SENSATION AND AND PERCEPTION

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SENSATION AND AND PERCEPTION
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Young girl?.
Woman looking in Vanity?...
Or old woman?
Or Skull?
Womans Silhouette?...
Or Man Playing Horn?
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Sensation Perception

• S. the collection of information by sensory
  organs
• P. the interpretation of sensory information

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Psychophysics
G. F. Fechner (1801 1887)
E. H. Weber (1795 1878)

• How physical stimuli relate to psychological
  phenomena
• How much light to detect? (DETECTION)
• How small difference in sound can be detected?
  (DIFFERENCE)
• Perception of changes in stimulus magnitude
  (SCALING)

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Detection
HOW MUCH ENERGY?
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Absolute Thresholds

• Vision Candle flame from 30 miles on a
  clear night
• Hearing Tick of a watch from 20 feet in
  total quiet
• Smell 1 drop of perfume in a 6-room
  apartment
• Touch Wing of a bee on your cheek from 1 cm
• Taste 1 tsp. sugar in 2 gal. water

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Subliminal Perception

• Can we detect subliminal (below awareness
  threshold) information?
• Priming (Doctor Nurse vs. Doctor Coffee)
• Can we be influenced by subliminal information?
• CBC Experiment (1958)

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Signal Detection
Or Whats Green and Swets?

• Detection of signals involves both sensory
  processing and decision making
• Physiological sensivity
• Bias (motivation, personality, expertise, etc.)

FALSE ALARM
HIT
CORRECT REJECTION
MISS
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Difference Thresholds (JND)

• Difference threshold (JND) - the minimum amount
  by which stimulus intensity must be changed in
  order to produce a noticeable variation in
  sensory experience.

• Webers Law - the JND is a constant proportion of
  the initial stimulus value.

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• Webers Constants
• Pitch of a tone 1/333
• Lifted weight 1/50
• Visual brightness 1/60
• Cutaneous pressure 1/7
• Taste for saline 1/5

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Scaling
S.S. Stevens (1906-1973)
How do changes in stimulus intensity change our
perceptions of the stimulus magnitude?
Stevens Power law perceived stim mag (actual
mag)K
1 in. (1 in.)1
2 in. (2 in.)1
12 in. (12 in.)1
4 lbs. (2 lbs.)2
144 lbs. (12 lbs.)2
1 lb. (1 lb.)2
1 lux (1 lux).5
2 lux (4 lux).5
3 lux (9 lux).5