Introduction to Psychology
Sensation & Perception
• Pr BARAKAT
• Summer Session
1
Sensation: your window to the
world
Perception: interpreting what
comes in your window.
Learning Outcomes
• Define and differentiate between sensation and
perception
• Identify the parts of the eye, describe the
properties of light and the theories of color vision
• Describe how visual perception is organized
• Identify the parts of the ear; explain the sense of
hearing
• Describe the kinesthetic and vestibular senses
• Explain why psychologists are skeptical about
extra sensory perception
What are Sensation and Perception?
• The stimulation of sensory receptors and
transmission of sensory information to the
central nervous system
• The process by which sensations are
organized and interpreted to form an inner
representation of the world
• E.g., Recognizing people from their hair,
etc., but not face
Absolute Threshold
• Weakest amount of a stimulus that can be
distinguished from no stimulus at all
– Detected 50% of the time
2. Absolute Threshold
• Weakest amount of a stimulus that can be
distinguished from no stimulus at all
– Detected 50% of the time
Difference Threshold
• Minimum difference in magnitude of two stimuli
required to tell them apart
– Detected 50% of the time
– Standard of difference
- Light – 2% of intensity
- Weight – 2% of weight
- Sound – one-third of 1% change in pitch
(frequency)
-Taste – 20% difference in saltiness
Influences on Perception
• Stimulus characteristics and psychological
factors interact to influence whether a
stimulus is detected
– Psychological factors such as learning,
motivation, and psychological states
(attention)
– Perceptual set- what we expect to
perceive
– Attention (Inattentional blindness)
– Social perception
Transduction & Adaptation
Transduction
• Sensory receptors- •
detect and respond
to
one
type
of
sensory
stimuluslight, smell, etc.
• the
sensory
receptors
convert
the
sensory
stimulation
into
neural impulses.
Adaptation
After a time, the
sensory receptors
grow accustomed
to
constant,
unchanging levels
of stimulus-sights,
smell,
etc.
Therefore,
we
notice it less &
less.
Transduction
• Transforming signals
into neural impulses
• Information
goes
from the senses to
the thalamus , then
to the various areas
in the brain
Sensory Adaptation
• Decreased
responsiveness
to
stimuli
due
to
constant stimulation.
Do you feel your underwear all day?
Cocktail-party phenomenon
• The
cocktail
party
effect
describes
the
ability to focus one's
listening attention on a
single talker among a
mixture of conversations
and background noises,
ignoring
other
conversations.
• A
form
of
selective
attention.
Energy Vs. Chemical senses
Energy Senses
Chemical Senses
Vision
• Our
most
dominating sense.
• Visual Capture
Vision & Light
• Spectrum of electromagnetic energy
– Vary in wavelength
• Human eyes can perceive only a very
thin band of electromagnetic waves,
known as the visible spectrum (400 –
700 nanometers)
• Within
visible
light,
color
is
determined by wavelength
The Visible Spectrum
Phase One: Gathering Light
• The height of a wave gives us it’s intensity
(brightness).
• The length of the wave gives us it’s hue (color).
• The longer the wave the more red.
• The shorter the wavelength the more violet.
Phase II: Getting the light in the eye
Phase III: Transduction
Transduction (Cont.)
• Order is Rods/Cones
to Bipolar to Ganglion
to Optic Nerve.
• Sends
info
to
thalamus- area called
lateral
geniculate
nucleus (LGN).
• Then sent to cerebral
cortexes.
• Where
the
optic
nerves cross is called
the optic chiasm.
Phase Four: In the Brain
• Goes to the Visual
Cortex located in the
Occipital Lobe of the
Cerebral Cortex
• Feature Detectors
We have specific cells that
see the lines, motion,
curves and other features
of this turkey. These cells
are
called
feature
detectors.
• Parallel Processing
Color Vision
Two Major Theories
Trichromatic Theory
Three types of cones:
• Red
• Blue
• Green
• These three types of
cones can make millions
of
combinations
of
colors.
• Does
not
explain
afterimages
or
color
blindness well.
Opponent-Process theory
The sensory receptors
come in pairs.
• Red/Green
• Yellow/Blue
• Black/White
• If
one
color
is
stimulated, the other
is inhibited.
Afterimages
Perceptual Dimensions of Color
• Afterimage
– Persistent sensation of color are followed by
perception of the complementary color when the first
color is removed
• Colour-Blindedness



Trichromat
–
Normal color vision
Monochromat
–
Totally color blind
Dichromat
–
Partial color blindness
–
Discriminate between two colors (red & green,
or blue & yellow)
–
More common in males (sex-linked trait)
Visual Perception
• Process
used
to
impressions caused
strikes our eyes
organize
sensory
by the light that
• Sensation is a mechanical process
• Perception is an active process
– Involves experience, expectations and
motivations
End of the First Part
SECOND PART
Perceptual Organization
1. Visual Perception
• Process used to organize sensory impressions caused
by the light that strikes our eyes
• Sensation is a mechanical process
• Perception is an active process
– Involves experience, expectations and motivations
Perceptual Organization (Cont.)
Figure – Ground Perception
Ambiguous, unstable figures, we shift back &
forth
Gestalt Rules for Perceptual
Organization
• Common Fate
– Elements moving together are grouped together
(runners)
• Closure
– Fit bits of information into familiar patterns;
– Perception of a complete figure, even when
there are gaps in sensory information
• Proximity
– Nearness of objects
• Similarity
– Similarity of objects
• Continuity (Series of points having unity)
Hearing
Our auditory
sense
We hear sound WAVES
• The height of the wave gives us the
amplitude of the sound.
• The frequency of the wave gives us the
pitch of the sound.
The Ear
Transduction in the ear
• Sound waves hit the eardrum
then anvil then stirrup then
oval window.
• Everything is just vibration.
• Then the cochlea vibrates.
• The cochlea is lined with mucus
called basilar membrane.
• In basilar membrane, there are
hair cells.
• When hair cells vibrate they
turn vibrations into neural
impulses which are called organ
of Corti.
• Message Sent then to thalamus
up auditory nerve.
It is all about the
vibrations!!!
Pitch Theories
Place Theory and
Frequency Theory
Place Theory
• Different
hairs
vibrate
in
the
cochlea when they
receive
different
pitches.
• So
some
hairs
vibrate when they
hear
high
and
other vibrate when
they
hear
low
pitches.
Frequency Theory
• All the hairs vibrate
but at different
speeds.
Deafness
Conduction Deafness
• Something
goes
wrong
with
the
sound
and
the
vibration
on the
way to the cochlea.
• You can replace the
bones or get a
hearing aid to help.
Nerve (sensorineural)
Deafness
• The hair cells in the
cochlea get damaged.
• Loud noises can cause
this type of deafness.
• NO WAY to replace the
hairs.
• Cochlea
implant
is
possible.
The Skin Senses
Touch & Pressure
• Sensory receptors in skin fire when skin
surface is touched
– Active touching
• Some areas of the body are more sensitive
– Nerve endings are more densely packed
– More sensory cortex is devoted to
perception of sensations
Touch & Pressure (Cont.)
• Receptors located in
our skin.
• Gate Control Theory of
Pain
Temperature
• Receptors are located just beneath the
skin
– Skin temperature increases – receptors
for warmth fire
– Skin temperature decreases – receptors
for cold fire
• Sensations for temperature are relative
Pain
• Receptors in skin are stimulated
– Pain is usually sharpest where nerve
endings are densely packed
– Pain can be felt deep within body
– No nerve endings for pain in the
brain
Pain (Cont.)
• Prostaglandins
– Facilitate transmission of pain message
– Heighten circulation to injured area
(inflammation)
– Pain-relieving drugs inhibit production of
prostaglandins
– Emotional response and response to
stress affect degree of pain
Example (Phantom Limb Pain)
• 2 out of 3 combat veterans with
amputated limbs report phantom limb
pain
– May involve activation of nerves in the
stump of missing limb
– May also involve reorganization
motor and somatosensory cortex
of
Gate Theory of Pain
• Nervous system can only process a limited
amount of stimulation
– Rubbing the pained area competes
for neural attention
– Closes the “gate” on pain messages to the
brain
Acupuncture
• Ancient Chinese method of pain control
– Research shows it stimulates nerves to
the hypothalamus releasing endorphins
– Endorphins are similar in structure and
effect to morphine
Taste
• We have bumps on
our tongue called
papillae.
• Taste
buds
are
located
on
the
papillae (they are
actually all over
the mouth).
• Sweet, salty, sour
and bitter.
Vestibular Sense
• Tells us where our
body is oriented in
space.
• Our
sense
of
balance.
• Located
in
our
semicircular
canals in our ears.
Kinesthetic Sense
• Tells us where our
body parts are.
• Sense that informs
you about the position
and motion of your
body
– Sensory information
is sent to the brain
from
sensory
organs in joints,
tendons
and
muscles
Without
the
kinesthetic
sense you could touch the
button to make copies of
your buttocks.
Extrasensory Perception - ESP
• Perception through
sensory organs
– Pre-cognition
– Psycho-kinesis
– Telepathy
– Clairvoyance
means
other
than
Thank you