KEY THEME
Perception refers to the process of integrating, organizing, and interpreting sensory information into meaningful representations.
KEY QUESTIONS
What are bottom-
What is Gestalt psychology?
What Gestalt principles explain how we perceive objects and their relationship to their surroundings?
As we’ve seen, our senses are constantly registering a diverse range of stimuli from the environment and transmitting that information to the brain. But to make use of this raw sensory data, we must organize, interpret, and relate the data to existing knowledge.
Psychologists sometimes refer to this flow of sensory data from the sensory receptors to the brain as bottom-
But as we interact with our environment, many of our perceptions are shaped by top-
Both top-
But now look at the background in the photograph, which is more ambiguous. Deciphering these images involves both bottom-
To identify the mysterious object, you must interpret the sensory data. Top-
Clearly, bottom-
In the next few sections, we will look at what psychologists have learned about the principles we use to answer these perceptual questions. Much of our discussion reflects the work of an early school of psychology called Gestalt psychology, which was founded by German psychologist Max Wertheimer in the early 1900s
ESP: Can Perception Occur Without Sensation?
ESP, or extrasensory perception, means the detection of information by some means other than through the normal processes of sensation.
Do you believe in ESP? If you do, you’re not alone (Ridolfo & others, 2010). Recent surveys conducted by the Associated Press and the Gallup Poll have found that close to 50 percent of American adults “believe in ESP” (Fram, 2007; D. Moore, 2005).
Forms of ESP include telepathy, which is the direct communication between the minds of two individuals; clairvoyance, the perception of a remote object or event, such as “sensing” that a friend has been injured in a car accident; psychokinesis, the ability to influence a physical object without touching it; and precognition, the ability to predict future events.
MYTH SCIENCE
Is it true that most psychologists study extrasensory perception (ESP)?
The general term for such unusual abilities is paranormal phenomena. Paranormal means “outside the range of normal experience.” Thus, these phenomena cannot be explained by known laws of science and nature. Parapsychology refers to the scientific investigation of claims of various paranormal phenomena. Contrary to what many people think, very few psychologists conduct any kind of parapsychological research.
Have you ever felt as if you had just experienced ESP? Consider this example: Some years ago, Sandy had a vivid dream that her cat Nubbin got lost. The next morning, Nubbin sneaked out the back door, went for an unauthorized stroll in the woods, and was gone for three days. Did Sandy have a precognitive dream?
Such common instances are sometimes used to “prove” that ESP exists. However, two less extraordinary concepts can explain both occurrences: coincidence and the fallacy of positive instances. Coincidence describes an event that occurs simply by chance. For example, you have over a thousand dreams per year, most of which are about familiar people and situations. By mere chance, some aspect of some dream will occasionally correspond with reality.
The fallacy of positive instances is the tendency to remember coincidental events that seem to confirm our belief about unusual phenomena and to forget all the instances that do not. For example, think of the number of times you’ve had a dream that did not come true. Such situations are far more common than their opposites, but we quickly forget about the hunches that are not confirmed.
Why do people attribute chance events to ESP? Research has shown that believers in ESP are less likely to accurately estimate the probability of an event occurring by chance alone. Nonbelievers tend to be more realistic about the probability of events being the result of simple coincidence or chance (Dagnall & others, 2007; Rogers & others, 2009).
Parapsychologists attempt to study ESP in the laboratory under controlled conditions. Many initially convincing demonstrations of ESP are later shown to be the result of research design problems or of the researcher’s unintentional cuing of the subject. Another problem involves replication. To be considered valid, experimental results must be able to be replicated, or repeated, by other scientists under identical laboratory conditions. Skeptics claim, and most psychologists agree, that to date, no parapsychology experiment claiming to show evidence of the existence of ESP has been successfully replicated (Hyman, 2010).
One active area of parapsychological research is the study of clairvoyance using an experimental procedure called the ganzfeld procedure (J. Palmer, 2003; Westerlund & others, 2006). (Ganzfeld is a German word that means “total field.”) In a ganzfeld study, a “sender” in one room attempts to communicate the content of pictures or short video clips to a receiver in a separate room. Isolated from all contact and wearing goggles and headphones to block external sensory stimuli, the “receiver” attempts to detect the image that is being sent.
Summarizing dozens of ganzfeld studies conducted over 15 years, Lance Storm and his colleagues (2010, 2013) showed a “hit” rate that was well above chance, implying that some sort of transfer of information had taken place between sender and receiver. These results, published in a well-
The latest salvo in the ESP debate was fired by psychologist Daryl Bem (2011), who tested precognition in a series of nine experiments involving more than a thousand participants. Bem’s ingenious strategy was to “time-
For example, practicing a list of words makes the words easier to remember. In one experiment, participants taking a memory test better remembered words that they practiced after taking the test. In another experiment, participants predicted the location of a target image on a computer screen before they saw it.
In all, eight of Bem’s nine experiments showed small but statistically significant effects in favor of precognition. These, and similar findings from Bem’s series of experiments, cannot be easily explained (Judd & Gawronski, 2011).
Bem’s research sparked a flurry of media attention, including an appearance on The Colbert Report. It also triggered a firestorm of reaction from psychologists and other scientists (Alcock, 2011; Shermer, 2011). Much of the criticism focuses on the statistical methods used to analyze the data (Fiedler & Krueger, 2013; Rouder & Morey, 2011; Wagenmakers & others, 2011). So far, replication attempts have been mostly unsuccessful (Barus & Rabier, 2014; Galak & others, 2012; Ritchie & others, 2012). Undaunted, Bem and his colleagues (2014) published their own meta-
Of course, the history of science is filled with examples of phenomena that were initially scoffed at and later found to be real, such as the notion that moods affect health and immune system functioning. So keep an open mind about ESP, but also maintain a healthy sense of scientific skepticism. It is entirely possible that some day convincing experimental evidence will demonstrate the existence of ESP abilities (see French & others, 2010; Schlitz & others, 2006). In the final analysis, all psychologists, including those who accept the possibility of ESP, recognize the need for evidence that meets the requirements of the scientific method.
CRITICAL THINKING AND QUESTIONS
Why do you think that people who believe in ESP are less likely to attribute events to chance than people who don’t think ESP is a real phenomenon?
Can you think of any reasons why replication might be particularly elusive in research on extrasensory perception?
Why is replication important in all psychological research, but particularly so in studies attempting to prove extraordinary claims, like the existence of ESP?
Think Like a SCIENTIST
Do you have psychic powers? Go to LaunchPad: Resources to Think Like a Scientist about ESP.
(Wertheimer, 1923/2009). The Gestalt psychologists emphasized that we perceive whole objects or figures (gestalts) rather than isolated bits and pieces of sensory information. Roughly translated, the German word gestalt means a unified whole, form, or shape. Although the Gestalt school of psychology no longer formally exists, the pioneering work of the Gestalt psychologists established many basic perceptual principles (S. Palmer, 2002).
WHAT IS IT?
When you look around your world, you don’t see random edges, curves, colors, or splotches of light and dark. Rather, you see countless distinct objects against a variety of backgrounds. Although to some degree we rely on size, color, and texture to determine what an object might be, we rely primarily on an object’s shape to identify it.
FIGURE-
How do we organize our perceptions so that we see an object as separate from other objects? The early Gestalt psychologists identified an important perceptual principle called the figure–
You can experience the figure–
The early Gestalt psychologists noted that figure and ground have vastly different perceptual qualities (N. Rubin, 2001). As Gestalt psychologist Edgar Rubin (1921) observed, “In a certain sense, the ground has no shape.” We notice the shape of the figure but not the shape of the background, even when that ground is used as a well-
The separation of a scene into figure and ground is not a property of the actual elements of the scene at which you’re looking. Rather, your ability to separate a scene into figure and ground is a psychological accomplishment. To illustrate, look at the classic example shown in Figure 3.14. This perception of a single image in two different ways is called a figure–
Ways of Seeing: Culture and Top-
Do people in different cultures perceive the world differently? In Chapter 1, we described two types of cultures. Unlike people in individualistic cultures, who tend to emphasize independence, people in collectivistic cultures see humans as being enmeshed in complex relationships. This social perspective is especially pronounced in the East Asian cultures of Korea, Japan, and China, where a person’s sense of self is highly dependent upon his or her social context (Beins, 2011). Consequently, East Asians pay much closer attention to the social context in which their own actions, and the actions of others, occur (Nisbett, 2007; Varnum & others, 2010).
The Cultural Eye of the Beholders
Do these cultural differences in social perspective influence visual perception and memory? Take a few seconds to look at the photo on the right. Was your attention drawn by the tiger? Or its surroundings?
In one study, Hannah Faye Chua and her colleagues (2005) used sophisticated eye-
Rather than separating the object from its background, the Chinese students tended to see—
Similarly, Joshua Goh and his colleagues (2009) compared the visual response of U.S. and East Asian participants to changes in photographs. They found that U.S. participants paid more attention to changes in the objects, but East Asian participants paid more attention to changes in the background. The U.S. participants also tended to focus their attention on the object alone, while the East Asian participants alternated looking at the object and the background, paying more attention to the relationship between the object and background. “Culture,” the researchers observed, “may operate as a top-
Cultural Comfort Zones and Brain Functioning
Many psychologists now believe that these cultural differences in social and perceptual style also influence brain function (Park & Huang, 2010). For example, psychologist Trey Hedden and his colleagues (2008) compared brain functioning in East Asian and U.S. participants while they made rapid perceptual judgments comparing two images of a square with an embedded line as shown in this image on the right.
The relative task involved determining whether the lines in the two images were in the same proportion to the surrounding squares. The absolute task involved determining whether the two lines were the same absolute length, regardless of the size of the squares (see figure). Each participant made these judgments while his or her brain activity was tracked by an fMRI scanner.
Both groups were equally proficient at the task and used the same brain regions in making the simple perceptual judgments. However, the pattern of brain activation differed.
The individualistic U.S. participants showed greater brain activation while making relative judgments, meaning they had to exert more mental effort. The collectivistic East Asians showed the opposite pattern, devoting greater brain effort to making absolute judgments that required them to ignore the context. Essentially, all participants had to work harder at making perceptual judgments that were outside their cultural comfort zones.
The bottom line? People from different cultures use the same neural processes to make perceptual judgments. But, their culture trains them to use them in different ways. As John Gabrieli (2008) points out, “The way in which the brain responds to these simple drawings reflects, in a predictable way, how the individual thinks about independent or interdependent social relationships.” People from different cultures may not literally see the world differently—
PERCEPTUAL GROUPING
Many of the forms we perceive are composed of a number of different elements that seem to go together (Glicksohn & Cohen, 2011). It would be more accurate to say that we actively organize the elements to try to produce the stable perception of well-
The Gestalt psychologists studied how the perception of visual elements becomes organized into patterns, shapes, and forms. They identified several laws, or principles, that we tend to follow in grouping elements together to arrive at the perception of forms, shapes, and figures. These principles include similarity, closure, good continuation, and proximity. Examples and descriptions of these perceptual laws are shown in Figure 3.15.
(b) The law of closure is the tendency to fill in the gaps in an incomplete image. Thus, you perceive the fence rails as continuous straight lines even though the image is interrupted by the cowboy boots.
(c) The law of good continuation is the tendency to group elements that appear to follow in the same direction as a single unit or figure. Thus, you tend to see the straight and curved sections of the Chicago L-
(d) The law of proximity is the tendency to perceive objects that are close to one another as a single unit. Thus, you perceive these three puffins as two distinct units—
The Gestalt psychologists also formulated a general principle called the law of Prägnanz, or the law of simplicity. This law states that when several perceptual organizations of an assortment of visual elements are possible, the perceptual interpretation that occurs will be the one that produces the “best, simplest, and most stable shape” (Koffka, 1935). For an illustration, look at Figure 3.16 below. Do you perceive the image as two six-
According to the Gestalt psychologists, the law of Prägnanz encompasses all the other Gestalt principles, including the figure–
HOW FAR AWAY IS IT?
KEY THEME
Perception of distance and motion helps us gauge the position of stationary objects and predict the path of moving objects.
KEY QUESTIONS
What are the monocular and binocular cues for distance or depth perception, and how does binocular disparity explain our ability to see three-
What visual cues help us perceive distance and motion?
Why do we perceive the size and shape of objects as unchanging despite changes in sensory input?
Being able to perceive the distance of an object has obvious survival value, especially regarding potential threats, such as snarling dogs or oncoming trains. But simply walking through your house or apartment also requires that you accurately judge the distance of furniture, walls, other people, and so forth. Otherwise, you’d be constantly bumping into doors, walls, and tables. The ability to perceive the distance of an object as well as the three-
MONOCULAR CUES
We use a variety of cues to judge the distance of objects. Monocular cues require the use of only one eye (mono means “one”). When monocular cues are used by artists to create the perception of distance or depth in paintings or drawings, they are called pictorial cues. After familiarizing yourself with these cues, look at the photographs on the next page. Try to identify the monocular cues you used to determine the distance of the objects in each photograph.
Relative size. If two or more objects are assumed to be similar in size, the object that appears larger is perceived as being closer.
Overlap. When one object partially blocks or obscures the view of another object, the partially blocked object is perceived as being farther away. This cue is also called interposition.
Aerial perspective. Faraway objects often appear hazy or slightly blurred by the atmosphere.
Texture gradient. As a surface with a distinct texture extends into the distance, the details of the surface texture gradually become less clearly defined. The texture of the surface seems to undergo a gradient, or continuous pattern of change, from crisp and distinct when close to fuzzy and blended when farther away.
Linear perspective. Parallel lines seem to meet in the distance. For example, if you stand in the middle of a railroad track and look down the rails, you’ll notice that the parallel rails seem to meet in the distance. The closer together the lines appear to be, the greater the perception of distance.
Motion parallax. When you are moving, you use the speed of passing objects to estimate the distance of the objects. Nearby objects seem to zip by faster than do distant objects. When you are riding on a commuter train, for example, houses and parked cars along the tracks seem to whiz by, while the distant downtown skyline seems to move very slowly.
Another monocular cue is accommodation. Unlike pictorial cues, accommodation utilizes information about changes in the shape of the lens of the eye to help us estimate distance. When you focus on a distant object, the lens is flat, but focusing on a nearby object causes the lens to thicken. Thus, to some degree, we use information provided by the muscles controlling the shape of the lens to judge depth. In general, however, we rely more on pictorial cues than on accommodation for depth perception.
BINOCULAR CUES
Binocular cues for distance or depth perception require information from both eyes. One binocular cue is convergence—the degree to which muscles rotate your eyes to focus on an object. The more the eyes converge, or rotate inward, to focus on an object, the greater the strength of the muscle signals and the closer the object is perceived to be. For example, if you hold a dime about six inches in front of your nose, you’ll notice the slight strain on your eye muscles as your eyes converge to focus on the coin. If you hold the dime at arm’s length, less convergence is needed. Perceptually, the information provided by these signals from your eye muscles is used to judge the distance of an object.
Another binocular distance cue is binocular disparity. Because our eyes are set a couple of inches apart, a slightly different image of an object is cast on the retina of each eye. When the two retinal images are very different, we interpret the object as being close by. When the two retinal images are more nearly identical, the object is perceived as being farther away (Parker, 2007).
Here’s a simple example that illustrates how you use binocular disparity to perceive distance. Hold a pencil just in front of your nose. Close your left eye, then your right.
These images are quite different—
A stereogram is a picture that uses the principle of binocular disparity to create the perception of a three-
However, a stereogram is actually composed of repeating columns of carefully arranged visual information. If you focus as if you are looking at some object that is farther away from the stereogram, the repeating columns of information will present a slightly different image to each eye. This disparate visual information then fuses into a single image, enabling you to perceive a three-
WHERE IS IT GOING?
In addition to the ability to perceive the distance of stationary objects, we need the ability to gauge the path of moving objects, whether it’s a baseball whizzing through the air, a falling tree branch, or an egg about to roll off the kitchen counter. How do we perceive movement?
As we follow a moving object with our gaze, the image of the object moves across the retina. Our eye muscles make microfine movements to keep the object in focus. We also compare the moving object to the background, which is usually stationary. When the retinal image of an object enlarges, we perceive the object as moving toward us. Our perception of the speed of the object’s approach is based on our estimate of the object’s rate of enlargement (Harris & others, 2008). Neural pathways in the brain combine information about eye-
Neuroscientists do not completely understand how the brain’s visual system processes movement. It’s known that some neurons are highly specialized to detect motion in one direction but not in the opposite direction. Other neurons are specialized to detect motion at one particular speed. Research also shows that different neural pathways in the cerebral cortex process information about the depth of objects, movement, form, and color (Regan & Gray, 2009; Zeki, 2001).
Psychologically, we tend to make certain assumptions when we perceive movement. For example, we typically assume that the object, or figure, moves while the background, or frame, remains stationary (Rock, 1995). Thus, as you visually follow a bowling ball down the alley, you perceive the bowling ball as moving and not the alley, which serves as the background.
Because we have a strong tendency to assume that the background is stationary, we sometimes experience an illusion of motion called induced motion. Induced motion was first studied by Gestalt psychologist Karl Duncker (1903–
Why did subjects perceive the dot as moving? Part of the explanation has to do with top-
Another illusion of apparent motion is called stroboscopic motion. First studied by Gestalt psychologist Max Wertheimer in the early 1900s, stroboscopic motion creates an illusion of movement with two carefully timed flashing lights (Wertheimer, 1912). A light briefly flashes at one location, followed about a tenth of a second later by another light briefly flashing at a second location. If the time interval and distance between the two flashing lights are just right, a very compelling illusion of movement is created.
What causes the perception of stroboscopic motion? Although different theories have been proposed, researchers aren’t completely sure. The perception of motion typically involves the movement of an image across the retina. However, during stroboscopic motion the image does not move across the surface of the retina. Rather, the two different flashing lights are detected at two different points on the surface of the retina. Somehow, the brain’s visual system combines this rapid sequence of visual information to arrive at the perceptual conclusion of motion, even though no movement has occurred. The perception of smooth motion in a movie is also due to stroboscopic motion.
Consider this scenario. As you’re driving on a flat stretch of highway, a red SUV zips past you and speeds far ahead. As the distance between you and the SUV grows, its image becomes progressively smaller until it is no more than a dot on the horizon. Yet, even though the image of the SUV on your retinas has become progressively smaller, you don’t perceive the vehicle as shrinking. Instead, you perceive its shape, size, and brightness as unchanged.
This tendency to perceive objects, especially familiar objects, as constant and unchanging despite changes in sensory input is called perceptual constancy. Without this perceptual ability, our perception of reality would be in a continual state of flux. If we simply responded to retinal images, our perceptions of objects would change as lighting, viewing angle, and distance from the object changed from one moment to the next. Instead, color, size, and shape constancy promote a stable view of the world. Color constancy may help explain the otherwise puzzling phenomenon described in the In Focus box on the next page, “The Dress That Broke the Internet.”
SIZE AND SHAPE CONSTANCY
Size constancy is the perception that an object remains the same size despite its changing image on the retina. When our distance from an object changes, the image of the object that is cast on the retinas of our eyes also changes, yet we still perceive it to be the same size. The example of the red SUV illustrates the perception of size constancy. As the distance between you and the red SUV increased, you could eventually block out the retinal image of the vehicle with your hand, but you don’t believe that your hand has suddenly become larger than the SUV. Instead, your brain automatically adjusts your perception of the vehicle’s size by combining information about retinal image size and distance.
An important aspect of size constancy is that if the retinal image of an object does not change but the perception of its distance increases, the object is perceived as larger. To illustrate, try this: Stare at a 75-
Shape constancy is the tendency to perceive familiar objects as having a fixed shape regardless of the image they cast on our retinas. Try looking at a familiar object, such as a door, from different angles, as in the photograph on the left. Your perception of the door’s rectangular shape remains constant despite changes in its retinal image. Shape constancy has a greater influence on your perceptions than you probably realize (see Figure 3.17).
The Dress That Broke the Internet
It all started with a Facebook post showing a dress worn at a wedding on a tiny Scottish island. Picked up by a blogger and then by Buzzfeed, the photo blazed across the Internet, racking up an incredible 28 million views within 48 hours. The burning question: What color is the dress?
Even celebrities got into the “#The Dress” game. Kim Kardashian tweeted, “What color is that dress? I see white & gold. Kanye sees black & blue, who is color blind?”
Some suggested that subtle differences in the cones of the retina were involved. Others blamed the different types of screen displays, but that didn’t explain why people looking at the photo on the same screen saw radically different colors.
The most likely explanation seems to involve the phenomenon of color constancy (Novella, 2015; Pinker, 2015).
As you’ve learned, color perception is the result of a complex interaction between the light waves reflected off of an object and your brain’s interpretation of those signals. But in determining the color of an object, your brain takes additional factors into account, such as the amount and brightness of background illumination. The brain automatically compensates for shadows and other changing light conditions to perceive the color of familiar objects as unchanging.
For the record, the actual dress is blue and black. But in the photo, the light conditions are ambiguous. Is the dress in shadow or bright light? Those who made the unconscious assumption that the dress was in shadow or dim light saw it as white and gold, because white tends to look blue in dim light. But those who assumed that the dress was in bright light saw it as blue and black—
#The Dress is entertaining, but it also makes an important point about top-