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How do we make decisions about uncertain events?

How do we make decisions about uncertain events?. Psychophysics Absolute and Difference Thresholds Weber’s Law and Fechner’s Law The concept of the jnd (just-noticeable difference) Signal detection and Decision Theory Response bias: payoffs and expectations

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How do we make decisions about uncertain events?

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  1. How do we make decisions about uncertain events? • Psychophysics • Absolute and Difference Thresholds • Weber’s Law and Fechner’s Law • The concept of the jnd (just-noticeable difference) • Signal detection and Decision Theory • Response bias: payoffs and expectations • Liberal vs. conservative strategies

  2. Physical Stimulus Perception

  3. 100 90 80 70 60 50 40 30 20 10 0 Step function Ogive % presentations detected Idealized Actual 0 6 8 10 12 14 Intensity of stimulus The absolute threshold of detection:idealized and actual

  4. 100 90 80 70 60 50 40 30 20 10 0 % presentations detected 0 6 8 10 12 14 Intensity of stimulus How to obtain empirically an individual’s absolute detection threshold:

  5. “Is the stimulus there?” (yes, no) standard stimulus comparison stimulus “Is the comparison stimulus “stronger” than the standard stimulus?” (yes, no) Finding the Absolute threshold: Finding the Difference threshold:

  6. 100 90 80 70 60 50 40 30 20 10 0 % differences detected 10 11 12 13 14 15 Intensity of comparison stimulus How to obtain empirically an individual’s difference threshold: (standard stimulus) Difference threshold = I = 12.7 – 10 = 2.7 stimulus units

  7. I c I c I or I I (difference threshold) I (Intensity of Stimulus) Weber’s Law:

  8. Fechner’s Law: S = k log I S8 S7 S6 S5 S4 S (Sensation Units or JND’s) S3 S2 I I I S1 S0 0 20 40 60 80 100 I (Intensity of the stimulus)

  9. Stimulus present Stimulus absent Responds “yes” Responds “no” A single Signal Detection trial Reality: Hit False Alarm Decision: Miss Correct rejection

  10. Stimulus present Stimulus absent $2 -$2 Responds “yes” 70% 40% $0 $0 Responds “no” 30% 60% Session 17: Payoff matrix is $2 for hit and -$2 for false alarm Reality: Hit False Alarm Decision: Miss Correct rejection

  11. Stimulus present Stimulus absent $2 $0 Responds “yes” 100% 100% $0 $0 Responds “no” 0% 0% Session 22: Payoff matrix is $2 for hit and $0 for false alarm Reality: Hit False Alarm Decision: Miss Correct rejection

  12. Stimulus present Stimulus absent $0 -$2 Responds “yes” 0 0 $0 $0 Responds “no” 100% 100% Session 18: Payoff matrix is 0 for hit and -$2 for false alarm Reality: Hit False Alarm Decision: Miss Correct rejection

  13. Experimental Conditions (Payoff schedule) Hypothetical results (Hit, F.A.) % hits %F.A. 1. ($0, -$2 ) 0% 0% 2. ($1, -$2) 40% 10% 3. ($2, -$2) 70% 40% 4. ($2, -$1) 90% 70% 5. ($2, $0) 100% 100% Summary of sample results:

  14. 1. 0% 0% 0% 2. 25% 40% 10% 3. 50% 70% 40% 4. 75% 90% 70% 5. 100% 100% 100% Summary of sample results: Experimental Conditions (Expectation of signal) Hypothetical Results % hits %F.A. % of trials observer thinks signal is present

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