Transcript Sensation and Perception

Sensation and Perception
S and P
Introductory Concepts
24-7 stimuli from the outside world bombard
us. How do we construct our
representations of the outside world?
• Sensation: the
activation of our
senses
– In the body – the eye,
the ear, the nose, etc.
– collects external
information
– Data entry
• Perception: the
process of
interpreting the
sensory info and
understanding it
– In the brain
S and P
• In our everyday experience, S and P blend
into a continuous process. It’s a fine line
where one stops and the other begins
• Transduction: the point where S stops
and P begins. The point at which a part of
the body fires the info to the brain
– Optic nerve – vision
– Auditory nerve – hearing
– Olfactory bulb - smell
Bottom Up Processing
• Sensory analysis starts at entry level –
bottom up from the senses to the brain.
• We do not use our past experiences to
make a judgment. Instead we wait until
we have all of the info to build a complete
and accurate perception.
• Bottom up is slower but more accurate
Top Down Processing
• Sensory analysis based on our past experience
and expectations
• We use our Schema (expectations of how we
anticipate the world to be) to fill in the gaps and
make a judgment before we have all the
required info. Our schema predispose us to
experience the world in a particular way
• Top down is faster, but more prone to error
– Ex: I ope yo et a 5 on t AP e am.
– Ex: seeing images in a cloud
Top Down Processing
• I cnduo't bvleiee taht I culod aulaclty uesdtannrd waht I
was rdnaieg. Unisg the icndeblire pweor of the hmuan
mnid, aocdcrnig to rseecrah at Cmabrigde Uinervtisy, it
dseno't mttaer in waht oderr the lterets in a wrod are, the
olny irpoamtnt tihng is taht the frsit and lsat ltteer be in
the rhgit pclae. The rset can be a taotl mses and you can
sitll raed it whoutit a pboerlm. Tihs is bucseae the huamn
mnid deos not raed ervey ltteer by istlef, but the wrod as
a wlohe. Aaznmig, huh? Yaeh and I awlyas tghhuot
slelinpg was ipmorantt! See if yuor fdreins can raed tihs
too.
Thresholds – what stimuli do we detect? At
what intensity? Do we notice change in a
stimuli?
• Absolute threshold:
the smallest amount
of a stimuli we notice
50% of the time
• Subliminal
messages: below the
50% AT.
Absolute Threshold
Signal Detection Theory
• Our ability to detect a signal depends not
only on the strength of the signal but also
on our personal response criteria – our
experiences, expectations, motivation,
alertness, etc.
– Will the doctor see the tumor on the CAT
scan?
– Will the parent hear the baby crying?
– Will the QB see the open receiver in the end
zone?
Perceptual Mistakes
False Positive: We think we
perceive a stimulus that isn’t there
Ex: the doctor tells the patient that
have cancer, but they don’t
Ex: the parent runs to get the crying
baby but the baby is asleep
False Negative: we miss a
stimulus that is present
Ex: the doctor gives the patient a
clean bill of health but they have a
small tumor
Ex: the baby is crying and the
parent doesn’t hear it
Difference Thresholds – how much does a
stimulus need to change for us to notice?
• Just Noticeable Difference (JND) – once
we are aware of a stimulus it’s the
smallest change needed for us to notice
• Weber’s Law: JND is proportional to the
size of the original stimulus. The louder,
brighter, bigger the initial stimulus the
greater the JND
Sensory Adaptation
• Diminished sensitivity to an unchanging
stimulus
– I walk into the house and smell fresh baked
cookies, but after a few minutes don’t notice
the smell
– I get into a cold pool but after a bit I adjust
and the water no longer feels cold
Selective Attention
• https://www.youtube.com/wat
ch?v=Ahg6qcgoay4
• How many times does the
white team pass the ball?
• Inattentional Blindness –
failing to see visible objects
when our attention is
directed elsewhere
• Take away – be aware of
cyclists, pedestrians, and
don’t text and drive
• Your 5 senses take in
11,000,000 bits of info per
second. You consciously
process about 40 bits. We
choose what to attend to
• Ex - Cocktail party effect:
Your ability to attend to only
one voice among many –
focused listening – you hear
your name among the
backdrop of lots of
conversations
Ex – R/L hearing
Prosopagnosia – face blindness –
Sensation without Perception
• Can be caused by brain damage to
fusiform gyrus in temporal lobe (Right
brain)
• 6o Minutes Clip – Face blindness –
https://www.youtube.com/watch?v=dxqsBk7
Wn-Y
VISION
• Vision, hearing and touch=
energy senses
–We gather energy from light,
sound waves and pressure
• Taste and smell =
chemical senses
Vision = our most dominant sense
• Step 1: gather light
– Light is reflected off objects and gathered by
the eye.
– Visible light = small sections of the
electromagnetic spectrum
The Color we see depends on . . .
1. Light intensity
–How much energy the light contains
determines the brightness
–Energy is determined by the wave’s
amplitude/height
–The higher the amplitude, the
brighter the color; the lower, the
duller
The Color we see also depends on
2. Light wavelength
–Determines hue (color)
–Wavelength = peak to peak
–Wavelengths longer than visible light
–High frequency (short wave length) =
purples and blues
–Low frequency (long wave length) =
oranges/reds
Properties of a wave –
amplitude and frequency
Visual Spectrum
Step 2: Within the eye
1. Reflected light enters through the cornea
2. Light passes to the pupil. Muscles that control
the pupil (iris) open it (dilate) to let more light
in and make it smaller to let less light in
3. Light that enters the pupil is focused by the
lens
4. As light passes through the lens, the image is
flipped upside down and inverted and projected
onto the retina. The retina is like a screen at
the back of the eye.
Within the Retina – a series of nerves fires to
ultimately send the image to the brain – layer 1 =
rods and cones
CONES
• 6 million
RODS
• 120 million
• Center of retina – our
central vision
• Peripheral vision
• Sees color
• Black and white – no
color
• Detailed vision in daytime
• Good vision at night
• Not sensitive in dim light
• Very sensitive in dim light
Within the retina….
• 2nd layer of cells = bipolar cells
• 3rd layer of cells – ganglion cells
– Axon of the Ganglion cell is the optic nerve.
The optic nerve sends the info to the
thalamus to the occipital lobe for perception to
take place in the brain. The occipital lobe
processes the image – left occipital
processing images from the right visual field.
– The point at which the optic nerve leaves the
eye causes a blind spot.
Blind Spot
Theories of Color Vision
• There are competing theories
of how and why we see color
Trichromatic
• Oldest and most simple theory
• Says we have 3 types of cones in
the retina that detect blue, red and
green
• These cones are activated in
different combinations to produce all
the colors of the visual spectrum
Problems with Trichromatic
• Can’t explain afterimages
–green/red; blue/yellow, black/white
• Or colorblindness
–Can’t distinguish between
red/green or blue/yellow and can
only see shades of gray
Color Blind Test – CB people
typically don’t see shades of red
and green
Afterimage
Opponent Process Theory
• The sensory receptors arranged
in the retina come in pairs
–Red/green; blue/yellow; black/white
• If one sensor is stimulated, the
pair is inhibited from firing
Opponent Process Theory explanations
• Afterimages: if you stare at red long
enough then you tire the sensors,
therefore when you look at a blank
page, the opponent to red, green, will
fire and you will see a flash of green
• Colorblindness: pairs explain why you
can’t see both hues – the red/green
pair is dysfunctional
HEARING
Hearing also uses energy in the
form of waves; sound waves;
vibrations in the air are collected
by the ear. Vibrations go
through the process of
transduction where they are
converted into neural messages
and sent to the brain.
Sound Waves
• 1.) Amplitude – height
of wave, determines
loudness of sound
– Measured in decibels
– The higher the
amplitude the taller the
wave the louder the
sound
– Prolonged exposure to
85 decibels or higher
causes damage and
hearing loss
Sound Waves cont . . .
2. Frequency = length of wave
Determines pitch (measured in
megahertz)
Higher pitched sounds have higher
frequencies, waves are densely
packed together and speed by
quickly
Process of Hearing
Sound waves are collected in the outer
ear.
Then travel down the ear canal
(auditory canal) until they reach the ear
drum (the thin membrane that vibrates
as sound waves hit it.)
The eardrum is attached to first in a
series of three small bones – the
hammer, anvil, and stirrup
Process of Hearing
The vibration of the eardrum is
transmitted by these three bones to the
oval window (a membrane similar to the
eardrum)
The oval membrane is attached to the
cochlea (a structure shaped like a
snail’s shell and filled with fluid.)
The floor of the cochlea is lined with hair
cells which are connected to neurons
Process of Hearing cont . . .
When the fluid moves, the hair cells move and
transduction occurs- the neurons fire and these
impulses are carried to the brain by the auditory
nerve (to the temporal lobes of the brain)
Hair cells are extremely sensitive and quick .
. . damage to hair cells account for most
hearing loss. Once they are damaged, they
do not regenerate. Prolonged exposure to
loud sounds (85 decibels +) damages hair
cells (ringing in your ears)
Pitch Theories
Place Theory: the hair cells in the
cochlea respond to different
frequencies of sound based on where
they are located in the cochlea (like a
choir). Some bend in response to
high pitches and some to low. We
sense pitch because the hair cells
more in different places. (Accurately
describes how hair cells sense higher
pitch, not lower ones.
Pitch Theories cont . . .
Frequency Theory: Lower
tones are sensed by the rate at
which the cells fire. We sense
pitch because the hair cells fire
at different rates (frequencies)
in the cochlea (explains low
pitch).
Deafness
Conduction deafness: when
something goes wrong with the
system of conducting the sound
to the cochlea (in the ear canal,
eardrum, hammer/anvil/stirrup,
or oval window)
Deafness cont. . .
Sensorineural (Nerve) Deafness: occurs when
the hair cells are damaged (usually by loud
noises). “Ringing in your ears” often sign of
damaged hair cells. Once cells are destroyed,
they remain dead. More common type of
deafness – occurs gradually over time
OTHER SENSES
Touch
• When skin is indented, pierced, or experiencing change in
temperature, the sense of touch is activated.
• 4 sensations – pressure, temperature, texture, pain
• 1. some nerve endings respond to pressure, others to
temperature.
• 2. Brain interprets intensity and placement
• 3. Nerve endings more concentrated in some body parts
(fingertips = higher nerve concentration & more sensitive;
elbow = fewer concentration and less sensitive) – lips,
fingertips are most sensitive; torso is least sensitive
• 4. If touch and temperature receptors are stimulated sharply,
a different nerve ending, pain receptors, fire.
Touch cont. . .
• Gate Control Theory: explains how we
experience pain. Some pain messages
have high priority. The higher the
priority, the more the gate swings open,
the more we feel pain – like a
continuum
– Temps below 41 degrees and above 113
degrees cause us to feel pain
Taste
• Chemical Sense.
Chemicals from the
foods we eat are
absorbed by taste
buds.
• 1. Taste buds located
on papillae- visible
bumps you see on
tongue
• 2. Humans sense 4
types: sweet, salty,
bitter and sour
Taste cont. . .
• 3. People differ in ability to taste: more
densely packed buds = more chemical
absorbed = more intense taste – super
tasters
• 4. Flavor of food is actually a combo of
taste and smell (ex: close eyes, hold nose
and taste ability deceases . . . apple and
raw potato . . . explains why it isn’t as
enjoyable to eat when you have a cold and
you’re stopped up.
Smell
• Also a chemical sense
• 1. Molecules of substances rise in
the air, are drawn to your nose &
settle in a mucous membrane at the
top of each nostril and are absorbed
by receptor cells located there.
Receptor cells are linked to the
olfactory bulb which sends info to
the brain
Smell cont . . .
• 2. Nerve fibers from olfactory bulb connect
to the brain at the amygdale and
hippocampus, the limbic system
(responsible for emotional impulses and
memory)
• Smell doesn’t go through the thalamus like
all the other senses. This may explain why
smell triggers strong memories and
feelings
Smell cont . . .
• 3. Animals have many more olfactory
receptors (dogs, sharks, etc.)
• They can smell prey long before they
can see it.
• 4. Women typically have a stronger
sense of smell (connected to estrogen)
Body Position Senses
• 1. Vestibular Sense: tells
about overall body
orientation in space
• Three semicircular canals in
the inner ear give brain
feedback about body
orientation.
• Canals = tubes partially
filled with fluid: when head
moves, fluid moves, hair
cells move, activate neurons
which fire to the brain
Body Positions Senses cont
...
• 2. Kinesthetic Sense:
feedback about position
of specific body parts .
– hand –eye or foot-eye
coordination
• Receptors in muscles
and joints send info to
the brain about limbs.
PERCEPTION
Figure Ground Relationship
• Our brain designates
what the main figure
is and what the
background is. We
may perceive different
images from each
other based on this
designation
Gestalt Rules of Perception
• Gestalt psychologists study rules of perception. We
perceive images as groups – we see the whole picture,
not individual details
– 1.) Proximity – objects close together perceived
holistically
– 2.) Similarity – objects similar in appearance
perceived together
– 3.) Continuity – objects that form a continuous trail
are perceived together
– 4.) Closure – we mentally close in boundaries to
perceive a recognizable image
Proximity
Closure
Similarity
Continuity
Monocular Depth Cues
Monocular Cues require
one eye; tricks an artist
uses to make a 2-D
surface appear 3-d
1.) Linear Perspective
Monocular Depth Cues
2.) Relative Size
3.) interposition
Monocular Depth Cues
4.) texture gradient
5.) shadowing
What cues to you see….
Binocular Depth Cues
• Require both eyes – our ability to perceive
depth in the real world
– 1.) Binocular/retinal disparity: each eye sees
an object from a slightly different angle. Brain
gets the L and R image. The further away an
object is, the less disparity between the L and
R image. Closer images have greater
disparity
– 2.) Convergence: as objects get closer to our
face, the eyes converge to stay focused
CULTURE
• Culture also affects our perceptions