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Low target prevalence is a stubborn source of errors in visual search tasks
Jeremy M Wolfe1, Todd S Horowitz, Michael J Van Wert
1Visual Attention Lab, Brigham and Women's Hospital, Cambridge, Massachusetts 021139-4170, USA. wolfe@search.bwh.harvard.edu
Journal of Experimental Psychology. General
|November 15, 2007
Summary
Target detection is harder when targets are rare. This visual search study shows retraining with high target prevalence improves performance in low prevalence search tasks, reducing dangerous miss errors.
Area of Science:
- Cognitive psychology
- Human visual perception
- Search behavior
Background:
- Visual search tasks involve identifying targets among distractors.
- Target miss rates are significantly higher under low target prevalence conditions (1%-2%) compared to high prevalence (50%).
- Low prevalence search is critical in fields like airport security and medical screening, where misses have serious consequences.
Purpose of the Study:
- To investigate the robust 'prevalence effect' in visual search.
- To determine if the prevalence effect is due to a shift in decision criterion or a change in sensitivity.
- To explore methods for mitigating the negative impact of low target prevalence on search performance.
Main Methods:
- Conducted a series of experiments manipulating target prevalence in visual search tasks.
- Analyzed miss error rates across different prevalence levels.
- Utilized signal detection theory to interpret findings regarding criterion shifts versus sensitivity changes.
- Tested the efficacy of retraining strategies involving high prevalence and feedback.
Main Results:
- Confirmed the prevalence effect is highly robust, with significantly higher miss rates at low target prevalence.
- Demonstrated that the prevalence effect is primarily a criterion shift, not a change in perceptual sensitivity.
- Found that attempts to directly induce better criterion adoption were largely unsuccessful.
- Showed that brief retraining with high prevalence and full feedback enabled observers to maintain an appropriate criterion during low prevalence search without feedback.
Conclusions:
- The prevalence effect significantly impairs performance in critical low prevalence search tasks.
- Standard signal detection models explain the prevalence effect as a conservative criterion shift.
- Targeted retraining, simulating high prevalence conditions with feedback, offers a viable method to improve criterion control in low prevalence visual search.
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