Transcript Sensation and Reality - Mr. McMillen's Home Page

Sensation and Reality
A Window on the World
Sensation and Perception
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Sensation
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Transduction
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The processes by which our sense organs
receive information from the environment.
The process by which physical energy is
converted into sensory neural impulses.
Perception
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The processes by which people select,
organize, and interpret sensations.
General Properties of Sensory
Systems
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Our senses inform us of the presence of
stimuli or of any change in a stimulus.
The study of sensation is called the study
of psychophysics.
Sensory systems act like data reduction
systems
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A system that selects, analyzes, and
condenses incoming information
General Properties of Sensory
Systems
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Each of the senses routinely “boils” down
a flood of information into a stream of
useful data.
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All of the sensory systems are based on
the use of the neuron to process
information.
Sensation & Perception
Processes
General Properties of Sensory
Systems
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Sensory analysis is the separation of
sensory information into important
features.
In all of the senses, the “look” for
perceptual features in the environment.
Perceptual features are basic elements of
a stimulus pattern.
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Lines, shapes, edges, spots, colors, odors,
tastes, and sounds.
General Properties of Sensory
Systems
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After sensory systems have accomplished
selection and analysis, they code the
information.
Sensory coding means converting
important features of the world into neural
messages understood by the brain.
General Properties of Sensory
Systems
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Localization of function is a brain concept
that means that the type of sensation you
experience depends upon the area of the
brain that is activated.
Psychophysics
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The sense organs are magnificient
mechanisms. But for all that
magnificience, they have limits.
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Those limits are referred to as the
absolute thresholds.
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What is the absolute minimum amount of
energy necessary for a sensation to occur?
Psychophysics
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All sensory systems have absolute
thresholds.
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The smallest amount of stimulus that can be
detected at least 50 per cent of the time.
Absolute Thresholds
Perceptual Defense
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Sensory thresholds vary from person to
person and they also vary from time to
time in the same person.
The type of stimulus, the state of one’s
nervous system all make a difference .
Unpleasant stimuli may raise the threshold
for recognition.
Perceptual Defense
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The resistance to perceiving threatening
or disturbing stimuli is called perceptual
defense.
Subliminal Perception
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Anytime information is processed below
the conscious level of the limin ( also
called the absolute threshold), it is
subliminal perception.
The concept is a controversial one
because there have been conflicting study
results.
Subliminal Perception
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Basically, the concept is that if sensation
can be produced that exists just below the
conscious level of the limin, then it might
just have the ability to alter our thoughts or
behavior.
There have been no conclusive results
from any study thus far.
Difference Thresholds
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Psychophysics also involves the study of
difference thresholds.
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How much must a stimulus change
before(increase or decrease) before it
becomes noticeably different.
Difference Thresholds
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The study of JND’s led to the discovery of
Weber’s Law
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States that the amount of change needed to
produce a jnd is a constant proportion of the
original stimulus intensity.
Difference Thresholds
Vision
Dimensions of Vision
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The sense of vision is referred to as our most
essential sense or our dominant sense.
Light is the physical stimulus for vision.
The visual spectrum of light is made up of
various wave lengths of light.
What humans can see is called the visible
spectrum.
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400 nanometers to 700 nanometers
Vision
The Electromagnetic Spectrum
Structure of the Eye
Structure of the Eye
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Light enters the eye through the cornea,
the transparent protective coating over the
front of the eye.
It then passes through the pupil, the
opening in the center of the iris, the
colored part of the eye.
Structure of the Eye
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Inside the pupil, light passes through the
lens, which focuses it onto the retina, the
light sensitive inner lining of the back of
the eyeball.
The lens changes shape to focus on
objects that are closer or farther away.
Structure of the Eye
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On the retina and directly behind the lens
is a depressed spot called the fovea.
The fovea occupies the center of the
visual field. Vision is sharpest here.
Structure of the Eye
The Retina
The retina contains the receptor cells
responsible for vision.
These cells are sensitive to only one part of
the spectrum of visible light.
There are two kinds of receptor cells in the
retina: rods and cones
Structure of the Eye
The Retina
Photomicrograph of the rods and
cones in the retina.
Structure of the Eye
The Retina
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The cones of the retina number about 6.5
million. They work best in bright light
They also produce color sensations and
pick up fine details.
The rods number about 100 million and
are unable to see color.
They are responsible for light and dark
vision.
Structure of the Eye
The Retina
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The rods are much more sensitive to dim
light than the cones are.
The rods allows us to see in very dim light.
On the back of each retina is a blind spot
where the optic nerve leave the eye. This
blind spot is compensated for by the brain
overlapping images from both of the eyes
images.
Visual Problems
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The shape of the eye also affects focusing.
If the eye is too short nearby objects cannot be
focused, but distant objects are clear.
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This is called hyperopia (farsightedness)
If the eyeball is too long, the image falls short in
the retina, and distant objects can’t be focused.
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This is called myopia (nearsightedness)
Visual Problems
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When the cornea or the lens is
misshapen, part of the visual field will be
focused and part will not.
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This is called astigmatism.
As we age, the ability of the lens to bend
and focus on nearby objects will decrease.
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This is called presbyopia.
Light Control
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The iris and the pupil act together to adapt
to the changing intensity of light.
By making rapid changes to light
conditions, the iris allows us to move from
light to dark or the opposite.
In dim light, the pupils dilate to let in more
light. In bright light, the pupils constrict to
let in less light.
Light Control
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The control of light is very important since
the retina cannot adjust very quickly to
changes in light intensity.
Light Control
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Full dark adaptation takes place in about
30 to 40 minutes due to a chemical
reaction in the rods and cones.
The cones adapt first, but they are less
sensitive than rods.
The rods cannot discriminate color so that
is why we cannot make out color in very
dim light.
Light Control
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When re-entering a bright area, the rods
quickly lose their dark adaptation and the
eyes become light adapted as the cones
quickly take over.
Construction of the Retina
Rods and Cones
How the Brain Sees the World
How the Brain Sees the World
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According to Nobel Prize winning
psychologist, Hubel and Wiesel, we know
that the vision acts like a computer and
not like a camera.
The result of their work suggests that
specific brain cells are responsible for very
specific visual information
How the Brain Sees the World
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The brain seems to analyze incoming
information into lines, angles, shading,
movement, and other basci features.
Then other brain areas combine these
features into meaningful visual
experiences.
As much as 30 percent of the brain is
devoted to processing visual information.
Hubel & Wiesel’s Experiment
Some cells in the visual cortex respond only to certain types of
visual information, for example, a diagonal line moving up and
down.
These cells are called feature detectors.
Visual Acuity
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Visual acuity is the concept of the
sharpness of one’s vision.
Differences in the rods and cones affect
visual acuity.
Vision is sharpest when an image falls on
the fovea.
Acuity decreases as the image moves to
the edge of the retina
Peripheral Vision
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Areas outside the fovea account for
peripheral vision.
Much of peripheral vision is the
responsibility of the rods.
The rods are very sensitive to movement.
Seeing out of the corner of the eye is very
important to sports, driving, and walking
down dark streets.
Color Theories
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There are two basic theories for how we
see color:
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Trichromatic theory
Opponent process theory
Color Theories
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The Trichromatic theory proposes that there are
three kinds of color receptors in the eye, one
each for red, green, and blue.
Other colors are assumed to result from
combinations of these three color receptors.
A problem with this theory is the perception that
there are four primary colors: red, green, blue,
and yellow.
Trichromatic Theory
T. Young (1802) & H. von
Helmholtz (1852) both proposed
that the eye detects 3 primary
colors: red, blue, & green.
All other colors can be derived
by combining these three.
Color Theories
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The trichromatic theory explains that all colors
can be formed from the combination of the three
primary colors.
The second theory, called the oponent/process
theory holds that three sets of color receptors
(yellow-blue, red-green, black-white) respond in
an either or fashion to determine the color you
experience.
Color Theories
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It is assumed that the visual system can
produce message for either red or green,
yellow or blue, black or white.
Coding one color in a pair seems to block
the opposite message.
So a reddish green is impossible, but a
yellowish red can occur.
Color vision is derived from three
pairs of opposing receptors. The
opponent colors are blue and yellow,
red and green, and black and white.
Theory explains afterimages and color
deficiency.
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After Image
Color Theories
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The three color theory applies to the retina
where three types of visual pigments have
been found.
Each pigment is sensitive to a different
wavelength of light.
As a result, the three types of cones fire
nerve impulses at different rates when
various colors are viewed.
and
Color Weakness
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A person who is color blind cannot
perceive colors.
Colorblindness means the partial or total
inability to perceive color.
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Trichromats are people who can see all three
colors
Dichromats are blind to red-green or yellowblue
Color Blindness
and
Color Weakness
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Monochromats are people who are totally
color blind.
About 10 percent of men and 1 percent of
women are colorblind to some degree.
Color blindness is caused by changes in
the genes that control the pigments of the
cones.
and
Color Weakness
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The Ishihara test is a common measure of
color blindness
The background and the numbers are of
different colors.
A person who is colorblind sees only a
jumble of dots
The normal vision person can see the
numbers.
Hearing
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The ear functions to convert sound waves
from the external environment into nerve
impulses which reach the brain and then
are transformed into the sensations of
sound.
Hearing
Hearing
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Theories
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Place Theory
Frequency Theory
Types of Deafness
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Conduction
Nerve
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Stimulation nerve deafness
Temporary threshold shift
Loudness
Of
Sound
Taste
Taste
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There are four basic tastes
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Sweet
Sour
Bitter
Salty
Taste
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The receptors for taste are the taste buds.
Most of what we call taste is aroma
The taste buds are molecule receptors
and only respond to specific molecule
combinations
Taste
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The number of taste buds can vary from
person to person
From a low of 500 to more than 10,000
The high end of the scale represent super
tasters.
The Sense of Smell
The Sense of Smell
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Smell receptors are located in the top of
the nasal passage
The most primitive of all senses
Easily fatigued
No clear theory for how and why we can
detect specific odors
Lock and Key Theory
Pheromones
A Sixth Sense
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Air borne chemical signals
Vomeronasal organ is the sense organ for
pheromones
Humans may have them but not sure!
Involved in affecting mating, sexual behavior,
recognition of family members and territorial
marking in almost all mamals
Why would humans be different?
The Somesthetic Sense
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Skin senses
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Touch, pressure, pain, hot, cold, warmth
Vestibular sense
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Balance, gravity, acceleration, joint position,
body position
Sensitivity to Touch
Dynamic Touch
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Refers to the brain and the receptors
ability to combine sensations from skin
receptors with information from kinesthetic
sense information from muscles and
tendons.
Can provide very detailed information
about objects in the environment about us.
Sensory Adaptation
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The concept says that the longer we are
exposed to a stimulus, the fewer nerve
impulses that are sent to the brain.
Smell is the quickest receptor to do this.
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After about 15 minutes odors no longer
matter.
Smell is designed to tell us of a change in the
environment.
Sensory Adaptation
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Physiological nystagmus
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Rapid eye tremors that keep the rods and
cones of the eye from becoming fatigued and
thus keep the eyes sending information to the
brain.
Selective Attention
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Tune in/ Tune out
The brain is capable of attending to only
one level of major input at a time.
We have the ability to pick and choose
what it is that we want to “pay attention to”