The Effects of Raised Signal and Noise Amplitude During the Course of Vigilance Tasks

Abstract

Using the auditory vigilance task developed by Wilkinson, Edwards, and Haines (1966) in which tones of a short rather than a long duration are defined as signals, the amplitude at which both signals and non-signals were relayed to subjects was varied between four groups. In the 70 dB and 90 dB groups, the sound pressure level at the ear was 70 dB and 90 dB, respectively, for the duration of the task. For the 70/90 dB and 90/70 dB groups, the amplitude of the input was changed to the higher and lower levels, respectively, halfway through the task. All tests were conducted between 0800 and 0900 hours.

Although the changed amplitude did not affect the physical S/N ratio, changes in detections, false alarms, d’, and β resulted. Of particular interest were the findings (1) that increased amplitude increased d’ and reduced β, (2) that decrement resulted from both d’ and β changes, and (3) that whereas all other groups showed a significant decrement, the 70/90 dB group showed a “vigilance increment” over time.