1. Chapter 3 Sensation and Perception
General Psychology
Chapter 3
Sensation and Perception

2. Sensation and Perception
Sensation – process of detecting external stimuli and changing those stimuli into nervous system activity
Perception – cognitive process that involves the selection, organization, and interpretation of stimuli
Senses present us with information about the world, whereas perception represents that information and is affected by motivation, expectations, and past experiences.

3. Concepts Related to Sensory Processes
Sensory threshold – minimum intensity of a stimulus that will cause the sense organs to operate
Psychophysics – study of relationships between the physical attributes of stimuli and psychological experiences they produce

4. Figure 3.1: Examples of absolute threshold values for the five senses (i.e., these stimuli will be detected 50 percent of the time).

5. Concepts Related to Sensory Processes
Absolute threshold – physical intensity of a stimulus that a person reports detecting 50% of the time
Used to see whether a person’s senses are operating properly

6. Concepts Related to Sensory Processes
Signal detection theory – states that stimulus detection is a decision-making process of determining whether a signal exists against a background of noise

7. Thresholds
Difference threshold – smallest difference between stimulus attributes that can be detected
Just noticeable difference (jnd) – amount of change in a stimulus that makes it just noticeably different from what it was

8. Sensory Adaptation
Occurs when our sensory experience decreases with continued exposure to a stimulus
Dark adaptation – process in which the visual receptors become more sensitive to light as we spend time in the dark
Light adaptation – process by which our eyes become more sensitive to dark when we spend time in the light

9. Figure 3.8: The dark adaptation curve.
In the graph on the left, we see that the cones begin adapting immediately, but then begin “dropping out” at about the 10-minute mark. Rods then begin adapting and continue until about 30 minutes have been spent in the dark. When these two curves are combined to give us a view of what happens in general with time spent in the dark, we have the curve at the right, which shows the “rod-cone break.”
Figure 3.8: The dark adaptation curve.

10. Light: Stimulus for Vision
Light – wave of electromagnetic energy
Wave amplitude – intensity or brightness of light
Wavelength – distance between any point in a wave and the corresponding point on next cycle (e.g., peak to peak), measured in nanometers (nm)
Determines the color or hue we perceive
Wave purity – refers to characteristic of saturation
Monochromatic refers to light waves of all one length or hue. Saturation – degree of purity of a light. White light consists of random mixes of wavelengths.

11. Wavelength gives rise to our experience of hue (or color), and wave amplitude determines our experience of brightness.
Figure 3.2: Representations of light waves differing in wavelength and wave amplitude.

12. Figure 3.3: The visible spectrum, in which wavelengths of approximately nanometers are visible to the human eye and are perceived as various hues.

13. Figure 3.4: Relationships between physical characteristics of light and our psychological experience of that light.

14. Figure 3.5: The major structures of the human eye.

15. The Eye: Receptor for Vision
Cornea – outer shell of eye
Protects structures at front of eye
First point where light rays are bent
Pupil – opening through which light enters eye
Iris – colored part of the eye that expands or contracts, depending on light intensity
Ciliary muscles – expand or contract to change shape of the lens to bring image into focus (accommodation)
Over time, lenses tend to harden and ciliary muscles weaken.

16. Figure 3.6: The major features of the human retina.

17. The Eye: Receptor for Vision
The eye is filled with two fluids:
Aqueous humor – provides nourishment to the cornea and other structures at the front of the eye
Vitreous humor – fills the interior of the eye, behind the lens, where it functions to keep the eyeball spherical

18. Vision
Begins to take place at the retina, where light energy is transduced to neural energy
Rods
Photosensitive cells that are most active in low levels of illumination and do not respond differently to different wavelengths of light
Cones
Photosensitive cells that operate best at high levels of illumination and are responsible for color vision
Transduce = convert energy from one form to another. There are about 120 million rods in each eye, and about 6 million cones.

19. The Eye, Con’t.
Optic Nerve – formed of fibers from ganglion cells; leaves the eye and starts back toward other parts of the brain
Fovea – small area of retina with the best visual acuity. It is packed with cones cells (no rods!).
Blind spot – where nerve impulses from rods and cones leave the eye

20. Figure 3.7: This figure provides two ways to locate your blind spot.
(A) Close your right eye and stare at the cross (+). Hold the page about a foot from your left eye and slowly move the page around until the star falls on your blind spot and disappears. (B) Close your right eye and stare at the cross (+). Hold the page about a foot from your left eye and slowly move the page around until the break in the line falls on your blind spot. The line will then appear to be unbroken.
Figure 3.7: This figure provides two ways to locate your blind spot.

21. Visual Pathway
Left visual field – everything off to your left ends up in right occipital lobe
Right visual field – everything off to your right ends up in left occipital lobe
Optic chiasma – sorting of which fibers of the optic nerve get directed where largely occurs here
Vision doesn’t happen in the eyes; it happens in the brain. Detection & interpretation of patterns of light shade and color and motion are functions of the cerebral cortex.

22. Figure 3.9: Cross Laterality.
In keeping with the principle of cross laterality, stimuli from the left visual field are sent to the right occipital lobe for further processing, whereas stimuli from the right visual field are sent to the left occipital lobe.
Figure 3.9: Cross Laterality.

23. Color Vision
Trichromatic theory – First proposed by Thomas Young and revised by Herman von Helmholtz
The eye contains 3 distinct receptors for color
Each responds best to one of 3 primary colors of light: red, blue, and green
By the careful combination of all 3, all other colors can be produced

24. Although there is considerable overlap, each type is maximally sensitive to wavelengths corresponding to the primary hues of light: blue, green, and red.
Figure 3.10: The relative sensitivities of three types of cones to lights of differing wavelengths.

25. Color Vision
Opponent-process theory – Ewald Hering proposed this theory in 1870
Three pairs of visual mechanisms that respond to different wavelengths of light
Blue-yellow processor
Red-green processor
Black-white difference/brightness processor
Each is capable of responding to either of the two hues that give it its name, but not both

26. Color Blindness
In dichromatism, there is a lack of one type of cone (supporting Young-Helmholtz’s theory)
However, color vision defects higher in the visual pathway support the opponent-process theory
Both theories are probably correct, each in its own way
Defective color vision takes place in about 8% of males and less than 0.5% in females. Most cases are genetic in origin.

27. Gender Differences in Perception of Color?
Reliable, stable differences in color preferences:
Women prefer “cool colors,” while men prefer bright, strong colors
Women are more likely to have a favorite color
Women can name more colors
Color matters more to women.
In 1897, Jastrow reported that men prefer blue to red, and women preferred red to blue. It may be that women have one more ohotopigment receptor than men do.

28. Sound: Stimulus for Hearing
Sound – series of pressures of air (or some other medium) beating against the ear
Amplitude – intensity that determines the psychological experience we call loudness
Zero point on decibel scale (perceived loudness) is lowest intensity of sound that can be detected – absolute threshold

29. Figure 3.11: Sound waves are manifested as changes in air pressure are produced as the tines of the tuning fork vibrate back and forth.

30. Sound, Con’t.
Frequency – number of waves exerted for every second of Unit of sound is called hertz (Hz) {20-20,000 Hz}
Pitch – how high or low a tone is (determined by wavelength)
Purity – timbre is character of sound that reflects degree of purity
White noise is a random mixture of sound frequencies
Human ear responds to wave frequencies between 20 and 20,000 Hz.

31. Figure 3.12: Loudness values in decibel units for various sounds.

32. Figure 3.13: A summary of the ways in which the physical characteristics of light and sound waves affect our psychological experiences of vision and hearing.

33. Ear: Receptor for Hearing
Cochlea – major structure of inner ear
Receptor cells (transducers for hearing) are here
When fluid inside cochlea moves, basiliar membrane is bent up & down, which stimulates receptors (hair cells)
Neural impulses travel on auditory nerve toward temporal lobe
Sound waves leave pinna (outside of ear) and go through auditory canal, then push against the tympanic membrane so that it vibrates at the same rate as the sound source. The eardrum transmits vibrations to three small bones: malleus, incus, and stapes. These bones amplify and pass sounds to oval window.

34. Figure 3.14: The major structures of the human ear.

35. Chemical Senses Taste = gustation
Four psychological qualities: sweet, salty, sour, and bitter
Taste buds – receptor cells for taste on tongue
We have about 10,000 taste buds
When parts die, new segments are regenerated.
All four qualities of taste can be detected at all locations of the tongue, but some may be more discernable in certain locations.

36. Figure 3.15: Enlarged view of a taste bud, the receptor for gustation.

37. Chemical Sense, Con’t. Smell = Olfaction
Pheromones – chemicals that many animals emit that produce distinctive odors that are used as a method of communication between organisms
VNO (vomeronasal organ) – primary organ used in detection of pheromones. Involved in mating, territoriality, and aggressiveness in animals.
Originates in hair cells high in nasal cavity. VNO is also found in humans.

38. Figure 3.16: The olfactory system, showing its proximity to the brain and transducers for smell — the hair cells.

39. The Skin-Cutaneous Senses
A square inch of skin contains nearly 20 million cells
Some skin receptor cells have free nerve endings, while others have encapsulated nerve endings
Our ability to discriminate among types of cutaneous sensation is due to a unique combination of responses the receptor cells have to various types of stimulation

40. Figure 3.17: A patch of hairy skin, showing the layers of skin and several nerve cells.

41. Even if you know that the coiled tubes contain only warm and cold water, when you grasp the tubes, they will feel very hot.
Figure 3.18: A demonstration that our sense of what is hot can be constructed from sensations of what is warm and cold.

42. Position Senses Kinesthetic sense Vestibular Sense
Tells us about the position of various parts of our bodies and what our muscles and joints are doing
Receptors are located primarily in our joints, but some information comes from muscles and tendons
Information from these receptors travels via the spinal cord
They provide examples of reflex reactions
Vestibular Sense
Tells us about balance, where we are in relation to gravity and about acceleration or deceleration
Receptors are located on either side of the head, near the inner ear (5 chambers)
Over-stimulation may result in motion sickness

43. A Special Sense: Pain Theories of pain:
Gate control mechanism (high in spinal cord) that opens to let pain messages race to brain or closes to block messages
Cognitive behavioral – pain is influenced by attitudes, expectations and behaviors
Nearly 80% of doctor’s visits are due to patients’ experience of pain.

44. Pain Management Drug therapy Hypnosis & cognitive self-control
Acupuncture
Placebo – a substance a person thinks will be helpful in treatment
Counterirritation – stimulating an area of the body near the location of the pain
There is evidence that sensitivity to pain is genetically based. Gender and cultural issues can influence individual response.

45. Paying Attention: A Process of Selection
Salient detail – one that captures our attention
Remembered better than peripheral details (which are part of the perceptual background)
Stimulus factors make some details more compelling than others
Personal factors – characteristics of a perceiver that influence which stimuli get attended to

46. Stimulus Factors
Contrast – extent to which a stimulus is physically different from the other stimuli around it
Most important factor in perceptual selectivity
The more intense a stimulus is, the more likely we are to attend to it
Motion is another dimension for which contrast is important
Repetition can also influence attention

47. Personal Factors in Processing
Bottom-Up Processing
Attend to a stimulus, organize and identify it, and then store it in memory
Top-Down Processing
Motivation, mental set, and past experience influence perceptual sensitivity
When we are psychologically predisposed to perceive something, we have formed a mental set.

48. How many THEs did you see when you first glanced at this figure? Why?
Figure 3.19: How we perceive the world is determined at least in part by our mental set, or our expectations about the world.

49. Gestalt Psychology
A gestalt forms when one sees the overall scheme of things: the whole, totality or configuration.
Gestalt Psychology – basic principle is figure-ground relationship
Of all the stimuli in your environment, those you attend to and group together are “figures”
All other stimuli become “ground”

50. Figure 3.20: (A) A classic reversible figure-ground pattern.
What do you see here? A white vase, or two black profiles facing each other? Can you see both figures clearly at the same time? (B) After a few moments’ inspection, a small square should emerge as a figure against a ground of diagonal lines.
Figure 3.20: (A) A classic reversible figure-ground pattern.

51. Grouping Stimuli with Bottom-Up Processing
Proximity
Similarity
Continuity
Common fate
Closure

52. Figure 3.21: Four Gestalt psychology examples of grouping.
(A) These Xs are organized as two groups, not as four rows or four columns, because of proximity. (B) Here we see two columns of Os and two columns of Xs because of similarity. (C) We tend to see this figure as two intersecting lines—one curved, the other straight—because of continuity. (D) This figure is perceived as the letter R, not because it is a well-drawn representation, but because of closure.
Figure 3.21: Four Gestalt psychology examples of grouping.

53. Figure 3.22: An example of subjective contour.

54. Grouping Stimuli with Top-Down Processing
Perceiving stimuli because we want to, expect to, or have experienced them together in the past
How we ultimately organize our experiences depends on both types of processing

55. Figure 3.23: An example of top-down processing.

56. Perceiving Depth & Distance
Ocular cues are built into our visual system and tell us about depth and distance
Retinal disparity – each eye gets a somewhat different view of a 3-dimensional object
Convergence – eyes turning in, toward each other, when something is viewed up close

57. This disparity gives us a cue that the object we are viewing is three-dimensional. Here we also note convergence — our eyes turn toward each other when we view an object that is close to us.
Figure 3.24: When looking at a three-dimensional object, such as a pen, the right eye sees a slightly different image than does the left eye — a phenomenon called retinal disparity.

58. Monocular Cues
Physical cues to depth and distance are those we get from the structure of our environment
Linear Perspective
Interposition
Relative Size
Texture gradient
Patterns of Shading
Motion Parallax
Require only one eye to have their influence.

59. Figure 3.25: At the level of the retina, we experience different images; yet we know we are looking at the same door because of shape constancy.

60. Constancy of Visual Perception
Perceptual constancies help us organize and interpret the stimulus input we get from our senses. They allow us to see stimuli as constant, regardless of changing conditions.
Size constancy
Shape constancy
Brightness constancy
Color constancy

61. When Constancy Fails…
Illusions – experiences in which our perceptions are at odds with what we know as physical reality
Illusions remind us that perception is a higher level process than sensation!

62. Figure 3.26: A few classic geometrical illusions.
In each case, you know the answer, but the relevant questions are: (A) Are the vertical and horizontal lines the same length? (B) Is the brim of the hat as wide as the hat is tall? (C) Are the two horizontal lines the same length? (D) Are the two horizontal lines the same length? (E) Are the two diagonals part of the same line? (F) Are the long diagonal lines parallel? (G) Are the two center circles the same size?
Figure 3.26: A few classic geometrical illusions.

63. Figure 3.27: Impossible figures — examples of conflicting visual information.

64. Figure 3.29: Müller-Lyer illusion.
(A) One attempt to “explain” the Müller-Lyer illusion as the representation of edges and corners, and a variant of the Müller-Lyer illusion. (B) The distance between circles A and B is equal to the distance between circles B and C. An explanation in terms of edges and corners no longer seems reasonable.
Figure 3.29: Müller-Lyer illusion.

65. Cultural Bias in Perception?
Yes! There is a role of culture in the development of depth perception.
However, with training, most cultural differences in the perception of depth disappear.
Cultural constraints may influence depth perception. People who live in the dense jungle cannot judge depth or distance when brought out into open, grassy plains. Pictorial representations of depth and distance tend to be meaningless to those who have not experienced them before.

66. One’s response to this question depends on the interpretation of pictorial or physical cues to depth and distance. Such interpretations vary across cultures.
Figure 3.28: Which animal — the antelope or the elephant — is the hunter about to spear?