Thresholds �& �Sensory Adaption�Module 16

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Principles of Sensation

• All senses receive stimuli on receptor cells then transform it to action potential then deliver the info to the brain.
• Transduction— process where physical energy is converted/transformed into neural signals the brain understands

Psychophysics

• This is how we experience our physical world.
• When you interact with the world around you, your brain is responding to different environmental stimuli through your senses. Psychophysics studies this.

• Classroom demo judging weight of pill bottles.
• Which one do you think weighs the most?
• The more compact weight “felt” heavier to your brain when in reality it weighed the same as the large container.

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Types of Threshold

• A Threshold is an edge or a boundary
• Psychologists are interested in our boundaries/thresholds when it comes to our senses.
• What’s the bare minimum we can sense?
• OR What’s the bare minimum required to make our receptor cells fire?

Absolute Threshold

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• The minimum stimulation necessary for a person to detect a particular stimulus 50% of the time. (see table for examples)
• What’s the absolute smallest amount of something in the environment needed for you to be able to detect it for the first time?

Difference Threshold/Just Noticeable Difference

• The minimum difference that a person can detect between two stimuli 50% of the time.
• What’s the bare minimum needed for a person to detect a change in their sensory information?

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Absolute Threshold vs. Difference Threshold

• If you put your hand on a burner and turned it on, the first time you felt something would be Absolute Threshold and the second you noticed it getting hotter would be Difference Threshold.

Weber’s Law

• Weber’s Law – detection of a stimulus depends on the original stimulus itself.
• Whether you detect a change depends on the original stimulus and how big the change was
• LARGE Stimuli require BIGGER Changes for us to notice them
• Example: If a 300 lb. person loses 20 lbs and a 120 lb. Person loses 20 lbs, which one would you notice lost the weight first? (120 lbs because 20 lbs is a larger % of their body weight)

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Which one would you notice the

$1 price drop more?

Which one would you notice a

2 inch haircut on?

Review Absolute, JND & Weber’s Law Here!

Thresholds: �Signal Detection Theory

• Set of formulas and principles that predict when we will detect the presence of a faint stimulus (signal) amid background stimulation (noise)
• Developed out of the Cold War & need to detect nukes
• Seeks to understand:
1. Why people respond differently to the same stimuli ?
2. Why the same person’s reactions would vary as circumstances change?
• Example: Tired parents of newborns will awaken to a whimper but sleep through their alarm.

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Signal Detection Theory�

• This theory replaced Weber’s Law
• Explains why people respond differently to same stimuli
• Whether or not you detect a stimulus is dependent upon 3 kinds of variables (assumes there is no absolute threshold):
1. Stimulus variables (how weak or strong the stimulus is)
2. Environmental variables (what’s going on around you)
3. Organismic variables (Your own experience, expectations, motivation and alertness)

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Detect “real” hamburger amongst soy burger

Where’s Waldo?

Detect poisonous snake amongst harmless ones

Signal Detection Theory

This can be used for jobs that depend on one’s ability to accurately detect a threat/stimulus. (Cold War Nuke Detection, Airport Security, Cancer Doctor, Referee)

Signal Detection Theory

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Liberal:

Person more likely to correctly detect

A signal but also more likely to falsely

detect a signal.

Conservative:

Person less likely

to detect a signal but more likely to correctly notice when stimulus is not there.

Do subliminal messages work?

• Subliminal messages make two assumptions:
• We can unconsciously sense the subliminal (below threshold) message. - TRUE
• Without our awareness, the stimuli have suggestive powers. - FALSE
• Subliminal messages can PRIME how we “feel” about something for a short period of time but CANNOT persuade us to actually go out and do something. (pg. 158 in text)
• Remember, weak stimuli have weak responses and strong stimuli have strong responses.
• Which would be better to remind you of your homework?
• A screen that flashes your assignment in 1/40 of a second?
• Saying it out loud while having it written on the screen behind me?

I Love Psych!!!

Did it work?

• Do you really love psychology now?
• It was worth a try!
• This is an example of priming someone to feel or think a certain way for a very short period of time.

Sensory Adaptation

Sensory Adaptation

• Diminished sensitivity to an unchanging stimululs
• If a stimulus is constant, eventually a person may fail to respond to it
• Move your watch up your wrist an inch or put your ring on a different finger. You will feel it at first but later you won’t notice it. Your senses have adapted to it.
• This is why the lake water is cold at first but you “get used to it.”
• Also why you don’t feel your glasses on your nose or your clothes on your body.
• Remember the displacement goggles experiment from class. This showed motor adaptation to a change in vision.

Come on in, the water’s fine