Vigilance Performance Declines Faster When Monitoring for a Signal in Two Modalities Compared to One

Vigilance is the maintenance of attention over prolonged periods, often required when attempting to detect infrequent and/or difficult to detect stimuli, such as in baggage screening or sonar monitoring. This type of attention is characterized by the vigilance decrement: longer reaction times and decreased accuracy as time-on-task increases. Research previously demonstrated the vigilance decrement in auditory and visual vigilance tasks. However, little research has compared the strength and onset of the vigilance decrement in unimodal (auditory or visual) versus bimodal (auditory and visual) modalities. This knowledge gap was investigated in an experiment that first equated the discriminability of stimulus type at ~80% to control for stimulus difficulty and then by tracking subjects' target identification rate and reaction time for a target intermixed with a nontarget across three conditions: auditory, visual, and audiovisual. Overall, accuracy was worse in the bimodal condition relative to the unimodal condition. Target detection accuracy in the auditory bimodal condition declined more over time relative to the auditory unimodal task, with reaction time data suggesting the decrease was not due to a speed-accuracy trade-off. Results indicate that monitoring for targets in two modalities is more difficult, resulting in a greater vigilance decrement than unimodal vigilance.