SYSTEM OPERATOR RESPONSE TO WARNINGS OF DANGER - A LABORATORY INVESTIGATION OF THE EFFECTS OF THE PREDICTIVE VALUE OF A WARNING ON HUMAN RESPONSE-TIME

An automated detector designed to warn a system operator of a dangerous condition often has a low positive predictive value (PPV); that is, a small proportion of its warnings truly indicate the condition to be avoided. This is the case even for very sensitive detectors operating at very strict thresholds for issuing a warning because the prior probability of a dangerous condition is usually very low. As a consequence, operators often respond to a warning slowly or not at all. Reported here is a preliminary laboratory experiment designed in the context of signal detection theory that was conducted to examine the effects of variation in PPV on the latency of participants' response to a warning. Bonuses and penalties placed premiums on accurate performance in a background tracking task and on rapid response to the warnings. Observed latencies were short for high values of PPV, bimodal for middle-to-low values, and predominantly long for low values. The participants' response strategies for different PPVs were essentially optimal for the cost-benefit structure of the experiment. Some implications for system design are discussed.