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Sensation and Perception
Ch. 3 PSY 110
Sensation and Perception
Sensation – the process through
which our senses pick up auditory,
visual, and other sensory stimuli
Perception – the process by which
the brain actively organizes and
interprets sensory information
Absolute Thresholds
Vision
- A candle flame 30 miles away on a clear night
Hearing
- A watch ticking 20 feet away
Taste
1 tsp of sugar dissolved in 2 gallons of water
Smell
A single drop of perfume in a three room house
Touch
- A bee’s wing falling a distance of one centimeter onto the
cheek
Difference Threshold
The smallest increase or decrease in a physical
stimulus required to produce a difference in
sensation that is noticeable 50% of the time.
Example- Can 1 apple make a difference in the
bag of groceries you are carrying in making it
appear heavier to you? If not one apple, how
many apples?
Just noticeable difference
Smallest change in sensation that a person is able
to detect 50% of the time.
What is Sensory Adaptation?
The process in which sensory receptors grow
accustomed to constant, unchanging levels of
stimuli over time.
Example – Smokers of many years may notice
less and less the odor of smoke on their clothing,
in their hair, etc. Whereas someone who doesn’t
smoke will notice it right away.
Very strong stimuli (like smell of ammonia or
a horrible taste) are not likely to apply to
sensory adaptation principle
Vision
Our eyes respond to light in the visible
spectrum
The narrow band of electromagnetic waves that
are visible to the human eye
Electromagnetic waves are measured in
wavelengths
A measure of distance from the peak of a light
wave to the peak of the next wave
- Shortest we can see appear violet
Longest we can see appear beyond red
The Eye
Retina – a layer of tissue about the size of
a small postage stamp and as thin as onion
skin
- Image that is projected to retina is upside
down and reversed from left to right
- Nearsightedness (myopia) is when lens focuses
images of distant object in front, rather than on,
the retina. See well close up.
- Farsightedness (hyperopia) is when lens focuses
on images of close objects behind, rather than on,
the retina. See well far away.
Vision and the Brain
Nerve fibers from the right half of
each retina go to the right
hemisphere, and those from the left
half go to the left hemisphere
The cross over is important in that
visual perception from a single eye can
be represented in the visual cortex on
both sides of the hemisphere.
Color Vision Theory
Opponent – Process
Afterimage – a visual sensation that remains after
the images is gone
After you have stared at one pair of colors
(red/green, yellow/blue/, white/black), the
afterimage gives you the exact opposite of those
colors.
Color Vision
Color Blindness
Do color blind people see world in black or white?
Color Blindness refers to an inability to distinguish
certain colors from one another.
7% males experience this and fewer than 1% of
females
Most common colors confused are red and green
Has varying levels of severity
Like who has trouble deciphering if things are navy and
black?
Taste
- Taste buds – the life span of each taste bud is only about 10
days, and therefore they are constantly being replaced.
- Individuals vary widely in their capacity for experiencing taste
sensations.
Nontasters – unable to taste sweet and bitter compounds, but they
do taste other substances with just maybe a little bit less sensitivity.
- Supertasters – taste sweet and bitter compounds with far stronger
intensity than other people.
- Do you think supertasters are more overweight than medium or
nontasters?
- NO the opposite is true.
- Why? Because they are never deliberately trying to cut out one food group?
Touch
Tactile – one’s sense of touch
Pain – What causes it?
Gate Control Theory
- Area in spinal cord is blocked and acts like a “gate”, and it either blocks
pain messages or transmits them to the brain.
- Only so many messages can go through pain at one time.
- You feel pain when message goes through the gate in a small, slow-
conducting nerve
- Pain is blocked when large, fast-conducting nerve reach gate, cause it to
open, but blocks the message
- Example: After you stub toe, you apply pressure to it to decrease pain, this is
actually stimulating the large, fast-conducting nerve
- Other examples include applying ice, heat, or electrical stimulus to the large, fast-
conducting nerve
Touch Cont.
Endorphins – Body’s naturally produced
painkillers
Block pain and produce a feeling of well-being
Endorphins are released when you’re injured,
when you experience stress, and when you
laugh, cry, and exercise.
Some people release endorphins even when they
think they are receiving pain meds. (Remember
the placebo effect, this is it.)
Influences on Perception
Attention – sorting through sensations and selecting some
of them for further processing.
EX: We effortlessly know when we see a car, but attention allows
us to know which cars to pay special attention to (like ones in the
lane right beside us, ones that are attempting to pass us, etc.)
Because we can pay attention to everything around us,
sometimes we shift our attn. several times and fail to notice
changes in the things we’re not directly paying attention to. This
is known as Inattentional Blindness.
“Where did that car come from?” We are surprised when a car
comes flying up behind us because we hadn’t been paying
attention to that particular car the entire time.