Transcript Sensation and Perception

Sensation and Perception
AP Psychology
Sensation is referred to as being bottom-up
processing, detecting environmental stimuli
from senses up to the brain.
Sensing the World: Some Basic Principles
•An Absolute Threshold is the lowest amount of stimulus needed to notice it 50% of
the time.
•The Difference Threshold (just noticeable difference or jnd) is the lowest difference
you can detect between 2 stimuli 50% of the time.
Weber’s Law states that two stimuli must differ in percentages or ratios, not amount, for a
person to detect it (jnd).
But your detection of a stimulus also depends on your state of
arousal, expectations, experiences, and motivation.
•This is described by the Signal Detection Theory – predicting when we will notice a
weak stimulus (signal).
A stimulus is Subliminal if it is below your
absolute threshold, you detect it less than 50%
of the time. i.e., a microscopic cell is
subliminal to you because you cannot see it
with your naked eye.
Subliminal advertisements (Drink Coke, eat
popcorn etc.), does have an affect on you
but do not persuade you.
Sensory Deprivation
(Blind Person Example)
Some aspects of perception might be innate
Others involve experiences
Critical period for development of sensation and
perception is infancy
Sensory Adaptation – lowered sensitivity due to constant exposure from a stimulus.
For example, when you go into someone’s house you notice an odor…but this only
lasts for a little while because sensory adaptation allows you to focus your attention
on changing environment; it is irritating to be constantly reminded that your foot is
in contact with the floor.
Transduction refers to
Sensory energy
being converted (transformed) into
Neural energy/impulses.
Light is composed of electromagnetic waves with
Wavelengths (distance from one peak to another
peak on a wave) and Amplitudes (height of the wave)
WAVELENGTH determines HUE (Color, i.e. Red,
Blue, Green) and PITCH/FREQUENCY in sound.
AMPLITUDE
determines INTENSITY (Brightness,
i.e. Bright red, dark red) and LOUDNESS in sound
~External Light entering the eye first travels through the Cornea (protective layer)
~ Pupil (an adjustable opening) control by Iris (muscle around the pupil)
~ Lens (an oval transparency) that changes shape to focus light by a process called
Accommodation
~Light is then focused onto the back of the eye called Retina (multi-neuron surface).
The Retina has 2 types of receptor cells :
Rods (detect brightness of light, sensitive in dark),
Cones (detect color and detail, sensitive in daylight).
Cells connecting these detectors form the Optic Nerve that sends the impulses to brain.
#1
#2
(Focal point)
#4
#3
Everyone has a Blind Spot, a small region in the visual
field where nothing could be seen.
This is because there are no receptor cells where the
optic nerve leaves the eye in the retina.
Normally, we don’t witness this effect because we
have two eyes that compensate for each other’s blind
spot, and the fact that our eyes are constantly
moving.
Fovea is the region in the retina where light is
centrally focused.
The fovea has no rods, only cones.
There are 3 basic types of Acuity (how
sharp/clear vision is) : normal,
nearsightedness (only see near things clearly),
and farsightedness (only see far things clearly)
Nobel prize winners Hubel and Wiesel discovered Feature Detectors in
the brain cortex that are sensitive to specific features in what we see
(i.e. shape, color, depth, movement, form, and even postures, arm
angle, gaze).
Parallel Processing - Our brain Processes lots of
information simultaneously.
For example, looking at an orange, the brain processes the
orange color, the round shape, and the bumpy texture all at the
same time.
Color processing is described in 2 stages :
1) Young-Helmholtz trichromatic (three-color) theory – Light is detected by 3 types of cones
each specifically sensitive to Red, Blue, or Green. Combinations of them produce intermediate
colors (yellow, cyan, purple)
2) Opponent-Process theory – Color is then processed by their opponent colors (red-green,
blue-yellow, black-white). Some cells are excited by blue and inhibited by yellow, vice versa.
Thus, you cannot see a bluish-yellow.
Color constancy refers to the importance of surrounding background
effects on perceived color.
Color constancy states that colors don’t look different even in different illumination (i.e. sunlight
or dark room). Green leaves will still be green whether on a clear or cloudy day.
Sound is composed of electromagnetic waves with Wavelengths
(distance from one peak to another peak on a wave) and Amplitudes
(height of the wave)
WAVELENGTH determines HUE (Color, i.e. Red, Blue, Green) and
PITCH/FREQUENCY in sound.
Frequency (Pitch) is the number of waves travelling through a point in
one second, relates to how fast a wave travels.
AMPLITUDE determines INTENSITY (Brightness, i.e. Bright red, dark
red) and LOUDNESS in sound
Audition, or hearing, requires sounds waves
converted into neural impulses, and this is
done in the ear.
Sound travels through the 3 sections of the ear to the brain :
OUTER EAR : Auditory Canal
MIDDLE EAR: Ear drum (tight membrane) ~ Hammer, Anvil, Stirrup
(3 small bones connected to ear drum that vibrates when sound waves hit
ear drum)
INNER EAR : Cochlea (coiled, fluid-filled tube) that contains the Basilar
Membrane, which is lined with hair cells that vibrates to excite nerve fibers.
The fibers form the Auditory Canal connecting to the brain.
Place theory
says that we hear different pitches because specific “places” in
the cochlea are stimulated.
Frequency theory
says that we hear different pitches because the speed of neural
impulses traveling to the brain matches the speed of the sound
waves (“frequency”).
We can tell which direction a sound is coming from because if it is closer to our right ear, the
right ear will receive the sound slightly faster than left ear and the brain calculates this
difference.
Consequently, if the sound is directly behind or in front, where the distance between 2 ears is
the same, then it is difficult to differentiate.
Conduction Deafness – loss of hearing due to damage of eardrum, and/or
the tiny bones in middle ear. (Could be fixed by hearing aid)
Nerve Deafness – loss of hearing due to damage to cochlea, basilar membrane, and/or
hair cells in the inner ear. (Could be fixed by a bionic ear, implanting a cochlea)
Taste is a Chemical Sense composed of 4 basic senses : Sweet, Sour, Salty, and Bitter.
Taste receptors (taste buds) regenerate every 1 or 2 weeks, but age, smoking, and alcohol will
lower taste bud number and sensitivity.
Smell or Olfaction is also a Chemical Sense that directly transmits information from nose to
the temporal lobe.
**The only sense that doesn’t first relay impulses to the Thalamus! (smell)
Sensory Interaction is when one sense affects another
sense, thus interacting. For example, tasting apples and
potatoes seem the same if we cannot see it or smell it.
Touch
is composed of 4 senses : Warmth, Pain, Cold, and Pressure
Pressure is the only sense with identifiable receptors.
The other three don’t have specific receptors
Combinations of these create “feelings”:
Warmth and Cold = HOT
Pressure and Cold = WET
Pressure and Pain = TICKLING ITCH
Pain is merely a physical and
psychological interpretation.
Distraction methods, where attention
is focused elsewhere, can ease the felt
pain.
Phantom Limb Sensations occur when pain is felt in a
nonexistent limb. Even though the leg is not present, the
receptive neurons previously connected to them are still there
and will fire, resulting in pain sensations.
The Gate-Control Theory states that the spinal cord has “gates”
that open/close to transmit pain impulses.
Small fibers open Gate = pain. Large fibers close Gate = no pain.
Kinesthesis (using sensors in muscles, tendons,
and joints)
Vestibular sense (using fluids in semicircular canal,
cochlea, and vestibular sacs in inner ear)
Both sense our position, movement, and
balance.
Sidenote: I want these shoes SUPER bad 
Psychologists use REST (Restricted Environmental Stimulation
Therapy), where you are put into a warm bath with eyes closed,
or in a totally dark room, to lower stimulation and reduce stress,
or unwanted behaviors.
Much of our perception comes not just from world “out there”, but
also from behind the eyes and between the ears 
Perception
is a top-down process: the brain
interprets stimulation based on our own
state of arousal, expectations,
experiences, and motivation.
Experiences, assumptions, and
expectations give us Perceptual set:
mental set up to perceive one thing
and not another
Lochness Monster or a Tree Trunk?
Selective attention:
focusing only on one thing at a time;
focused awareness only on limited aspect
of all that is capable of experiencing; you
aren’t aware of nose in line of vision
Cocktail Party Effect: (example of selective
attention) ability to focus only on one voice
in a huge crowd
(Unnoticed stimuli has effect: women who
had listened to tunes previously played to
them while unnoticed preferred it later on)
Visual capture: phenomenon when a conflict occurs between vision and
another sense, vision dominates; vision captures other senses (overrides)
In theaters, sound comes from behind (projector), yet perceive as from screen
Perceiving voice coming from ventriloquist’s dummy
Humans organize clusters of sensation into gestalt: organized
“whole”; human tendency to order pieces of info into a
meaning picture
Gestalt is a psychology term which means "unified whole". It refers
to theories of visual perception developed by German
psychologists in the 1920s.
These theories attempt to describe how
people tend to
organize visual elements into groups or
unified wholes when certain
principles are applied.
First perceptual task: to perceive figure (object) as
distinct from ground (background)
Figure-ground: organization of visual field into the
figure(s) that stand out from the ground
(FIRST GESTALT PRINCIPLE…LETS MIND KNOW WHAT TO “GROUP”)
Next, organize figure into meaningful form (color, movement, like-dark
contrast)
To process forms, use grouping: rules mind follows to organize stimuli into
logical groups
Grouped into Proximity, Similarity, Continuity, Closure, Connectedness
Similarity occurs when objects look
similar to one another.
People often perceive them as a group or
pattern.
The example above (containing 11 distinct objects) appears as a
single unit because all of the shapes have similarity.
Unity occurs because the triangular shapes at the bottom of the
eagle symbol look similar to the shapes that form the sunburst.
This displays uniform connectedness
since all six buttons share the same
enclosing shaded box. Additionally,
within the box, this example displays
uniform connectedness between each
icon and the text with which it shares a
button.
Continuity occurs when the eye is compelled
to move through one object and continue to
another object.
Continuation occurs in the example (right)
because the viewer's eye will naturally follow a
line or curve. The smooth flowing crossbar of
the "H" leads the eye directly to the maple
leaf.
Proximity
occurs when
elements
are placed
close
together.
They tend to
be
perceived as
a group.
Closure occurs when an
object is incomplete or a
space is not completely
enclosed.
If enough of the shape is
indicated, people perceive
the whole by filling in
the missing information.
Depth perception: ability to see objects in 3D even though image sensed by
retina are 2D; allows distance judgment - partly innate (born with)
Gibson and Walker placed 6-14 months old infants on edge of a visual cliff
(table half glass, half wood), making the
appearance of a drop-off.
Mother then tries to convince infant to crawl
pass the normal part of the table onto glass;
most refused, indicating innate
perception of depth
Visual cliff: laboratory device for testing
depth perception in infants/animals
Cultural Influences on Depth Perception
•
Binocular cues: depth cues that depend on both eyes
Eyes apart, slightly different images, brain sees difference
Retinal disparity: binocular cue in which the greater the difference between
images, the closer the object
Convergence: binocular cue in which the more the eyes turns inward, the
closer the object
Monocular cues: distance cue that are available to either eye; allow relative
distance and depth to be judged
Examples: relative size, interposition, relative clarity, texture gradient, relative
height, relative motion, linear perspective, relative brightness
Retinal image size allow us to judge distance
based on our past and present experience and
familiarity with similar objects (same object
but smaller = further away)
When objects of known distance subtend
a smaller and smaller angle, it is
interpreted as being further away.
Parallel lines converge with increasing
distance such as roads, railway lines,
electric wires, etc
linear perspective
Monocular cues
relative size
relative height
Interposition cues
occur when there is
overlapping of
objects. The
overlapped object is
considered further
away.
Even at same size, linear perspective
causes one to see one object bigger
Texture:
coarse=close
fine=distant
Relative Clarity: hazy object seen as more distant
Monocular cues
Relative Height: higher objects seen as more distant
Relative Motion: closer objects seem to move faster
Relative Brightness: closer objects appear brighter
Light and Shadow: nearby objects reflect more light to our eyes.
Muller-Lyer Illusion
Brain computes motion base partly on
assumption that objects moving away is
shrinking & vise versa
Brain reads rapid series of slightly different
images as movement; phenomenon called
stroboscopic movement
Another illusion of movement is phi
phenomenon: perception of movement
when lights blink one after the other; Police
car lights
Perceptual constancy:
perception that objects are not changing
even under different lighting; allowing
identification regardless of angle of view
[a door is a door even at 45 degree (shape
constancy) angle or 20 feet away(size
constancy)]
Experiences, assumptions, and expectations give us
Perceptual set:
mental set up to perceive one thing and not another
Can’t resist finding a pattern on unpatterned stimuli
Impossible Image
Impossible Staircase
50% of Americans believe in extrasensory perception (ESP):
claim perception occurring without sensory input
Parapsychology: study of paranormal phenomena
(profession called Parapsychologists)
Is there Extrasensory Perception?
• Extrasensory Perception: claim that perception can occur
apart from sensory input.
– Astrological predictions, psychic healing,
communication with the dead
– Telepathy- mind to mind
– Clairvoyance- perceiving remote events
– Precognition- perceiving future events
– Psychokinesis- mind over matter
–Example- light as a feather stiff as a board
Three varieties of ESP:
Telepathy (sending or reading thoughts),
Clairvoyance (perceiving an event unfolding),
Precognition (seeing future)
Vague predictions can later be interpreted to match events
(Nostradamus claimed his prophecies could not be interpreted till after
the event)
After many experiments, never had a reproducible ESP phenomenon or
individual who can convincingly demonstrate psychic ability