Cardiovascular and eye activity measures as indices for momentary changes in mental effort during simulated flight

This study examines effects of momentary changes in mental effort on cardiovascular and eye activity measures. A total of 19 male pilots performed an instrument flight task. Task load was manipulated by having the pilots perform flight manoeuvres of varying complexity. Multilevel analyses demonstrated clear effects of momentary changes in mental effort on both the cardiovascular and the eye activity measures. An increase in task load resulted in an increase of heart rate and a decrease in heart rate variability, mean dwell time and fixation duration. Heart rate differentiated between resting period and task execution. Heart rate variability from short data segments provided more insight in intermediate levels of mental effort. The eye activity measures were sensitive to intermediate levels of mental effort as well. Attitude changes resulted in an increase of mean dwell time and mean fixation duration. Task analysis is required to use eye measures as valid indices of mental effort. Having indications of the effects of changing mental demands during daily work of operators is of great importance nowadays. This paper presents an approach to estimate such effects on the basis of heart rate and eye activity measures. In particular, the use of averaged short-term heart rate variability measures is a relatively new aspect.     

Cardiovascular and eye activity measures as indices for momentary changes in mental effort during simulated flight

This study examines effects of momentary changes in mental effort on cardiovascular and eye activity measures. A total of 19 male pilots performed an instrument flight task. Task load was manipulated by having the pilots perform flight manoeuvres of varying complexity. Multilevel analyses demonstrated clear effects of momentary changes in mental effort on both the cardiovascular and the eye activity measures. An increase in task load resulted in an increase of heart rate and a decrease in heart rate variability, mean dwell time and fixation duration. Heart rate differentiated between resting period and task execution. Heart rate variability from short data segments provided more insight in intermediate levels of mental effort. The eye activity measures were sensitive to intermediate levels of mental effort as well. Attitude changes resulted in an increase of mean dwell time and mean fixation duration. Task analysis is required to use eye measures as valid indices of mental effort. Having indications of the effects of changing mental demands during daily work of operators is of great importance nowadays. This paper presents an approach to estimate such effects on the basis of heart rate and eye activity measures. In particular, the use of averaged short-term heart rate variability measures is a relatively new aspect.     

Physiological workload reactions to increasing levels of task difficulty

The sensitivity of physiological measures to mental workload was investigated in a flight simulator. Twelve pilots had to fly through a tunnel with varying levels of difficulty. Additionally, they had to perform a memory task with four levels of difficulty. The easiest memory task was combined with the easiest tunnel task and the most difficult memory task with the most difficult tunnel task. Between the tunnel tasks, subjects had to fly a pursuit task in which a target jet had to be followed. Rest periods before and after the experiment were used as a baseline for the physiological measures. Mental workload was measured with heart period, continuous blood pressure, respiration and eye blinks. Several respiratory parameters, heart rate variability, blood pressure variability and the gain between systolic blood pressure and heart period (modulus) were scored. All measures showed differences between rest and flight, and between the pursuit and the tunnel task. Only heart period was sensitive to difficulty levels in the tunnel task. Heart rate variability increased when respiratory activity around 0.10 Hz increased, which occurred often. The modulus was hardly influenced by respiration and therefore appears to be a better measure than heart rate variability. Among the respiratory parameters, the duration of a respiratory cycle was the most sensitive to changes in workload. The time in between two successive eye blinks (blink interval) increased and the blink duration decreased as more visual information had to be processed. Increasing the difficulty of the memory task led to a decrement in blink interval, probably caused by subvocal activity during rehearsal of target letters. The data show that physiological measures are sensitive to mental effort, whereas rating scales are sensitive to both mental effort and task difficulty.     

Workload measurement using physiological and activity measures for validation test: A case study for the main control room of a nuclear power plant

In design of safety-critical and social-technical systems such as a nuclear power plant, practitioners are required to conduct a performance-based Integrated System Validation (ISV) test to verify that the system design could support the safe operation of the plant. Measurement of workload should be included. However, subjective workload measurements could not provide detailed information and continuous monitoring of the changing workload. This study compared physiological (heart rate difference, heart rate variability, respiration rate and breathing wave amplitude) and activity (number of walking steps, peak acceleration, activity level, and inclination) measures with workload defined as intensity of task demand and estimated with a task complexity measure in an ISV test. The test was conducted on a full-scale simulator using a beyond design-basis accident scenario. The results show that heart rate difference and respiration rate are positively correlated with the estimated workload, while heart rate variability and breathing wave amplitude are negatively correlated with the estimated workload. For operations using traditional panels, high workload is accompanied by larger number of walking steps, higher activity level, and smaller angles of inclination. It is suggested that continuous monitoring of cardiovascular, respiration, and activity measures can detect workload change during the ISV test. Relevance to industry: This study provides recommendations for continuous monitoring of workload during an ISV test of a nuclear power plant. The identified physiological and activity measures can be applied in detecting workload change. The findings are supportive in meeting regulatory requirements and improving system design in the nuclear domain.     

Development of a decision support system for neuro-electrostimulation: Diagnosing disorders of the cardiovascular system and evaluation of the treatment efficiency

The study describes a preliminary stage of the decision support system development for physician performing neuro-electrostimulation of neck neural formations for patients suffering from cardiovascular system disorders. The arterial hypertension was used as the clinical model of the disorders. The study consisted of two steps: diagnosing of the arterial hypertension and an evaluation of the treatment efficiency during the neuro-electrostimulation application. For the diagnosing part, a clinical study was conducted involving heart rate variability signals recorded while performing tilt-test functional load. Heart rate variability signal is an indirect mean of accessing autonomic nervous system functioning. Disturbances of the autonomic nervous system are essential in pathology of arterial hypertension. Performance of different machine learning techniques and feature selection strategies in task of binary classification (healthy volunteers and patients suffering from arterial hypertension) were compared. The genetic programming feature selection and quadratic discriminant analysis classifier reached the highest classification accuracy. Best feature combinations were used to evaluate treatment efficiency. Predictions based on the selected heart rate variability features have a high level of agreement with the arterial pressure dynamics. The results indicate the potential of the proposed decision support system.     

Heart rate variability in relation to psychological factors

Fluctuations in heart rate are related to both physiological and psychological factors. A possible link between those factors has been investigated by examining heart rate variability (HRV)

In two groups of subjects characterized by a large difference in psychic state, psychiatric patients and normals, an investigation was conducted into what extent factors of neural cardiovascular control (for example, respiratory arrhythmia and blood pressure oscillations) are reflected in HRV. With help of cluster analysis methods applied to parameters extracted from the HRV power spectra, it was found that four different groups could be identified. The results indicated likely differences in neural cardiovascular control activity in psychiatric patients and normal subjects     

Physiological responses during data retrieval: Comparison of constant and variable system response times

Ten subjects solved 50 database queries consecutively presented on a video display terminal (VDT). Each query required solution within 45 s of its initial presentation to avoid a reduction in potential earnings. A solution required the correct selection of 3 successive hypertext indices hierarchically structured from the query to the data answer. Under a constant system response time (SRT) condition, each selection of a hypertext index was followed by an 8-s delay before another database level, consisting of both indices and data, was presented. Under a variable SRT condition, SRTs varied between 1 and 30 s, with a mean of 8 s. Twenty-five successive queries were presented under each condition, and the order of conditions varied unsystematically across subjects. Systolic blood pressure, mean arterial blood pressure, and heart rate showed pronounced elevations during task performance, in comparison to a resting baseline. Diastolic blood pressure and masseter muscle electromyograph (EMG) response did not change reliably over baseline. Intersubject variability in EMG response was, however, related to heart-rate variability during task performance. No differential physiological effects of SRT conditions were observed. An eleventh novice subject's cardiovascular responses habituated over five successive performance sessions, but when new queries were introduced, heart rate magnitude increased, showing the reversibility of the effect under novel performance demands. These data show that tonic cardiovascular responses may be evoked by a time-pressured and realistic human-computer interaction. The laboratory preparation may emulate functional properties of conditions that prevail in the VDT workplace.     

The Ergonomics Society The Society's Lecture 1985

Psychophysiological effects of computer system response time (slow vs. rapid) and method of pay (incentive vs. nonincentive) were assessed in a computer-based data entry task among forty-five professional typists. Cardiovascular responses (i.e., heart rate and blood pressure) were monitored on a regular basis over four consecutive workdays. Heart rate and blood pressure did not vary singificantly with slow or rapid response times. Incentive pay, however, significantly increased blood pressure and decreased heart rate variability across the workdays compared to nonincentive pay. Irrespective of response time or method of pay, performance of the data entry task for sustained periods of time was associated with reduced heart rate and increased heart rate variability. This temporal effect was indicative of reduced effort or increased mental fatigue. The results of this study suggest that incentive pay programmes in data entry work may produce stress-related physiological reactivity among healthy workers.     

Psychophysiology of the passive user: Exploring the effect of technological conditions and personality traits

This purpose of this study was to investigate physiological response patterns of passive users versus active users under varying technological conditions. The relationship between user personality traits and physiological responses was also explored. In work systems, different types of users interact with technologies in different ways. Active users may control technologies, while passive users may watch the active user and the technology. While they are both important stakeholders in the system, little empirical research has been conducted to understand the passive users to date. A mixed design experiment was conducted to investigate passive user psychophysiological state, while active and passive users operated a technology under varying technological states (normal, unreliable, and difficult). Physiological measures were collected from passive users while technologies were being operated, these included electrodermal and cardiovascular (heart rate and heart rate variability). Results show that individual active users and passive users have distinct physiological response patterns in heart rate and heart rate variability while using the technology. Exploratory analyses indicated that conscientiousness was positively related to individual active users' task performance; openness, agreeableness, and extraversion were associated with passive users' electrodermal and cardiovascular responses. In addition, social interaction is more influential for passive users' physiological responses, compared to task performing. The effects of active and passive user personality traits on technology interactions are illustrated through distinctive physiological responses.Relevance to industryFindings from this study suggest that to improve passive user experience, systems that include both active and passive users should be designed to facilitate communication and information sharing between users.     

System response time and method of pay: cardiovascular stress effects in computer-based tasks

Psychophysiological effects of computer system response time (slow vs. rapid) and method of pay (incentive vs. nonincentive) were assessed in a computer-based data entry task among forty-five professional typists. Cardiovascular responses (i.e., heart rate and blood pressure) were monitored on a regular basis over four consecutive workdays. Heart rate and blood pressure did not vary significantly with slow or rapid response times. Incentive pay, however, significantly increased blood pressure and decreased heart rate variability across the workdays compared to nonincentive pay. Irrespective of response time or method of pay, performance of the data entry task for sustained periods of time was associated with reduced heart rate and increased heart rate variability. This temporal effect was indicative of reduced effort or increased mental fatigue. The results of this study suggest that incentive pay programmes in data entry work may produce stress-related physiological reactivity among healthy workers.     

Autonomic information flow improves prognostic impact of task force HRV monitoring

Heart rate variability (HRV) represents the cardiovascular control mediated by the autonomic nervous system and other mechanisms. In the established task force HRV monitoring different cardiovascular control mechanisms can approximately be identified at typical frequencies of heart rate oscillations by power spectral analysis. HRV measures assessing complex and fractal behavior partly improved clinical risk stratification. However, their relationship to (patho-)physiology is not sufficiently explored. Objective of the present work is the introduction of complexity measures of different physiologically relevant time scales. This is achieved by a new concept of the autonomic information flow (AIF) analysis which was designed according to task force HRV. First applications show that different time scales of AIF improve the risk stratification of patients with multiple organ dysfunction syndrome and cardiac arrest patients in comparison to standard HRV. Each group's significant time scales correspond to their respective pathomechanisms.     

Driving in an urban environment,the stress response and effects of exercise

Driving may be detrimental to health, with one hypothesis suggesting that driving may elicit an acute stress response and, with repeated exposures, may become a chronic stressor. The present study examined the stress response to driving and the effectiveness of a prior exercise bout in dampening this response. Twenty healthy adults performed three tasks: control, driving and exercise plus driving. Heart rate (HR), heart rate variability (HRV), blood pressure (BP) and cortisol were measured to quantify the acute stress response to each condition. Data indicated a stress response to driving: HR was elevated and HRV was reduced during the driving task compared with control. HR was elevated and HRV was reduced comparing the exercise plus driving with the driving condition. BP and cortisol were not different among conditions. The potential of interventions, such as exercise, to counter daily stressors should be evaluated to safeguard long-term health.

Practitioner Summary: this study confirms that driving induces a stress response, with the exercise intervention providing mixed results (an increase in cardiovascular measures and a decrease in cortisol measure trending significance). Given the known consequences of stress and evidence that exercise can mitigate acute stress, further evaluation of exercise interventions is recommended.     

The role of respiratory measures to assess mental load in pilot selection

While cardiovascular measures have a long tradition of being used to determine operator load, responsiveness of the respiratory system to mental load has rarely been investigated. In this study, we assessed basic and variability measures of respiration rate (RR), partial pressure of end-tidal carbon dioxide (petCO₂) as well as performance measures in 63 male pilot candidates during completion of a complex cognitive task and subsequent recovery. Mental load was associated with an increase in RR and a decrease in respiratory variability. A significant decrease was also found for petCO₂. RR and respiratory variability showed partial and complete effects of recovery, respectively, whereas petCO₂ did not return to baseline level. Overall, a good performance was related to a stronger reactivity in RR. Our findings suggest that respiratory parameters would be a useful supplement to common measures for the assessment of mental load in pilot selection.

Practitioner Summary: Respiratory measures are a promising yet poorly investigated approach to monitor operator load. For pilot selection, we assessed respiration in response to multitasking in 63 candidates. Task-related changes as well as covariation with performance strongly support the consideration of respiratory parameters when evaluating reactivity to mental load.     

Heart period variability and respiratory changes associated with physical and mental load: non-linear analysis

In the investigation of heart rate and heart rate variability, the discrimination between mental workload, physical activity and respiration is known to be methodologically difficult. At most, heart rate variability measures are more likely to be coarse-grained measures with variability confounded by heart rate. Moreover, the spectral analysis of heart rate variability shows broad-band frequency characteristics, pointing towards non-stationarity or non-linearity. From this it is suggested to focus on non-linear dynamic analyses that are variance-insensitive. The experimental section of the paper focuses on the estimation of two non-linear measures for both heartbeat dynamics and respiration, the correlation dimension indicating complexity and the Lyapunov exponents indicating predictability. The results indicate that the complexity of heart dynamics is related to the type of task and that the predictability of heart dynamics is related to the amount of load.     

基于光体积描述记成像技术的非接触低成本生理信息的检测

在最近几十年,人们对低成本、非接触和普适方法测量生理信息(心率、心率变异性、血氧饱和度等)产生了浓厚的兴趣。传统的临床测量生理信息的方法包括Ag/AgCl电极测量心率和心率变异性,二氧化碳分析仪测量呼吸率状态,脉搏血氧饱和度仪测量血氧饱和度。这些方法虽然可以获得完美的信号,但是他们价格昂贵、使用麻烦、不方便。基于光体积描述记成像技术检测生理信息提供了一个人体生理健康检测的新方法。血流速度、血流量和血压可间接地评估血容量,反过来,血容量间接反映了这些生理参数的变换。光在人体组织的反射或透射可以得到血容量的变化。使用电脑摄像头或手机摄像头扑捉的人体皮肤表面成像,通过对成像光信号的处理和分析,获得一些生理信息,如心率、呼吸率、心率变异性和血氧饱和度等。在本文中,我们回顾使用光体积描述记成像技术在非接触健康检测领域里的最新发展,论述面临的挑战和将来的发展方向。     

Spectral and cross-spectral analysis of heart rate and arterial blood pressure variability signals

A parametric method for autoregressive (AR) auto- and cross-spectral analysis is presented for the contemporaneous processing of heart rate and arterial blood pressure variability signals. In particular, the introduced bivariate spectral analysis (phase and coherence spectra) provides quantitative and objective means which are useful to measure the role played by the neural controlling systems (sympathetic and parasympathetic systems) on the cardiovascular signals under different pathophysiological conditions. Algorithmic aspects, connected to the way of processing discrete numerical series synchronized to single cardiac beats, are particularly stressed. Important applications are foreseen both in physiological studies and in clinical practice as an aid to the detection of various relevant cardiovascular pathologies such as hypertension and diabetes.     

Combining electrodermal responses and cardiovascular measures for probing adaptive automation during simulated flight

Adaptive automation increases the operator's workload in case of hypovigilance and takes over more responsibility if workload becomes too high. Two consecutive studies were conducted to construct a biocybernetic adaptive system for a professional flight simulator, based on autonomic measures. Workload was varied through different stages of turbulences. In a first study with 18 participants, electrodermal responses of experimental subjects oscillated very close to the individual set point, demonstrating that workload level was adjusted as a result of adaptive control, which was not the case in yoked control subjects without adaptive automation. Combining electrodermal responses with heart rate variability in a second study with 48 participants further enhanced the adaptive power which was seen in even smaller set point deviations for the experimental compared to the yoked control group. We conclude that the level of arousal can be adjusted to avoid hypovigilance by combining autonomic measures in a closed loop.     

Perceived fatigue after mental work: an experimental evaluation of a fatigue inventory

The aim of this study was to investigate the perceived fatigue after mental work and to test the Swedish Occupational Fatigue Inventory (SOFI). Twenty male and 20 female participants worked with proof reading (2 x 90 min) and a vigilance task (2 x 60 min). After each task session, perceived fatigue was rated with the SOFI and Borg's CR10O-scale. In addition, physiological reactions were registered; blood pressure, heart rate, heart rate variability and muscle activity in corrugator supercilii, as well as measures of performance: reaction time, number of pages read and number of proof errors found, number of detected signals. As expected, the highest ratings were obtained on Lack of energy, Lack of motivation and Sleepiness, particularly after the vigilance task. High ratings after both work tasks were also found on the CR10-scale. Men and women did not differ significantly with respect to their ratings. No clear-cut physiological reactions were found to correlate with ratings of fatigue. The results indicate the validity of the mental dimension of the SOFI.     

An experimental evaluation of instantaneous self-assessment as a measure of workload

Instantaneous self-assessment (ISA) is a technique that has been developed as a measure of workload to provide immediate subjective ratings of work demands during the performance of primary work tasks such as air traffic control. This paper reports a study that compared the results of ISA with those gathered from other established workload evaluation techniques; subjective ratings collected at the end of the task, mean heart rate and heart rate variability, and error in the primary task of tracking. ISA ratings were found to be correlated significantly with the post-task ratings of workload, heart rate variability, and task performance. Generally each of the techniques was sensitive to variations in task difficulty. However, performance on the primary tracking task was found to be poorer during periods when ISA responses were required, regardless of whether they were spoken or manual responses. This finding suggests that the usefulness of the technique is limited in comparison to less intrusive measures of workload.     

自适应人脸多区域分析的视频心率检测

心率是衡量人体心血管健康状况和情绪压力的重要生理参数.然而,基于视频的非接触式心率检测技术在真实场景中,会由于人脸运动和光照变化等导致检测准确性的降低.为了解决上述问题,考虑到心率检测算法中感兴趣区域(region of interest, ROI)的选取与检测准确度高度相关.故提出一种自适应超像素分割多区域综合分析的心率检测新方法.首先利用人脸检测和追踪算法,裁切获得人脸图像;之后采用自适应超像素分割算法将ROI划分成互不重叠的子块;再通过色度特征提取构建各子块原始血液容积脉搏矩阵;最后对脉搏矩阵使用多指标综合分析并挑选出最佳区域进行心率估计.实验结果表明,通过自适应超像素分割和多区域分析优选可以有效提升心率检测准确性.在静止状态下和运动干扰条件下准确性分别达到99.1%和95.6%,光照干扰条件下准确性相对传统方法最高提升8.2%.增强了真实场景下心率检测的鲁棒性.