1. © 2014 John Wiley & Sons, Inc. All rights reserved.
Chapter four
Sensation and Perception
Understanding sensation
How we see and hear
Our other important senses
Understanding perception
© 2014 John Wiley & Sons, Inc. All rights reserved.

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Things You’ll Learn in Chapter 4 Q1
Do athletes have a higher pain tolerance than non-athletes? Q2
Can looking at a photograph of a loved one lead you to feel less pain? Q3
How can listening to loud music on headphones damage your hearing? Q4
Why do premature babies grow faster when they receive skin-to-skin contact? Q5
Why do people rate themselves as more athletic if they compare themselves to the Pope than to a professional basketball player?
© 2014 John Wiley & Sons, Inc. All rights reserved.

3. Understanding Sensation
While your brain floats in complete silence and darkness, your body is bombarded with stimuli from outside.
Sensing the stimuli is not enough – our brains must receive, convert and adapt the information into meaningful representations of the world
What are some of these stimuli?
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4. Understanding Sensation
Sensation = process of detecting, converting and transmitting raw sensory information from the external and internal environments to the brain
Perception = process of selecting, organizing, and interpreting sensory info into meaningful patterns
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5. Understanding sensation
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Sensation: the basics
Receptor cells in sense organs detect appropriate stimuli
Convert stimuli (transduction) into neural impulses (action potential)
Transmit message to brain through different routes, allowing brain to differentiate physical stimuli (coding)
Brain assigns meaningful sensory information
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7. Stimulation Overload?
Some brain structures purposely reduce some sensory information they receive
What types of things can humans not detect?
Ultraviolet light, microwaves, dog whistle, infrared heat patterns
Field of psychophysics studies link between physical stimuli and psychological experience
What if this sensory reduction didn’t occur?
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8. What Can We Detect?
Consciously aware of only a narrow range of stimuli at one time
Difference Threshold (AKA Weber’s Law of just noticeable differences or JND) = minimal difference in stimulus strength that is detectable 50% of the time (Ernst Weber)
Absolute Threshold = minimum stimulation needed to consciously detect stimulus 50% of the time (Gustav Fechner)
How could these be measured?
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9. Subliminal Stimuli
Studies on subliminal perception use a tachistoscope to flash images too quickly for conscious perception (but slowly enough for the brain to register them)
At the movies “eat popcorn”? satanic verses when music is played backward? hidden sexual messages in Disney films?
Can subliminal stimuli change your behavior?
Subliminal stimuli are WEAK and don’t lead to subliminal persuasion
© 2014 John Wiley & Sons, Inc. All rights reserved.

10. Sensory Adaptation
Suppose you visit a neighbor’s house with 10 cats. You smell the animals, but the owner doesn’t.
Sensory adaptation = when a constant stimulus is presented, the sensory receptors become less sensitive and fire less frequently
Normally, smell and touch experience sensory adaptation readily; vision and intense stimuli do not.
Why not?
Why? What perspective in psychology might explain this?
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Intense pain often resists sensory adaptation to signal danger Q1
Do athletes have a higher pain tolerance than non-athletes?
Endorphins are the body’s natural painkiller and are released during physical exertion
Does the experience of playing sports change pain tolerance?
Or are people with high pain tolerance drawn to athletics?
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What about pain?
Gate-control theory = experience of pain depends on whether the message gets past the “gatekeeper” in the spinal cord
Normally, the gate is shut and pain signals are blocked, but when body tissue is damaged, impulses open the gate to allow the message of pain through
Messages from the brain also control the gate, allowing some to continue through the pain (athletes, military, first responders)
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Massaging an injury eases discomfort because pressure on larger-diameter neurons interferes with pain signals
Endorphins from the brain, distraction by fear or competition, actively listening to music – or looking at a picture – can close the gate and reduce pain and anxiety
Focusing on pain amplifies it Q3
Can looking at a photograph of a loved one lead you to feel less pain?
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What about pain?
Phantom limb pain = when amputee continues to feel sensations (pain, tickling) in the missing limb
Nerve cells send conflicting messages to the brain, producing “static” that is interpreted as pain
Prosthetic limbs and mirror visual therapy can help reduce phantom limb pain
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How we see and hear
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Vision
Receptor cells in retina (rods and cones) convert light waves into messages sent along the optic nerve
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Vision Problems
Visual acuity problems result from small abnormalities in the shape of the eye, causing the image not to be in focus at the retina
Nearsightedness – image reaches focus in front of the retina
Farsightedness – image reaches focus behind the retina
Presbyopia – lenses lose elasticity with age
Blind spot – no receptor cells where the optic nerve exits the eye
Rods manage dark adaptation – changing from sunny to dark environment leaves you temporarily blind
Cones manage light adaptation – changing from dark to bright environment activate cones
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Hearing
Outer ear captures sound, three tiny bones in middle ear transmit eardrum’s vibration to the inner ear where cochlea transforms waves into neural impulses
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Pitch and Volume
Frequency of sound waves provides information about pitch of sound
Place theory for hearing = hair cells at different locations along the basilar membrane are stimulated by high-pitched sounds
Frequency theory for hearing = hair cells vibrate at the same low frequency as the low-pitched sounds they detect
Loud sounds have higher peaks and lower valleys than soft sounds, measured by decibels
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Hearing Problems
Conduction hearing loss (conduction deafness) = problems with mechanics of sending sound waves to cochlea. Hearing aids and some surgery help
Sensorineural hearing loss (nerve deafness) = damage to hair cells or auditory nerve Q3
How can listening to loud music on headphones damage your hearing?
Result of loud noise, disease, and biological changes; damage to receptor cells and auditory nerve is irreversible
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21. Our other IMPORTANT senses
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Smell
Smell and taste are “chemical senses” because they use chemoreceptors and are sensitive to chemical molecules
Olfactory receptors in the nose transduce info from odorants (molecules with odor) directly to olfactory bulb at base of frontal lobe, where info is processed and sent to other brain regions
Olfaction is the only sensory system NOT routed through the thalamus
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Taste
Purpose of taste is to avoid poisonous foods (which are usually bitter); nonpoisonous foods with good energy are often sweet
Dissolved food particles pass over papillae on the tongue and down into taste buds (taste receptors), which transduce info to the brain
Taste buds are distributed all over the tongue, NOT in dedicated regions by taste
Umami – savory; sensitivity to glutamate found in meat, broth, MSG
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24. Taste Preferences Shaped in Utero
Mennella, Jagnow & Beauchamp, 2001
Group 1: carrot juice 4x week for 3 weeks during pregnancy
Group 2: carrot juice 4x week for 3 weeks after baby was born (breast-feeding mothers)
Group 3: no carrot juice
Mothers rated babies’ facial reactions to different foods and quantity of carrot-flavored cereal baby would eat
Babies exposed to carrots in utero or through breast milk liked the taste of carrots better
Engage Your Students! Hold a small group or class discussion on these questions:
Did the study use descriptive, correlational, and/or experimental research?
If descriptive, is this a naturalistic observation, survey/interview, case study, or archival research?
If correlational, is this a positive, negative, or zero correlation?
If experimental, label the IV, DV, experimental groups, and control group.
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25. Body Senses – Skin Sense
Skin sense detects pressure, temperature, and pain
Touch receptors are most concentrated in face and hands (that’s why paper cuts hurt!)
Why do premature babies grow faster when they receive skin-to-skin contact? Q4
Kangaroo care – skin-to-skin contact between mother and baby recommended immediately after birth, especially for low-birth-weight babies
Provides warmth, reduces pain, lowers stress arousal, improves sleep, which leads to growth
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26. Body Senses - Vestibular
Vestibular sense tells the brain how our body (especially head) is oriented in 3-dimensional space
Hair cells in the semicircular canals of the inner ear and in the vestibular sacs transduce the position of the head into neural impulses
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27. Body Senses - Kinesthesis
Kinesthesis provides information about body posture, orientation and movement of individual body parts
Kinesthetic receptors in muscles, joints, and tendons tell the brain what is moving, how weight is distributed, where body parts are in relation to the whole
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28. Understanding perception
Perception = process of selecting, organizing, and interpreting incoming sensations into useful mental representation of the world
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Perception Problems
“Seeing is believing, but seeing isn’t always believing correctly” (Lilienfeld et al, 2010, p. 7)
Illusion = false or misleading impression produced by errors in the perceptual process or by actual physical distortions
Illusions are NOT the same as hallucinations (false sensory experience WITHOUT external stimuli) or delusions (false beliefs)
What does this mean?
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Selection
Cannot pay attention to all stimuli
Selective attention = paying attention to important information and filtering the rest
Feature detectors = specialized neurons to respond to specific stimuli, like faces
Prosopagnosia – inability to identify person by facial features
Habituation = decrease in responding to repeated stimulation of same stimuli; more responsive to changes in environment
Compliments from strangers are more exciting than from long- term partner!
The song you HATED on first listen might grow on you!
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How do advertisers and political campaigns use selective attention, feature detectors, and habituation?
Capture attention with intense, novel, moving, contrasting stimuli and repetition
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32. Organization: Form Perception
Gestalt psychologists studied how the brain organizes sensory impressions into a “form” or “whole”
Figure-Ground: objects are distinct from the background
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33. Organization: Depth Perception
Depth Perception: ability to perceive 3-dimensional space using binocular and monocular cues
realworldpsychology
Visual cliff: crawling infants refuse to move to the “deep end”
Engage Your Students:
Hold your index finger at arm’s length in front of you and watch it as you bring it closer until it is right in front of your nose. What are your eyes doing? As they turn in, your brain uses the cues from the muscles in your eyes as they converge (turn in). That information is used to perceive depth.
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34. Organization: Constancies Perception
Perceive the environment as stable, despite changes in object’s size, shape, color and brightness
Why is this important?
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35. Organization: Color Perception
Trichromatic theory of color = three “color systems”, each of which is sensitive to red, green and blue; mixing lights of these three colors yields the full spectrum of colors
Opponent-process theory = each of the color systems is sensitive to two opposing colors (ex: either blue or yellow)
Black-and-white systems respond to differences in brightness
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Engage Your Students!
Stare at the dot in the middle of the flag for 60 seconds, then stare at a plain white piece of paper or a blank wall. What do you see?
How does opponent-processing theory explain the afterimage?
Neural system that processes green, black, and yellow gets fatigued from staring
When you look at plain white paper, which reflects all wavelengths, a reverse opponent process occurs: each fatigued receptor responds with opposing red, white, and blue.
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37. Color-Deficient Vision
Color confusion on specific color spectrums, such as red-green or blue-yellow
Is anyone here “colorblind”? What is it like?
Engage Your Students!
Assign students to try a simple color acuity test. Low scores typically reflect better color acuity.
© 2014 John Wiley & Sons, Inc. All rights reserved.

38. Organization: Interpretation
Perceptual set = readiness to perceive stimuli in a particular manner, based on expectations
We see what we expect to see
Frame of reference = perception is influenced by context Q5
Why do people rate themselves as more athletic if they compare themselves to the Pope than to a professional basketball player?
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Processing
Bottom-up processing = raw sensory data “sent up” to the brain for higher level analysis
Top-down processing = perceptual analysis starts “at the top” with expectations and knowledge driving the process of perception
You learn to read from bottom-up processing of letters and words
Now, your aiblity to raed uisng top-dwon prcessoing mkes it psosible to unedrstnad this sntenece desipte its mnay mssiplllengis
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Sixth Sense?
Extrasensory Perception (ESP) = “psychic” perceptual abilities that supposedly go beyond the known senses
Telepathy, clairvoyance, precognition
Research in ESP don’t withstand scrutiny, failure to replicate by rival research labs
Why do some believe in ESP?
Motivation and interests influence our perceptions, creating selective perception
Strong emotions about the subject mask faulty reasoning
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