Transcript chapter 5 notes

Chapter 5 Sensation
Reading Map
• Friday, Nov 18
193-199
• Monday, Nov 21
199-204
• Tuesday, Nov 22
Quiz chapter 4/study guide and cards due
• Wednesday, Nov 23
essay in class
• Thursday, Nov 24
204-212
• Friday, Nov 25
212-219
• Monday, Nov 28
219-229 – take home Chapter 5 quiz
• Tuesday, Nov 29
231-238 – hand in Chapter 5 quiz/study
guide/cards
Sensation - Introduction (193)
• To represent the world in our head, we must
detect physical energy from the
environment and encode it as neural signals.
This process is called sensation.
• When we select, organize and interpret our
sensations, this is called perception.
The Forest Has Eyes (193)
Bottom-Up and Top-Down
Processing (193)
• Bottom-Up sensory analysis starts at the sense
receptors and works up to the brain - ex. We start
by seeing colour and lines and eventually our
brain “sees” the faces in the forest.
• Top-Down is guided by higher-level mental
processes. We build perceptions drawing on our
experience and perceptions - ex. We know the title
of the painting and “see” the faces in the forest.
• TG p.4 - likelihood principle
Prosopagnosia (193)
• Failures of perception may occur anywhere
between sensory detection and perceptual
interpretation.
• Ex - temporal lobe area damage can lead to
prosopagnosia where you have complete sensation
but you cannot top-down process the information
to recognize faces.
• On-line prosopagnosia test
http://www.faceblind.org/facetests/index.php
Sensing the World (194)
• What stimuli cross our threshold for
conscious awareness?
• Could we unknowingly be influenced by
subliminal stimuli too weak to be
perceived?
• Why are we unaware of unchanging stimuli,
such as the watch pressing against our
wrist?
Psychophysics (194)
• The study of how physical energy relates to
our psychological experience.
• What stimuli can we detect? At what
intensity?
• How sensitive are we to changing
stimulation?
Absolute Thresholds (194)
• The minimum stimulation needed to detect
a particular stimulus 50% of the time
• Ex. Sound of a mosquito?
Signal Detection Theory (194)
• Whether we detect a signal depends on the
strength of he signal and our psychological states
of experience, motivation, expectation and
alertness
• This theory predicts when we will detect weak
signals.
• People have different thresholds in different
circumstances - ex. What do you hear outside your
tent!
• People’s detection diminishes after about 30
minutes of judging when a faint signal appears.
Subliminal Stimulation (195)
• Subliminal means below
one’s absolute threshold
for conscious awareness
• Krosnick (1992) flashed
kittens or dead body just
before pictures of people.
Subjects gave higher
ratings to people paired
with the kittens
Subliminal Stimulation (195)
• Can it prime our later
memory? Bar &
Biederman (1998) - flash a
hammer then other images
then the hammer again.
Your chances of naming
hammer are now 1 in 3
rather than 1 in 7 if
hammer was flashed once.
Subliminal Stimulation (196)
• Bornstein & Pittman
(1992) - flash the
imperceptible word
“bread” and subjects
later detect a related
word like “butter”
faster than an
unrelated word like
“bottle”
The Bottom Line
• We can process subliminal information. It
may have a subtle, fleeting effect on our
thinking but it does not have a lasting effect
• Remember chapter 1 (p. 40) - in the tape
experiment we saw the placebo effect. If I
think I get the self-esteem tape, my selfesteem goes up regardless that my
subliminal tape was on memory.
Difference Thresholds (197)
• Aka just noticeable
difference - is the
minimum difference a
person can detect
between an 2 stimuli
half of the time.
• (Do envelop test)
Weber’s Law (197)
• The difference threshold increases with the
magnitude of the stimulus - you will notice a 10
gram increase to a 100 gram weight but not to a
1000 gram weight because the difference
threshold has increased.
• BUT, Weber’s Law says that regardless of the
magnitude, 2 stimuli must differ by a constant
proportion for their difference to be perceptible
• Light must differ by 8%, weight by 2% and tone
by 0.3% for differences to be noticeable.
Sensory Adaptation (198)
• Our diminishing
sensitivity to unchanging
stimulus
• After constant exposure to
stimulus, our nerve cells
fire less frequently
• Enables us to focus on
informative changes in our
environment without
being distracted by the
constant stimulation of our
normal surroundings
Vision (199)
• Transduction converting stimulus
energy into neural
messages or impulses.
• Our eyes receive light
energy and tranduce it
into neural messages
that the brain then
processes into what
you consciously see.
Stimulus Input:
Light energy (200)
• Wavelengths visible to the
human are the short waves
of blue-violet light to
longer waves of red light
• Other organisms see other
portions of the spectrum
• What we “see” as colour
are pulses of
electromagnetic energy
Wavelength and Amplitude (200)
• Wavelength - determines hue -- short are blue and
long are red
• Amplitude - big is bright and small is dull
The Eye (201)
• Pupil - adjustable
opening in centre of
eye through which
light enters
• Iris - coloured muscle
surrounding pupil.
Responds to light
intensity. Iris scanners
detect uniqueness of
our irises.
The Eye
• Cornea - protects eye
• Lens - transparent
structure behind pupil.
Accommodation of the
lens is change to its
curvature and
thickness to focus near
or far images on the
retina
The Eye
• Retina - surface on which light
rays focus
• Contains the receptor rods and
cones
• Image is inverted on the retina.
We see right-side-up because
the retina doesn’t read the
image as a whole. Instead, its
receptor cells convert light
energy into neural impulses
(transduction) that are sent to
the brain and constructed there
into a perceived, up-right
image.
Acuity (201)
• Acuity is our
sharpness of vision.
• It can be affected by
small distortions in the
shape of the eye.
• With normal acuity,
the image is focused
by the cornea and lens
on the retina.
Nearsightedness (201)
• Nearsighted - misshapen
eyeball focuses light rays
from distant objects in
front of retina so when the
image reaches the retina
the rays are spreading out,
blurring the image
• Nearsighted people see
nearer objects more
clearly than far objects.
Farsightedness (201)
• Farsighted - light rays
from nearby objects
reach the retina before
they focus behind the
retina.
Quinn Study (1999) (200)
• A study of 479 children found that 10% of
children who slept in the dark before age 2
later became nearsighted, as did 34% of
those who slept with a night light and as did
55% of those who slept in the light
• TURN OFF THE LIGHTS!!!
20/20 Vision
You see at 20
feet what
someone with
normal vision
sees at 20 feet
The Retina (202)
• Contains receptor rods and
cones
• Light energy striking rods and
cones produces chemical
changes that generate neural
signals which activate the
bipolar cells which activate the
ganglion cells. The axons from
the ganglion cells converge like
a rope to form an optic nerve
that carries information to the
brain. Where the optic nerve
leaves the eye there are no
receptor cells - creating a blind
spot
Rods and Cones (202)
• Rods - 120 million - more
sensitive to light - detect
black, white, grey
• Cones - 6 million - more
sensitive to colour and
detail - clustered in the
fovea (the retina’s area of
central focus) - work
better in good light
Adapting to Dark (203)
• In a dark room our pupil’s dilate to let more
light to reach the rods in the retina’s
periphery. It takes about 20 minutes before
our eyes adapt. 20 minutes parallels the
average natural twilight transition between
the sun’s setting and darkness.
Visual Information Processing
(203)
• During fetal
development a piece
of brain migrates to
the retina.
• Information travels --retina --- bipolar cells
--- ganglion cells --optic nerve --thalamus --- occipital
lobe
Feature Detection (204)
• Hubel & Wiesel (1979) discovered feature
detectors in the brain. Certain neurons respond to
certain features. Perception arises from the
interaction of many neurons, each performing a
simple task. The visual cortex passes the
information to areas in the temporal and parietal
cortex.
• Hubel & Wiesel clip (1 minute)
http://www.youtube.com/watch?v=IOHayh06LJ4
Different Brain Areas (205)
• Different areas of our brain respond to
different objects and events
• Perrett identified nerve cells that specialize
in responding to a specific gaze, head angle,
posture or body movement.
The Necker Cube (205)
• As your perception of
the Necker cube shifts
every few seconds, so
does neural activity in
your visual cortex.
Although the same
image continues to
strike the retina, the
brain constructs
varying perceptions.
Parallel Processing (206)
• Our brains parallel process - does several things at
once.
• We construct our perceptions by integrating the
work of different visual areas - colour, depth,
movement, form - that work in parallel.
• The retina projects to many different visual cortex
areas. Facial recognition uses about 30% of the
cortex. Hearing only uses about 3%.
• Computers are faster but linear/humans are slower
but parallel.
Blindsight (207)
• If you loose a portion of your brain’s visual
cortex to surgery or stroke, you may
experience blindness in part of your field of
vision. However, you may still “know”
what is in your blind field spot.
• Shown a series of sticks in the blind field,
patient will report seeing nothing but they
will know that all the sticks were vertical.
Colour Vision (208)
• Our difference
threshold for colour is
so low that we can
detect 7 million colour
variations
• 1 in 50 is colour
deficient - usually this
person is male because
the defect is
genetically sex-linked
Young-Helmhotz
Trichromatic Theory (209)
• Retina contains 3 colour
receptor cones sensitive to
red, green or blue. When
we stimulate combinations
of these cones we see
other colour. Ex. When
red and green are
stimulated, we see yellow.
Paint v. Light
• Mixing paint is
subtractive --- red,
blue and yellow makes
black (no light is
reflected).
• Mixing light is
additive ---- green,
blue and red makes
white (all light is
reflected)
Colour Deficient People (209)
• Most lack functioning red
or green cones so their
vision is dichromatic
instead of trichromatic
• People with a red-green
deficiency have trouble
perceiving the number
within this design.
Ewald Hering
Afterimages (209)
• Hering explained how people blind to red
and green could still see yellow.
• He discovered opponent colours. When you
stare at the first colour and then look away,
you will see the opponent colour - or the
afterimage.
• Opponents are red/green, blue/yellow and
black/white.
Afterimages
• Opponent process theory
explains afterimages. We
tire our green response by
staring at green. When we
then stare at white (which
contains all colours,
including red) only the red
part of the green/red
pairing will fire normally.
Colour Vision Summary
• Occurs in 2 stages
• The retina’s red, green and blue cones respond in
varying degrees to different colour stimuli (YH
theory)
• Their signals are then processed by the nervous
system’s opponent-process cells, en route to the
visual cortex.
• And now ----- add colour contancy as a concept
Colour Constancy (210)
• Perceiving familiar objects
as having consistent
colour, even if changing
light alters the
wavelengths reflected by
the object.
• Our experience of colour
comes not just from the
object, but also from its
context. If we vary the
context, the colour appears
to change even though it
really doesn’t change.
Hearing (212)
Sound Wave (212)
• Compressed and
expanded air
• Brief air pressure
changes that our ear
detects and then
changes into neural
impulses which our
brain decodes as
sound (transduction)
Loudness and Pitch (212)
• Sound waves vary in
length (frequency) - a
long wave is a low
pitch and a short wave
is a high pitch.
• Sound waves also vary
in strength (amplitude)
which determines
loudness.
Decibels (212)
• Measure sound energy
• 0 decibels = absolute
threshold for hearing
• Every 10 decibels = a 1fold increase in sound
• Prolonged exposure to
sounds over 85 decibels
leads to hearing loss
The Ear (213)
•
•
•
•
•
•
Outer ear channels sound waves
through auditory canal to ear drum
Ear drum vibrates
Middle ear’s hammer, anvil and
stirrup amplify and relay vibrations
into the cochlea (inner ear) which
is filled with fluid
Fluid vibrations cause the basilar
membrane (lined with hair cells) to
ripple bending the hair cells
Hair cell movements trigger neural
impulses in the nerve fibers that
converge to form the auditory
nerve
Temporal lobe’s auditory cortex
decodes the neural impulses
Loudness (214)
• Loudness is
interpreted by the
number of hair cells
activated.
• If a hair cell loses
sensitivity to soft
sounds, it may still
respond to loud
sounds.
A Noisy Noise Annoys (214)
• Brief, extremely intense sound or
prolonged, intense sound both damage
receptor cells and auditory nerves
• A noise is harmful if you can’t talk over it
• Ringing ears is an alert to potential damage
• Unpredictable, uncontrollable, loud noise
causes more frustration and error.
Bone-Conducted Sound (TG)
• TG 5-14 - hanger
• Beethoven (who was
deaf) could hear his
piano by putting his
walking stick in his
mouth and resting it
on the piano
Pitch - Place Theory (214)
Herman Helmhotz’s Place Theory
- sound waves trigger different places along the
cochlear basilar membrane
- High pitches at the beginning and low pitches at
the end o the membrane
- This theory is good for high pitches but it doesn’t
explain low pitches because the neural impulses
they generate are not so neatly organized on the
basilar membrane
Pitch - Frequency Theory (215)
• Says that the whole basilar membrane vibrates and
sends neural impulses = to the frequency. So a
sound wave of 100 waves/second sends a
matching wave in neural impulses to the brain.
• This theory is good for low pitches BUT neurons
can’t fire faster than 1000 times per second yet
many pitches (upper 1/3 of piano) have faster
frequencies.
• SO, we need a third theory!
Pitch - Volley Theory (215)
• Neurons alternate
firing so that a group
of neurons can achieve
frequencies above
1000/second.
• This theory is best for
middle pitches
• Think of a firing squad
How do we locate sound? (215)
• Our ear placement allows us to hear
stereophonic hearing (3 dimensional)
• Sound travels at 750 miles/hour and
our ears are 6 inches apart.
• Sound waves will strike one ear
sooner and more intensely. Our
auditory system can detect a just
noticeable difference of .000027
second.
• Brain parallel processes timing and
intensity then merges the information
to pinpoint the sound’s location.
• Finger snap demo
Hearing Loss (216)
2 types of of hearing loss
1. Conduction Hearing
Loss
2. Sensorineural
Hearing Loss
Conduction Hearing Loss (216)
• Damage to the mechanical
system that conducts
sound waves to the
cochlea
• Ie. Eardrum puncture
• Damage to hammer, anvil
stirrup
• Digital hearing aids help
by amplifying vibrations
and compressing sound
Sensorineural Hearing Loss (216)
• Damage to cochlea’s
receptor (hair) cells or to
the auditory nerves (AKA
nerve deafness)
• Caused by disease, aging,
prolonged exposure to
loud noise
• Once dead, the cells stay
dead
Cochlear Implants (216)
• Electronic device that
translates sounds into
electric signals that, wired
into the cochlea’s nerves,
convey information to the
brain.
• They don’t work for
people whose young
brains never learned to
process sound
Sensorineural Hearing Loss (216)
• Forge (1993) discovered ways to chemically
stimulate hair cell regeneration in guinea
pigs and rat pup.
• Some day, we may be able to trick the
human cochlea into regenerating hair cells
• Until then, we are limited to use of the
cochlear implants.
Ethics of Hearing (217)
• The deaf say it is not a
disability and they object
to using cochlear implants
on young children who
haven’t learned to speak
• Signing is considered a
unique and valid language
• Should deaf children learn
both sign and English?
• A deaf person’s auditory
cortex is more sensitive to
touch and visual stimuli.
Touch (219)
• Sense of touch is a combination of 4 skin senses:
pressure, warmth, cold and pain
• But, there is no simple relationship between what
we feel at a given spot and the type of specialized
nerve ending found there. The relationship
between warmth, cold and pain and the receptors
that respond to them is a mystery.
• Only pressure has identifiable receptors
Warm + Cold = Hot (220)
• If you grab hoses for ice cold water and
warm water at the same time, you will
perceive the combined sensation of burning
hot
• See figure 5.24
Pain (220)
• Protects us from unchecked infections and further
injury
• Is a property not only of the senses, but also of the
brain
• - ex. Phantom pain in amputated limbs indicates
that the brain can misinterpret spontaneous
nervous system activity that occurs in the absence
of normal sensory input
• Other senses can also be “phantom”
Vision v. Pain (221)
• Unlike vision, the pain system is not located
in a simple neural cord running from a
sensing device to a definable area in the
brain
• There is no single type of stimulus that
triggers pain (like light) and no special
receptors for pain (like rods and cones)
Pain Gate-Control Theory (221)
• Theory by Melzack (psychologist) and Wall
(biologist) (1965)
• The spinal cord contains a neurological gate that
either blocks pain signals or allows them to pass
on to the brain
• The spinal cord contains small nerve fibers that
conduct most pain signals and large fibers that
conduct most other sensory signals. When tissue
is injured, he small fibers activate and open the
neural gate and you feel pain. Large fiber activity
closes the gate blocking the pain
Pain Gate-Control Theory
• So, a way to treat pain is to stimulate
(electrically, massage, acupuncture) gateclosing activity in the large fibers - ie. Icing
a bruise triggers gate-closing cold messages
• The pain gate can also be closed by the
brain if we are distracted from pain and
soothed by the release of endorphins.
Memory and Pain (222)
• We tend to remember
pain’s peak and how much
pain we felt at the end of a
procedure.
• We tend to overlook a
pain’s duration.
• So, doctors should
lengthen painful
procedures but taper their
intensity (rather than
doing it quickly but really
painfully)
Pain Control (222)
• Pain is physical and
psychological and is
treated in both ways
• Drugs, surgery,
acupuncture, electrical
stimulation, massage,
exercise, hypnosis,
relaxation therapy,
thought distraction
Pain Control (222)
• An example is the
Lamaze method of
childbirth that uses
relaxation (deep
breathing and muscle
relaxation), counterstimulation (massage)
and distraction (focus
on a photo)
Fire Walking (223)
• Is this mind over
matter?
• Or do the wood coals
poor conductors of
heat?
• I don’t think I will
insist on gather
empirical data on this
one!
Taste (224)
• Involves 4 basic
sensation of sweet,
sour, salty and bitter
• A 5th sense of taste
for “umami” has been
discovered (MSG
flavour enhancer)
Taste (224)
• Inside each bump on your
tongue are about 200 taste
buds. Each taste bud
contains a pore that
catches food chemicals.
Taste receptor cells
project antenna-like hairs
into the pore. The
receptor cells respond to
different taste stimuli.
Taste (224)
• Taste receptor cells reproduce themselves
every week or so. As you age, the number
of your buds decrease and so does your
taste sensitivity. Smoking and alcohol
speeds up the loss of taste buds.
Taste and Emotion (224)
• Emotional response to taste is inate.
• Newborns react to sweet and better as do
adults.
• There is a sensory interaction (one sense
may influence another) between taste and
smell.
Smell (225)
• Called olfaction
• Is a chemical sense like taste
• Molecules of substance carried in the air reach a
tiny cluster of 5 million receptor cells at the top of
each nasal cavity which respond selectively to
certain smells
• Smell receptors recognize odors individually odor is not separated into elemental odors like
light is.
Smell (225)
• The receptor cells send
messages to the brain’s
olfactory bulb, and then to
the temporal lobe’s
primary smell cortex and
to the parts of the limbic
system involved in
memory and emotion
Odor Molecules (225)
• Odor molecules have a unique shape and
size but we don’t have 1 distinct receptor
for each odor. Instead odors trigger a
combination of receptors.
Smell (225)
• Smell peaks in adulthood then declines
• An odor’s attractiveness is learned
• Odors can evoke memories and feelings. A
hotline runs between the brain area that gets
information from the nose and the brain’s
ancient limbic centers associated with
memory and emotion.
The 6th Sense (227)
• Our sixth sense is our awareness of our
body position and movement.
• Kinesthesis - the sense of our body’s
position and movement (of individual body
parts)
• Vestibular sense - our sense of the head
(and thus our body’s) position and
movement
Vestibular Sense (227)
• Our ear’s semicircular
canals and vestibular sacs
contain fluid that move
when our head rotates or
tilts. This stimulates the
hair-like receptors to send
signals to neurons and we
sense our body position
and maintain our balance.