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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.