Sensation and Perception

1
Sensation and Perception
chapter 6
2
Overview
chapter 6

• Our sensational senses
• Vision
• Hearing
• Other senses
• Perceptual powers
• Puzzles of perception

3
Definitions
chapter 6

• Sensation
• The detection of physical energy emitted or
  reflected by physical objects
• Occurs when energy in the external environment or
  the body stimulates receptors in the sense organs
• Perception
• The process by which the brain organizes and
  interprets sensory information

4
Ambiguous figure
chapter 6

• Colored surface can be either the outside front
  surface or the inside back surface.
• But not simultaneously both
• The brain can interpret the ambiguous cues in two
  different ways.

5
Riddle of separate sensations
chapter 6

• Sense receptors
• Specialized cells that convert physical energy
  into electrical energy that can be transmitted as
  nerve impulses to the brain

6
Sensation and perception
chapter 6
7
Specific nerve energies
chapter 6

• Different sensory modalities exist because
  signals received by the sense organs stimulate
  different nerve pathways leading to different
  areas of the brain.
• Synesthesia
• A condition in which stimulation of one sense
  also evokes another

8
Absolute threshold
chapter 6

• The smallest quantity of physical energy that can
  be reliably detected by an observer

9
Absolute thresholds
chapter 6

• Vision
• A single candle flame from 30 miles on a clear
  night
• Hearing
• The tick of a watch from 20 feet in total quiet
• Smell
• One drop of perfume in a 6-room apartment
• Touch
• The wing of a bee on the cheek, dropped from 1 cm
• Taste
• One teaspoon of sugar in 2 gallons of water

10
Difference threshold
chapter 6

• The smallest difference in stimulation that can
  be reliably detected by an observer when two
  stimuli are compared
• Also called the Just Noticeable Difference (JND)

11
Signal-detection theory
chapter 6

• A psychophysical theory that divides the
  detection of a sensory signal into a sensory
  process and a decision process

12
Sensory adaptation and deprivation
chapter 6

• Adaptation
• The reduction or disappearance of sensory
  responsiveness when stimulation is unchanging or
  repetitious
• Prevents us from having to respond continuously
  to unimportant information
• Deprivation
• The absence of normal levels of sensory
  stimulation

13
Sensory overload
chapter 6

• Over-stimulation of the senses
• Can use selective attention to reduce sensory
  overload
• Selective attention the focusing of attention on
  selected aspects of the environment and the
  blocking out of others

14
Vision
chapter 6

• What we see
• An eye on the world
• Why the visual system is not a camera
• How we see colors
• Constructing the visual world

15
What we see
chapter 6

• Hue
• Visual experience specified by color names and
  related to the wavelength of light
• Brightness
• Visual experience related to the amount of light
  emitted from or reflected by an object
• Saturation
• Visual experience related to the complexity of
  light waves

16
What we see
chapter 6
17
An eye on the world
chapter 6

• Cornea
• Protects eye and bends light toward lens
• Lens
• Focuses on objects by changing shape
• Iris
• Controls amount of light that gets into eye
• Pupil
• Aperture through which light reaches the retina

18
An eye on the world
chapter 6

• Retina
• Neural tissue lining the back of the eyeballs
  interior containing the receptors for vision
• Rods
• Visual receptors that respond to dim light
• Cones
• Visual receptors involved in color vision

19
Structures of the retina
chapter 6
20
Your turn
chapter 6

• You have a hard time locating your red car at
  night, in the poorly lit mall parking lot. Why?
• 1. Your rods are less sensitive to color in dim
  light.
• 2. Your cones, which detect color, do not
  function well in dim light.
• 3. Your ganglion cells receive insufficient
  overall stimulation to
• function.
• 4. Your rods, which detect color, do not
  function well in dim light.

21
Your turn
chapter 6

• You have a hard time locating your red car at
  night, in the poorly lit mall parking lot. Why?
• 1. Your rods are less sensitive to color in dim
  light.
• 2. Your cones, which detect color, do not
  function well in dim light.
• 3. Your ganglion cells receive insufficient
  overall stimulation to
• function.
• 4. Your rods, which detect color, do not
  function well in dim light.

22
The visual system is not a camera
chapter 6

• Much visual processing is done in the brain
• Some cortical cells respond to lines in specific
  orientations (e.g., horizontal).
• Other cortical cells respond to other shapes
  (e.g., bulls-eyes, spirals, faces).
• Feature detectors
• Cells in the visual cortex that are sensitive to
  specific features of the environment

23
Huble and Wiesels experiment
chapter 6
24
Trichromatic theory
chapter 6

• Young (1802) and von Helmholtz (1852) both
  proposed that the eye detects 3 primary colors
• Red, blue, and green
• All other colors derived by combination

25
Opponent-process theory
chapter 6

• A competing theory of color vision, which assumes
  that the visual system treats pairs of colors as
  opposing or antagonistic
• Opponent-process cells are inhibited by a color,
  and have a burst of activity when it is removed.

26
Form perception
chapter 6

• Gestalt principles describe the brains
  organization of sensory building blocks into
  meaningful units and patterns.

27
Gestalt principles
chapter 6

• Proximity
• Things close to one another are grouped together
• Closure
• The brain tends to fill in gaps to perceive
  complete forms

28
Gestalt principles
chapter 6

• Similarity
• Things that are alike are perceived together
• Continuity
• Seeing continuity in lines that could be
  interpreted as either continuous or abruptly
  shifting in direction.

29
Your turn
chapter 6

• Which Gestalt principle is illustrated by the
  fact that we see columns of dots rather than rows
  in this diagram?
• 1. Similarity
• 2. Proximity
• 3. Closure
• 4. Continuity

30
Your turn
chapter 6

• Which Gestalt principle is illustrated by the
  fact that we see columns of dots rather than rows
  in this diagram?
• 1. Similarity
• 2. Proximity
• 3. Closure
• 4. Continuity

31
Depth and distance perception
chapter 6

• Binocular cues visual cues that require the use
  of both eyes
• Convergence
• Turning inward of the eyes, which occurs when
  they focus on a nearby object
• Retinal disparity
• The slight difference in lateral separation
  between two objects as seen by the right and left
  eyes

32
Depth and distance perception
chapter 6

• Monocular cues visual cues that can be used by
  one eye

33
Visual constancies
chapter 6

• The accurate perception of objects as stable or
  unchanged despite changes in the sensory patterns
  they produce
• Shape constancy
• Location constancy
• Size constancy
• Brightness constancy
• Color constancy

34
The Müller-Lyer illusion
chapter 6
35
Fooling the eye
chapter 6

• The cats in (a) are the same size.
• The diagonal lines in (b) are parallel.
• You can create a floating fingertip frankfurter
  by holding hands as shown, 510 inches in front
  of face.

36
What we hear
chapter 6

• Loudness
• The dimension of auditory experience related to
  the intensity of a pressure wave
• Pitch
• The dimension of auditory experience related to
  the frequency of a pressure wave
• Timbre
• The dimension of auditory experience related to
  the complexity of a pressure wave

37
An ear on the world
chapter 6
38
Auditory localization
chapter 6

• Sounds from different directions are not
  identical as they arrive at left and right ears.
• Loudness
• Timing
• Phase
• The brain calculates a sounds location by using
  these differences.

39
Other senses
chapter 6

• Taste savory sensations
• Smell the sense of scents
• Senses of the skin
• The mystery of pain
• The environment within

40
Taste savory sensations
chapter 6

• Taste buds
• Nests of taste-receptor cells

41
Five tastes
chapter 6

• Five basic tastes
• Salty, sour, bitter, sweet, umami
• Different people have different tastes based on
• Genetics
• Culture
• Learning
• Food attractiveness

42
Smell the sense of scents
chapter 6

• Airborne chemical molecules enter the nose and
  circulate through the nasal cavity.
• Vapors can also enter through the mouth and pass
  into nasal cavity.
• Receptors on the roof of the nasal cavity detect
  these molecules.

43
Sensitivity to touch
chapter 6
44
Gate-control theory of pain
chapter 6

• Experience of pain depends in part on whether the
  pain gets past a neurological gate in the
  spinal cord.

45
Gate-control theory revised
chapter 6

• The matrix of neurons in the brain is capable of
  generating pain (and other sensations) in the
  absence of signals from sensory nerves.

46
The environment within
chapter 6

• Kinesthesis
• The sense of body position and movement of body
  parts
• Equilibrium
• The sense of balance
• Semicircular canals
• Sense organs in the inner ear, which contribute
  to equilibrium by responding to rotation of the
  head

47
The visual cliff
chapter 6

• Glass surface, with checkerboard underneath at
  different heights
• Visual illusion of a cliff
• Baby cant fall
• Mom stands across the gap.
• Babies show increased attention over deep side at
  age 2 months, but arent afraid until about the
  age they can crawl.

48
Critical period
chapter 6

• If infants miss out on experiences during a
  crucial period of time, perception will be
  impaired.
• When adults who have been blind since birth have
  vision restored, they may not see well.
• Other senses such as hearing may be influenced
  similarly.

49
Psychological and cultural influences
chapter 6

• We are more likely to perceive something when we
  need it.
• What we believe can affect what we perceive.
• Emotions, such as fear, can influence perceptions
  of sensory information.
• Expectations based on previous experiences can
  influence perception.
• Perceptual set a habitual way of perceiving,
  based on expectations
• All are influenced by culture.

50
Perception vs. persuasion
chapter 6

• Although subliminal priming can influence
  judgments and preferences, research doesnt
  support its success in major levels of persuasion.

51
Extrasensory perception
chapter 6

• The ability to perceive something without
  ordinary sensory information
• Has not been scientifically demonstrated