Thresholds & sensory adaptation

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)

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?

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

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)

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

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?