The Limits of Visual Inspection
Interesting research:
Target prevalence powerfully influences visual search behavior. In most visual search experiments, targets appear on at least 50% of trials. However, when targets are rare (as in medical or airport screening), observers shift response criteria, leading to elevated miss error rates. Observers also speed target-absent responses and may make more motor errors. This could be a speed/accuracy tradeoff with fast, frequent absent responses producing more miss errors. Disproving this hypothesis, our experiment one shows that very high target prevalence (98%) shifts response criteria in the opposite direction, leading to elevated false alarms in a simulated baggage search. However, the very frequent target-present responses are not speeded. Rather, rare target-absent responses are greatly slowed. In experiment two, prevalence was varied sinusoidally over 1000 trials as observers’ accuracy and reaction times (RTs) were measured. Observers’ criterion and target-absent RTs tracked prevalence. Sensitivity (d’) and target-present RTs did not vary with prevalence. These results support a model in which prevalence influences two parameters: a decision criterion governing the series of perceptual decisions about each attended item, and a quitting threshold that governs the timing of target-absent responses. Models in which target prevalence only influences an overall decision criterion are not supported.
This has implications for searching for contraband at airports.
David • February 8, 2010 5:16 PM
Wait a second, is this saying that by changing the search for a rare threat, say bombs, into a search for something more common like 3+oz hair gel containers they actually catch more bombs (since it’s part of the larger class)?
Is the ban/search for nail files and scissors really the best way to search for more dangerous knives and weapons?
If so, it could explain the odd policy behavior of the TSA, even if these are in fact misconceptions.