General Psychology

1
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

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 persons 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.
10
LightStimulus 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

11
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 380-760 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 EyeReceptor 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)

16
Figure 3.6 The major features of the human
retina.
17
The EyeReceptor 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
19
The Eye, Cont.

• 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.
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

22
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
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-Helmholtzs 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

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.

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, Cont.

• 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

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
EarReceptor 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

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

36
Figure 3.15 Enlarged view of a taste bud, the
receptor for gustation.
37
Chemical Sense, Cont.

• 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.

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
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
• 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 SensePain

• 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

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

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

48
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.
51
Grouping Stimuli with Bottom-Up Processing

• Proximity
• Similarity
• Continuity
• Common fate
• Closure

52
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
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

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.
63
Figure 3.27 Impossible figures examples of
conflicting visual information.
64
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.

66
Figure 3.28 Which animal the antelope or the
elephant is the hunter about to spear?