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GOOD MORNING, TRIPLETS  Long before the sun rises, Liz Allen is awake, making sure that her 13-year-old triplets Emma, Zoe, and Sophie make it to school on time. First she walks into the bedroom of Emma and Zoe.

The floor may be sprinkled with toys if Emma has been awake in the night. She likes to climb inside her toy box and toss out everything. Zoe is a better sleeper, but she too might be up for several hours at a time. “They’re pretty active at night,” explains Liz. When sleeping, Emma and Zoe are almost certain to be found cuddled lengthwise, feet-to-head.

Gently shaking the girls, Liz says, “Wake up. Let’s get ready,” but she needn’t utter a word. She “speaks” to Emma and Zoe by moving her hands, and they “listen” by feeling her fingers dance through the motions of sign language. Emma and Zoe are completely blind and deaf. During the day, the triplets use cochlear implants, electronic devices that provide them with some degree of hearing. But these implants only provide a hearinglike experience; they do not “fix” deafness (UCSF Medical Center, 2015). The third triplet, Sophie, is easier to rouse, as she possesses some limited vision. Flipping the light switch is enough to get her started on her morning routine.

Welcome to the world of Emma, Zoe, and Sophie. They are, as far as we know, the world’s only deaf and blind triplets.

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LO 1 Define sensation and perception and explain how they are different.

Have you ever wondered what it is like to be blind and deaf? Most people depend on sights and sounds for virtually every daily activity, from buttering toast to answering the phone. Thanks to our eyes and ears, we can tell the difference between 12:00 noon and 12:00 midnight, soft jazz and a screaming ambulance. Sights and sounds are a source for thoughts and memories. When we think about people, we “see” their faces and “hear” their voices in our minds.

How does a deaf-blind person function in the world? We humans are adaptive creatures; when faced with disabilities, we make the best of what we have. Emma, Zoe, and Sophie have come to rely on their other senses—touch, smell, and taste—to compensate for what they cannot see or hear. Instead of rising to an alarm clock or the sunlight streaming through their window, Emma and Zoe feel their mother nudging them and signing “Wake up” and “Let’s get ready” into their hands. They recognize Mom by touch and smell, and they find their way around new places by running their fingers along the edges and contours of objects and walls. “You would think . . . that they are missing out on a lot,” Liz says, “but they don’t miss much.”

Note: Quotations attributed to Liz Allen are personal communications.

SENSATION VERSUS PERCEPTION The subject of this chapter is sensation and perception, the absorbing and deciphering of information from the environment. Sensation is the process by which receptors in our sensory organs (located in the eyes, ears, nose, mouth, skin, and other tissues) receive and detect stimuli. Perception is the process through which information about these stimuli is organized, interpreted, and transformed into something meaningful. Sensation is seeing a red burner on the stove; perception is thinking hot. Sensation is hearing a loud, shrill tone; perception is recognizing it as the warning sound of a fire alarm. Sensation and perception work together to provide a coherent experience of the world around and inside you. But how does this happen without your effort or awareness? How does the vast amount of stimuli outside and inside your body get transformed into experiences that seem so personal—how are beams of light turned into an image of a beautifully colored sunrise, and chemical sensations into your experience of a sweet strawberry?

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LO 2 Define transduction and explain how it relates to sensation.

TRANSDUCTION Sensation begins when your sensory systems receive input from the environment. Each of your sensory systems is designed to respond to stimuli of a certain kind. Light waves and sound waves accost your eyes and ears, heat waves bathe your skin, molecules of different chemical compositions float into your nostrils and descend upon your taste buds, and physical objects press against your body. But none of these stimuli can have an impact on your brain unless they are translated into a language it understands: electrical and chemical signals. This is the job of the specialized sensory cells located in the back of your eyes, the caverns of your ears and nose, the spongy surface of your tongue and within your skin, muscle, and other tissues. The process of transforming stimuli into the electrical and chemical signals of neurons is called transduction, and it is the first step of sensation. The neural signals are then processed by the central nervous system, resulting in what we consciously experience as sensations (seeing a person’s face or smelling smoke).

For sensations to be useful, we must assign meaning to them (that face belongs to my girlfriend or the scent of smoke signals fire). And even though we describe and explain sensation and perception as two distinct events, there is no physical boundary in the brain marking the end of sensation and the beginning of perception. The processing of stimuli into sensations and perceptions is quick and automatic.

DATA-BASED AND KNOWLEDGE-BASED PROCESSING Psychologists often distinguish between two ways that we process sensory and perceptual information. Data-based processing describes how the brain takes basic sensory information and processes the incoming stimuli. Knowledge-based processing generally involves the next step, utilizing our past experiences and knowledge to understand sensory information. Data-based processing is the equivalent to what cameras and video recorders do best—collect data without any preconceived notions or expectations. Knowledge-based processing is the arena where humans excel. The brain constructs a representation of the world based on what we have learned and experienced in the past.

How do these concepts figure into psychology, the scientific study of behavior and mental processes? Sensation and perception are the starting points for every psychological process you can imagine, from writing an e-mail to building relationships. Psychologists continue to discover the many ways that sensation and perception affect such processes. How? Through careful and systematic observation of behavior.

Liz began to suspect that her triplets had vision and hearing impairments when she noticed irregularities in their behavior. When Zoe lost her hearing, for example, she became frustrated with one of her favorite toys—a cube that made music when she pushed its buttons. Liz’s careful observation of her daughter’s activities prompted her to consult a specialist. Eventually, it became clear that there was a problem with the sensory receptors in Zoe’s ears, but Liz initially noticed a behavioral change.

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HUMAN SENSATION Studying sensation means studying human beings, who are complex and variable. Not everyone is born with the same collection of stimulus-detecting equipment. Some people have eyes that see 20/20; others have been wearing glasses since they were toddlers. There is even variation within a given individual. The ability to detect faint stimuli, for instance, depends on your state of mind and body (such as how preoccupied or bored you happen to be, how stressed you feel, or whether you’ve had your morning cup of coffee).

This variability in one’s ability to sense can have profound consequences. If you get in your car immediately following a heated argument, you may be less likely to notice (that is, sense) a bicyclist in your rearview mirror—who on any other day would catch your eye. This is because your attention is divided, just as it is when you are multitasking. Research has found that approximately 2% of people might be able to multitask flawlessly; however, the great majority of us are limited in our ability to attend to the environment, especially when focusing on more than one demanding task (Watson & Strayer, 2010). In particular, researchers have demonstrated that distracting social activities, such as Facebook and text messaging, are linked with poorer grades in college students (Junco & Cotten, 2012). Unfortunately, human beings do not have sensory organs that are equivalent to light meters, sound meters, motion detectors, and thermometers. Our sensory systems are prone to interferences from outside and within, which challenge psychologists as they search for ways to accurately measure sensory abilities.

LO 3 Describe and differentiate between absolute thresholds and difference thresholds.

ABSOLUTE THRESHOLDS Researchers can determine various types of sensory thresholds, which are the smallest levels of stimulation people can detect. Of particular interest to psychologists are absolute thresholds, defined as the weakest stimuli that can be detected 50% of the time. The absolute threshold commonly cited for vision, for instance, is described as the equivalent of being able to see the flame of one candle, in the dark of night, 30 miles away 50% of the time (Galanter, 1962). But, remember, the state of a person’s body and mind can influence his ability to sense a faint stimulus: Although absolute thresholds have been established for the general population (Infographic 3.1; Galanter, 1962), these thresholds are not necessarily absolute for a particular person over time. Absolute thresholds are important, but there is more to sensation than noting the presence of a stimulus. Many everyday sensory experiences involve detecting changes in environmental stimuli.

SENSORY ADAPTATION Have you ever put on cologne or perfume and wondered if it was too strong, but within a matter of minutes you don’t even notice it? Or perhaps you have jumped into an ice-cold swimming pool, and within 30 minutes you are oblivious to the frigid temperature. Our sensory receptors become less sensitive to constant stimuli through a process called sensory adaptation, a natural lessening of awareness of unchanging conditions. This allows us to focus instead on changes in our environment—a skill that has proven invaluable for survival.

DIFFERENCE THRESHOLDS Intrigued by this keen sensitivity to change, early psychologists decided to figure out how different stimuli need to be in order for someone to notice their difference. Through careful experimentation, they established various difference thresholds, or the minimum differences between two stimuli noticed 50% of the time.

Let’s say you are blindfolded, holding a 100-gram stick of butter, and somebody places a thinly sliced pat of butter weighing only 0.5 grams on top of the stick (adding 0.5% of the weight of the stick of butter). Do you think you’d notice the added weight of the pat of butter? Probably not. But if someone added a much larger pat of butter on top, say, a pat weighing 5 grams (5% of the stick’s weight), then you would almost definitely notice the change, right? Somewhere in between that tiny pat and the larger pat of butter is the difference threshold.

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According to Ernst Heinrich Weber (1795–1878), difference thresholds are determined by ratios, not absolute numbers. In fact, the just noticeable difference for weight is 2%; that is, the proportion of added weight needed for you to feel the difference 50% of the time. Getting back to our stick of butter (which is getting a little soft now), we only need to add a slice of butter weighing 2 grams (2% of the weight of the stick) for you to notice someone has added to your burden. What if you were holding 500 grams (or 5 sticks) of butter? How much would need to be added for you to detect the difference in weight^*? Weber's law states that ratios, not raw number values, determine these difference thresholds. The five senses each have their own constant Weber ratios.

Difference thresholds vary slightly from person to person because each of us has a unique sensory toolkit. But is there variation across people from different cultures? In one study, researchers compared participants’ ability to detect changes to pictures (for example, their brightness and color) of flowers, balloons, rabbits, and other objects (see photo above). The just noticeable difference was the same for the Chinese and Dutch participants “for most images” (Qin et al., 2010, p. 25). The implication is that this aspect of sensation and perception might not be influenced by cultural factors.

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That being said, the brain does register information presented at an unconscious or nonconscious level. Neuroimaging studies suggest that neural activity is evident in response to the “subliminal presentation” of stimuli (Axelrod, Bar, Rees, & Yovel, 2014; Kouider & Dehaene, 2007). These subliminal messages may be able to influence fleeting moods through priming (stimulating memories beneath awareness through previous exposure; Chapter 6). One study found that if you expose people to ugly scenes (for example, pictures of dead bodies or buckets of snakes) for several milliseconds (thus “priming” them), they then will rate a neutral picture of a woman’s face as less likable than when exposed to feel-good subliminal images (such as pictures of kittens and bridal couples) (Krosnick, Betz, Jussim, & Lynn, 1992).

Thus far, we have focused on the stimulus itself. But what about other environmental factors, such as background stimuli competing for the observer’s attention, or internal factors like the observer’s state of mind—do these variables enter the equation as well?

SIGNAL DETECTION THEORY As previously noted, our ability to detect weak stimuli in the environment is based on many factors, and the theory that draws them all together is called signal detection theory (Infographic 3.1). It is based on the idea that “noise” from our internal and external environments can interfere with our ability to detect weak signals. Imagine you are participating in an experiment studying the detection of weak stimuli, and you are told to push a button when you see a light flash. The strength of the flashes will range from clearly noticeable to undetectable. You sometimes press the button, but it turns out no light flash occurred: a false alarm. Other times you will press the button and be correct: a hit. How many hits and false alarms you have depends on many internal factors, including how tired you are, when you last ate, your expectations about the importance of success, your motivation, and so on. It also depends on external variables, such as the light level in the room and the dust in the air.

Signal detection theory is useful in a variety of real-world situations. In one study, researchers applied the theory to explain how nurses respond and make decisions about patient safety—how background noises influence their ability to hear patient alarm monitors, for example. One of the specific issues raised by this study was the impact of “missed signals,” that is, medical errors resulting from interference with the nurses’ ability to detect and interpret patient signs and symptoms (Despins, Scott-Cawiezell, & Rouder, 2010).

In situations like this, the ability to sense and perceive may have life or death implications. But how exactly does each of the five senses collect and process information? Let’s start by exploring the sense that is generally considered most dominant: vision.

Question 1

1. Perception

2. Transduction

3. Sensation

4. Signal detection

Question 2

Question 3

1. sensation.

2. transduction.

3. perception.

4. sensory adaptation.