1. Sensation and Perception
Modules 16-18

2. Basic Principles of Sensation
Sensation is the process that detects stimulation from our bodies and our environment.

3. Basic Principles of Sensation
Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.

4. Basic Principles of Sensation
Psychophysics is the study of how physical stimuli are translated into psychological experience.

5. Sensory Information Must Be Converted into Neural Impulses
Sound, light, etc. cannot travel through our nerves to the brain.
Sensory organs convert their physical properties into neural impulses.
This conversion process is called transduction.

6. Sensory Information Must Be Converted into Neural Impulses
Transduction takes place at sensory receptors.
Next, connecting neurons in the sense organs send this information to the brain.
The brain processes these neural impulses into what we experience.
Some stimuli are just as real as those that we can transduce, but they are not a part of our sensory experience.

7. Our Senses Vary in Their Sensitivity Thresholds
Absolute threshold: the lowest level of intensity of a given stimulus that a person can detect half the time
As people age, their absolute thresholds for all senses increase.

8. Our Senses Vary in Their Sensitivity Thresholds
Signal-detection theory contends that detection of a stimulus is influenced by observers’ expectations.
How likely is the stimulus to occur?
How important or rewarding is detecting it?
So absolute threshold may vary.
It is usually defined as the intensity of a stimulus that can be detected 50% of the time.

9. Sensation--Thresholds25 50 75
100
Low
Absolute
threshold
Medium
Intensity of stimulus
Percentage
of correct
detections
Subliminal
stimuli
When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”

10. Our Senses Vary in Their Sensitivity Thresholds
Difference threshold is the smallest difference between two stimuli that is detected half (50%) of the time.
It is also called the “just-noticeable difference” or jnd.

11. Our Sensory Receptors Adapt to Unchanging Stimuli
Sensory adaptation: the tendency for our sensory receptors to have decreasing responsiveness to stimuli that continue without change.
Auditory adaptation occurs much more slowly than adaptation to odors, tastes, and skin sensations.

12. Sensory Adaptation

13. We See Only a Narrow Band of Electromagnetic Radiation
Wavelengths of visible light range from 400 to 750 nanometers.
Shorter wavelengths are experienced as violet.
Intermediate ones as blue, green, and yellow.
Longer ones as red.
Other forms of electromagnetic energy that our eyes cannot detect are:
Radio
Infrared
Ultraviolet
X-ray radiation

14. Vision Spectrum of Electromagnetic Energy

15. Physical Properties of Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Small amplitude
(dull colors, soft sounds)

16. Color and Wavelength of Light
An object appears as a particular color because it absorbs certain wavelengths of light and reflects others.
These wavelengths are simply energy; colors are created by our nervous system in response to them.
Species differ in what they see when looking at the same object.
Our difference threshold for colors is so low that the average person can discriminate about 2 million different colors.

17. Major Structures of the Human Eye

18. Retina’s Reaction to Light

19. Photoreceptors in the Retina
Rods (125 million)
Located at the edges of the retina.
Are not involved in color vision.
Function best under low-light conditions.
Cones (7 million)
Located near the center of the retina (the fovea).
Require bright light to be activated.
Play a key role in color vision.

20. Vision--Receptors Receptors in the Human Eye Cones Rods Number
Location in
retina
Sensitivity in
dim light
Color sensitive?
Yes
Low
Center
6 million No
High
Periphery
120 million

21. Pathways from the Eyes to the Visual Cortex

22. Visual Information Processing
Feature Detectors
nerve cells in the brain that respond to specific features of the stimulus
shape
angle
movement
Stimulus
Cell’s
responses

23. Young-Helmholz Trichromatic Theory of Color Vision
Any color can be created by combining three primary colors—red, green, and blue.
The retina has three types of color receptors that produce the primary color sensations of red, green, and blue.

24. Additive and Subtractive Color Mixing

25. Opponent-Process Theory of Color Vision
Hering proposed a theory that color perception depends on receptors that make opposing responses to three pairs of colors:
black-white
red-green
blue-yellow

26. Afterimage

27. Color Constancy
The relative constancy of perceived color under different conditions of illumination.

28. Color-Deficient Vision
People who suffer red-green blindness have trouble perceiving the number within the design

29. Sound Is the Stimulus for Hearing
Soundwaves (pressure) are created when an object vibrates.
Wave speed or frequency corresponds to pitch.
Amplitude (wave height) corresponds to loudness of a sound.
Most sounds are a combination of many different waves of different frequencies.
This sound complexity is caled timbre.

30. Auditory System: Three major parts of the Ear
Outer ear:
The pinna is the most visible part of the outer ear.
The auditory canal is funnel shaped.
The eardrum is at the end of the auditory canal and it vibrates in sequence with sound waves.

31. Audition- The Ear

32. Auditory System: Three major parts of the Ear
Middle ear:
The ossicles are three tiny interconnected bones—the hammer, anvil, and stirrup —that move and amplify sound waves before sending them to the inner ear.

33. Auditory System: Three major parts of the Ear
Inner Ear
innermost part of ear, containing the cochlea, semicircular canals and vestibular sacs
Cochlea
coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

34. Sound Localization
Sound localization: the ability to locate objects in space solely on the basis of the sounds they make
Because the ears are only 6 inches apart, the time lag between the sound reaching both ears is very short.
Even such small time lags provide the auditory system with sufficient information to locate the sound.

35. Sound Localization

36. Pitch Perception: Place Theory
Place theory: contends that we hear different pitches because different sound waves trigger hair cells on different places of the cochlea’s basilar membrane.

37. Pitch Perception: Frequency Theory
Frequency theory: contends that pitch is determined by the frequency with which the basilar membrane vibrates.

38. Pitch Perception
Place theory best explains high-frequency sounds, while frequency theory best explains low-frequency sounds. Mid-frequency sounds are best explained by volley theory, a revision of frequency theory.

39. The Intensity of Some Common Sounds

40. Smell and Taste: The Chemical Senses
Olfaction: the sense of smell
The stimuli are airborne molecules
Olfactory receptor cells are at the top of the nasal cavity.
These cells transmit information to the olfactory bulb at the base of the brain.
The olfactory bulb processes this information and sends it to the primary olfactory cortex.

41. Smell

42. Olfaction
Olfactory sensitivity is determined by the number of receptors in the epithelium.
Odors can evoke memories and feelings associated with past events.
• The sense of taste became a “near” sense, providing the last check on the acceptability of food, while
• The sense of smell became a “far” sense, able to detect stimuli from a much farther distance.
Smell
Olfaction is the sense of smell, and its stimuli are airborne molecules.
• When you smell fresh-brewed coffee (see figure 4-10), you are sensing molecules that have left the coffee and traveled through the air to your nose.
o These molecules then enter your nasal passages and reach tiny receptor cells at the top of the nasal cavity.
o These olfactory receptors are located on a thin, dime-sized, mucous-coated layer of tissue known as the olfactory epithelium.
o The odor molecules from the coffee are then trapped and dissolved in the mucus of the epithelium, and this causes the olfactory receptor cells to transmit a neural impulse directly to the olfactory bulb at the base of the brain.
o From here, the signals are processed before being sent to the primary olfactory cortex, which is located in the frontal lobes.
o Olfaction is the only sensation that is not relayed through the thalamus on its way to the cortex.
o Once the coffee’s scent is processed by the brain, you appreciate its wonderful fragrance.
<<Figure 4-10: The Olfactory System>>
• Humans have hundreds of different types of olfactory receptor cells, with each type responding to only a limited family of odor molecules.
o This large number of different types of receptors stands in sharp contrast to the three basic receptors involved in vision.
o Although it is not yet known exactly how the brain processes all these different types of olfactory information, together these receptors allow us to distinguish among about 10,000 different smells.
o Having so many types of olfactory receptors may mean that a great deal of the processing necessary for odor perception occurs in the nose itself.
o Despite the staggering number of odors that we can distinguish, for some unknown reason, we have a hard time correctly identifying and attaching names to specific odors.
• Numerous studies indicate that we are drawn toward perfumelike fragrances, such as those of flowers and many food substances, and repulsed by foul and sulfurous odors.
o This suggests that our olfactory systems evolved to help us distinguish things that are poisonous from those that are edible.
o Cross-cultural studies further suggest that the smells we pay most attention to are those that help us survive in our immediate surroundings.
• Olfactory sensitivity is substantially determined by the number of receptors in the epithelium. Animals with more receptors than other animals have much keener senses of smell.
o The olfactory systems of many animals also have specialized receptors to detect airborne chemicals known as pheromones, which are released by other members of the same species.
? Once detected, these pheromones directly affect the animal’s behavior.
? Many species rely on pheromones to communicate their territorial boundaries, social status, and readiness to sexually reproduce.
o In the late 1960s, Martha McClintock, a college student, tried to answer these questions by conducting a scientific investigation into the folk notion that women who live in the same dorm develop synchronized menstrual periods.
? Inspired by her undergraduate research, McClintock became a biopsychologist and has devoted her career to investigating the existence and possible function of human pheromones.
? She and her colleagues have discovered that pheromone-like chemicals are secreted in blood, sweat, armpit hair, and semen, and that at least some of these chemical substances may unconsciously influence sexual attraction.
o Despite these discoveries, scientists are still unsure about whether humans possess sexual attractant pheromones.
? Even if such substances exist, it is extremely unlikely that they will be found to have the sort of direct effect on sexual behavior that is found among many animal species, because the human sexual response is much more complex than that of most other animals.
o Although human behavior is not as strongly shaped by olfactory information as is the behavior of other species, we do have the ability to identify people by their olfactory cues.
? Although studies suggest that humans as a group have a good deal of smell sensitivity, women’s sensitivity is much better than that of men.
• Finally, odors can also evoke memories and feelings associated with past events.
Taste
Taste, or gustation, is a near sensation, occurring when a substance makes contact with about 10,000 special receptor cells in the mouth.
• Most of these receptors are located on the tongue, but some are in the throat and on the roof of the mouth.
o The surface of the tongue contains many bumps, called papillae (Latin for “pimple”), most of which contain taste buds.
? Because of their constant contact with the chemicals they are designed to sense, as well as their exposure to bacteria, dirt, and dry air, these receptor cells wear out and die within 10 days.
? Fortunately, new cells emerge at the edge of the taste bud and migrate inward toward the center, replacing the old cells.
? Although this cycle of death and replacement of taste cells operates throughout our lives, it occurs more slowly among the elderly, which is one reason their taste sensitivity becomes less acute.
o When these taste cells absorb chemicals dissolved in saliva, they trigger neural impulses that are transmitted to one of two brain areas.
? One pathway involves information first being sent to the thalamus and then to the primary gustatory cortex, where taste identification occurs.
? The second pathway leads to the limbic system and allows you to quickly respond to a taste prior to consciously identifying it.
• In contrast to our olfactory system’s ability to distinguish among about 10,000 different smells, our taste receptors can detect only a handful of taste sensations.
o The receptor cells in each taste bud respond primarily to one particular taste, although they also respond weakly to other tastes.
o Most taste experiences are complex and result from the activation of some combination of these basic receptor cells in the taste buds.
o Although the taste of a particular substance depends on whether one or more of the five basic taste sensations is activated, the flavor of this substance is a combination of both its smell and its taste.
o The important role that olfaction plays in the flavor experience was demonstrated by one study in which some research participants were allowed to both taste and smell substances placed on their tongues, while others were only allowed to taste them.

43. Smell and Taste: The Chemical Senses
Gustation: the sense of taste
Gustation occurs when a substance makes contact with special receptor cells in the mouth, called taste buds.
Most taste buds are located on the tongue, but some are in the throat and on the roof of the mouth.

44. Gustation: the sense of taste
When taste cells absorb chemicals dissolved in saliva, they trigger neural impulses, transmitted to one of two brain areas:
First: information first sent to the thalamus and then to the primary gustatory cortex, where taste identification occurs
Second: information sent to the limbic system, which allows a quick response to a taste prior to conscious identification of it (example, spitting out sour milk)

45. The Five Primary Tastes

46. The Skin Senses Pressure, Temperature, & Pain
Our skin is our largest sensory organ.
Sense of touch is actually a combination of three skin senses:
Pressure: physical pressure on the skin
Temperature: The skin contains two kinds of temperature receptors, one sensitive to warm and the other to cold.

47. Pain: The Body’s Warning System
Pain is induced through tissue damage or intense stimulation of sensory receptors.
Gate-control theory proposes that small-diameter nerve fibers (S-fibers) and large-diameter nerve fibers (L-fibers) open and close “gateways” for pain in the spinal cord.
Pain gateways can be closed—thus preventing pain messages from reaching the brain—by a class of substances known as endorphins.

48. The Proprioceptive Senses: Body Movement and Location
Kinesthetic sense: provides information about the movement and location of body parts with respect to one another
This information comes from proprioceptors (receptors in muscles, joints, and ligaments.)
Vestibular sense: provides information on the position of the body in space by sensing gravity and motion (inner ear).

49. Perception
Organization and interpretation of stimuli.

50. Perceptual Organization
Gestalt
an organized whole
tendency to integrate pieces of information into meaningful wholes

51. Perceptual Organization
Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground)

52. Perceptual Organization- Gestalt Grouping Principles
proximity
similarity
continuity
closure
connectedness

53. Proximity
Similarity
Continuity
Closure
Connectedness

54. Depth Perception
Depth perception: the ability to perceive objects three-dimensionally
Binocular cues: depth cues that require information from both eyes
Monocular cues: depth cues that require information from only one eye

55. The Visual Cliff

56. Depth Perception – Binocular Cues
Binocular cues- depend on use of two eyes
retinal disparity
images from the two eyes differ
closer the object, the larger the disparity
convergence
neuromuscular cue
two eyes move inward for near objects

57. Depth Perception – Monocular Cues
Monocular Cues-available to either eye alone
relative size
interposition
texture gradient
relative motion
linear perspective

58. Relative Size

59. Overlap or Interposition

60. Monocular Depth Cues

61. Monocular Depth Cues

62. Linear Perspective

63. Perceptual Constancy
perceiving objects as unchanging despite changes in retinal image
color
shape
size

64. Shape Constancy

65. Size-Distance Relationship

66. Perceptual Illusions – Ames Room

67. Size-Distance Relationship

68. The Müeller-Lyer Illusion

69. Müller-Lyer Illusion

70. Perceptual Set
a mental predisposition to perceive one thing and not another
expectations that create a tendency to interpret sensory information in a particular way

71. Cultural Influence on Perception

72. Perceptual Set
What you see in the center is influenced by perceptual set

73. Perceptual Set
Flying Saucers or Clouds?

74. There Is Little Scientific Evidence for Extrasensory Perception
Extrasensory perception (ESP): the ability to perceive events without using normal sensory receptors
Parapsychology: the field that studies ESP and other paranormal phenomena

75. There Is Little Scientific Evidence for Extrasensory Perception
Types of ESP:
Mental telepathy: the ability to perceive others’ thoughts
Clairvoyance: the ability to perceive objects or events that are not physically present
Precognition: the ability to perceive events in the future
Psychokinesis: the ability to control objects through mental manipulation

76. Is There Extrasensory Perception?
controversial claim that perception can occur apart from normal sensory input
trickery (magician)
imagination
paranormal forces?????
Not a natural human ability

77. There Is Little Scientific Evidence for Extrasensory Perception
Reasons for skepticism include:
Generally, findings supporting the existence of paranormal abilities cannot be replicated in subsequent research.
Many published ESP studies have used flawed research methodologies or failed to detect outright fraud by those they were testing.

78. There Is Little Scientific Evidence for Extrasensory Perception
Until ESP phenomenon can be reliably replicated in carefully controlled scientific studies, it will remain only a highly speculative “extra-sense” to most practitioners of science.