Perceived urgency of and response time to multi-tone and frequency-modulated warning signals in broadband noise

Several pulse parameters that were believed to affect the perceived urgency and response time to auditory warning signals were investigated in a factorial experiment. The independent variables included pulse format (sequential, simultaneous, and frequency-modulated pulses), pulse level (65 and 79 dBC), and inter-pulse interval (0, 150 and 300 ms). The applications environments of interest were those having steady-state broadband noise. A probability monitoring task from the Criterion Task Set was used as an operator loading task to impose additional attentional demands during the signal detection and response task. The psychophysical methods of free-modulus magnitude estimation and paired comparison were used to measure subjective perceived urgency. An objective measure of response time to the signal was also obtained. Multivariate statistical analyses indicated that response time decreased significantly as perceived urgency increased. Perceived urgency of the signal increased and response time decreased as pulse level increased. Sequential signals took longer to detect and were rated as less urgent than the other two signal types. Shorter inter-pulse interval was associated with greater perceived signal urgency.