Chapter 2: Signal Detection and
Absolute Judgement
Slide Template
SIGNAL DETECTION THEORY
The Signal Detection Paradigm
• Hit, misses, false alarms and correct
rejections.
The Signal Detection Paradigm
• Change in the evidence variable caused by a
weak and strong signal.
The Signal Detection Paradigm
• Hypothetical distribution underlying signal
detection theory and sensitivity
Setting the Response Criterion:
Optimally in SDT
• Signal probability. Optimal beta.
• Payoffs. Expected value.
Setting the Response Criterion:
Optimally in SDT
• Human Performance in Setting Beta.
• Sluggish beta.
• Relationship between obtained and optimal
decision criteria.
Sensitivity
• Misses result because of high beta or low
sensitivity
THE ROC CURVE
Theoretical Representation
• Receiver Operating Characteristic (ROC) curve
Theoretical Representation
• Analysis of confidence ratings in signal
detection tasks.
Theoretical Representation
• Z-scores.
Empirical Data
• Distinction between theoretical data and
actual empirical data collected in an
experiment
FUZZY SIGNAL DETECTION THEORY
Fuzzy SDT
• Combining SDT and fuzzy logic.
• Mapping function.
APPLICATIONS OF SDT
Medical Diagnosis
• Disease prevalence.
Recognition Memory and Eyewitness
Testimony
• Relative judgment
Alarm and Alert Systems
• SDT and warning signals
Alarm and Alert Systems
• Alarm false alarms
– Minimum safe altitude warning
• Solutions:
– Use multiple alarm levels
– Raise automated beta slightly
– Keep the human in the loop
– Improve operator understanding of alarm false
alarms.
VIGILANCE
Target versus non-target events
• Vigilance level and vigilance decrement
Measuring Vigilance Performance
• Influences on sensitivity
• Changes in bias
Theories of Vigilance
• Arousal theory
Theories of Vigilance
• Sustained demand theory.
• Expectancy theory.
Techniques to Combat the Loss of
Vigilance
• Increasing sensitivity:
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show target examples
increase target salience
reduce the event rate
train observers
• Shift in Response Criterion.
– Instructions, knowledge of results, false signals,
confidence levels
• Other techniques
– Arousal and fatigue
Application
• Inside and outside the Laboratory
• Examples
– Situation Awareness
ABSOLUTE JUDGMENT
Quantifying Information
• Bits
Single Dimensions
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Experimental Results
Channel capacity
Bow Effect
Applictions
Multi-dimensional Judgment
• Orthogonal Dimensions
Multi-dimensional Judgment
• Correlated Dimensions
Multi-dimensional Judgment
• Dimensional Relations:
– Integral and Separable.
– Garner Sort task.
Multi-dimensional Judgment
• Configural Dimensions
– Emergent features.
• Summary
Multi-dimensional Judgment
• Implications of Multi-Dimensional Absolute
Judgment
– Example of configural dimensions for the heights
and widths of rectangles