Detecting hidden targets: a procedure for studying performance in a mine-detection-like task

We report preliminary results from an experiment designed to study the perceptual and learning processes involved in the detection of land mines. Subjects attempted to identify the location of spatially distributed targets identified by a sweeping a cursor across a computer screen. Each point on the screen was associated with a certain tone intensity; targets were louder than 'distractor' objects. We looked at the effects on target detection and false-alarm rates of the intensity difference between target and distractor signals, the number of distractor signals, the number of distractors and training order. The time to detect 50 percent of targets was measured by a rapid adaptive technique which generated reliable thresholds within few trials. The result are consistent with a simple model for the detection of cryptic prey by foraging predators: search was slower with more distractors, and the effect of distractors was greater when S/N ratio was lower. Although subjects got no accuracy feedback, performance improved somewhat with experience and was slightly better in the low S/N condition when it followed the high S/N condition. The procedure seems to be a useful one for studying more complex mine-related detection tasks with a range of signal types and numbers of concurrent detection signals.