1. Thresholds & sensory adaptation

2. Absolute Thresholds
The minimum stimulation needed to detect a particular stimulus 50% of the time
Changes with age
Mosquito ringtones
Welsh Shopkeepers
Dog Whistler: Everybody raise one hand in the air; when you hear the sound, lower your armh
The point at which you can hear the dog whistle is your absolute threshold
I can hear it at 15,000 Hz (Herz)

3. Signal Detection Theory
How and when we detect the presence of faint stimuli amid background stimulation
According to theory- there is no definite absolute threshold
What factors may change the threshold?

4. Subliminal Stimulation- “Below Threshold” (literally)
Below one’s threshold for conscious awareness
We CAN detect the stimulus some of the time (about half)
But do subliminal messages actually affect us?
Simple answer: NO!
Subliminal messages may prime us, but they will not actually alter our behavior
Hair Growth Subliminal
Zoolander Subliminal

5. Difference Threshold
Minimum difference between two stimuli required for detection 50% of the time (experienced as just noticeable difference)
Weber’s Law
To be perceived as different, two stimuli must differ by a constant percentage (rather than constant amount)

6. Sensory Adaptation
Diminished sensitivity as a consequence of constant stimulation
Smelly Houses
Allows us to focus on informative changes in our environment without being distracted by stimuli that are constantly present
We perceive the world NOT exactly as it is, but as it is useful for us to perceive it

7. Summary What are the absolute and difference thresholds?
Do stimuli below the absolute threshold have any influence?
What does sensory adaptation allow us to do?