Download Sensation and Perception

Chapter 4:
Sensation & Perception
“All knowledge has its origins in our
perceptions.” – Leonardo Da Vinci
Vision
Hearing
Smell
Taste
Touch
Definitions
Sensation

process of detecting, converting, and
transmitting raw sensory information
eyes, ears,
from the external and internal
nose, tongue,
environments to the brain (transduction) skin, & internal
Perception


Sense
organs:
process of selecting, organizing and
interpreting sensory information
enables us to recognize meaningful
objects and events
body organs
Happens in
the brain!
Processing
Bottom-Up (parts to whole)


Ex: you have
Information processing beginning “at ingredients and
the bottom” with raw sensory data that must put them
together to make
are sent “up” to the brain for higher
something edible
level analysis
Data driven processing that moves
from the parts to the whole
Top-Down (whole to parts)


Information processing starting “at the
top” with higher level cognitive
processes (such as expectations and
knowledge) and then “working down”
Conceptually driven processing that
moves from the whole to the parts
Ex: you have
ingredients and
a recipe &
picture of a
completed cake
and you must
recreate the
cake
Top-Down Processing example
Aoccdrnig to a rscheearch at
Cmabrigde Uinervtisy, it deosn't
mttaer in waht oredr the ltteers in a
wrod are, the olny iprmoetnt tihng
is taht the frist and lsat ltteer be at
the rghit pclae. The rset can be a
toatl mses and you can sitll raed it
wouthit porbelm. Tihs is bcuseae
the huamn mnid deos not raed
ervey lteter by istlef, but the wrod
as a wlohe.
Top down/ bottom up
Guitar player or old
people
Fruit or face
Sensation- Thresholds
Absolute Threshold
 minimum stimulation needed to detect
a particular stimulus
 usually defined as the stimulus needed
for detection 50% of the time
Ex: listen to
headphones
and indicate
the earliest
you hear a
tone
Difference Threshold
 minimum difference between two
stimuli that a subject can detect 50%
of the time
 just noticeable difference (JND)
 increases with magnitude
Ex: listen to
headphones
and indicate
when you hear
a change in
volume of
sound
Easier to tell the difference
between 100 & 101Hz than
1000 & 1001Hz
Sensation- Thresholds
100
Percentage
of correct
detections
75
When stimuli are
detectable less
than 50% of the
time (below one’s
50
absolute threshold)
Subliminal
stimuli
25
0
Low
Absolute
threshold
Intensity of stimulus
Medium
they are
“subliminal”.
Sensation- Thresholds
Weber’s Law- to perceive a difference
between two stimuli, they must differ
by a constant proportion



light intensity- 8%
weight- 2%
tone frequency- 0.3%
Sensory Adaptation: diminished
sensitivity with constant stimulation
- receptors higher up in sensory
system get tired and fire less
frequently
Apply it!
Come up
with 3
examples
Sensation- Thresholds
Signal Detection Theory

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

predicts how and when we detect the presence of a faint
stimulus (signal) amid background stimulation (noise)
assumes that there is no single absolute threshold
High expectations- false positives
Low expectations- false negatives
detection depends partly on person’s
-experience
-expectations
-motivation
-level of fatigue
Vision: Physical Properties of Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Small amplitude
(dull colors, soft sounds)
Perception of light and sound
Transduction: conversion of one
form of energy to another
Wavelength: Hue (color) and pitch
Amplitude: brightness and loudness
Purity of wavelength: saturation of
color and timbre for sound
Vision:
Spectrum of
Electromagnetic
Energy
Vision: Parts of the Eye
Cornea: transparent covering on the front of the eye
Fovea: central point of focus on the back of the eye
Pupil: adjustable opening in the center of the eye
Iris: a ring of muscle the forms the colored portion of the eye
around the pupil and controls the size of the pupil opening
Lens: transparent structure behind pupil that changes shape to
focus images on the retina
Accommodation: change in shape of lens focus near objects
Retina
 Layers of neurons on inner surface of eye
 light sensitive
 contains rods and cones
 beginning of visual information processing
Blind Spot: area of retina where optic nerve leaves back of eye
Vision: Parts of the Eye
Retina’s Reaction to Light Receptors
Cones
 near center of retina (fovea)
 fine detail and color vision
 daylight or well-lit conditions
Rods
• Located in periphery of
retina
• detect black, white and
gray
• twilight or low light
Receptors in the Human Eye
Cones
Rods
Number
6 million
120 million
Location in
retina
Center
Periphery
Sensitivity in
dim light
Low
High
Color sensitive?
Yes
No
Pathways from the Eyes to the Visual Cortex
Vision
Acuity: the sharpness of vision
Nearsightedness

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nearby objects seen more clearly
lens focuses image of distant objects in front of retina
Farsightedness


Farsighted
Vision
faraway objects seen more clearly
lens focuses near objects behind retina
Nearsighted
Vision
Normal
Vision
Color-Deficient Vision
People who suffer
red-green blindness
have trouble
perceiving the number
within the design
Visual Information Processing
Trichromatic (three color) Theory


Young and Helmholtz
The eye contains three different types of
cones capable of responding to various
wavelengths of light
 red
 green
 blue
Visual Information Processing
Opponent-Process Theory: opposing retinal
processes enable color vision
“ON”
“OFF”
red
green
green
red
blue
yellow
yellow
blue
black
white
white
black
The 2 Theories
Visual Perception:
Gestalt- the whole is
greater than the sum
of its parts
Gestalt Principles (gestalt =
an organized whole. We tend
to integrate pieces of info.
into meaningful wholes)

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Proximity
Simplicity (law of good form)
Connectedness
Closure
Continuity
Similarity
Phi Phenom
x
Depth Perception: The Visual Cliff


Binocular Cues: clues about distance using two eyes
 Retinal Disparity: the fact that the right and left eyes see slightly
different views of the object
 Convergence: the degree to which the two eyes must converge to
focus on the object
Monocular Cues: clues about distance based on the image in either eye
 Linear Perspective: parallel lines converge in the distance
 Relative Size: if two objects are the same, the larger one is seen as
closer
 Interposition: the nearer object overlaps the object farther in the
distance
 Texture Gradient: textures are coarser the closer they are
 Light and shadow
 Height in plane
Pictorial depth cues
Audition (Hearing)

Audition
 the sense of hearing

Frequency
 the number of complete wavelengths that pass a point in a given
time

Pitch
 a tone’s highness or lowness
 depends on frequency
The Stimulus
Vibrations of sound waves
 Amplitude: loudness
 Wavelength: pitch
 Purity: timbre
Audition: The Ear
Outer Ear (pinna)

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Auditory Canal
Eardrum
Middle Ear

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hammer
anvil
stirrup
Inner Ear

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oval window
cochlea
basilar membrane
hair cells (cilia)
Audition: Pitch Perception
Place Theory (high pitch)

the theory that links the pitch
we hear with the place where
the cochlea’s membrane is
stimulated
Frequency Theory (low pitch)

the theory that the rate of nerve
impulses traveling up the
auditory nerve matches the
frequency of a tone, thus
enabling us to sense its pitch
Touch
Numerous types of receptors lie in
varying depths in the skin
Four Basic Skin Senses

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Hot
Cold
Pressure
Pain
Conduction Hearing Loss
Audition:
Loss

hearing loss caused by damage to the mechanical
system that conducts sound waves to the cochlea
Nerve Hearing Loss

hearing loss caused by damage to the cochlea’s
receptor cells or to the auditory nerve
Amplitude required for
perception relative to
20-29 year-old group
Older people
tend to hear
low frequencies
well but suffer
hearing loss for
high frequencies
1
time
10
times
100
times
1000
times
32
64
128
256
512
1024 2048 4096
8192 16384
Frequency of tone in waves per second
Low
Pitch
High
Taste
Taste Sensations

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
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sweet
sour
salty
bitter
Sensory Interaction


the principle that
one sense may
influence another
as when the smell of
food influences its
taste
The Stimuli: chemical
substances that are soluble
The Anatomy: taste buds
act as the receptors for
taste (about every two
weeks)
Perception of taste & flavor

Numerous factors can
impact the flavor of food
(Ex: temperature of the
food, texture, prior condition
of the mouth, health state of
the organism, smell)
The
Tongue
Smell
Smell (Olfaction)
The Stimuli: chemical substances that are
soluble
The Anatomy: receptors are olfactory cilia
which lie on the roof of the nasal passage
and sinus
Sense DOES NOT get filtered by thalamus
Taste and smell interact to produce flavor
How We Locate Sounds
Localization of Sound


Sound is heard in the
nearest ear first
Sound is heard loudest
in the nearest ear
Perceptual Constancies:
Size,Shape,Brightness, Color
Visual Perception: Constancies
Perceptual Constancies: the ability to experience a constant
perception even when what is reflected on the retina changes

Color: an object will be perceived as the same color even if
the color reflected on the retina changes
(ex: when an object is placed in the shade)

Size: an object will be perceived as the same size even if the
size reflected on the retina changes
(ex: dog running toward you is not seen as growing in size)

Shape: an object will be perceived as the same shape even
if the shape reflected on the retina changes
(ex: door opening toward you is still perceived as rectangular)
Visual Information Processing
Feature Detectors
 neurons in the visual cortex
respond to specific features
 shape
 angle
 movement
Cell’s
responses
Stimulus
Parallel Processing
 simultaneous processing of several dimensions through
multiple pathways
 color
 motion
 form
 depth
Touch
Skin Sensations

pressure
 only skin
sensation with
identifiable
receptors
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hot
cold
pain
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
Body Position and Movement
Kinesthesis

the system for sensing the position and
movement of individual body parts
Vestibular Sense
the sense of body movement and
body’s position relative to gravity
 including the sense of balance
 Semicircular canals in ears

Parapsychology
Paranormal- beyond normal
telepathy, ESP, out of body experience…