Task engagement, cerebral blood flow velocity, and diagnostic monitoring for sustained attention

Loss of vigilance may lead to impaired performance in various applied settings including military operations, transportation, and industrial inspection. Individuals differ considerably in sustained attention, but individual differences in vigilance have proven to be hard to predict. The dependence of vigilance on workload factors is consistent with a resource model of sustained attention. Thus, measures of attentional resource availability may predict the operator's subsequent vigilance performance. In this study, we investigated whether a diagnostic battery of measures of response to a cognitive challenge would predict subsequent sustained attention. Measures that may relate to the mobilization of resources in response to task demands include subjective task engagement and coping, and a novel psychophysiological index, cerebral bloodflow velocity (CBFV). A two-phase design was used. First, participants were exposed to a challenging battery of short tasks that elevated CBFV. Second, participants performed a 36-min vigilance task. Two subgroups of participants performed either a sensory vigilance (N = 187) or a cognitive vigilance (N = 107) task. Measures of task engagement, coping, and CBFV response to the short task battery were compared as predictors of subsequent vigilance. Both subjective and CBFV indices of energization predicted sensory and cognitive vigilance, consistent with resource theory. Structural equation modeling was used to develop a latent factor model of influences on sustained attention. It is concluded that measures of resources, conceptualized as multiple energization processes, are potentially useful for diagnostic monitoring in applied settings. Use of a diagnostic task battery in military and transportation settings is discussed, along with some potential limitations on validity of the diagnostic test.

Functional Fidelity, Context-Matching, and Individual Differences in Performance

Conventional personality questionnaires are often only weak predictors of operational performance. A major problem is that personality effects are moderated by contextual factors which may be mismatched across laboratory and real-world studies. Context mismatch threatens the ‘functional fidelity’ of laboratory performance tasks; the extent to which the individual behaves as they would in the operational environment. Three research strategies for enhancing the functional fidelity of laboratory studies of individual differences are proposed. First, contexts relevant to specific personality traits may be developed in the laboratory. For example, socially threatening environments may be necessary to find meaningful effects of neuroticism. Second, traits linked to a specific performance context may be employed. The validity of traits for driver stress vulnerability supports this approach. Third, psychophysiological responses to simulations of the cognitive demands of the work environment may be used. Our recent work shows that stress and hemodynamic responses to short high-workload tasks predict longer-duration sustained performance.

A Multivariate Test Battery for Predicting Vigilance

It has proved difficult to predict individual differences in vigilance from standard psychometric tests. We report a study that explored the utility of a multivariate battery in predicting vigilance on a task requiring monitoring of a tactical display. A two-phase design was employed. Participants performed a short vigilance task (SVT) prior to the longer criterion monitoring task. We investigated the predictive ability of cognitive ability, personality, performance on the SVT, and stress responses to the SVT. Four versions of the criterion task were used, to test generalization of predictive validity. Key predictors of vigilance were found to include ability, SVT performance, and subjective task engagement and coping. Multiple regression analyses suggested that together these predictors explained about 30% of the variance in vigilance (with some differences for prediction of different task versions). Results are discussed in relation to the resource theory of vigilance, and the practical issues arising from selecting vigilant operators.

Affective Biases in Information Search during Tactical Decision-Making

Tactical decision-making may be an emotional experience for an operator. Emotion, whether extrinsic or intrinsic to the task, may bias attention to task critical information. The current study used a feedback manipulation to induce positive and negative affect (PA and NA) during a decision-making task requiring information search. In a task based on a rescue scenario, participants were randomly assigned to either a “success” or “failure” condition and instructed to evaluate the costs and benefits of different routes along separate legs of the rescue mission, similar to reaching a “fork in the road.” Feedback was effective in manipulating emotion. PA and NA were significantly correlated with information sampling frequencies, but no general mood-congruent bias was found. Instead the role of mood appears to depend on the general affective context, a finding interpreted in relation to the mood-as-input hypothesis. The practical relevance and limitations of the study are discussed.

Team Member Personality, Performance and Stress in a RoboFlag Synthetic Task Environment

Effective teamwork is an important component in the control of multiple unmanned vehicles (UVs). Personality traits of individual team members may be a factor influencing overall team performance and individual levels of perceived workload and stress. In this study, a multiple UV environment was simulated by use of the RoboFlag game. Participants played the RoboFlag game individually or in two-person teams and were presented with this sequence of task-phases: RoboFlag alone, RoboFlag with a secondary task, RoboFlag alone. It was predicted that the RoboFlag performance would relate to ‘Big Five’ personality traits. It was also expected that Neuroticism would relate to higher workload and stress, especially in more demanding task conditions. The results suggested that the influence of personality is generally limited, but may sometimes be important. Specifically, high Neuroticism individuals showed higher workload and stress in a team player condition, which may impose social as well as task demands.

A Comparison of Cerebral Hemovelocity and Blood Oxygen Saturation Levels during Vigilance Performance

This study compared measures of cerebral blood flow velocity (CBFV) and blood oxygen saturation (rSO2), during the performance of a 40-min vigilance task. Observers monitored a simulated air-traffic control display for flight path deviations which occurred in a unidirectional or a multidirectional context. CBFV and rSO2 measures were secured from the medial cerebral arteries in the left and right cerebral hemispheres and from the corresponding frontal lobes, respectively. Performance efficiency was greater in the unidirectional than the multidirectional condition and declined over time in both conditions, more so in the multidirectional condition. This pattern of results was paralleled in different ways by the two hemodynamic measures. A result of this sort challenges the assumption of a close tie between cerebral blood flow and oxygen saturation (Siesjo, 1978) and supports recent findings (Mintun et al., 2001) that cerebral blood flow and oxygen levels are not tightly coupled in active brain states.

Effective treatment of injecting drug users with recently acquired hepatitis C virus infection

BACKGROUND & AIMS

Patients with acute hepatitis C virus (HCV) infection who receive treatment achieve high rates of sustained virologic response (SVR), but few studies have examined outcomes among injecting drug users (IDUs). We evaluated the efficacy of treatment of recent HCV infection in IDUs with acute and early chronic HCV.

METHODS

We analyzed data from the Australian Trial in Acute Hepatitis C-a prospective study of the natural history and treatment outcomes of patients with recent HCV infection. Participants eligible for the study had their first anti-HCV antibody-positive test result within the past 6 months and either acute clinical HCV within the past 12 months or documented anti-HCV seroconversion within 24 months. Participants with HCV received pegylated interferon-alfa-2a (180 microg/wk, n = 74); those with HCV/human immunodeficiency virus (HIV) co-infection received pegylated interferon-alfa-2a (180 microg/wk) with ribavirin (n = 35) for 24 weeks.

RESULTS

From June 2004 to February 2008, 167 participants were enrolled in the Australian Trial in Acute Hepatitis C; 79% had injected drugs in the previous 6 months. Among 74 with only HCV, the SVRs were 55% and 72% by intention-to-treat and per-protocol analysis, respectively. In multivariate analyses, baseline factors independently associated with lower SVR included decreased social functioning and current opiate pharmacotherapy. Adherent participants had higher SVR rates (63% vs 29%; P = .025). Of the 35 participants with HCV/HIV co-infection, the SVRs were 74% and 75% by intention-to-treat and per-protocol analysis, respectively.

CONCLUSIONS

Treatment of recent HCV infection among IDUs, including those with HIV co-infection, is effective. Strategies to engage socially marginalized individuals and increase adherence should improve treatment outcomes in this population.

On tracking the course of cerebral oxygen saturation and pilot performance during gravity-induced loss of consciousness

OBJECTIVE

The aim of this study was to track the course of cerebral tissue oxygen saturation (rSO2) and pilot performance during an episode of gravity-induced loss of consciousness (GLOC).

BACKGROUND

GLOC, a major problem facing pilots of high-performance aircraft, is brought about by a sudden reduction in rSO2 as a result of increased +Gz force. It consists of 24 s of complete functional impairment followed by a prolonged period of performance recovery. This study tested the hypothesis that delayed recovery in GLOC is caused by a slow return of rSO2 following removal of the g-force that induced the episode.

METHOD

GLOC was induced in U.S. Air Force personnel via a centrifuge with math and tracking tasks emulating flight performance. A near-infrared spectroscopy unit provided the rSO2 measure.

RESULTS

Declines in rSO2 from baseline pinpointed when pilots would cease active flight control and when GLOC would set in. Counter to expectation, rSO2 returned to baseline levels shortly after the centrifuge came to a complete stop following GLOC onset. Nevertheless, performance deficits continued for 49.45 s thereafter.

CONCLUSION

The prolonged performance recovery time in GLOC cannot be attributed to delays in the return of rSO2. This finding explains why previous ergonomic efforts to shorten the duration of GLOC episodes by increasing the rate of return of rSO2 have not been fruitful. Evidently, another approach is needed.

APPLICATION

Such an approach might use the close linkage between loss of rSO2, performance deterioration, and GLOC onset to develop a warning system that would permit pilots to take effective action to avoid GLOC incapacitation.

Trait Anxiety and Affective Bias in Tactical Decision-Making

Affective states may influence decision-making at different stages of information processing, including selective attention, situation assessment and choice of action. Studies of state anxiety, a negative emotional state, reveal multiple biases including an attentional bias to threat-related stimuli and biases at later stages. The present study examined the effects of threat and both trait and state anxiety on decision-making in a simulated rescue task. Participants were induced into a mood (neutral or anxious) and asked to choose the fastest route leading to a lost party by evaluating uncertain benefits and costs for several routes. The results confirm that mood induction methods can be used for decision-making tasks. Additionally, these findings suggest that different forms of ‘affect’ may relate to different biases. Task-related threat and induced mood influenced route choice, but trait and state anxiety influenced selective attention to benefits and costs.

Effects of Training with Knowledge of Results on Diagnosticity in Vigilance Performance

Making accurate diagnostic decisions about signal presence/absence is critical for success in many failure intolerant monitoring technologies requiring sustained attention or vigilance. This study examined the effects of training with knowledge of results (KR) on observer diagnosticity in a vigilance task. Diagnosticty was measured in terms of decision theory measures of positive predictive power (PPP) -precision in indicating when signals were actually present and negative predictive power (NPP) - precision when indicating signal absence. Initial training with KR enhanced observers' diagnosticity on a subsequent test task in terms of PPP but not NPP. The picture of performance efficiency reflected by both diagnostic measures differed from results indexed by signal detection theory (SDT) measures of perceptual sensitivity (d') and response bias (c). However as predicted from the computational mechanics of the decision theory and SDT measures, both diagnostic measures correlated positively with d' while NPP correlated negatively with c. These findings indicate that combinations of perceptual ability and level of responding can influence the behavioral metrics signifying diagnosticity in vigilance performance

Predicting Vigilance Performance and Stress with Individual Difference Measures

In this study, personality and intelligence measures were used to predict vigilance performance and the stress associated with the performance of an abbreviated vigilance task adapted from Temple et al. (2000). Personality was measured using broad personality traits (NEO-FFI), as well as factor-analytically derived personality dimensions that yielded the four factor solution of Cognitive Disorganization, Heightened Experience, Sleep Quality, and Impulsivity. Intelligence was measured by two tests extracted from the ETS Kit of Factor-Referenced Cognitive Tests (Ekstrom et al., 1976). Stress was measured using the Dundee Stress State Questionnaire (DSSQ). Fluid intelligence and extraversion emerged as predictors for vigilance performance. With regard to stress, Neuroticism and Conscientiousness emerged as predictors for both pre- and post-task distress and worry. While the derived personality battery did not directly predict performance, the Cognitive Disorganization and Impulsivity factors predicted the stress associated with vigilance tasks.

Vesicle recycling at ribbon synapses in the finely branched axon terminals of mouse retinal bipolar neurons

In retinal bipolar neurons, synaptic ribbons mark the presence of exocytotic active zones in the synaptic terminal. It is unknown, however, where compensatory vesicle retrieval is localized in this cell type and by what mechanism(s) excess membrane is recaptured. To determine whether endocytosis is localized or diffuse in mouse bipolar neurons, we imaged FM4-64 to track vesicles in cells whose synaptic ribbons were tagged with a fluorescent peptide. In synaptic terminals, vesicle retrieval occurred at discrete sites that were spatially consistent over multiple stimuli, indicative of endocytotic "hot spots." Retrieval sites were spatially correlated with fluorescently labeled synaptic ribbons. Electron microscopy (EM) analysis of bipolar cell terminals after photoconversion of internalized FM dye revealed that almost all of the dye was contained within vesicles approximately 30 nm in diameter. Clathrin-coated vesicles were observed budding from the plasma membrane and within the cytosol, and application of dynasore, a dynamin inhibitor, arrested membrane retrieval just after the budding stage. We conclude that synaptic vesicles in the fine branches of mouse bipolar axon terminals are retrieved locally near active zones, at least in part via a clathrin-mediated pathway.

Predicting vigilance: a fresh look at an old problem

Individual differences in vigilance are ubiquitous and relevant to a variety of work environments in industrial, transportation, medical and security settings. Despite much previous work, mostly on personality traits, it remains difficult to identify vigilant operators. This paper reviews recent research that may point towards practically useful predictor variables for vigilance. Theoretical approaches to identifying predictors that accommodate the heterogeneous nature of vigilance tasks are compared. The article surveys recent empirical studies using personality measures, ability tests and scales for stress and coping as predictors of vigilance. Promising new constructs include trait scales linked to fatigue, abnormal personality and the stress state of task engagement. Implications of the data reviewed for occupational selection are discussed. Selection should be based on a multivariate assessment strategy, cognitive task analysis of the operational vigilance task and use of work sample measures to capture typical stress responses to the task. This review paper surveys recent research that may point towards practically useful predictor variables for vigilance. The article surveys recent empirical studies using personality measures, ability tests and scales for stress and coping as predictors of vigilance. Selection should be based on a multivariate assessment strategy.

Effects of sensory modality on cerebral blood flow velocity during vigilance

Transcranial Doppler sonography was used to measure cerebral blood flow velocity (hemovelocity, CBFV) from the left and right middle cerebral arteries during the performance of 40-min auditory and visual vigilance tasks. Reductions in stimulus duration were the critical signals for detection in both tasks, which were equated for stimulus salience and discrimination difficulty. Signal detection responses (correct detections and false alarms) and CBFV declined significantly over time in a linear manner for both modalities. In addition, the overall level of CBFV and the temporal decline in this measure were greater in the right than the left cerebral hemisphere. The results are consistent with the view that a right hemispheric system is involved in the functional control of vigilance and that this system operates in a similar manner in the auditory and visual channels.