Auditory vigilance as affected by signal rate and intersignal interval variability

Abstract

Vigilance performances consisting of auditory threshold, latency and false-positive responses measures were obtained from 24 Navy and civilian subjects during the course of six daily 48-minute monitoring sessions in which Ss pressed a microswitch to report single tones in signal trains of increasing intensity. Six signal densities from 2.5 to 120 signals per hour, and six intersignal intervals ranging from 0 to 108 seconds around a signal rate of one per minute were found to have no differential effect on auditory threshold. An improvement of 3.25 dB in signal/noise detection occurred when signal density was increased from 2.5 to 15 per hour. Higher rates were not additionally effective. Below the rate of 15/hour, response latency increased regularly with the slower rates, though there was no further improvement with higher signal densities. Thus a rate of about one signal every four minutes was the most efficient density. Time-on-watch analysis revealed large individual differences. An analysis of false-positive responding indicated that false alarms were unrelated to signal rate, intersignal variability, or listening session.