Psych lecture 12 October 22, 2013
• Subliminal perception
• Visual systems
• What do Weber fractions tell you about sensation?
• Can we perceive subliminal messages?
• How do visual systems work?
Next Time: More about vision pages 150-158
• How do we perceive the world around us
• Psychophysics: relationship between physical and psychophysical response
o Fechner is the father of psychophysics
o Can determine a just noticeable difference (JND)
o Threshold: value of stimulus characteristics required to produce some response
o Absolute: lower limit
Vision: can see candle flame at 50km
Hearing: tick of a watch at 6m
Taste: tsp. of sugar in 8L of water
Smell: 1 drop of perfume in a 6 room apartment
Touch: wing of a fly falling on cheer from 1cm
Difference: amount of change for JND
• Relationship: brightness & perceived brightness. (not 1:1
• Webers law (see picture on phone) size of difference threshold
relative to physical intensity of test is constant. (JND for hearing =
• The value of a JND is not cons