Chapter 6: Sensation and Perception
I.
Sensing the World: Some Basic Principles
a. Sensation: The process by which our sensory receptors and
nervous system receive and represent stimulus energies from our
environment.
b. Perception: the process of organizing and interpreting sensory
information, enabling us to recognize meaningful objects and
events.
c. Bottom-up processing: sensory analysis that starts at the entry
level (sensory receptors) and moves to the brain
d. Top-down processing: guided by higher level mental processing, as
we construct perceptions drawing on experience and expectation.
e. Psychophysics: the study of relationships between the physical
characteristics of stimuli, such as their intensity, and our
psychological experience of them.
f. Thresholds:
i. Absolute: the minimum simulation needed to detect a
particular stimulus 50% of the time
1. Vary with age
ii. Signal detection
1. Signal detection theory: predicts how and when we
will detect the presence of a faint stimulus (signal)
amid background stimulation (noise)
a. Says there is no single absolute threshold and
that it depends on
i. Experience
ii. Expectation
iii. Motivation
iv. Fatigue
2. Subliminal stimulation
a. Subliminal: below one’s absolute threshold
for conscious awareness
b. Priming: the activation, often unconscious, of
certain associations, thus predisposing one’s
perception, memory, and response.
i. Sometime s we feel what we do not
know and cannot describe
c. But does this actually lead to lasting
persuasion?
i. Greenwald (1991,1992) experiment
says no
3. Difference Thresholds
a. Difference threshold (or just noticeable
difference JND): the minimum difference
between two stimuli required for detection
50% of the time.
b. Weber’s Law: to be perceived as different,
two stimuli must differ by a constant
minimum percentage.
i. Light: 8%
ii. Weight: 2%
iii. Tones: .3%
g. Sensory Adaptation: diminished sensitivity as a consequence of
constant stimulation
i. After constant exposure to a stimulus, our nerve cells fire
less frequently.
ii. We perceive the world not exactly as it is, but as it is useful
for us to perceive it.
II.
Vision
a. The Stimulus Input: Light Energy
i. Transduction: conversion of one form of energy to another;
in sensation, the transforming of stimulus energies into
neural impulses our brains can interpret.
ii. What strikes our eye is electromagnetic energy that our
visual system perceives as color.
iii. Electromagnetic spectrum
iv. Wavelength (high/low frequency): the distance from one
peak to the next
1. Determines hue (color)
v. Intensity (great/small amplitude): the high of the waves
1. Determines brightness
b. The Eye
i. The Retina
1. Receives an upside down image, it itself doesn’t
“see” a whole image
2. The thalamus receives and distributes visual
information
3. Where the optic nerve leaves the eye, there are no
cells and this leaves a blind spot.
4. Rods: detect black, white and gray (6 million)
a. Peripheral vision
b. Twilight vision
5. Cones: detect fine detail and color (20 million)
a. Daylight
b. Well-lit conditions
c. Visual Information Processing
III.
i. Feature detection
1. Nerve cells in that brain respond to specific features
of the stimulus, such as shape, angle, or movement.
2. Supercell clusters, See image p.241
ii. Parallel Processing
1. Computers do step-by-step serial processing
2. Brain uses parallel processing, doing many things at
once (Gestalt)
3. We can prove this through studying brain injuries
4. Combines things like color, motion, form, and depth
into one perceptual experience
iii. Color Vision
1. “A tomato’s color is our mental construction.”
2. “Color, like all aspects of vision, resides not in the
object but in the theatre of our brains.”
3. We can differentiate 7 million different color
variations
4. Young-Helmholtz trichromatic (three-color) theory
a. Theory that the retina contains three
different color receptors
i. Red
ii. Green
iii. Blue
5. Opponent-process theory
a. Theory that opposing retinal processes
enable color vision
i. Red-green
ii. Yellow-blue
iii. White-black
Hearing
a. The Stimulus Input: sound Waves
i. The Ears
1. Ears transform vibrating air into nerve impulses,
which our brain decodes as sounds.
2. Amplitude: strength, determines loudness
3. Frequency: length, determines pitch
4. Measured in decibels
IV.
ii. Hearing Loss and Deaf Culture
Other Important Senses
a. Touch
i. Kinesthesis: your sense of the position and movement of
your body parts
1. Located in sensors in your joints, tendons, bones,
ears, and skin
ii. Vestibular sense: monitors you head’s position and
movement
b. Pain
i. Biological Influences
1. Gate-control theory: spinal chord contain a
neurological gate that blocks pain signals or allows
them to pass on to the brain.
ii. Psychological Influences
1. Distraction
2. Expectations
iii. Socio-cultural Influences
1. Presence of others
2. Empathy for others’ pain
3. Cultural expectations
c. Taste
i. Sweet, Salty, Sour, Bitter, Umami
ii. Taste is evolutionary
iii. Taste is chemical
d. Smell
V.
Perceptual Organization
a. Form Perception
i. Figure and Ground: the organization of the visual field into
objects (the figures) that stand out from their surroundings
(ground).
b. Grouping
i. Proximity
ii. Similarity
iii. Continuity
iv. Connectedness
v. Closure
c. Depth Perception
i. Visual cliff: research shows that even infants can perceive
depth
ii. Binocular cues: depth cues, such as retinal disparity, that
depend on the use of two eyes
1. Retinal disparity: by comparing images from the
retinas in the two eyes, the brain computes distance;
d.
e.
f.
g.
h.
the greater the disparity between the two images,
the closer the object.
a. Floating finger sausage!
iii. Monocular cues
1. Depth cues, such as interposition and linear
perspective, available to either eye alone.
a. Relative height
b. Relative size
c. Interposition
d. Linear perspective
e. Light and shadow
f. Relative motion
Motion Perception
Perceptual Constancy
i. Shape and Size
1. Perceived size and perceived distance
ii. Lightness/ Brightness
1. Relative luminance: the amount of light an object
reflects relative to its surroundings
iii. Color
1. Our experience of color comes not just from the
object itself, but from everything around it as well.
Perceptual Interpretation
i. Sensory deprivation and restored vision
1. Is perception due to nature or nurture?
2. “Experience guides, sustains, and maintains the
brain’s neural organization.”
3. Sensory deprivation at young ages is particularly
harmful
a. “Critical period”
4. Nurture sculpts what nature has endowed
Perceptual Adaptation
i. In vision, the ability to adjust to an artificially displaced to
even distorted field
ii. George Stratton and the inverted world
Perceptual Set
i. A mental predisposition to perceive one thing and not
another
1. Schemas: concepts, organize and interpreter
unfamiliar information
ii. If told there is vinegar in your beer, you will perceive it as
tasting worse than if you are not told that (expectation) and
most people report McDonald’s fries as better tasting when
in a McDonalds bag than in a plain white one (I might be the
opposite…as I generally hate McDonald’s fries…)
iii. Context effects
1. Stereotypes
a. Gender
b. Race
VI.
2. Differences exist in the perceptions of the beholder
iv. Emotion and Motivation
1. Our emotions influence our perceptions
2. It is bio-psycho-social
v. Perception and the Human Factor
1. Human factors: a branch of psychology that explores
how people and machines interact and how
machines and physical environments can be made
safe and easy to use
Is There Extrasensory Perception?
a. ESP: controversial claim that perception can occur apart from
sensory input; includes telepathy, clairvoyance, and precognition.
b. Parapsychology: the study of paranormal phenomenon, including
ESP
c. 96% of scientists in the U.S. National Academy of Sciences are
skeptical that such phenomena exist.
d. Claims of ESP
i. Telepathy: mind to mind communication
ii. Clairvoyance: perceiving remote events
iii. Precognition: perceiving future events
e. Premonitions of Pretensions?
i. Generating more predictions increases the odds of one of
them being right
ii. Vague predictions are easier to interpret multiple ways
iii. The power of coincidence
f. Putting ESP to the Experimental Test
i. What parapsychology needs is a reproducible phenomenon
and a theory to explain it.