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Chapter 4
Sensation & Perception
Sensation
• The process by which
stimulation of a sensory
receptor produces
neural impulses that the
brain interprets as
sound, a visual image,
an odor, a taste, a pain,
or other sensory
images.
• The registration of
information.
Perception
• A process that makes sensory patterns
meaningful.
How Do We Interpret Sensations?
• STIMULUS - energy
that affects what we
do.
• RECEPTORS –
specialized cells that
convert environmental
energies into signals
for the nervous
system.
How Does Stimulation
Become Sensation?
The brain senses the world
indirectly because the sense
organs convert stimulation
into the language of the
nervous system: neural
impulses.
Transduction
Transformation of
one form of energy
into another –
especially the
transformation of
stimulus
information into
nerve impulses.
Sensory pathways –
Bundles of neurons that carry
information from the sense organs
to the brain.
Sensory Adaptation
• Loss of
responsiveness in
receptor cells after
stimulation has
remained
unchanged for a
while.
Thresholds
• Absolute threshold –
Amount of stimulation necessary
for a stimulus to be detected.
• Difference threshold –
Smallest amount by which a stimulus can
be changed and the difference be
detected (also called just noticeable
difference – JND).
Approximate absolute thresholds for the
5 senses:
• Vision - Candle flame seen at 30
miles on a clear, dark night.
• Hearing - Tick of a watch under
quiet conditions at 20 feet.
• Taste - 1 Teaspoon of sugar in 2 gallons of
water.
• Smell - 1 Drop of perfume diffused into a threeroom apartment.
• Touch - A bee's wing falling on your cheek from
1 centimeter above.
Thresholds
• Weber’s law
– The JND is
always large
when the stimulus
intensity is high,
and small when
the stimulus
intensity is low.
Signal Detection Theory
• Signal detection theory –
Perceptual judgment as a combination of
sensation and decision-making processes.
Stimulus event
Neural activity
Comparison with
personal standard
Action (or no action)
Subliminal Persuasion
• Studies have found that
subliminal words
flashed briefly on a
screen can “prime” a
person’s later
responses.
• No controlled research
has ever shown that
subliminal messages
delivered to a mass
audience can influence
people’s buying habits.
THE EYE
Video
The Structure of the EYE
• PUPIL – an
adjustable opening in
the eye through which
light enters.
• IRIS – the colored
structure on the
surface of the eye.
The Structure of the EYE
• CORNEA – a rigid
transparent
structure on the
outer surface of
the eyeball.
• LENS – a flexible
structure that can
vary in thickness,
enabling the eye to
accommodate.
The Structure of the EYE
• RETINA – a layer of
visual receptors
covering the back
surface of the eyeball.
Visual Sensation
Retina:
Photoreceptors – Light-sensitive cells in the
retina that convert light energy to neural
impulses.
Rods – Sensitive to dim
light but not colors.
Cones – Sensitive to
colors but not dim light.
Fovea –
Area of sharpest
vision in the retina.
Visual Receptors
• Cones
– color vision
– daytime
– detailed
• 5-10% of visual
receptors in the
retina are cones
• 7 million
Visual Receptors
• Rods
– night vision
– black and white
• 125 million
Interactive
The Visual Pathway
Optic nerve –
Bundle of
neurons that
carries visual
information from
the retina to the
brain.
The Visual Pathway
• Blind spot –
The point where the
optic nerve exits the
eye and where there
are no photoreceptors.
DO IT YOURSELF!
page 122
Review from Chapter 3!!!
In which area of the
brain are visual
signals
processed???
Answer:
• VISUAL CORTEX
Part of the brain in the occipital
lobe where visual sensations are
processed.
Neural Pathways in the Human Visual System
How the Visual System Creates Color
• Electromagnetic
spectrum –
Entire range of
electromagnetic energy,
including radio waves,
X-rays, and visible light.
• Visible spectrum –
Tiny part of the
electromagnetic
spectrum to which our
eyes are sensitive.
How the Visual System
Creates Brightness
Wavelength
Intensity
(amplitude)
Color
Brightness
Trichromatic Theory
• The idea that colors are sensed by 3
different types of cones; explains the
earliest stage of color sensation.
• Blue
• Green
• Red
Opponent-Process Theory
• We perceive color not in terms of
independent colors but in terms of a
system of paired opposites.
• Red vs. Green
• Yellow vs. Blue
• White vs. Black
Afterimages
• Sensations that linger after the stimulus is
removed.
• Most often called negative afterimages
• Try the activity on page 121
Color Blindness
• Vision disorder that prevents an individual
from discriminating certain colors.
Red-Green Colorblindness
• Difficulty distinguishing red from green and
either red or green from yellow.
The Camera
• When you look at an object, light
rays are reflected from the object
and enter the eye through the
pupil.
• The light rays are bent, refracted
and focused by the lens. The
lens' job is to make sure the rays
come to a sharp focus on the
retina. The resulting image on
the retina is upside-down.
• Here at the retina, the light rays
are converted to electrical
impulses which are then
transmitted through the optic
nerve, to the brain, where the
image is translated and perceived
in an upright position!
Hearing
Hearing
• The Physics of Sound
Amplitude –
Physical strength of a wave.
High Amplitude
Low Amplitude
Hearing
• The Physics of Sound
Frequency –
Number of cycles completed by a wave in a
given amount of time, usually a second.
Low Frequency
High Frequency
Hearing
• Hertz (Hz) –
unit of
frequency
representing
one cycle
(vibration) per
second.
How Sound Waves Become Auditory
Sensations
Tympanic membrane –
The eardrum
How Sound Waves Become Auditory
Sensations
Cochlea –
Where sound
waves are
transduced
How Sound Waves Become Auditory
Sensations
Cochlea
Basilar membrane –
Thin strip of tissue
sensitive to
vibrations
How Sound Waves Become Auditory
Sensations
Auditory nerve –
Neural pathway
connecting the ear
and the brain
Review from Chapter 3!!!
In which area of the
brain are auditory
signals
processed???
Answer:
• Auditory cortex –
Portion of the temporal lobe that
processes sounds.
ANSWERS
•
•
•
•
•
•
(a) outer ear (pinna)
(b) ear canal
(c) eardrum
(d) hammer, anvil, and stirrup
(e) cochlea
(f) auditory nerve
The Psychology of…
• Pitch –
Sensory characteristic of sound produced
by the frequency of the sound wave.
• Loudness –
Sensory characteristic of sound produced
by the amplitude (intensity) of the sound
wave.
Video Clip
• Timbre –
Quality of a sound wave that derives from
the wave’s complexity.
Hearing Loss
• Conduction
Deafness –
An inability to
hear resulting
from damage to
structures of the
middle or inner
ear.
Hearing Loss
• Nerve
Deafness –
An inability to
hear that is
linked to a deficit
in the body’s
ability to transmit
impulses from
the cochlea to
the brain,
usually involving
the auditory
nerve.
The Senses:
Smell,
Taste, &
Touch
Position and Movement
• Vestibular sense –
Sense of body orientation with respect to
gravity.
– Tells us how our bodies
are positioned.
– Movement and motion.
3 semicircular canals
Position and Movement
• Kinesthetic sense –
Sense of body position and movement of
body parts relative to each other.
– Makes you aware when you are crossing your
legs.
– Provides constant sensory
feedback.
Olfaction
• Sense of smell.
• Smell can influence
mood, memory,
emotions, mate
choice, and the
endocrine system
(hormones).
Olfaction
• Olfactory bulbs –
Brain sites of
olfactory
processing.
Olfaction
Taste
• Gustation – The sense of taste.
Taste buds –
Receptors for taste
(primarily on the
upper side of the
tongue)
Taste Receptors
•
•
•
•
Sweet
Salty
Sour
Bitter
– Umami
• Savory
sensation
TASTE & SMELL
• Our sense of smell is
responsible for about
80% of what we taste.
• All other flavors that we
experience come from
smell. This is why,
when we have a cold,
most foods seem bland
or tasteless.
• Our sense of smell
becomes stronger
when we are hungry.
The Skin Senses
•
•
•
•
•
Touch
Warmth
Cold
Texture
Pain
Review from Chapter 3!!!
Sensory information
related to the skin senses
is processed within
which part of the
brain???
Answer:
• SOMATOSENSORY CORTEX
Pain
Gate-control theory
• An explanation for
pain control that
proposes we have a
neural “gate” that
can, under
circumstances,
block incoming pain
signals.
Pain
• Placebos –
Substances that appear to be drugs but
are not.
• Placebo effect –
A response to a placebo caused by
subjects’ belief that they are taking real
drugs.
What is the Relationship
Between Perception
and Sensation?
Perception brings meaning
to sensation, so perception
produces an interpretation
of the external world, not a
perfect representation of it.
Perception and Sensation?
• Percept –
Meaningful
product of a
perception.
• What we
perceive.
The Machinery of
Perceptual Processing
• Feature detectors –
Cells in the cortex
that specialize in
extracting certain
features of a
stimulus.
The Machinery of
Perceptual Processing
• Binding problem –
A major unsolved
mystery in cognitive
psychology,
concerning the
physical processes
used by the brain to
combine many aspects
of sensation to a single
percept.
Bottom-Up and
Top-Down Processing
• Bottom-up processing –
Analysis that emphasizes characteristics of
the stimulus, rather than internal
concepts (stimulus-driven processing).
• Top-down processing –
Emphasizes perceiver's expectations,
memories, and other cognitive factors
(conceptually-driven processing).
Perceptual Constancy
• Ability to recognize the same object under
different conditions, such as changes in
illumination, distance, or location.
Size
Color
Shape
ILLUSIONS
• An incorrect experience of a stimulus
pattern, shared by others in the same
perceptual environment.
Muller-Lyer Illusion
Ponzo Illusion
Muller-Lyer Illusion
Ambiguous Figures
• Images that are
capable of more
than one
interpretation.
Gestalt Psychology
The whole is greater than the sum of its parts.
The Gestalt Approach
• Gestalt psychology –
An approach to psychology that seeks to
explain how we perceive overall patterns.
• Figure –
Part of a pattern that commands
attention.
• Ground –
Part of a pattern that does not
command attention; the
background.
The Gestalt Approach
• Closure –
Tendency to fill in gaps in figures
and see incomplete figures as complete.
The Gestalt Laws of Perceptual
Grouping
Similarity
Proximity
Continuity
Common fate
Prägnanz
The Gestalt Approach
• Similarity – we tend to group similar
objects together in our perceptions.
The Gestalt Approach
• Proximity – we tend to group objects
together when they are near each other.
The Gestalt Approach
• Continuity – we prefer perceptions of
connected and continuous figures to
disconnected and disjointed ones.
The Gestalt Approach
• Common Fate – we tend to group similar
objects together that share a common
motion or destination.
The Gestalt Approach
• Law of Prägnanz
– The simplest
organization,
requiring the least
amount of cognitive
effort, will emerge
as the figure.
A
BIRD
IN THE
THE HAND
Depth Perception
• Visual Cliff Experiment
• Develops
around
6 months
of age
Depth Perception
• Binocular cues – information taken in by
both eyes that aids in depth perception,
including convergence and retinal
disparity.
Depth Perception
• Monocular Cues – information about depth
that relies on just one eye; includes relative size,
light and shadow, interposition, relative
motion, and atmospheric perspective.
Theoretical Explanations for
Perception
• Learning-based inference –
View that perception is primarily shaped
by learning, rather than innate factors.
• Perceptual set –
Readiness to detect a particular stimulus
in a given context.
End of Chapter 4