Impact of Cognitive Demand on Vigilance Decrement: An Overview

Abstract

Vigilance refers to the ability of the individuals to maintain their focus of attention and to remain alert to stimuli over prolonged periods of time (Davies & Parasuraman, 1982; Parasuraman, 1986; Warm, 1984, 1993). The progressive decline in performance with time on vigilance task has been termed the decrement function (Dember & Warm, 1979) or the vigilance decrement (Davies & Parasuraman, 1982). Although vigilance research started long ago but interest in this area keeps mounting by the day. Vigilance is a phenomenon which attracts researchers not only for its practical implications in automation driven world but also because it provides an opportunity to understand almost all of the factors that may be considered to influence attention. Enthusiasm in vigilance research remains intact as human-machine interaction has evolved to new dimensions where human operator has become merely a passive observer waiting for critical signals that demand decision and action (Adams, Stenson, & Humes, 1961; Adams, 1963; Sheridan & Ferrell, 1974). Viewed in the context of an automation-oriented society, in which failures to detect critical signals can often be disastrous the problem of vigilance assumes considerable significance.Vigilance performance has been found to be related to a wide variety of factors. These include several psychophysical parameters like background event rate, sensory modality and signal conspicuity as well as several neurophysiological parameters as revealed through pupilary responses, EEG activity, blood catecholamines levels and the actions of pharmacological agents (Dember & Warm, 1979; Davies & Parasuraman, 1982; Beatty, 1982). In addition to these measures of vigilance performance, there are a number of studies that have shown that vigilance imposes high workload and is stressful (Warm, Parasuraman, & Matthews, 2008) and that the workload and stress of vigilance is moderated by the psychophysical properties of the task and the categories described in the taxonomy (Warm, Dember, & Hancock, 1996). Researchers have used various tasks in vigilance studies. These tasks can be presented in different sensory modalities and use different psychophysical dimensions to define critical signals. This led to a view that vigilance is not a unitary process, instead vigilance was considered to be task specific and controlled by the different processes in different tasks. To resolve this diversity in findings of vigilance research Parasuraman and Davies proposed attentional resource theory (Fisk & Scerbo, 1987; Fisk & Schneider, 1981; Kahneman, 1973; Wicken, 1984) as a framework. Resource model propagated that vigilance tasks arc highly demanding leading to depletion of information processing resources at a high rate which are not replenished in the time available. This leads to vigilance decrement. The more demand a task imposed on the observer, more is the depletion of resources.Cognitive demandVigilance tasks have traditionally been viewed as mentally undemanding and under stimulating. However, recent discoveries in vigilance research have proven that consideration to be wrong. It has been established through a number of studies that vigilance imposes high workload and is mentally demanding. Parasuraman (1979) proposed that vigilance tasks could be categorized by whether target detection required successive or simultaneous discrimination and that these tasks imposed differential demands on attentional resources. Successive tasks require absolute judgment in which observers need to compare current input with a standard retained in memory to separate target signals from non-target. Whereas, simultaneous tasks require comparative judgment in which all the information necessary to distinguish target stimuli from non-target stimuli is available in the stimuli itself. Successive tasks are more capacity demanding than simultaneous tasks due to involvement of distinct memory functions. …