Reading Reference: Chapter 5
- How do we perceive the world around us?
- Psychophysics & psychophysiology
Psychophysics: relation between physical stimulus and psychological response
Ex. Light stimulates visual system which enables vision (response)
- Fechner: “father” of psychophysics
- Can determine a just noticeable difference (JND)
o Value of a stimulus characteristics required to produce some response
o Absolute lower limit of perception
- Vision: Candle flame at 50km. on a dark clear night with no obstructions
- 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 cheek from 1 cm.
Difference Threshold: Amount of change for JND
- What is the relation?
- Ex. Brightness and perceived brightness
- Not a 1 to 1 ratio
- Size of difference threshold relative to physical intensity of the test stimulus is constant
- Δ I/ I = C
- Ex. If I = 50db and a JND is reported at 55db… C = 5/ 50 = 1/10
1. Can predict other JND’s, if a JND is at 100db? 10 Δ I = 100 ΔI = 10
o A JND would occur at:
New test + 10 = 110 db
New test – 10 = 90 db
o The JND is proportional to test intensity
o The value of a JND is NOT constant
o The relative difference is constant
2. Can compare sensitivity of different systems: the smaller the Weber constant, the better
and more sensitive the system.
o Vision ( brightness) = 1/60
o Kinesthesis (weights) = 1/50
o Pain (thermal) = 1/30
o Audition (mid. Pitch; mod. Loud)