Psychology Lecture 13
Psychophysics, Subliminal Perception, Visual System
1. What do Weber fractions tell you about sensation?
2. Can we perceive subliminal messages?
3. How does the visual system work?
How do we perceive he world around us?
Psychophysics and psychophysiology
Relationship between physical stimulus and psychological response
Fechner – Father of psychophysics
Can determine a just noticeable difference (JND)
Change something and measure how they notice a difference
Value of a stimulus characteristic required to produce some response
Absolute: Lower limit
o Absolute Thresholds
Candle flame at 50km
Tick of a watch at 6m
Tsp. of sugar in 8L of water
1 drop of perfume in a 6 room apartment
Wing of a fly falling on your cheek at a distance
of 1 cm
o Amount of change necessary for a JND
o Ex. Brightness and perceived brightness
Not a 1 to 1 relationship
Doubling light in a room doesn’t make it twice
as bright for a person perceiving it
o Weber’s Law
Size of difference threshold relative to physical intensity
of test is constant ( Change in Intensity (I) / I = Constant Ex. If I is 50 db, and a JND is reported at 55 db
Would be 5/50 therefore 1/10
o Can predict other JND at other
What is JND at 100 db?
1/10 = Change in I / 100
So Change in I is 10
Therefore JND wil