review of Gestalt Groupings Proximity – Is the grouping of objects because of how close the are together. Similarity - refers to our tendency to group things together based upon how similar to each other they are. Continuity – refers to our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern. This is why we see a cross as one object instead of two distinct intersecting lines.
Closure – We prefer complete forms to incomplete ones. Common Fate – Objects moving in one direction will be grouped. Like a flock of geese. Simplicity – People prefer the simplest explanation
Figure and Ground Distinguishing objects from its surroundings. Dr. Foley says that ―Gestalt psychologists have devised ambiguous figure-ground relationships—that is, drawings in which the figure and ground can be reversed—to illustrate their point that the whole is different from the sum of its parts. Consider the accompanying illustration entitled ―Figure and Ground.‖ You may see a white vase as the figure, in which case you will see it displayed on a dark ground. However, you may also see two dark faces that point toward one another. Notice that when you do so, the white area of the figure becomes the ground. Even though your perception may alternate between these two possible interpretations, the parts of the illustration are constant. Thus, the illustration supports the Gestalt position that the whole is not determined solely by its parts.‖
Perceptual Constancy Is the tendency to perceive objects as relatively stable and unchanging despite changing sensory information. (Morris and Maisto, 1993) This is why once we have a stable perception of an object we can recognize it at almost any distance or level of light. Types of Constancy: There are essentially four types of perceptual Constancy, Lightness, Color, shape and size constancy. Lightness Constancy: Means that our perception of an object’s lightness or darkness remains constant despite changes in illumination. Everyone flip over the packet over so that you see the backside of the last page. With the lights on you see that the paper appears white. [Turn off two lights] If we turn off two lights then the paper still appears white. [Turn off all lights except for the projector] Even with very little light the paper still appears white. [Lights back to normal state] This illustrates an important perception principle and that is that perception is relative. We determine the lightness and darkness of the paper relative to other items in the room. Color Constancy Perceive the color of an object as the same despite changes in lighting conditions. Dr. Foley says: ―You have experienced color constancy if you have ever worn a pair of sunglasses with colored lenses. In spite of the fact that the colored lenses change the color of light reaching your retina, you still perceive white objects as white and red objects as red. The explanations for color constancy parallel those for lightness constancy.‖
Shape Constancy Perceive objects as retaining the same shape despite changes in their orientation. Take out your book and hold it up with the cover facing you. The book is clearly in the outline of a rectangle. Now rotate the top of the book forward to a 45 degree angle. The image should now be trapezoidal with the bottom edge closer it looks larger than the top edge. Despite the trapezoidal image we still perceive the book as a rectangle. Size Constancy Tendency to perceive object as staying the same size despite changes in our distance from them. For example, we see a person off in the distance we don’t perceive them tiny as they appear. We perceive them as their normal size. The same goes for seeing a skyscraper or mountain off in the distance. Review of Constancy Lightness Constancy – refers to our perception of an object’s lightness or darkness remains constant despite changes in illumination Color Constancy - refers to our ability to recognize that color remains the same regardless of how it looks under different levels of light Shape Constancy - allows us to perceive that plate as still being a circle even though the angle from which we view it appears to distort the shape Size Constancy - refers to our ability to see objects as maintaining the same size even when our distance from them makes things appear larger or smaller
Depth Perception The ability to see the world in three dimensions and perceive distance. (Foley, 2005) Monocular Cues These are things that we can perceive with one eye. Several animals such as fish, birds, and deer rely on monocular cues entirely because their eyes are located on the sides of their heads. Interposition When one item overlaps another we discern the covered object to be further away. (Foley, 2005) Take the two straws we provided you and place one in each hand. Hold your hands out in front of you so that one straw is a couple of inches in front of the other. Now close one eye. From this perspective it is difficult to tell which straw is in front of the other. Now move the straws so they overlap. We know the object that overlaps the other is closer. How we use interposition to tell depth perception. Atmospheric Perspective: Air contains fine particles of water vapor, dust, and smoke. These particles scatter light and change its direction. The presence of scattering shows distant subjects in pictures as having a haze. The greater the distance, the more haze one will perceive. (Foley, 2005)
Texture Gradient
Take a look at the ceiling. You will notice that the part of the ceiling directly above you has a vivid texture where as further away it is less distinct.
Linear Perspective: Refers to the fact that parallel lines appear to converge with distance eventually reaching a vanishing point on the horizon. (Foley, 2005) Artist use linear perspective to create the appearance of three dimensional space. Notice how this image looks two dimensional. But then if we move the road to the horizon it creates the appearance of depth. Motion Parallax: Objects at different distances from you appear to move at different speeds when you are in motion. (Foley, 2005) The next time you are walking in a parking lot walking towards a store. As you are walking turn your head and look off in the distance. You will see that the closer items, such as the car, appear to be moving faster than the objects in the distance. When you are driving home look at a light off in the distance it will appear to be moving slower than the lights near you. Binocular Cues According to Morris and Maisto binocular clues are visual cues that requiring the use of both eyes. Take out one of the straws we provided you. Hold it out in front of you and with both eyes open line it up with parallel with a line in this room. Close your right eye then open your right eye and close your left. The straw jumps between our original alignments. This phenomenon is known as Binocular Disparity.
Illusions Occurs when what the brain perceives differs substantially from the actual qualities of and object or stimulus. (Foley, 2005) An illusion is a sort of mistake in sensory perception. Dr. Foley says that psychologist study illusions because they provide important clues about the functioning of perceptual systems. Lets look at some types of illusions: Illusion of length: Illusions of length typically occur when additional line segments interfere with our perception on an object. For example, these three pillars are the same length.
Poggendorff Illusion The Poggendorff illusion was discovered in 1860 by physicist and scholar J. C. Poggendorff The illusion is that the line segment passing behind the rectangle are offset when they are aligned.
Muller-Lyer Illusion
One of most famous illusions is the Muller-Lyer Illusion crated by German psychiatrist Franz muller-lyer in 1889. Exercise: Look at the following animation and when you perceive the lines as being identical in length remember that number. Ok what kind of numbers did you pick. Well the correct answer was 6. If you picked 4 or 5 then your perception tricked by the Muller-Lyer Illusion. A simple explanation is that the wings provide depth cues. In this situation, our brain incorrectly interprets the depth cues, resulting in the optical illusion.
Ponzo illusion: The Ponzo Illusion is named after Itialan psychologist Mario Ponzo. The two lines do not appear similar in length but in fact they are. We interpret the diagonal lines as indicating depth, because our mind believes that the top line is farther away we perceive it as longer.
Illusions of Shape: Zollner Illusion In the Zollner Illusion a square appears trapezoidal, wider at the top than at the bottom, because of the horizontal lines in the background. Illusions of Size: Look at the following photograph. The girl on the right appears gigantic compared to the women on the left. This is an illusion of depth that forces us to misperceive the size of objects. This picture is of an Aims Room named after Albert Aims who first made the room in the 1940s. And anyone who has seen the Fellowship of the Ring has been tricked by the Abrams Room.
Illusions of Contours: If you look at the figure most likely you perceive a white trinangle. But if you look closely there are each side of the triangle is white space. According to Dr. Foley Gestault psychologist indicate that people prefer a well organized whole rather than individual parts. Impossible Figures:
This occurs when we perceive objects as reasonable but they are actually impossible. How many legs does the elephant have?
Reversible figures Do you see a young woman with her back to you or old women with a wart on her nose? According to Dr. Foley reversible figures aren’t true illusions because there isn’t an error in the perception. However they do allow more than one interpretation. Conclusion: Hopefully our presentation has enhanced your understanding of the human visual perception system. We have learned about Gestalt groupings like proximity, closure and simplicity. We have also gained a better understanding of perceptual constancy which is our a tendency to perceive objects as stable and unchanging despite changing sensory information. We discussed depth perception and the difference between monocular and binocular clues. Lastly we studied illusions. We hope that you come away from our presentation with a greater understanding of human visual perception.