How do we make decisions about uncertain events? - PowerPoint PPT Presentation

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How do we make decisions about uncertain events?

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How do we make decisions about uncertain events?
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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