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.
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.
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,
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.
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.
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).
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?
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,
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
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
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?
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?
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:
Sensory Adaptation
How does sensory adaptation help us understand the world around us?
Sensory Adaptation
How does sensory adaptation help us understand the world around us?
Why is understanding sensory adaptation important
• in what cases would sensory adaptation be “bad”? • in what cases would sensory adaptation be “good”?
