1. Chapter 4 Sensation and Reality

2. Psychophysics
Study of relationship between physical stimuli and sensations they evoke in a human observer
Absolute threshold: Minimum amount of physical energy necessary to produce a sensation
Subliminal perception: Perception of a stimulus below the threshold for conscious recognition
Difference threshold: A change in stimulus intensity that is detectable to an observer

3. General Properties of Sensory Systems
Perceptual features: Basic stimulus patterns
Sensory coding: Converting important features of the world into messages understood by the brain
Just Noticeable Difference (JND)
Any noticeable difference in a stimulus

4. Sensation and Perception
Sensation: Information arriving from sense organs (eye, ear, etc.)
Perception: Mental process of organizing sensations into meaningful patterns
What can go wrong in these two processes?

5. Absolute thresholds define the sensory worlds of humans and animals, sometimes with serious consequences. The endangered Florida manatee (“sea cow”) is a peaceful, plant-eating creature that can live for more than 60 years. For the last decade, the number of manatees killed by boats has climbed alarmingly. The problem? Manatees have poor sensitivity to the low-frequency sounds made by slow-moving boats. Current laws require boats to slow down in manatee habitats, which may actually increase the risk to these gentle giants (Gerstein, 2002).
Absolute thresholds define the sensory worlds of humans and animals, sometimes with serious consequences. The endangered Florida manatee (“sea cow”) is a peaceful, plant-eating creature that can live for more than 60 years. For the last decade, the number of manatees killed by boats has climbed alarmingly. The problem? Manatees have poor sensitivity to the low-frequency sounds made by slow-moving boats. Current laws require boats to slow down in manatee habitats, which may actually increase the risk to these gentle giants (Gerstein, 2002).
p. 120

6. Using Your Senses
In partners, I will give you pieces of paper with the names of different objects written on them. Do not to show the words to any other group. Have each group figure out how much sensory information there is in each of the written common objects. Use all 5 of your senses in their description.

7. Vision: The Key Sense
Visible spectrum: Narrow spread of the electromagnetic spectrum to which the eyes respond

8. Parts of the Eye Lens: Structure in the eye that focuses light rays
Photoreceptors: Light-sensitive cells in the eye

9. More Parts of the Eye
Retina: Light-sensitive layer of cells in the back of the eye
Easily damaged from excessive exposure to light (staring at an eclipse)
Cornea: Transparent membrane covering the front of the eye; bends light rays inward

10. Accommodation
Changes in the shape of the lens of the eye

11. Figure 4.3
The visible spectrum.
Fig. 4-3, p. 123

12. Visual pop-out. Pop-out is so basic that babies as young as 3 months respond to it.
Fig. 4-1, p. 122

13. Vision Problems
Hyperopia: Difficulty focusing nearby objects (farsightedness)
Myopia: Difficulty focusing distant objects (nearsightedness)
Astigmatism: Corneal, or lens defect that causes some areas of vision to be out of focus; relatively common
Presbyopia: Farsightedness caused by aging

14. Light Vision
Cones: Visual receptors for colors and bright light (daylight); 5 million in each eye
Rods: Visual receptors for dim light; only produce black and white; about 120 million total
Blind spot: Area of the retina lacking visual receptors

15. Anatomy of the retina. The retina lies behind the vitreous humor, which is the jelly-like substance that fills the eyeball. The rods and cones are much smaller than implied here. The smallest are 1 micron (one millionth of a meter) wide. The lower-left photograph shows rods and cones as seen through an electron microscope. In the photograph the cones are colored green and the rods blue.
Figure 4.7
Fig. 4-7, p. 125

16. Experiencing the blind spot
Experiencing the blind spot. (a) With your right eye closed, stare at the upper-right cross. Hold the book about 1 foot from your eye and slowly move it back and forth. You should be able to locate a position that causes the black spot to disappear. When it does, it has fallen on the blind spot. With a little practice you can learn to make people or objects you dislike disappear too! (b) Repeat the procedure described, but stare at the lower cross. When the white space falls on the blind spot, the black lines will appear to be continuous. This may help you understand why you do not usually experience a blind spot in your visual field.
Fig. 4-8, p. 126

17. More on Light Control Visual acuity: Sharpness of visual perception
Fovea: Area at the center of the retina containing only cones (50,000)
Peripheral vision: Vision at edges of visual field; side vision
Many superstar athletes have excellent peripheral vision
Tunnel vision: Loss of peripheral vision

18. Color Vision

19. Trichromatic Theory
Color vision theory that states we have three cone types: red, green, blue
Other colors produced by a combination of these

20. Opponent Process Theory
Color vision theory based on three “systems”: red or green, blue or yellow, black or white
Exciting one color in a pair (red) blocks the excitation in the other member of the pair (green)
Afterimage: Visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken)

21. Example of Opponent Process Theory
Negative afterimages. On the following slide, stare at the dot near the middle of the flag for at least 30 seconds. Then look immediately at a plain sheet of white paper or a white wall. You will see the American flag in its normal colors. Reduced sensitivity to yellow, green, and black in the visual system, caused by prolonged staring, results in the appearance of complementary colors. Project the afterimage of the flag on other colored surfaces to get additional effects.

22. Fig. 4-12, p. 128

23. Color Blindness
Color blindness: Inability to perceive colors; lacks cones or has malfunctioning cones
Total color blindness is rare
Color weakness: Inability to distinguish some colors
Red-green is most common; much more common among men than women
Recessive, sex-linked trait on X chromosome

24. Figure 4.17
A replica of the Ishihara test for color blindness.
Fig. 4-17, p. 130

25. Dark Adaptation
Increased retinal sensitivity to light after entering the dark; similar to going from daylight into a dark movie theater
Rhodopsin: Light-sensitive pigment in the rods; involved with night vision
Night blindness: Blindness under low-light conditions; hazardous for driving at night

26. Light Adaptation
In pairs, observe each other’s pupils. Flip a coin to select the “subject.” I will darken the room for a few minutes. Then turn on the lights and estimate how many seconds it takes your partner’s pupils to return to their original degree of constriction.

27. Hearing Sound waves: Rhythmic movement of air molecules
Pitch: Higher or lower tone of a sound
Loudness: Sound intensity

28. Anatomy of the ear. The entire ear is a mechanism for changing waves of air pressure into nerve impulses. The inset in the foreground (Cochlea “Unrolled”) shows that as the stapes moves the oval window, the round window bulges outward, allowing waves to ripple through fluid in the cochlea. The waves move membranes near the hair cells, causing cilia or “bristles” on the tips of the cells to bend. The hair cells then generate nerve impulses carried to the brain.
Figure 4.20
(See an enlarged cross section of cochlea in • Figure 4.21.)
Fig. 4-20, p. 133

29. This is how the cochlea looks “unrolled”
This is how the cochlea looks “unrolled”. How does this diagram of sound waves explain why you can hear the bass from a big car stereo from far away?
Figure 4.22
Here we see a simplified side view of the cochlea “unrolled.” Remember that the basilar membrane is the elastic “roof” of the lower chamber of the cochlea. The organ of Corti, with its sensitive hair cells, rests atop the basilar membrane. The colored line shows where waves in the cochlear fluid cause the greatest deflection of the basilar membrane. (The amount of movement is exaggerated in the drawing.) Hair cells respond most in the area of greatest movement, which helps identify sound frequency.
Fig. 4-22, p. 134

30. How Do We Detect Higher and Lower Sounds?
Frequency theory: As pitch rises, nerve impulses of a corresponding frequency are fed into the auditory nerve
Place theory: Higher and lower tones excite specific areas of the cochlea

31. Hearing Loss Noise Induced Hearing Loss
Damage caused by exposing hair cells to excessively loud sounds
Typical at rock concerts
By age 65, more than 40% of hair cells are gone
Sensorineural Hearing Loss
Caused by damage to hair cells or auditory nerve
Hearing aids little or no help in these cases
Cochlear implant: Electronic device that stimulates auditory nerves directly
Conduction Hearing Loss:
Poor transfer of sounds from tympanic membrane to inner ear
Compensate with amplifier (hearing aid)

32. Figure 4.25
Loudness ratings and potential hearing damage.
Fig. 4-25, p. 135

33. Smell Olfaction: Sense of smell
Dysosmia: Loss or impairment of sense of smell
Lock-and-key theory: Odors are related to shapes of chemicals and molecules
Pheromones: Airborne chemical signal
Vomeronasal organ: Sense organ for pheromones

34. Smell Habituation
Ammonia, rotten eggs, vinegar and other smelly materials can be brought to class. Students rate the smell at the start of class and every 10 minutes after, and should quickly experience olfactory adaptation (habituation).
I didn’t want to stink up the classroom, but does anyone have any experience with this?

35. Gustation Sense of taste
Four taste sensations: sweet, salt, sour, bitter
Most sensitive to bitter, less to sour, less to salt, least sensitive to sweet
Umami: Possible fifth taste sensation; brothy taste

36. How do these work together?
As the text points out, “flavor,” as we experience it subjectively, is actually a combination of olfaction and gustation. This can be demonstrated relatively easily.
I need a volunteer who can eat something.
Have a student volunteer taste bits of each while blindfolded. Discriminating between different foods should be simple in this condition. Next, test the blindfolded volunteer while he or she pinches the nostrils closed. With more olfactory cues reduced, correctly identifying the food bits should be more difficult (although not impossible). Even if they correctly identify the foods in the second test, subjects will usually report greater difficulty. Typically, they must rely more on texture than on “taste” when olfactory cues are reduced

37. Somesthetic Senses
Sensations produced by skin, muscles, joints, viscera, and organs of balance
Skin senses (touch): Light touch, pressure, pain, cold, warmth
Kinesthetic: Detect body position and movement
Vestibular: Balance, acceleration, and position in space
Sensory organs for touch, pressure, pain, cold, and warmth

38. Pain Visceral pain: Pain originating in internal organs
Referred pain: Pain felt in one part of the body, but coming from another
Somatic pain: Sharp, bright, fast; comes from skin, joints, muscles, tendons

39. Types of Pain
Warning system: Pain carried by large nerve fibers; sharp, bright, fast pain that tells you body damage may be occurring (e.g., knife cut)
Reminding system: Small nerve fibers; slower, nagging, aching, widespread; gets worse if stimulus is repeated; reminds brain that body has been injured

40. Vestibular System
Otolith organs: Sensitive to movement, acceleration, and gravity
Semicircular canals: Fluid-filled tubes in ears that are sensory organs for balance
Crista: “Float” that detects movement in semicircular canals
Ampulla: A wider part of the canal

41. Figure 4.31
The vestibular system. (See text for explanation.)
Fig. 4-31, p. 141

42. Sensory Conflict Theory
Motion sickness results from a mismatch between information from vision, vestibular system, and kinesthesis
After spinning and stopping, fluid in semicircular canals is still spinning, but head is not
Mismatch leads to sickness
Medications, relaxation, and lying down might help

43. Gate Control Theory of Pain
Gate control theory: Pain messages from different nerve fibers pass through the same “neural” gate in the spinal cord.
If gate is closed by one pain message, other messages may not be able to pass through

44. Phantom Limb
Missing limb feels like it is present, like always, before amputation or accident

45. Controlling Pain
Fear, or high levels of anxiety, almost always increase pain
If you can regulate a painful stimulus, you have control over it
Distraction can also significantly reduce pain
The interpretation you give a stimulus also affects pain

46. Coping With Pain
Prepared childbirth training: Promotes birth with a minimal amount of drugs or painkillers
Counterirritation: Using mild pain to block more intense or long-lasting pain

47. CUTANEOUS TWO-POINT THRESHOLD
1. Be sure the subject is securely blindfolded. 
2. Apply even, firm, but not excessive pressure with one point or two, as directed. You should avoid causing pain to (or breaking the skin of) the subject.
3. Make exact measurements when setting the two points for each trial.
4. Do not repeat any trials.
5. Ask the subject for a response after each application of pressure.
6. Do not give hints or clues to help the subject. Encourage the subject to make an immediate response.
For each response made by the subject, put a 1 or 2 in the appropriate box.