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What is the difference between sensation and perception?

Sensation: Perception:

The process of detecting a stimulus, such as

• light waves (vision) ,

• sound waves (hearing) , • chemical molecules (smell

and taste ), • heat or pressure (touch).

The process of integrating, organizing and interpreting sensations.

You might want to think of sensation and perception as two ends of a continuum. There is no clear dividing line between sensation and perception. Where sensation ends and perception begins is difficult to determine.

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How many right angles do people perceive?

How many right angles are there?

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The Basic Senses and What They Detect

What do we detect?

Light waves

pressure waves

Image source: Psychology (2011), Schacter et al.

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Wave properties and their relation to perception

Image source: Psychology (2011), Schacter et al.

Image source: Psychology (2011), Schacter et al.

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Signal Detection Theory Signal detection theory states that detecting a stimulus [by a person] is not an objective processes (page 178). Detecting a stimulus is a subjective decision involving (1) sensitivity to the stimulus in the presence of distractions from other stimuli (noise) and (2) the criteria used to make judgments from ambiguous information (also see response bias, page 178). When detecting light stimuli,

(1) The reality of the light is that it is on or off, and (2) you must decide if it is on or off.

Image source: Psychological Science, 4

th edition, (2013), Gazzaniga, Heatherton, and Halpern

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Signal Detection: Intensity of the Stimulus

Higher Intensity

Your response Your response

Light presented

yes, yes, yes, yes, yes, yes, yes, yes

no, no

Light not

presented

yes, yes

no, no, no, no, no, no, no, no

Lower Intensity

Your response Your response

Light presented

yes, yes, yes, yes, yes, yes

no, no, no, no

Light not

presented

yes, yes, yes, yes

no, no, no, no, no, no

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Signal Detection: Response bias

Liberal: You are more likely to say “yes”. Your standards are more lax.

Your response Your response

Light presented

yes, yes, yes, yes, yes, yes, yes, yes

no, no

Light not presented

yes, yes, yes, yes, yes, yes, yes, yes

no, no

There is a higher risk of false positives (false alarm) where you will respond when there is no actual event (light)

Conservative: You are more likely to say “no”. Your standards are high.

Your response Your response

Light presented

yes, yes,

no, no, no, no, no, no,

no, no

Light not

presented

yes, yes

no, no, no, no, no, no,

no, no

There is a higher risk of missing something that really is there where you won’t respond to something that actually is there.

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Signal Detection: Response bias

Liberal: If people haven’t paid their taxes, was it an honest mistake (Ming) and be forgiving?

Be forgiving

Come down hard on them

The person made an honest mistake

Correct decision miss

The person was trying to cheat on

their taxes

false positive Correct decision

There is a higher risk of false positives (false alarm) where you will respond when there is no actual event (light)

Conservative: If people haven’t paid their taxes, did they try to cheat the system (Boris) and need come down hard on them?

Be forgiving

Come down hard on them

The person made an honest mistake

Correct decision miss

The person was trying to cheat on

their taxes

false positive Correct decision

There is a higher risk of missing something that really is there where you won’t respond to something that actually is there.

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Signal Detection: Response bias

Liberal: You are more likely to accept new information, regardless of whether it is accurate or not.

Believe it Dismiss it

New information is true

Correct decision miss

New information is

false

false positive Correct decision

There is a higher risk of false positives (false alarm) where you believe lots of things that are not true.

Conservative: You are less likely to accept new information, regardless if it is true or not.

Believe it Dismiss it

New information is true

Correct decision miss

New information is

false

false positive Correct decision

There is a higher risk of missing something that really true, but don’t believe it.

Critical thinking can help you evaluate incoming information. However, we are prone to use biased thinking (see Chapter 1 and Psy 202).

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Signal Detection: Response bias

Signal Detection Theory: An observation that the response to a stimulus depends both on

• Intensity of the stimulus • on a person’s response bias.

Is the Light on?

Image source: Psychology (2009), Schacter et. al

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In the real world, we have to make judgments under uncertainty such as school closures due to bad weather, surgery for cancer, detection of enemy aircraft, assessment of bomb threats, lie detection, etc.

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When distributing financial aid, there are some people who may need it, and some who may not really need it.

Award financial aid

Reject financial aid

Sam needs financial aid

Correct decision miss

Chris doesn’t

need financial aid

false positive Correct decision

Should you perform a medical procedure for breast cancer?

Perform surgery Not perform

surgery

you have breast

cancer*

Correct decision miss

you have don’t

have breast cancer*

false positive Correct decision

* there is uncertainty in detection of cancer

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A decision at 5:00 am needs to be made: Should you close the school?

Close school Keep school open

Weather will get

worse

Correct decision miss

Weather will get

better

false positive Correct decision

Is the bomb threat real?

Evacuate Not evacuate

There is a bomb

Correct decision miss

There is NO bomb

false positive Correct decision

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Should you attack an unknown aircraft?

Shoot aircraft down

Hold your fire

Enemy aircraft

Correct decision miss

Friendly aircraft

false positive Correct decision

Is the person lying about stealing $100 when the lie detector is “spiking”?

I think they are lying

I think they are telling the truth

They lied about

stealing

Correct decision miss

They are telling the truth about

stealing

false positive Correct decision

What are other decisions that can be looked at with the signal detection framework?

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How much product should I order?

I order a lot of product

I order a small amount of product

The product will

sell

Correct decision miss

The product won’t

sell

false positive Correct decision

As a police officer, do I shoot that person?

I shoot I hold my fire

The person is a

criminal

Correct decision miss

The person is not

a criminal

false positive Correct decision

• is the person dangerous?

Is the item a weapon?

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Sensory Processes

There are some basic concepts that psychologists use when talking about the sensitivity of the senses (pages 177 - 178

• Sensory adaptation: A decrease in sensitivity to a constant level of stimulation (page 178).

Sensory adaptation: The decline in sensitivity of the basic senses to a constant stimulus. Therefore, a stronger stimulus is required to activate the senses (another definition). Smell: Touch

Hearing:

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Sensory Adaptation

How does sensory adaptation help us understand the world around us?

Image source: unknown

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Sensory Adaptation

How does sensory adaptation help us understand the world around us?

Image source: unknown

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How Sensitive are the Senses?

The absolute threshold is the [average] smallest possible strength that can be detected half the time.

Image source: Psychology (2011), Schacter et al.