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Sensation and Perception
Principals of Behavior
Chapter Three
Sensation
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Sensation is the process by which we
detect and process stimuli in the
environment.
Sensation is the process by which we detect
physical energy such as light, sound and heat
from the environment by specialized sensory
receptors and encoding it as neural signals.
Transduction
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The process of transforming physical energy
into neural signals via sensory signals.
Sensory receptors cells in one the sense
organs ( eye) receive stimulus such as light.
If the amount of stimuli, via the light is
strong enough the receptor cell (neuron)
fires sending a neural signal (action
potential) to the appropriate area of the
brain  occipital lobe.
Psychophysics
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The field that studies links between the
physical properties of stimuli and a person’s
experience of them.
Thresholds-as we are constantly bombarded with
energy,( x-rays, radio waves, ultraviolet and
infrared light) Our senses allow only a restricted
awareness of this energy as in what stimuli we can
detect.
This “restricted awareness” are called thresholds,
and they are different for each sensory system.
Sensory Thresholds
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Absolute threshold
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Difference threshold
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Just noticeable Difference
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Subliminal Perception
The Visual System
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Properties of Light
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Energy is the form of light wave
Brightness-amplitude of the wave
Saturation-purity of the wave (presence of
more than one wave is less pure or saturated)
Color-length of the wave.
The Structure of the Eye
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Cornea-transparent protector through which light enters the eye.
Curved surface bends the light to focus at the back of th eye
Pupil-a small adjustable opening that regulates the amount of light
that enters the eye through a colored muscle called the iris.
Lens-transparent structure behind the pupil that also focuses The
cornea does most of the bending, while the lens fine tunes the focus in
process called accommodation.
 accommodation –affects acuity which is the sharpness of our
vision, which can be affected by small distortions in the shape
of the eye.
 The shape of the eye influences the focus of the image on the
retina.
Accommodation
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Farsightedness- lens is longer and
flatter than normal and therefore
unable to bring close objects into focus.
Focusing the image behind the retina
Nearsightedness-- eyeball is shorter
than normal, causing focus to later
than normal and therefore objects up
close appear blurred. Focusing the
image in front of the retina.
Parts of the Eye
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Retina-the light sensitive outer surface of the eye,
containing the receptors that begin visual processing
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receptor cells- located at the back of the
retina and converts light into a neural signal
Two types of receptor cells, rods and cones.
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rods- located around the outside of the retina,
responsible for black, white & gray vision, vision
in dim light, and peripheral vision.
cones-located near the fovea, which was the
central focal point in the retina, which is
responsible for color, fine detail and vision in day
light.
Photoreceptors
Receptor Cells (Rods & Cones)
Bipolar Cells
Ganglion Cells
Optic Nerve ( axons of Bipolar cells)
How the Eye Works
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Blind spot-is the point at which the optic
nerve leaves the eye and is called the blind
spot because there are no receptors there.
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Optic nerve-the bundle of axons that
carries neural messages from each
eye to the brain.
Optic chiasm-point near the base of
the brain where some, not all of the
optic nerve fibers split and cross to
the other side of the brain.
Hemispheric projection:Visual fields
Theories of Color Perception
Trichromatic Theory
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Proposed three types of cones: red, blue, green
Different shades of color correspond to different
amounts of light received by each of these three
types of cones.
Cones fire message to the occipital lobe
Combination of which cones are firing as well as
the rate of firing that determines the color
perceived.
Problem: After image
Stare at the cross in center of the
flag for 30 seconds, now stare at
white wall or piece of paper
Theories of Color Perception:
Opponent Process
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Four primary colors: red, green, blue, yellow
Cones are arranged in pairs, red with green, blue
with yellow
If one memory of the pair is stimulated, i.e. red,
the other member of the pair is turned off, i.e.
green.
Afterimage-if a person stares at a red object too
long, it weakens that members ability to inhibit the
other cell. So, if staring at a red image for too long,
one might begin to see green as an after-image.
Auditory Conduction
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Stimulus is sound waves which consist of
compressed and expanded air.
Sound wave-change in pressure caused when
molecules of air collide with one another and
then move apart again.
Properties of the sound waves:
Amplitude = loudness (height of the wave)
Frequency = pitch (length of the wave)
longer-lower, shorter- higher. (Hz)
Structure of the Ear
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Outer ear
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Middle Ear
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Pinna (Ear Flap) channels sound waves through
the auditory canal to the eardrum, which is a
tight membrane that vibrates with the waves.
consists of three tiny bones ( ossicles),the
hammer, anvil and stirrup which hit each each
other in a sequence that carries the vibrations
to the inner ear.
Inner Ear
Inner Ear
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Oval Window: Vibrations from the stirrup
on the oval window set up another chain
reaction within the inner ear.
Cochlea: is a fluid filled a snail like
structure to which the oval window is
attached. Vibrations of the oval window
cause the fluid of the cochlea to begin to
vibrate.
Basilar membrane-membrane running
through the middle of the cochlea.
Sound Conduction
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Organ of Corti-rests on top of the basilar
membrane.
contains receptor cells in the form of hair
fibers.
 Hair fibers bend in response to the
vibrations which in turn causes the receptor
cells to fire (action potential).
 Sends a neural impulse to the auditory nerve
which connects to the temporal lobe region
of the brain.
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Theories of Pitch Perception
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Place theory-pitch perceived depends on
the place where the hair cells were
stimulated on the organ of corti ( High
pitch corresponds to bending of hair cells
closest to the oval window).
Frequency theory-pitch corresponds to the
how fast the basilar membrane vibrates (
the higher the pitch, the faster the
vibrations).
Volley Principle
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Volley Principal-combination of both theories.
Place theory works for pitches above 1000
Hz.
Frequency theory works for pitch below 100
hz.
Volley-In between, say 300 hz, groups of
neurons take turns sending the message to
the brain, Group one, 100 hz, Group two,
100 hz, etc.
Hearing Impairments
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Conduction deafness damage to the mechanical
system that conducts sound to the cochlea.
(punctured eardrum or damage to the small inner
bones) Hearing aid could help by amplifying
vibrations.
Nerve deafness damage to the hair cell receptors
or associated nerves. Usually caused by disease or
something else biological.
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cochlear implant can help restore hearing via an
electronic device that translates sounds into electrical
signals, which are wired into the cochlea’s nerves,
conveying some information about sound to the brain.
Touch
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Essential for Survival
Deprivation of touch in animal and human
infants leads to failure to thrive and/or death.
Sense of touch is actually a mix of at least four distinct
skin senses:
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-pressure,
warmth,
cold
pain.
Pain
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Pain is essential as it is the body’s way of telling you that
something is wrong.
People who cannot feel pain die by early adult hood
because they cannot tell when they have an infection or
they are hurt .
Pain has a strong psychological component, not easily
understood.
No theory of pain explains all the phenomenon.
Many psychological influences on pain such as distraction or
endorphin release can modulate pain. (i.e athletes that
continue to play while they are injured.)
Gate Control Theory
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Spinal cord contains a “ gate” that either blocks pain signals
or allows the signal to pass on to the brain.
Gate can be closed by non-pain signals coming from the
body and by signals coming from the brain.
“Gate” not a physical structure, represents a relative
balance in neural activity within the spinal cord.
Stimulation of the pain receptors releases substance P
which activates neurons that open the spinal gates,
resulting in a pain signal that is sent to the brain
Perception of Pain
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Message sent from spinal cord to brain.
Areas of the brain, influenced by physiological
and psychological factors, interprets the pain
sensation that either opens the gates further 
increasing the pain, or closes the gates, thus
dampening the pain.
The activity of the gate can be closed by signals
coming from stimulation of competing signals
from other skin sensations such as rubbing,
which can reduce the feeling of pain.
Taste
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Chemical sense -involves four basic sensationssweet, sour, salty, and bitter.
Taste buds, which are bumps on our tongues, for
each of the four basic taste sensations.
Taste buds contain a pore that catches food
molecules.
Taste receptors are antenna like hairs the project
into the pore that respond to one of the four
sensations.
Taste receptors reproduce themselves every week
or two although this diminishes with age.
Taste is enhanced by smell. Smell + taste =
flavor.
Olfaction (Smell)
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Chemical Sense-most primitive
Odors have power to evoke memories and feelings due
to a direct connection between olfaction and the limbic
system.
Sense of smell is activated by a complex protein in the
nasal gland called Oderant Binding Protein that binds
with airborne molecules in the olfactory epithelium.
Olfactory receptors recognize odors individually, and
respond selectively to different aromas.
Axon fibers of receptor cells go directly to the olfactory
bulb, which in turn sends a message to the temporal
lobe which records the awareness of smell.
Perception
Terms
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Perceptions- perceive the world through
our senses, however we transform
meaningless sensations into meaningful
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perceptions.
Selective Attention-Our conscious
attention is selective, therefore at any one
moment we focus our awareness on only a
limited aspect of all that we are capable of
experiencing.
Cocktail Party Effect-the ability to attend
selectively to only one voice among many
Perceptual Organization
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Gestalt-given a cluster of sensations, the
human perceiver organizes them into an
organized whole.
Figure-ground- our first perceptual task
is to perceive any object called the
figure, distinct from its surroundings,
called the ground. (i.e. words on paper).
Grouping- To bring order and form to
these basic sensations, and our minds
follow certain rules.
Grouping Rules
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Proximity- We group nearby figures together.
Similarity- Figures similar to each other we
group together.
Continuity- We perceive smooth continuous
patterns rather than discontinuous ones.
Connectedness-When they are uniform and
linked we perceive spots, lines or areas as a
single unit.
Closure- the tendency to “fill in” gaps in a
stimulus so that the image makes sense.
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Depth Perception
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Seeing objects in three dimension when our
retinal images are only two dimensional. This
enables us to estimate their distance.
Monocular cues-distance cues, such as linear
perspective and overlap, available to either
eye alone.
Binocular cues-depth cues such as retinal
disparity and convergence, that depend on
the use of two eyes.
Monocular Cues
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Interposition- If one object partially blocks our view
of another we see it as closer.
Texture gradient-a gradual change from a coarse
distinct texture to a fine indistinct texture signals
increasing distance. Far objects appear smaller and
more densely packed.
Linear perspective-parallel lines, such as railroad
tracks, appear to converge with distance. The more
the lines converge, their greater their perceived
distance.
Light and Shadow- Nearby objects reflect more light
to our eyes. Thus given two identical objects, the
dimmer one seems farther away.
Binocular Cues
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Because our eyes are about 2 ½ inches
apart, our retina receive slightly different
images of the world.
Retinal disparity- When the brain
compares these two images, the
difference between them is called retinal
disparity and provides an important cue
to the relative distance of different
objects.
Motion Perception
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Our brain computes motion based partly
on its assumption that shrinking objects
are retreating and enlarging objects are
approaching.
Phi phenomenon-when two adjacent
stationary lights blink on and off in quick
succession, we perceive a single light
moving back and forth between them
Visual Illusions
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Illusions due to misleading cues in
stimuli that give rise to inaccurate or
impossible perceptions.
Escher Photos