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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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Sensory Processes: Signal Detection Theory

Your ability to detect sensory information depended not only on the intensity of the stimulus (e.g. how bright the light is), but it involved human judgment (also see response bias, page 137).

Signal Detection Theory: A theory of perception based on the idea that the detection of a faint stimulus requires a judgmentit is not an all-or-none process (page 136, 137).

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Signal Detection Theory

Signal Detection Theory: A theory of perception based on the idea that the detection of a faint stimulus requires a judgmentit is not an all-or-none process (page 136, 137).

Is the light on?

Image source: Psychological Science, 4th 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 wont respond to something that actually is there.

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Signal Detection: Response bias

Liberal: If people havent 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 havent 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 wont respond to something that actually is there.

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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 persons 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 doesnt need financial aid

false positive Correct decision

Should you perform a medical procedure for breast cancer?

Perform surgery Not perform surgery

The diagnosis is correct and you

have breast cancer

Correct decision miss

The diagnosis is wrong and you have dont have breast cancer

false positive Correct decision

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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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Sensory Processes

There are some basic concepts that psychologists use when talking about the sensitivity of the senses (pages 135 - 137

Sensory adaptation: A decrease in sensitivity to a constant level of stimulation (page 137).

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.