Jennifer M. Ross

A Meta-Analysis of Performance Response Under Thermal Stressors:

Objective: Quantify the effect of thermal stressors on human performance. Background: Most reviews of the effect of environmental stressors on human performance are qualitative. A quantitative review provides a stronger aid in advancing theory and practice. Method: Meta-analytic methods were applied to the available literature on thermal stressors and performance. A total of 291 references were collected. Forty-nine publications met the selection criteria, providing 528 effect sizes for analysis. Results: Analyses confirmed a substantial negative effect on performance associated with thermal stressors. The overall effect size for heat was comparable to that for cold. Cognitive performance was least affected by thermal stressors, whereas both psychomotor and perceptual task performance were degraded to a greater degree. Other variables were identified that moderated thermal effects. Conclusion: Results confirmed the importance of task type, exposure duration, and stressor intensity as key variables impacting how thermal conditions affect performance. Results were consistent with the theory that stress forces the individual to allocate attentional resources to appraise and cope with the threat, which reduces the capacity to process task-relevant information. This represents a maladaptive extension of the narrowing strategy, which acts to maintain stable levels of response when stress is first encountered. Application: These quantitative estimates can be used to design thermal tolerance limits for different task types. Although results indicate the necessity for further research on a variety of potentially influential factors such as acclimatization, the current summary provides effect size estimates that should be useful in respect to protecting individuals exposed to adverse thermal conditions.

The Effect of Automation Reliability on User Automation Trust and Reliance in a Search-and-Rescue Scenario

Advances in modern day technology are rapidly increasing the ability of engineers to automate ever more complicated tasks. Often these automated aids are paired with human operators who can supervise their work to ensure that it is free of errors and to even take control of the system if it malfunctions (e.g., pilots supervising an autopilot feature). The goal of this collaboration, between humans and machines, is that it can enhance performance beyond what would be possible by either alone. Arguably the success of this partnership depends in part upon attributions an operator develops that help guide their interaction with the automation. One particular factor that has been shown to guide operator reliance on an automated ‘teammate’ is trust. The following study examined 140 participants performing a simulated search-and-rescue task. The goal of this experiment was to examine the relationship between automated agents reliability, operator trust, operator reliance, and performance scores. Results indicated that greater automation reliability is positively correlated with greater user reliance (r = .66), perceived trust (r = .21), and performance scores (r = .34). These results indicate that more reliable aids are rated as significantly higher in terms of perceived trust and relied upon more than less reliable aids. Additionally, the size of the effect is much larger for operator behaviors (i.e., reliance) compared to more subjective measures (i.e., self-reported trust).

THE EFFECTS OF WHOLE-BODY VIBRATION ON HUMAN PERFORMANCE: A META-ANALYTIC EXAMINATION

Whole-body vibration exerts a substantive influence in many work environments. The primary objective of the present paper was to ascertain the effect of whole-body vibration and identify those moderating variables that influence the degree to which human performance is affected. A comprehensive meta-analysis was conducted which quantified the existing research evidence. Following a screening process of the collected literature, a total of 224 papers and reports were identified for analysis. From these papers, 115 effect sizes were derived from 13 experiments which survived the screening procedure. Results indicate that vibration acts to degrade the majority of goal-related activities, especially those that rely on visual perception and fine motor control. Gaps in the extant research literature are identified and suggestions offered with regard to a more theoretically-driven approach to testing stressor effects on human performance.

Individual Differences in Dispositional Pessimism, Stress, and Coping as a Function of Task Type

Individual differences in dispositional pessimism and choice of coping strategy on performance and stress, in target detection were investigated. The results were consistent with prior research indicating that higher levels of pessimism were associated with higher levels of stress and less effective coping strategies. Similarly, pessimism predicted emotion focused coping only in tasks with spatial uncertainty. There was evidence that the influence of personality on post-task stress may be mediated by pre-task state. Pessimism also predicted avoidant coping and task focused coping, although this prediction was only meaningful in the context of the combination of a temporal discrimination and spatial uncertainty. Hence, the degree to which pessimistic operators engage in the three coping strategies depends upon the characteristics of the task.

PERFORMANCE, WORKLOAD, AND STRESS CORRELATES OF TEMPORAL AND SPATIAL TASK DEMANDS

Increased understanding of the mechanisms by which stress impacts performance is essential to the design and operation of complex information systems. This study represents a test of the hypothesis of Hancock, Szalma, and Weaver (2002) that the attentional narrowing observed under stressful conditions results from spatial and temporal perception drawing on common resource capacities. Although the present results were unable to resolve the specific issue to a satisfactory degree, a novel finding was observed that noise increases leniency in responding. The impact of noise on performance thus depends on the characteristics of the task to be performed, with spatial uncertainty exerting a significant influence on perceived workload.

A meta-analysis of performance under thermal stress

The goal of this work was to perform a quantitative review of temperature effects on human performance, with the aim of advancing both theory and practice. Meta-analytic methods were applied to the available literature on thermal stress and performance. Two-hundred-ninety-one references were collected resulting in forty-nine publications that met selection criteria. These studies provided 528 effect sizes. Analyses revealed an overall detrimental effect of temperature on performance. Effect-size for heat was comparable to that for cold temperatures. Temperature effects were task dependent, that is cognitive performance was least affected by thermal stress, while both psychomotor and perceptual task performance were degraded to a greater degree. Other moderating variables were identified and observed to influence the effect of thermal stress. Although the results clearly indicate more empirical research is necessary to achieve more accurate estimates, the current study provides initial effect-size estimates that should be considered when designing human-machine systems.

Effect of Audio-Visual Alerts on Situation Awareness and Workload in a Net-Centric Warfare Scenario

The goal of net-centric warfare (NCW) is to give soldiers an information advantage that leads to a war-fighting advantage. However, the inherent nature of NCW systems is often quite complex and dynamic, which leads to impaired situation awareness (SA) and heightened levels of mental workload for the human operator. The following study investigated the moderating effects of automated audio-visual alerts on user SA and perceived workload while using a net-centric warfare system. Twenty-six participants observed battlefield scenarios on a simulation of the common NCW system, Force XXI Battle Command Brigade and Below (FBCB2), and were required to pay attention and remember critical events (e.g., the appearance of an enemy unit). The system was presented with or without an automated alerting aid that provided combined auditory and visual alerts when certain critical events occurred (i.e., System to Help Implement and Empower Leader Decisions; SHIELD). Results revealed that contrary to current assumptions the use of an automated alerting aid did not impact user SA; however, perceived workload was significantly lower with the addition of the alerting aid. This work demonstrates that the automated alerts used in this NCW experiment do not affect SA (either positively or negatively) and decreased perceived workload.

Empirical Examination of Trust in Automation Across Multiple Agents in a Search and Rescue Operation

Automation has become increasingly prevalent in modern day society. With this progress, the shift from operators serving as active controllers (directly involved with the system) to supervisory controllers (indirect management of a system) has become more common. Accompanying this evolution of the operator from their original role, there is a need to explore the components that influence effective cooperation between operators and semi-autonomous agents. Two key factors moderating this relationship are operator trust in the agent and the complexity of the task itself (i.e., number of agents an operator monitors). This work examines trust and automation theory as it applies to an operator monitoring a complex, two agent, simulated search-and-rescue task. The effect of source characteristics of the two automated systems will be evaluated across reliability conditions for their impact upon reliance and perceived trust of automation. The purpose of this research is to extend knowledge in the theory of human-agent trust interaction and offers potential applied benefits in leveraging the aspects of system design that lead to optimizing human-agent interaction in a complex and possibly imperfect system.

THE IMPACT OF DISPOSITIONAL OPTIMISM AND PESSIMISM ON STRESS AS A FUNCTION OF PSYCHOPHYSICAL TASK CHARACTERISTICS

In this study we tested the effect of individual differences in dispositional optimism and pessimism on target detection. Following proximal task dimensions set out by the Model of Maximal Adaptability, three tasks were employed in the current study, varying in their spatial and temporal emphasis. Performance as measured by self report of stress was examined in light of individual differences in attentional narrowing across the three task levels. Prior research indicates that optimism predicts increased Task-Engagement, but in this study there was a novel finding that higher levels of optimism predicted decreased Task-Engagement in spatial-dominant tasks. Optimism was also found to predict increased levels of post-task Worry in temporal-dominant tasks. However, expected relations between pessimism as post-task stress state were not observed. Although the results of the current study did not confirm the hypotheses regarding joint resource capacities for spatial and temporal task components, results did indicate that dispositional optimism does impact Task-Engagement, signifying a need for further research on the relation between this trait and participant stress. The results extend prior findings that the relationship between these traits and stress states may depend on the psychophysical characteristics of the target detection task employed.