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Sensation and Perception
Unit 3
Sensation and Perception
Basic concepts of Sensation
I. Sensation
1.
2.
The detection of physical energy
from the environment, it is then
encoded into neural signals

Occurs when energy in the
external environment or the
body stimulates receptors in
the sense organs
Sensory receptors- specialized
cells that detect sensory stimuli
(light, sound, odors) & convert
them into neural impulses

Found throughout body in eyes,
ears, nose, mouth & joints &
muscles
Basic concepts of Sensation
II. Thresholds
1.
Absolute threshold- the smallest amount of
a stimulus that a person can sensed
Vision
The flame from a single candle flickering about 30
miles away on a dark, clear night
Hearing
The ticking of a watch placed about twenty ft. away
from a listener in a quiet room
taste
About one teaspoon of sugar dissolved in 2 gallons
of water
smell
About one drop of perfume dispersed in a small
house
touch
The wing of a bee falling on the cheek from about
one centimeter away
Basic concepts of Sensation
2.
Difference threshold (just-noticeable difference)- minimal
difference in the magnitude of energy needed for people to
detect a difference between stimuli (comparing)
Weber’s Constant

Weber’s law- Sensation
Principle: difference
thresholds grow with Saltiness of food
the magnitude of the Pressure on skin
stimulus
Loudness of sounds
(approximate)
1/5 (20%)
1/7
1/10 (10%)
odor
1/20
Heaviness of weights
1/50 (2%)
Brightness of lights
1/60
Pitch of sounds
1/333
Absolute & Difference Threshold




Select a sense
Design an experiment to find an absolute
threshold
test the just noticeable difference for an
increase or decrease in the intensity of the
stimulus.
Create a hypothesis about the intended
results
Basic Concepts of Sensation
III.
IV.
V.
VI.
Signal-detection theory- detection
of a stimulus depends on factors
such as the intensity of the stimulus,
the level of background stimulation,
and the biological and physical
characteristics , and expectations of
the perceiver.
Sensory Adaptation-process by
which sensory receptors adapt to
constant stimuli by becoming less
sensitive to them.
Sensory Deprivation-absence of
normal levels of sensory stimulation
Sensory overload- too much stimuli

ASD
Conservative or liberal
Vision
I.
1.
Process by which light energy is converted into neural
impulses that the brain interprets to produce the
experience of sight
Light- physical energy in the form of electromagnetic
radiation
Colors are caused by different wavelengths within
the visible spectrum

red = longest Violet = shortest Roy G. Biv
Vision
II.
1.
The Eye
Cornea- transparent covering on the eye’s surface
through which light enters
Iris- regulates the size of the pupil to adjust to
changes in the level of illumination
2.
3.
Pupil- allows light to enter the eye
4.
Lens- focuses light rays on the retina

5.
Accommodation-process by which the lens changes its shape
(thickness) to focus images more clearly on the retina
Fovea- center of focus for clearer vision
Structure of the Eye
Vision
6.
Retina-Neural tissue lining the back of the eyeball’s interior containing
the receptors for vision; retina contains:

Photoreceptors- light-sensitive cells in the eye that register light
a)
Rods- Visual receptors that are sensitive to intensity of light
(dim)
b)
Cones- Visual receptors involved in color vision & fine
details; humans have 3 types: blue, green, red
7.
Optic nerve- carries neural impulses generated by light stimulation
from the eye to the brain
6.
Blind spot- contains no photoreceptor cells; Place where the optic nerve
leaves the eye
Structures of the Retina
Vision
III.
Color vision
2 major theories~
Trichromatic theory- the ability to see different colors
depends on the relative activity of three types of color
receptors in the eye (red, green, and blue-violet) all
other colors derived by a combination
Opponent-process theory-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.
1.
2.
a)
Color vision:
Afterimage- image remains after stimulus is removed;
cones become tired
o
Trichromats-people with normal color vision
o
Monochromats- no color vision
o
Dichromats- some color vision
Hearing
I.
Audition (sense of hearing):
1)
Travels in waves; exists only in mediums such as
air, liquids, gases & solids
2)
Vibration

Amplitude, Pitch
3)
Auditory Localization

Sounds from different directions are not
identical as they arrive at left and right
ears. The brain calculates a sound’s
location by using these differences.

Loudness (Intensity, amplitude
{height of wave}, measured in
decibels)

Pitch(frequency{number of cycles
per second}, hertz)
Hearing
II. The Ear: structured to capture sound waves
1.
Eardrum- vibrates in response to external stimuli & transmits
waves to middle ear
2.
Ossicles- tiny bones (hammer, anvil, & stirrup) in the middle
ear that vibrate in response to eardrum
3.
Cochlea- contains sensory receptors for hearing

Nerve (hair) cells- receptors that transform vibrations
into neural impulses that are transmitted to the brain via
the…
4.
Auditory nerve- carries neural impulses from ear to brain
Hearing
Hearing
How You Hear
When an object makes a noise, it sends vibrations (better known as sound waves)
speeding through the air. These vibrations are then funneled into your ear canal by
your outer ear. As the vibrations move into your middle ear, they hit your eardrum and
cause it to vibrate as well. This sets off a chain reaction of vibrations. Your eardrum,
which is smaller and thinner than the nail on your pinky finger, vibrates the three
smallest bones in your body: first, the hammer, then the anvil, and finally, the stirrup.
The stirrup passes the vibrations into a coiled tube in the inner ear called the cochlea.
The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia.
When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia
change the vibrations into messages that are sent to the brain via the auditory nerve.
The auditory nerve carries messages from 25,000 receptors in your ear to your brain.
Your brain then makes sense of the messages and tells you what sounds you are
hearing.
2 types of deafness:
1.
Conductive Deafness:
•
Caused by damage to
middle ear; prevent
people from hearing
sounds that aren’t loud
enough
•
Hearing aids provide
amplification
2.
Sensorineural (nerve)
deafness:
•
Can be mild, moderate or
severe
•
Damage to cells or
auditory nerve in inner
ear
•
Cochlear implants will
help
 “Ringing sensation”
is nerve damage
Deafness
Conductive Deafness
• Conductive deafness occurs because of damage to the middle ear,
which is the part that amplifies sound.
• Hearing aids can provide for the function of the middle ear by
amplifying sound.
Sensorineural Deafness
• Sensorineural deafness occurs when sounds of certain
frequencies are not heard.
• It is usually caused by damage to the inner ear.
• Loud sounds can destroy neurons in the ear.
• Cochlear implants can help people with sensorineural deafness.
Chemical Senses
I.
Olfaction (sense of smell)

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 (olfactory hairs) on the roof of the nasal cavity detect
these molecules. Intensity depends on # of receptors firing.

Passes through the olfactory nerve, olfactory bulb, to the
olfactory cortex and also structures in the Limbic System
(memory and emotion)
Chemical Senses
II. Taste
1.
Depends on odor, texture, & temperature; role in adaptation &
survival
2.
Papillae (taste receptors)
1.
taste buds- pores or openings on the tongue containing taste
cells

(receptors) inside the bud; 50 to 100 receptors/bud

Regenerate in 5-10 days
2.
Genetic factors, expectations, and context play a significant role in
taste sensitivities and preferences
3.
Five basic tastes:





Sweet
Salty
Sour
Bitter
Umami
Taste
1. Decrease with age
2. Supertasters- 2 or more
times the taste buds,
Hypersensitive, 1 in four
people
3. Medium tasters
4. Non-tasters
ALERT: receptors are
actually mixed and
located throughout the
mouth…back of throat,
roof, cheeks and tongue
Skin Senses
III. Skin Senses (largest sensory organ)
1.
The senses of pressure, temperature, and pain that involve stimulation
of sensory receptors in the skin
2.
Pressure
a)
Sensory receptors at the root of body hair
b)
Pressure sensitivity varies throughout the body

Fingertips, lips, nose, & cheeks
3.
Temperature
a)
Receptors are just beneath the skin (warm & cold)
4.
Pain
a)
Pain sensitivity varies
b)
Prostaglandins: chemical that carries pain messages; Aspirin
production
c)
Pain message sent from spinal cord to thalamus to cerebral cortex
(somatosensory cortex)
Skin Senses
Brain generates pain
1.
a.
b.
c.
Phantom Pain
Injured athlete doesn’t
feel pain
No Pain???
Gate Theory
2.
a.
Only a certain amount of
information can be
processed by the brain
at one time
Pain Disorders

Hereditary Sensory Autonomic Neuropathy



Pain and temp nerve fibers (receptors) never developed
Insensitivity to pain means that the painful stimulus is
not even perceived: a patient cannot describe the
intensity or type of pain.
Indifference to pain means that the patient can perceive
the stimulus, but lacks an appropriate response: they
will not flinch or withdraw when exposed to pain
Body Senses (Balance)
1.
2.
Kinesthesis (Greek: to move & perception)- sense that
informs people about the position of their bodies
a)
Sensory info is fed from receptor cells in joints,
tendons and muscles to the brain

Allows for navigation, movement coordination, &
feel muscle contraction; interacts with vision
Vestibular sense- movement, the sense that keeps us
informed about balance and the position of our body in
space, equilibrium, enables you to keep your balance;
cerebellum, head position
a)
Semicircular canals- in the inner ear; crystals;
sense changes in the direction & movement of the
head
 Senses speed, motion and balance
 Dizzy
b)
Vestibular sacs- fluid filled, send messages to the
cerebellum
Controversies in Perception
I.
Subliminal perception: perception of
stimuli that are presented below the threshold
of conscious awareness
Controversies in Perception
II.
A.
Parapsychology- seeks to investigate the existence and
the causes of psychic abilities
Extrasensory perception (ESP):perception that
occurs without benefit of the known senses
1.
2.
3.
4.
Telepathy- communication of
thoughts from one mind to another
that occurs without using the known
senses
Clairvoyance- ability to perceive
objects and events without using the
known senses
Precognition- ability to foretell the
future
Psychokinesis (telekinesis)-ability
to move objects by mental effort
only
Psychic test #1
Psychic test #2
Ganzfeld experiment
Perception
Perception- process by which the brain integrates, organizes,
& interprets sensory impressions to create
representations of the world
Perceptual set- tendency for perception to be influenced by
one’s expectations or preconceptions
• context effects
l3
Mary had a
a little lamb
Perception
Perception Principles
I.
Gestalt (whole) principles: the brain organizes sensory
information into meaningful units and patterns
1.
Visual field is organized into figure (shapes) and ground
(no shape) stand out from surroundings
Principles of grouping/organization:
2.
Proximity-things near are grouped
3.
Closure- brain fills in gaps
4.
Continuity- lines & patterns continue into space
Perception
Depth Perception- see objects in 3D (visual cliff)

Cues for depth: perspective, clearness, overlap, shadow,
texture
1.
Binocular cues: visual cues that require the use
of both eyes
a)
Convergence -Turning inward of the eyes,
which occurs when they focus on a nearby
object
b)
Retinal disparity - The slight difference in
lateral separation between two objects as
seen by the right and left eyes; 2 ½ in. apart
2.
Monocular cues (depth): visual cues that can be
used by one eye
a)
Relative height, motion, size; interposition, linear
perspective, light & shadow
Perception
1.
Perceptual Constancy- The
accurate perception of
objects as stable or
unchanged; context

Shape, size, color
shape constancy
color constancy
size constancy
Monocular cues
Perception
Visual Illusions
•
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, 5–10 inches in front of face.
Perception
Visual Illusions:
I.
I.
The Müller-Lyer illusion