Effects of signal to noise variability over repeated sessions in an auditory vigilance task

Subjects listened to a sequence of Gaussian noise pulses of 0.5-sec duration, occurring at 2.5-sec intervals. Performance was compared under two conditions: One group detected the occurrence of a 1.8-dB increment in noise pulses; a second group detected the occurrence of increments of 1.3, 1.8, or 2.3 dB. All Ss performed for three 90-min sessions on different days The usual trends were noted for hits and false alarms. TSD indices, d’ and β were also derived. For both groups, it was found that d′ increased slightly over sessions and decreased almost negligibly during sessions, and criterion indices, β generally increased slightly both within and over sessions. Performance was generally comparable under the fixed- and mixed-signal conditions.