1. Chapter 4(B): Thresholds and Sensory Adaptation
Ms. Saint-Paul
A.P. Psychology

2. Transduction
The process of converting one form of energy into another that your brain can use.
All of our senses
Receive sensory stimulation from a physical stimulus
Transform that stimulation into neural impulses
Deliver the neural information to our brain
Example: Think of this as the way a bar-code reader converts a series of lines into an electrical signal that a computer can match with a price.

3. Psychophysics
The study of relationships between the physical characteristics of stimuli (such as their intensity) and our psychological experience of them
Physical World
Psychological World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet

4. Thresholds Absolute Threshold:
The minimum stimulation needed to detect a particular stimulus 50% of the time
Proportion of “Yes” Responses
Stimulus Intensity (lumens)
Absolute Threshold:

6. Difference Threshold
The minimum difference that a person can detect between two stimuli.
Also known as Just Noticeable Difference (JND)
The smallest amount by which a stimulus can be changed and the difference be detected, half of the time.
Think about when you are watching TV and a commercial comes on. Can you tell a difference?

7. Thresholds Subliminal:
Below one’s absolute threshold for conscious awareness

8. Let’s look at a few subliminal clips
Wendy’s
Frozen
Disney

9. Laws of sensation : Weber’s Law
Ernst Weber noted that for people to really perceive a difference, the stimuli must differ by a constant "proportion" not a constant "amount". 

10. Signal Detection Theory
Assumes that we do not have an absolute threshold.
Predicts how we detect a stimulus amid other stimuli.
We detect stuff based on our experiences, motivations and fatigue level.
Reactions to a stimulus can be categorized as:
hit, miss, false alarm, correct rejection

11. Sensory Adaptation
Sensory adaptation is the diminishing responsiveness of our sensory systems to prolonged stimulation.
Unless it is quite intense or painful, stimulation that persists without change in intensity usually shifts to the background of our awareness.
Until now, many of you are probably unaware that your sense of touch had adapted to the pressure of the chair against your legs.
Do you feel your underwear all day?

12. Review
What is psychophysics? How does it connect sensation with perception?
What is an absolute threshold?
What are some implications of Signal Detection Theory?
What does Weber’s Law suggest about difference thresholds?