The FROC Curve: A Representation of the Observer's Performance for the Method of Free Response

In a YES-NO signal detection task, the observer's performance can be represented by an ROC curve. In a free-response task, an ROC curve cannot be plotted because the observation interval is not defined. However, if the responses can be partitioned into hits and false alarms, then the observer's performance can be represented by an FROC curve, which possesses many of the properties of an ROC curve. FROC curves are obtained from a single observer in a vigilance task to demonstrate its use.