1. SENSATION & PERCEPTION
CHAPTERS 4 & 5
AP PSYCHOLOGY

2. SENSATION

3. How do we take in information?
A sense is a system that translates information from outside the nervous system into neural activity.
Messages from senses are called sensations
For example, vision is the system through which the eyes convert light into neural activity. This tells the brain something about the source of the light (brightness) or about the objects from which the light is reflected (round, red, etc).

4. Elements of a Sensory System
Energy (light, sound waves, etc) contains info about the world
Accessory Structures (lens, ear, etc) modify energy.
Transduction- the process of converting incoming energy into neural activity through sensory receptors
Sensory nerves transfer the coded activity to the Central Nervous System.
Thalamus processes and relays the neural response (except in smell).
Cortex receives input and produces the sensation and perception

5. Figure 4.1: Elements of a Sensory System

6. How does physical energy get converted into neural activity?
CODING - translation of the physical properties of a stimulus into a pattern of neural activity that specifically identifies those physical properties.
Doctrine of Specific Nerve Energies - stimulation of a particular sensory nerve provides codes for that one sense, no matter how the stimulation takes place
Temporal Code - involves changes in the timing of the neurons firing. Ex: A bright light will cause some neurons in the visual system to fire faster than a dim light.
Spatial Code - the location of the firing neurons provides information about the stimulus (tells us where the sensation is coming from).

7. HEARING
Sound is a repetitive fluctuation in the pressure of a medium, such as air.
In a place like the moon, which has almost no atmospheric medium, sound cannot exist
When you speak, your vocal cords vibrate, producing fluctuations in air pressure that spread as waves. A wave is a repetitive variation in pressure that spreads out in 3 dimensions.

8. Physical Characteristics of Sound
Amplitude- (intensity) difference in air pressure from the baseline to the peak of a wave.
Wavelength- the distance from one peak wave to the next.
Frequency- number of complete waves, or cycles, that pass by a given point in space every second. Described in a unit called hertz, (Hz). 1 cycle per second is 1 hertz

9. Figure 4.2: Sound Waves and Waveforms

10. Psychological Dimensions of Sound What do we actually hear?
Loudness- determined by amplitude. Greater amplitude = Louder sounds
Pitch- how high or low a tone sounds. Determined by frequency.
High frequency = High Pitch
Low Frequency = Low Pitch
Timbre- (pronounced “tamber”) is the quality of the sound

11. The Ear
Auditory accessory structures modify sound waves before information affects neural signals
Pinna – crumpled part of ear that funnels sound through the ear canal
Tympanic Membrane – eardrum – tightly stretched membrane in the middle ear where sound waves strike
Vibrations of the tympanic membrane are transferred through 3 tiny bones - malleus (hammer), incus (anvil), stapes (stirrup)
Sound Waves 1

12. Auditory Transduction
After sound passes through the oval window, it enters the inner ear or cochlea - this is where transduction occurs
The basilar membrane forms the floor of this long tube
Sound waves bend hairs of the organ of Corti – a group of cells which rest on the membrane
Hair cells connect with fibers from the auditory nerve, a bundle of axons that goes into the brain
Sound Waves 2
Figure 4.4: The Cochlea

13. Auditory Pathways Auditory nerve  brainstem  thalamus
The information coded in the activity of auditory nerve fibers is conveyed to the brain and processed further
Information is relayed from the auditory nerve to an area of the cerebral cortex called the primary auditory cortex
Various aspects of sound processed in different regions of auditory system.
Certain parts of auditory cortex process certain types of sounds.

14. Auditory Transduction

15. How we hear?

16. Sensing Pitch
Different people may experience the “same” sound as different pitches.
Pitch-recognition abilities influenced by genetics.
Cultural factors are also partly responsible for the way in which a pitch is sensed.

17. Locating Sounds
Determined partly by the very slight difference in when sound arrives at each ear.
The brain also uses information about the difference in sound intensity at each ear.

18. Coding Intensity and Frequency
The more intense the sound, the more rapid the firing of a given neuron.
Frequency appears to be coded in two ways: place theory and frequency-matching theory

19. Coding Frequency: Place Theory
Sounds produce waves that move down the basilar membrane.
Where the wave peaks depends on the frequency of the sound.
Hair cells at a particular place on the membrane respond most to a particular frequency.

20. Coding Frequency: Frequency Matching Theory
Firing rate of an auditory nerve matches a sound wave’s frequency.
Sometimes called the “volley theory” of frequency coding.

21. Vision Light – electromagnetic radiation
Visible light has a wavelength from just under 400 nanometers to 750 nanometers
Light intensity –
How much energy the light contains
Determines the brightness of light
Light Wavelength –
The difference between peaks in light waves
Determines what color we see

22. Figure 4.7: Spectrum of Electromagnetic Energy

23. The spectrum of electromagnetic energy

24. Physical Properties of Light 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)

25. Accessory Structures of the Eye
Cornea – curved, transparent layer through which light rays enter the eye
Pupil – opening in the eye through which light passes
Iris – colorful part of the eye which adjusts the amount of light entering the eye
Lens – bends rays, focusing them on the retina
Retina – Surfaces at back of the eye onto which the lens focuses light rays

26. Figure 4.8: Major Structures of the Eye

27. Vision
Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina
Acuity- the sharpness of vision
Nearsightedness- condition in which nearby objects are seen more clearly than distant objects because distant objects in front of retina
Farsightedness- condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

28. How Light enters the eye

29. Vision
Normal Vision
Nearsighted
Farsighted

30. Converting Light into Images
Visual transduction is the conversion of light energy into neural activity.
Conversion done by photoreceptors in the retina.
Two main types of photoreceptors: Rods and cones.

31. Rods and Cones Rods Cones peripheral retina
detect black, white and gray
twilight or low light
Cones
near center of retina
fine detail and color vision
daylight or well-lit conditions

32. Interactions in the Retina
Photoreceptor cells connect to bipolar cells and then to ganglion cells
Axons of the ganglion cells form the optic nerve, which extends out of the eye and into the brain
Each neuron of a sensory system has a receptive field – part of the retina and the region of the environment to which that cell responds

33. Figure 4.11: Center-Surround Receptive Fields of Ganglion Cells

34. Figure 4.12: The Hermann Grid
The cell whose receptive field includes the space at the intersection has more whiteness shining on its inhibitory surround than the cell whose receptive field is just to the right of the intersection. The output of the intersection cell will be lower than that of the one on the right, creating the impression of a shadow.

35. Visual Pathways
Axons from ganglion cells converge as a bundle of fibers called the optic nerve and exit the eyeball at one spot
The exit point has no photoreceptors and is insensitive to light creating a blind spot
About ½ the fibers of the optic nerve cross over to the opposite side of the brain at the optic chiasm (part of the bottom surface of the brain)

36. Visual Pathways con’t
Axons from most of ganglion cells in retina form synapses in the thalamus, in a specific region called the lateral geniculate nucleus (LGN)
Neurons in the LGN relay the visual input to the primary visual cortex, located in the occipital lobes in the back of the brain

37. Pathways from the Eyes to the Visual Cortex

38. Visual Representations
Receptive fields of neurons are characterized by parallel processing and hierarchical processing
Parallel Processing of visual properties: Brain conducts separate kinds of analysis simultaneously on the same information.
The “what” system
The “where” system
Hierarchical Processing of visual properties:
Individual cells in the visual cortex receive input from several LGN neurons.
Cortical cells respond to specific features of objects in the visual field – Feature detectors
Light Conversion

39. Seeing Color
Hue – color determined by the dominant wavelength in the mixture of the light (excludes black, white, gray)
Saturation – purity of a color
Brightness – overall intensity of the wavelengths that make up light

40. Visual Information Processing
Trichromatic (three color) Theory
Young and Helmholtz
three different retinal color receptors

41. Trichromatic Theory of Color
Any color can be produced by mixing pure lights of blue, green, and red.
There are three types of cones, each most sensitive to particular wavelengths.
Ratio of the activities of the three types of cones indicates what color is sensed.

42. Opponent-Process Theory
Ewald Hering
Each of the three color sensitive elements are organized as pairs, where each pair member opposes, or inhibits, the other
Red-Green
Blue-Yellow
Black-White

43. Trichromatic and Opponent-Process Theories

44. Opponent-Process Theory

46. Figure 4.20: Color Coding and Ganglion Cells

47. The Chemical Senses Olfaction detects airborne chemicals
Our sense of smell
Gustation detects chemicals in solution that come into contact with receptors inside the mouth
Our sense of taste

48. Figure 4.23: The Olfactory System

49. Olfactory System Employs about 1,000 different types of receptors.
Only sense that does not send its messages through the thalamus.
Processing in several brain regions including frontal lobe and amygdala
Strong relationship between olfaction and emotional memory

50. Olfactory System (cont’d.)
Only sense that does not send its messages through the thalamus.
Pathways from olfactory bulb sends information on for further processing in several brain regions.
Including frontal lobe and amygdala.
Strong relationship between olfaction and emotional memory.

51. Pheromones
Chemicals released by one animal, and when detected by another, can shape the second animal’s behavior or physiology.
Role of pheromones in humans not clear

52. Age, Sex and Sense of Smell
Women
Men
Age Group 4 3 2
Number
of correct
answers
Women and young adults
have best sense of smell

53. Smell, Taste, and Flavor
Smell and taste act together to form system known as flavor.
Tastes and odors can prompt strong emotional responses.
Nutritional state can affect taste and flavor of food and motivation to eat particular foods.
Flavor includes other characteristics of food.

54. Somatic Senses and the Vestibular System
Somatosensory systems are spread throughout the body
Somatic senses include:
Skin senses of touch, temperature, and pain
Kinesthesia
Vestibular system tells the brain about the position and movement of the head

55. Touch Energy detected is physical pressure on tissue.
Many nerve endings in the skin act as touch receptors.
Touch is both an active and passive sense.
Changes in touch provide most important sensory information.

56. Coding of Touch Information
Intensity of the stimulus is coded by:
Firing rate of individual neurons and
The number of neurons stimulated.
Location is coded by the location of the neurons responding to the touch.

57. Temperature
Some of the skin’s sensory neurons respond to a change in temperature.
“Warm” and “cold” fibers
Sensations of touch and temperature sometimes interact.
Stimulation of the touch sense can have psychological and physiological effects.

58. Pain Pain provides information about impact of world on body.
Information-carrying aspect of pain very similar to that of touch and temperature.
Two types of nerve fibers carry pain signals from skin to the spinal chord.
Cerebral cortex plays role in the experience of pain.

59. Figure 4.25: Pain Pathways

60. Modulating Pain Gate Control Theory
theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain
“gate” opened by the activity of pain signals traveling up small nerve fibers
“gate” closed by activity in larger fibers or by information coming from the brain
Natural Analgesics
Serotonin
Endorphins

61. Proprioceptive Senses
Sensory systems that provide information to the brain about:
The position of the body.
What each of part of the body is doing.
Vestibular sense indicates the position of the head in space and its general movements.
Sense of balance.

62. Vestibular Sense Organs: Neural connections to: Vestibular sacs
Otoliths
Semicircular canals
Neural connections to:
The cerebellum
The autonomic nervous system
The eye muscles

63. Kinesthesia
Sense that indicates where the parts of the body are with respect to one another.
Necessary guide for movement.
Kinesthetic information comes primarily from the joints as well as muscles.

64. PERCEPTION

65. Three Approaches to Perception
Computational – tries to determine the computations that a machine would have to solve perceptual problems
Constructivist – reality is constructed from fragments of sensory information
Ecological – environment contains most of the information needed to form perceptions

66. Psychophysics
Describes the relationship between the physical energy in the environment and the psychological experience of that energy
Absolute Threshold – the minimum detectable amount of environmental energy a sensory system can detect

67. Absolute Thresholds Table 5.1

68. Signal-Detection Theory
Sensitivity – a person’s ability to pick out a particular stimulus or signal
Response Criterion – a person’s willingness or reluctance to say that a stimulus is present
Signal-Detection Theory – model of our personal sensitivity and response criterion combined to determine whether or not a near-threshold stimulus has occurred

69. Figure 5.4: Signal Detection

70. Judging Differences Between Stimuli
Difference Threshold or Just-Noticeable Difference (JND)
JND determined by two factors:
How much of a stimulus was there to begin with?
Which sense is being stimulated?
Click the link below to see how JND impacts the consumer world:

71. Weber’s Law Weber’s Constant Law States That JND = KI
K is the Weber’s constant for a particular sense.
I is the amount, or intensity, of the stimulus.
The smaller K is, the more sensitive a sense is to stimulus differences

72. Magnitude Estimation
Magnitude estimation is how our perception of stimulus intensity is related to actual stimuli strength
Fechner’s Law
Constant increases in physical energy will produce smaller increases in perceived magnitude
Steven’s Power Law
Describes a wider range of sensations

73. Perceptual Illusions Illusion – incorrect perception of a stimulus
Delusion – a false belief
Hallucination – a perception in the absence of a stimulus

74. Figure 5.5: Length Illusions

75. Figure 5.6: Organize This!

76. Perceptual Illusions
Ames room

77. Perceptual Illusions
Ames room

78. Basic Processes in Perceptual Organization
Figure-Ground Organization
Perceptual apparatus picks out some objects to be figures, while others are less relevant in the background
Grouping
Inherent properties of the stimulus environment lead people to group them together
Grouping Principles
Proximity--group nearby figures together
Similarity--group figures that are similar
Continuity--perceive continuous patterns
Closure--fill in gaps
Connectedness--spots, lines, and areas are seen as unit when connected
Synchrony – occur at the same time
Common region – located within some boundary
Connectedness – connected by other elements

79. Figure 5.7: Reversible Images

80. Figure-Ground

81. Figure 5.8: Gestalt Principles of Perceptual Grouping

82. More Grouping Principles

83. Perceptual Organization
Likelihood Principle
We perceive objects in the way that experience tells us is the most likely physical arrangement (consistent with Constructivism)
Simplicity Principle
We organize stimulus elements in a way that gives us the simplest possible perception

84. Figure 5.9: Impossible Objects

85. Perception of Location and Distance
Two-Dimensional Location – uses an equation that takes information about where an image strikes the retina and adjusts it based on information about movement of your eyes and head
Visual dominance – bias toward using visual information when it conflicts with information from other senses

86. Depth Perception
Our ability to perceive distance, allowing people to experience the world in three-dimensions
Interposition – closer objects block the view of things further away
Relative Size – the object producing a larger image on the retina is perceived as closer
Height in the Visual Field – more distant objects are higher in the visual field
Texture Gradient – graduated change in texture – less detailed as distance increases
Linear Perspective – the closer together 2 converging lines are, the greater the perceived distance
Clarity, Color, Shadow – distant objects appear hazier
Motion Parallax – objects closer appear to move rapidly, while those distant appear motionless

87. Figure 5.10: Stimulus Cues for Depth Perception

88. Cues Based on Physiology
Accommodation – muscles surrounding the lens either tighten (to focus on close objects) or relax (to focus on distant objects)
Convergence – each eye rotates inward to see closer objects
Binocular Disparity – the difference between the two retinal images of an object provides distance cues

89. Perceptual Organization: Depth Perception
Visual Cliff

90. Perceptual Organization: Depth Perception
Relative Size

91. Perceptual Organization: Depth Perception
Interposition

92. Perceptual Organization: Depth Perception

93. Perception of Motion
Looming – a rapid expansion in the size of an image so that it fills the retina and is perceived as an approaching object
Stroboscopic Motion – our tendency to perceive motion through a series of flashing rapid light

94. Perceptual Constancy
The perception of objects as constant in size, shape and color
Size Constancy – occurs as objects move closer or farther away
Shape Constancy – occurs as an object appears the same, even though the shape of its retinal image changes
Brightness Constancy – occurs so that no matter how the amount of light striking an object changes, its perceived brightness remains constant

95. Figure 5.12: A Size Illusion

96. Perceptual Organization: Muller-Lyer Illusion

97. Figure 5.13: Brightness Contrast

98. Recognizing the Perceptual World
The brain analyzes the incoming pattern of the stimulus and compares that pattern to information stored in the memory
Top-down processing – guided by knowledge and expectations
Our experiences create schemas, or mental representations of what we know about the world
Bottom-up processing – relies on specific, detailed information from sensory receptors that are integrated and assembled into a whole

99. Parallel Distributed Processing Models (PDP)
Units in a network operate parallelsimultaneously
Each element is connected to all other computational elements
Recognition occurs as a result of the simultaneous operation of connected units

100. Attention
The process of directing and focusing certain psychological resources to enhance perception, performance, and mental experience

101. Articles

102. Illusions

103. Blind Spot Demonstration

104. Jeopardy

105. More Information on Sensation and Perception

106. References