Results of empirical studies using computerized tests of sustained attention are summarized. Factors that affect vigilance performance fall into three broad categories: task parameters, environmental or situational factors, and subject characteristics. Complex interactions of factors from each category affect performance further. Such interactions may help to explain inconsistencies in the literature regarding effects on vigilance. Implications for both research and clinical practice are discussed.

The purpose of this study was to compare a recently developed response-inhibition task (Conners, 1995) to slow-and fast-event-rate versions of the traditional A-X Continuous Performance Test (CPT). Among 146 normal adults, results revealed signi®cant differences between tasks in omission and commission error rates, reaction time, reaction time variability, and responses to critical signals. Effects of environmental noise and participant anxiety also differed for the three tasks. Traditional CPTs produced time-related performance decrements, but the response-inhibition task produced improvement across initial blocks of trials. The response-inhibition task may measure``executive control'' rather than sustained attention, and therefore may represent functions of different brain systems.In both clinical practice and experimental research, neuropsychologists need tests of fundamental attention skills, including the ability to sustain attention over time. The continuous performance test (CPT) is a``vigilance task'' used to study sustained attention and to assess``attention de®cits''. Several variations of the task have been marketed, some of which differ markedly from the traditional CPT. For such tests to be useful, the factors affecting performance must be carefully delineated and compared with the rich body of literature on vigilance tasks. The purpose of the present study was to compare one of the newer tasks with traditional CPTs. The following sections present a description of the traditional CPT, a brief overview of factors affecting CPT performance, and a summary of neuroanatomical models of attention. Next, the characteristics of the``S tandard'' task marketed by Multi-Health Systems (MHS-Standard; Conners, 1995) are compared to those of traditional CPTs. Finally, results are presented from an empirical study of performance on the MHS-Standard and two variations of the traditional CPT.

In a sample of 163 college undergraduates, the effects of task demand, noise, and anxiety on Continuous Performance Test (CPT) errors were evaluated with multiple regression and multivariate analysis of variance. Results indicated significantly more omission errors on the difficult task. Complex interaction effects of noise and self-reported anxiety yielded more omissions in quiet intermittent white noise, particularly for high-anxious subjects performing the difficult task. Anxiety levels tended to increase from pretest to posttest, particularly for low-anxious subjects in the quiet, difficult-task condition, while a decrease was seen for high-anxious subjects in the loud, easy-task condition. Commission errors were unrelated to any predictor variables, suggesting that "attention" cannot be considered a unitary phenomenon. The variety of direct and interactive effects on vigilance performance underscore the need for clinicians to use a variety of measures to assess attentional skills, to avoid diagnosis of attention deficits on the basis of a single computerized task performance, and to rule out anxiety and other contributors to poor vigilance task performance.

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