ROC Curves for Multiple-Signal Levels in a Detection Task

Abstract

Seven signal levels were presented to four observers in a pseudorandom fashion. A 500-Hz tone was used, and the signal duration was maintained at 100 msec with a rise-decay time of 10 msec. Wide-band (100–3000 Hz) continuous noise was used as the masker. The listening interval was indicated by a light, and observers were instructed to clarify or rate the loudness of the masked signal by using one of 10 ordered push buttons. On some trials noise alone was present; on the remaining trials (2E/N0)12 ranged from 2.0–5.0. Receiver operating characteristics were plotted for each signal level, and a remarkably small number of trials was needed to yield satisfactory curves. The multiple-level rating procedure yields smooth curves for seven signal levels in about the same time previously needed for only one level. The observer's task, to rate the loudness of the stimulus, appeared to be simpler than that of earlier studies, in which he was asked to rate his “certainty” that a signal was present. [Work supported by a contract with the Naval Ship Systems Command, Department of the Navy, and through a grant from the National Aeronautics and Space Administration.]