The Vigilance Decrement Reflects Limitations in Effortful Attention, Not Mindlessness Rebecca A. Grier, Joel S. Warm, William N. Dember, Gerald Matthews, and Traci L. Galinsky, University of Cincinnati, Cincinnati, Ohio, James L. Szalma, University of Central Florida, Orlando, Florida, and Raja Parasuraman, Catholic University of America, Washington, D.C. Robertson, Manly, Andrade, Baddeley, and Yiend (1997) proposed that the decline in performance efficiency over time in vigilance tasks (the vigilance decrement) is characterized by "mindlessness" or a withdrawal of attentional effort from the monitoring assignment. We assessed that proposal using measures of perceived mental workload (NASA-TLX) and stress (Dundee Stress State Questionnaire). Two types of vigilance task were employed: a traditional version, wherein observers made button-press responses to signify detection of rarely occurring critical signals, and a modified version, developed by Robertson et al. to promote mindlessness via routinization, wherein button-press responses acknowledged frequently occurring neutral stimulus events and response withholding signified critical signal detection. The vigilance decrement was observed in both tasks, and both tasks generated equally elevated levels of workload and stress, the latter including cognitions relat- ing to performance adequacy. Vigilance performance seems better characterized by effortful attention (mindfulness) than by mindlessness. Actual or potential appli- cations of this research include procedures to reduce the information-processing demand imposed by vigilance tasks and the stress associated with such tasks. INTRODUCTION Vigilance or sustained attention tasks typi- cally require observers to monitor displays over extended periods for the occasional occurrence of critical events (signals). The signals are usual- ly embedded in a context of recurrent nonsignal (neutral) events that, unlike signals, require no overt response from observers. Signal probabil- ity is low: Typically, in laboratory research, only 2% to 5% of the events displayed are critical signals. In "real-world" instances, signal proba- bility may be even lower (Parasuraman, Warm, & Dember, 1987). Vigilance tasks and the pro- cesses that influence their performance are of interest to human factors/ergonomics special- ists because of the vital role that vigilance plays in automated human-machine systems in trans- portation, process and quality control, medi- cine, and - of special interest currently - bag- gage inspection at airport security checkpoints (Hancock & Hart, 2002; Wickens & Hollands, 2000). Traditionally, vigilance tasks have been con- sidered as tedious but benign assignments that place little demand on monitors, and the vigi- lance decrement - the decline in signal detections over time that typifies vigilance performance -has been viewed as resulting from task underload and consequent underarousal (Nachreiner & Hanecke, 1992). Recent studies indicate, howev- er, that vigilance tasks, though tedious, impose a substantial mental burden on monitors, as reflect- ed in high scores on the NASA Task Load Index (NASA-TLX), a measure of the perceived mental workload incurred in performing a task (Hitch- cock, Dember, Warm, Moroney, & See, 1999; Temple et al., 2000; Warm, Dember, & Hancock, Address correspondence to Joel S. Warm, D tmetUof Psychology, University of Cincinnati, Cincinnati, OH 45221; joel.warnm@uc.edu. HUMAN FACTORS, Vol45 Nj3 Fall 2003, pp. 349-359. Copyright © 2003, Human Factors and Ergonomics Society. All rights reserved.