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Sensation: Modules 12-14
General Psych 1
February 22, 2005
Class #9
Sensation and Perception
• Sensation
– The conversion of energy from the
environment into a pattern of response by
the nervous system
• Perception
– The active mental process or organizing
and interpreting our sensation
To use a computer concept…
• Input
• Information processing
• Output
Vision
• Receptors
– Our sensory organs including our eyes are
packed with these
– Stimuli activate receptors which then send
messages to our brain
The Stimulus Input: Light Energy
• Electromagnetic energy
– Scientifically speaking, what strikes are eyes is not
color but rather pulses of electromagnetic energy
that our visual system experiences as color
• Important note:
– The textbook utilizes several diagrams of the eye
which illustrates many of the eye’s components
– You will only be tested on those covered in class
discussions
The Eye
• In some ways, the eye functions like a
camera
– In both, light is admitted through a small
opening (the pupil)
• The size of the pupil and therefore the
amount of light entering the eye is regulated
by the iris
– This muscle surrounds and dilates (swells,
expands) or contracts (shrinks or lessens)
the eye
The Eye
• Accommodation
– The lens (which is located behind the
pupil) will focus incoming rays by changing
its curvature
– These rays are focused on a light sensitive
surface called the retina – a very flexible
structure
– As light passes through the eye, the lens
along with the cornea focus light on the
retina
– The cornea is a rigid, transparent structure
Feature Detection
• Cortical neurons that receive
information from the visual cortex
helping us to respond to specific
features of a scene
Parallel Processing
• This is the ability to process information
in parallel, or at the same time
– This is in direct contrast to serial
processing where each process is done one
after the other
• Think of serial processing as waiting in line at
some store that only has one register
• Parallel processing would have multiple
registers so that many people could be handled
at the same time
Common Disorders of Vision
•
Myopia
– Near-sightedness
– Here the focusing system is too strong for
the length of the eye – basically leading
to blurry images for long distance
– About 50% of 20-year-olds
– Glasses, contacts, or laser surgery
Common Disorders of Vision
•
Hyperopia
– Far-sightedness
– The light rays from near objects entering
through the cornea and lens reach the
retina before they have converged
How do we perceive color?
Geldard (1972):
– How many different shades of color are
there?
• Would you believe about 7 million?
Wavelengths and Color Sensations
• 3 separate aspects of sensation:
– Hue
• The essential color determined by the dominant
wavelength
– Saturation
• This is the purity of color
• The more pure the more intense
• Bright colors are most pure whereas pastels are
said to be desaturated
– Brightness
• This is the overall intensity of all wavelengths
Two types of photoreceptor cells
in the retina:
• Rods
– Dim light
• Cones
– Color
• Each cone contains structures sensitive to:
– Red, green, or blue
Color Vision Theories
– Young-Helmholtz Trichromatic
Theory
– Hering’s Opponent Process
Theory
Young-Helmholtz Trichromatic Theory
• This theory dates back to early 1800’s
– States that the retina has three types of color
receptors, each especially sensitive to one of the
three primary colors
– Only when combinations of these are stimulated
are other colors perceived
– Out of these three, the visual system is able to
derive all other perceptible colors
• For example, although we have no receptors
for yellow – if both red and green sensitive
cones are stimulated then yellow is perceived
Hering’s Opponent Process Theory
• This theory was formulated in late 1800’s
– This is the idea that we do not perceive color in
terms of independent colors but in terms of a
system of paired opposites – not all of which are
primary colors – red vs. green, yellow vs. blue,
white vs. black
– So if you detect one of these colors at a particular
point of the retina – you can not simultaneously
detect the opposing color at the same point
• You therefore, can not see a greenish-red, or a
whitish-black, or a yellowish-blue
Hering’s Opponent Process Theory
• Negative Afterimages
– Hering’s theory tries to explain this experience of
seeing the paired opposite after the removal of
the first
– So, if you have been looking at something red for
an extended period and this is removed you will
then see a green afterimage and vice versa
– This has to do with the visual system becoming
fatigued
• If cells in the visual system have been stimulated too
long they basically get tired and inhibited (unable to
express itself and then the paired afterimage takes over
– the opposite’s cells have been stimulated)
• See next slide for an example…
Color Blindness
• Malfunction of the retina
– Cause: Genes
– Basically, just a social inconvenience
– Big gender difference…
Color Blindness
• In color-deficient individuals one of
these three structures fails to function
properly…
– Almost all color deficient people have
either red or green deficiency
– Blue is extremely rare
Module 13: Hearing
• The Stimulus Input: Sound Waves
– Air-pressure waves composed of moving
bands of compressed and expanded
air…like the ripples of a pond
The Stimulus Input: Sound Waves
• Amplitude
– Height of the waves determines loudness
• Frequency
– Length of the waves determines the pitch
• Note:
– On page 212 there is picture of ear and its many
components. Just as with the eye diagrams you
are responsible for only the parts of the ear
discussed in class
How do we perceive pitch?
Theories:
(1) Place theory
• Presumes that we hear different pitches
because sound waves of various frequencies
trigger activity at different places along the
cochlea's basilar membrane
• Thus, the brain can determine the pitch of a
sound by recognizing the place on the
membrane from which it receives neural
signals
• Explains how we hear high-pitched
sounds but fails to explain how we hear
low-pitched sounds
Pitch Theories
(2) Frequency-Matching Theory
• The basilar membrane vibrates with the
incoming sound wave and will trigger
neural impulses to the brain
• The firing rate of a neuron in an
auditory nerve matches the frequency
of a sound wave
– Explains how we perceive low pitches but
not high pitches
Hearing Loss
• Conduction Deafness
– Problems with the mechanical system of the ear
– Results when bones connected to the eardrum fail
to transmit sound waves properly
– Hearing aids often help
• Nerve Deafness
– Damage to the inner ear (cochlea, hair cells, or the
auditory nerve)
– Main causes: hereditary, disease, biological
changes linked to aging, prolonged exposure to
ear-splitting music
Module 14: The Other Senses
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Touch
Taste
Smell
Body Position and Movement
Somatic Senses
• Touch and Temperature
– Sense of touch is actually a mix of
several distinct skin senses…
• Pressure
• Warmth
• Cold
• Pain
The House of Pain
• Pain receptors – simple, bare nerve
endings that send messages to the
spinal cord.
– A complicated mixture of sensation and
emotion (finally back to psychology!)
– No pain…no gain? Be careful…
Gate Control Theory of Pain
• Melzack and Wall (1965)
– Neurological gate
– May have to do with attention – physical
and psychological…
• “Line drive right up the middle”
Pain Control
• Wide variety of therapies – many with a
physical/psychological combo
– Drugs
• Pain Killers
– Transcutaneous Electrical Nerve Stimulation
(TENS)
– Acupuncture
– Distraction Therapies
• Lamaze method of childbirth, etc.
Drugs – Pain Killers
• Quickest and easiest form of pain
control but…
T.E.N.S.
• Replace pain impressions with massagelike sensations
– Athletes, elderly among others
Acupuncture
• Used for most common ailments – backaches,
headaches, arthritis, allegies, muscles aches and
spasms, etc.
– Shen Nung (Father of Chinese Medicine)
• Qi
– Energy running through our body
• 14 main meridians
– Needles bring us back to homeostasis
• Deqi
– Sensation is felt (not painful)
Acupuncture
• How it relates to the Gate Control
theory of Pain…
Distraction Therapies
• The “ice-water” experiments
– Worthington (1983)
• Participants put into three groups
– Group 1: Lamaze method used
– Group 2: No instructions
– McCaul and Malott (1984)
• Participants put into three groups
– Group 1: Pleasant images
– Group 2: Count backwards
– Group 3: No instructions
• What are experimental and control groups in above
experiments?
• What are DV and IV’s???
Pain of the Phantom Limb
• Approximately 80% of amputees have some
phantom limb sensations…
– Sometimes, its a tingling sensation that they feel
– Others experience pain
– Intensity, duration, and severity all are variable
from patient to patient
• Are they just some form of obsession
neurosis stemming from the trauma of losing
one's body part?
• Or is there a biological explanation for all
this?
The Chemical Senses: Taste and Smell
Taste (Gustation)
• Four basic sensations – sweet, sour,
salty, and bitter
• Special sensitivities on tongue’s surface:
– Tip of tongue: Sweet and salty tastes
– Back of tongue: Bitter tastes
– Middle sides: Sour
Taste Buds and Receptors
• At least 200 taste buds
50 taste receptor cells
• Doesn’t take much to trigger a
response…
– For example: “Can I have a taste”
• Reproduce every week
Slow decline…
• Aging factor
– Taste buds and receptors start slow decline
after the age of 30
• Other factors:
– Smoking
– Alcohol
Sensory Interaction
• Taste is influenced by smell
– Example: Bad cold
The Chemical Senses: Taste and Smell
• Smell (Olfaction)
– The “intimate” sense
• Social function especially in animals
– Pheromones
– Olfactory receptor cells that respond selectively
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Associated with memory
Starts early – nursing infants
Peaks at 30
Most animals have more
– Bloodhounds: some reports say 2 million times the
sense of smell as we do
Smell loss…
• Aging is most common cause
– Usually okay until we’re 60
• Viral infections
• Disease of nasal cavity
• Medications, smoking, radiation,
etc.
Proprioception
• Proprioception systems provide information to
the brain concerning the position of your
body an what each of its parts are doing
– Kinesthesia
• Tells you where the parts of your body are with respect to
each other
• Helps guide our movements
– Vestibular Sense
• Tells the brain about the position of your head in space
and about its general movements
• Gives us our sense of balance
• Keeps us from getting dizzy