Extended Abstract: Utilizing Event Rate As a Manipulation of Task Difficulty in Vigilance
Authors: Claypoole Victoria L. , Denver Daryn , Denues Kody , Szalma James L. 
Published: October 2017

Vigilance refers to the ability of an observer to maintain attention over extended periods of time, and to respond to critical signals that occur (Davies & Parasuraman, 1982). Vigilance has been examined since the late 1940s when anecdotal evidence suggested that naval operators missed more critical signals (signifying the presence of enemy submarines) on their displays the longer they were on watch. Mackworth (1948) confirmed this anecdotal evidence; vigilance declined quickly as the task progressed and more critical signals were missed the longer a participant stayed on task (i.e. the vigilance decrement). Although the research on vigilance originated almost 70 years ago, it continues to be of importance to human factors psychologists (Reinerman-Jones, Matthews, Langheim, & Warm, 2011).

Recently, research has looked towards other domains of psychology (i.e. social psychology) for variables that may also be motivational factors to attenuate the vigilance decrement. One such factor is the construct of social facilitation. The study of social facilitation involves investigating how social presence affects an individual’s performance (Guerin & Innes, 1982). Typically, the social presence of another individual enhances performance on a simple, or a well-learned, task, while it impairs performance on a complex, or an unfamiliar task (Bond & Titus, 1983). The research on social facilitation and vigilance is limited. To date, only a handful of studies have indicated that social presence may influence task performance on a vigil (Bergum & Lehr, 1963; Claypoole & Szalma, 2017; Funke et al., 2016; Putz, 1975; Yu & Wu, 2015). The results of these experiments have been inconsistent. For example, the type of social presence utilized varies from co-actors (Funke et al., 2016) to merely present individuals (Yu & Wu, 2015) to evaluative observers (Claypoole & Szalma, 2017; Putz, 1975). Moreover, the type of performance affected also ranges from proportion of hits (Bergum & Lehr, 1963) to response time (Yu & Wu, 2015) to proportion of false alarms (Claypoole & Szalma, 2017). These inconsistencies may be the result of the type of task used.

The construct of social facilitation relies on the operationalization of improved performance on a simple, or a well-learned, task and impaired performance on a complex, or an unfamiliar task (Bond & Titus, 1983; Zajonc, 1965). Therefore, it is possible that some of the previous tasks were “too difficult” for social facilitation effects to occur on all areas of performance. Therefore, it is necessary to statistically establish whether a task is “easy” or “difficult” for use in research on social facilitation and vigilance. Previous research has suggested that one way to manipulate task complexity is through the use of event rate (Warm & Jerison, 1984).

Event rate refers to the presence of background signals typically separated into two categories, complex and simple, where the number of events per time unit in a complex event rate is greater than the number of events in a simple event rate (Stearman & Durso, 2016). With the occurrence of a faster, more complex event rate, performance tends to diminish (Warm & Jerison, 1984). This supports an inverse relationship between vigilance and event rate where the hit rate of a critical signal diminishes with the increase in complexity of the event rate (Guralnick, 1973). With a more complex event rate, greater “capacity” is needed to successfully complete the task (Parasuraman & Giambra, 1991). With the increased presentation of neutral targets, the quality of attention tends to diminish over time (Warm & Jerison, 1984). Researchers investigating vigilance, and potential factors that may alleviate the decrement, may use event rate to determine performance on unfamiliar tasks with ranging difficulties.

The purpose of the present study is to statistically establish a difference in task difficulty between two versions of the same task in order to provide additional evidence that event rate may be used as a manipulation of task difficulty. Event rate has been previously established as a manipulation of “relative task difficulty” because it requires different amounts of information processing (Warm & Jerrsion, 1984). Difficulty, in this instance, is quantified as the amount of information processing required to complete a task. If one task has more information to process, it is thus considered to be more difficult. As such, if the versions do differ in difficulty, then significant differences in performance and perceived workload should be observed.

The present study utilized two, 24-minute cognitive tasks in order to study the effects of event rate on vigilance. Across both conditions, typical vigilance effects were observed. The decrement manifested as a significant decrease in proportion of correct detections as a function of time on watch. Additionally, response time as increased across both conditions as a function of period on watch. Typical vigilance effects were also observed in sensitivity and response bias, such that there was a significant decrease in sensitivity across both conditions as a function of period of watch and there was a significant increase in response bias across conditions as a function of period of watch. These results indicate that the task parameters utilized in the present study are appropriate for examining the effects of vigilance.

Utilizing the NASA-TLX to measure perceived workload, the results indicated high global workload across both conditions, a typical trend in vigilance research. Furthermore, the results indicated that those in the “more difficult” version reported higher levels of overall workload, mental demand, and effected performance than those in the “easy” version. Overall, these results provide further evidence that event rate can be used as a manipulation to change relatively task difficulty.