Sensation and Perception

Sensation: your window to the world Perception: interpreting what comes

in your window.

Sensation

• Sensation - The passive process of receiving and detecting a stimulus by the nervous system.

• Process of sensing our environment through taste, sight, sound, touch and smell

• Example: Hearing Mrs. Joseph speak, the sound waves travel to the ears. The hair on the cells in the cochlea help transmit the information to the brain

Perception• Perception - The active process of

selecting, organizing, and interpreting the information brought to the brain by the senses

• Perception is the way we interpret sensations and therefore make sense of everything around us

• Based on our prior experiences and expectations

• Example:– Seeing letters on a page and

interpreting them as our favorite passage in a novel

Bottoms-up Processing• Bottoms Up Processing (AKA -

Feature analysis)• Begins with the sensory

receptors and works its way up to the brain

• Use the features of the object itself to process the information

• Examples: – seeing the individual fruits in this

picture– Hearing a voice speak about AP

Psych

Top Down Processing• Top Down Processing - Processing

information from the senses with higher level mental processes using our experiences and expectations

• Using your background knowledge to fill in the gaps

• Examples: – Seeing the face in the picture made up of fruit– I _ope yo_ get an 5 on t_ _ A _e_am– Negative expectations about the pain of

childbirth can increase pain during the birthing process

• Find the following hidden items:

• Scissors• Banana• Screwdriver• Horn • Heart• fish • boat • Shoe• needle

• Aoccdrnig to a rscheearch at an Elingsh uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, th olny iprmoetnt tihng is that frist and lsat ltteer is at the rghit pclae. The rset can be a toatl mses and youcan still raed it wouthit a porbelm. This is bcuseae we do not raed erveylteter by it slef but the word as a wlohe.

Selective Attention

• Selective Attention - Ability to focus our conscious awareness on a particular stimulus

• Example: Cell phone usage while driving a car

Selective AttentionExample

The Stoop Effect

• Stroop Effect - Demonstrates the nature of automatic processing versus conscious visual control. The difficulty you had reading it was due to semantic interference

Cocktail-party phenomenon• cocktail party effect -

ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

• Form of selective attention.• Example:

– You are at the football game and are cheering for the Comets when you hear Ms. Short call your name

Selective Inattention • Change Blindness/Inattentional

Blindness - Falling to notice changes in the environment– Example: Eating your lunch in the cafeteria, when

your friend switches your sandwich and you don’t notice

– Choice Blindness - failure to notice a switch in a choice that is made

• Example: Participants asked to pick between two photographed faces, when photographs are switched…

– Change deafness – failure to notice a change in voices that are speaking

• Example: Listening to Mrs. Joseph speak, failure to notice that Mrs. Harvey is now speaking

Create your own examplesPick two that you are having the most difficulty with and make your partner

come up with a new example• Sensation• Perception• Bottoms-up processing• Tops-down processing• Selective Attention• Stroop Effect• Cocktail Party effect• Inattentional Blindness• Choice Blindness• Change Deafness

No stinky examples!

Pop Out Effect

• Pop out – stimuli we don’t chose to attend to but they draw our eyes and demand our attention

• Example: Picture on the left

Complete sensation in the absence of complete perception is best illustrated

by

Weber’s

Law

Proso

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Color consta

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Senso

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1. Weber’s Law2. Prosopagnosia3. Conduction

deafness4. Color constancy5. Sensory interaction

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The process by which we select, organize, and interpret sensory information in order to recognize meaningful

objects and events is called

Senso

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Paralle

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Sensa

tion

Perception

accomodation

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1. Sensory adaptation2. Parallel processing3. Sensation4. Perception5. accomodation

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Patients' negative expectations about the outcome of a surgical procedure can increase their postoperative experience of pain.

This best illustrates the importance of

Transducti

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Accomodati

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Top down proce

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1. Transduction2. Accomodation3. Sensory adaptation4. Difference

thresholds5. Top down

processing

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Researchers found that 40% of people focused on repeating a list of challenging words, failed to notice a

change in the person speaking. This illustrates

Top Down Proce

...

Bottoms up Pro

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The Diff

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...

Change Deafnes..

.

Perception

20% 20% 20%20%20%1. Top Down Processing2. Bottoms up Processing3. The Difference

Threshold4. Change Deafness5. Perception

You typically fail to consciously perceive that your own nose is in you line of vision. This illustrates

Sublim

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.

Change blindne...

Perception

Selecti

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The cock

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20% 20% 20%20%20%1. Subliminal perception

2. Change blindness3. Perception4. Selective Attention5. The cocktail party

effect

Psychophysics

• Psychophysics - Study of how physical stimuli are translated into psychological experience.

• Psychologists use thresholds to measure these events

• Example: Tracking a person’s eye movements jumping every .33 of a second

Thresholds• Threshold – the point at which a sensory

information is strong enough to be noticed

• Absolute threshold – The smallest amount of a sensory stimulus needed to notice that the stimulus is there at all

• Examples: Light A candle flame at 30 miles on a dark, clear night.

Sound The tick of a mechanical watch under quiet conditions at 20 feet.

Taste One teaspoon of sugar in two gallons of water.

Smell One drop of perfume diffused into the entire volume of a three-bedroom apartment.

Touch The wing of a bee falling on your cheek from a distance of one centimeter.

Signal Detection Theory• Signal Detection Theory -

Predicts how and when we detect a signal amid background noise

• Assumes no absolute threshold

• Detection depends partly on a person’s experience, expectations , motivation and alertness…people respond differently to same stimuli

• Example: Enemy submarine,• Waiting for the Pizza man to

come at a busy party

Subliminal Stimulation

• Subliminal – below one’s absolute threshold for conscious awareness

• Example: – Listening to tapes in your to get you

to lose weight

• Priming – increased sensitivity to certain stimuli due to prior experience outside conscious awareness– Example: Seeing a picture of a mouse

before viewing the picture on the left

Do Subliminal Messages work?• Based on studies, some people

do respond to stimuli below the absolute threshold, under some circumstances. – People behave differently at

different threshold levels– Priming can briefly influence

preferences or perceptions– Complex behaviors are NOT

influenced by subliminal messages

– Some people are more suggestible than others

– Placebo effect

0

25

50

75

100

LowAbsolutethreshold

Medium

Intensity of stimulus

Percentageof correctdetections Subliminal

stimuli

Subliminal messaging vs. Priming

• Why the difference between priming studies and subliminal message studies?– priming: immediate, short-term effect on

simple judgments and actions– subliminal messages: aim for long-term

effects on consumer purchases, voter sentiment, or even suicide – most studies not proven to provide long term effects

Difference ThresholdDifference Threshold (AKA Just

Noticeable Difference) – the amount a change needed in a stimulus (stronger or weaker) for us to recognize the change has occurred

• the greater the intensity (ex., weight) of a stimulus, the greater the change needed to produce a noticeable change.

• Example:– Some people are better at detecting slight

variations in the taste of pop

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

Just noticeable difference

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Just noticeable difference

Just noticeable difference

Weber’s Law

• Weber’s Law (Related to JND) - For people to really perceive a difference, the stimuli must differ by a constant "proportion" not a constant "amount".

• Proportion varies depending on the stimulus

Weber’s Law• JND

– Pitch = .003 ( if someone sings a little off key, we will be able to tell)

– Loudness = .10– Saltiness = .20– Light = .08

• Example:– JND for a 10oz weight = 1 oz. To notice a 50 oz

weight would be 5oz– JND for a 10 decibel sound = .10 decibels . To

notice a sound of 30 decibels would be _______?

Sensory Adaptation

• Sensory Adaption - Diminished sensitivity as a consequence of constant stimulation

• Example:Jumping into a cold swimming pool, doesn’t feel cold after a while

Your eyes when you turn off the lights

Do you feel your underwear all day?

After listening to the television for 10 minutes, you fail to notice how loud the

volume is. This is an example of

Weber’s

Law

Habitu

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Just

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1. Weber’s Law2. Habituation3. Sensory adaptation4. Just noticeable

difference5. Absolute threshold

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Which theory emphasizes that personal expectations and motivations influence the level

of absolute thresholds?

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1. Signal detection theory

2. Just noticeable difference

3. Weber’s law4. Bottoms-up theory5. Tops-down theory1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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The minimum amount of stimulation a person needs to detect a stimulus 50 percent of the time is called the

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1. Adaptation threshold

2. Difference threshold3. Absolute threshold4. Subliminal threshold5. Change threshold

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A subliminal message is one that is presented

while

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1. while an individual is under hypnosis.

2. below one's absolute threshold for awareness.

3. in a manner that is unconsciously persuasive.

4. with very soft background music.

5. Repetitiously1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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