Sensation and Perception

Sensation

• Process that detects stimuli from one’s body

or environment

• Picks up auditory (vibrations), visual (light) ,

and other sensory stimuli (touch,

temperature) through sensory receptors and

transmits to brain or spinal cord

• It does not interpret!!!!

Perception

• Process that organizes

sensations/information

into meaningful patterns

• Provides the finished

product

• Interprets the information

about the world

• No two people “perceive”

in the same way

Example: Dr. P• Was not near-sighted

– He could see a pin on the floor

• He had visual sensations of people’s facial

features

• Could not organize them into recognizable faces

– Pick up wife’s hair as his hat, pat fire hydrants

thinking they were children’s heads

Absolute Threshold

• The minimum

(smallest, weakest)

amount of stimulation a

person can detect 50%

of the time when a

stimulus is presented

over and over

– Method of constant

stimuli (experiments

where researchers

present the stimulus)

Absolute Thresholds for Daily

Stimuli (p. 93)

• Vision-

– See a candle

flame at 30 miles

on a dark, clear

night

Absolute Thresholds for Daily

Stimuli

• Hearing-

– Hear the tick of a

watch under

quiet conditions

at 20 feet

Absolute Thresholds for Daily

Stimuli

• Taste-

– Taste 1

teaspoon of

sugar dissolved

in 2 gallons of

water

Absolute Thresholds for Daily

Stimuli

• Smell-

– Smell one drop

of perfume in a 3

room house

Absolute Thresholds for Daily

Stimuli

• Touch-

– Feel the wing of

a bee falling on

your cheek at a

distance of .4 of

an inch

Absolute Threshold

• Individual Differences

– Some people are more sensitive

– Sensitivity can change daily

– Sensitivity can change from occasion to

occasion

– Differences are minimal!!

Difference Threshold

(Just Noticeable Difference)

• The minimum amount

of change in a

stimulation that can

be detected 50% of

the time

• Varies from person to

person

Difference Threshold • Example:

– Certain amount of

sugar has to be

added to coffee to

tell a difference in

the taste

– If you are holding 5

pounds, you will

notice if a pound is

added…but if you

are holding 100

pounds, you will not

notice a pound

difference

Weber’s Law

• Amount of change in

intensity of stimulation

needed to produce

just noticeable

difference (jnd) is a

constant (fraction)

• Not the same for all

senses or people

Weber’s Law• Example:

– Jnd for weight is 1/53• 50 ounces- 1 ounce

• 100 ounces- 2 ounces

– Jnd for pitch is 1/333• People can tell when a tone rises or falls in pitch

by one-third of 1%

• The greater the original stimulus, the more it must be increased or decreased for the difference to be noticed

Signal Detection Theory

• Signal Detection Theory

– Detection of stimulus depends on the

intensity and the physical (some people have

better senses) and psychological (Human

bias: past experiences, expectations of

current situations, motivation, learning) state

of the individual

Signal Detection Theory

• Example:

• Boss is going to call at 6:00 to tell you if you got promoted

• Get home from the gym at 5:45 and want to take a shower

• Constantly you find yourself tuning in every little sound- you are worrying that you will miss the phone call- think you constant hear the phone

Sensory Adaptation• The tendency of the

sensory receptors to

respond to less and less

to a constant stimulus….

Otherwise clothes would

drive us crazy!!!

– Example:

• Water is cold (pool),

we get used to it

• Water is hot (bath), we

get used to it

• Something smells bad,

we get used to it

Sensory Adaptation vs. Habituation

• Habituation

– Tendency of the brain to

stop attending to

constant, unchanging

information

– Example: When people

don’t really “hear” the

noise of the air

conditioner unless it

would shut off…They

hear it, they just don’t

pay attention to it

Subliminal Perception (p. 93)

• The ability to detect

stimuli that are below the

level of conscious

awareness

• Stimuli are just strong

enough to activate the

sensory receptors but

not strong enough for

people to be consciously

aware of them

• Does it work?