Eye-strain and changes in accommodation of the eye and in visual evoked potential following quantified visual load

The measurements were made of the muscular contractions and relaxations of accommodation (infrared optometer) and of visual evoked potential (VEP) (photic stimulation) before and after one hour's visual load, checking calculations (1800 questions/hour and 900 questions/hour). The results showed that the relaxation time in accommodation lengthened and the latency of the positive wave appearing at about 100 ms in VEP increased with the increase in visual load. In addition, the complaint rate for eye-strain was higher in the group given heavier visual work. In this group, there was no significant difference in amplitude of VEP before and after the visual task. The difference in the relaxation time before and after the visual task tended to be negatively correlated to the difference in amplitude of VEP and positively related to that in the latency. In the group given lighter visual work there were significant differences in the latency and the amplitude of VEP before and after the visual task, neither were correlated to the difference in the relaxation time. These results suggest that not only peripheral hypofunction but also the decrease of centrencephalic activity level may be responsible for the development of eye-strain caused by visual tasks.     

Proposal of an Index to Evaluate Visual Fatigue Induced During Visual Display Terminal Tasks

The study described in this article was designed to evaluate visual fatigue induced during video display terminal (VDT) tasks. Newly developed equipment was used that can simultaneously measure pupillary change, focal accommodation, and eye movement. The changes in these 3 physiological measures, taken during a VDT task, were used to propose an index for evaluating visual fatigue. Through multiple regression analysis, an index to describe the psychological sense of visual fatigue was obtained. In this index, the minimum pupil diameter, velocity of focal accommodation for constriction, and width of focal accommodation were included. The results suggest that visual fatigue in VDT tasks can be evaluated effectively using both pupil diameter and focal accommodation. The index can be used to assess visual fatigue induced during a VDT task if the following 3 conditions are satisfied:

1. Head movement is limited and infrequent.

2. The task requires focal accommodation.

3. During the task, there is no outstanding change in the lighting environment such as luminous intensity or brightness.     

Visual accommodation and subject performance during a stereographic object task using liquid crystal shutters

Virtual reality has become popular in a variety of fields. Three experiments to study visual accommodation and task performance during stereographic vision were carried out in order to better understand the human response to virtual reality. Visual accommodation to stereograms on CRT was studied. Subjects could see the target on the CRT display binocularly through liquid crystal shutters. Accommodation to a stereogram with step changes in distance was tested first. As the second experiment, accommodation to a stereogram with gradual changes in distance, and comparison of ability to perform a colour photograph stereogram task were tested. Finally, accommodation and subject performance during a prolonged stereographic object task were observed for 30min. A virtual ‘gate’ was formed at a position 1.2?m from the subject. The virtual target moved forward and backward through this gate between the positions of 0.8?m and 20?m. The subjects were asked to focus on the target and press a button as it moved through the virtual gate. Subjective response to the task and the error between the position where the button was pressed and the gate was recorded. It was concluded that there are some people who exhibit large changes in accommodation while performing a stereographic task. There is a tendency to accommodate to a distance nearer than the baseline. Prolonged stereoscopic viewing caused visual fatigue or loss of accommodation and diminished task performance.     

Workload Management in Teleoperation of Unmanned Ground Vehicles: Effects of a Delay Compensation Aid on Human Operators’ Workload and Teleoperation Performance

ABSTRACT

Workload management is of critical concern in the teleoperation of unmanned vehicles because teleoperation is often employed in high-risk industries wherein high workload can lead to sub-optimal task performance and can harm human operators’ long-term well-being. This study aimed to assess the detrimental effects of time delays in teleoperation on operators’ workload and performance, and how a delay compensation aid mitigated such effects. We conducted a human-in-the-loop experiment with 36 participants using a dual-task teleoperation platform, where participants drove a simulated High Mobility Multipurpose Wheeled Vehicle (HMMWV) and performed a one-back memory task under three conditions: the delay condition, the delay with compensation aid condition, and the ideal no delay condition. A model-free predictor was used as the compensation aid. Results indicate that with a time delay of 0.8-s participants’ workload increased and performance degraded significantly. Moreover, the model-free predictor mitigated the detrimental effects of time delay on workload and task performance. Our findings suggest that participants are more sensitive in their perceived workload compared to the objective and physiological measures of workload. In addition, without any delay compensation algorithms, continuous teleoperation may not be ideal for operations with long time delays.     

Effect of varying levels of mental workload on startle eyeblink modulation

Previous research using punctuate reaction time and counting tasks has found that the startle eyeblink reflex is sensitive to attentional demands. The present experiment explored whether startle eyeblink is also modulated during a complex continuous task and is sensitive to different levels of mental workload. Participants (N = 14) performed a visual horizontal tracking task either alone (single-task condition) or in combination with a visual gauge monitoring task (multiple-task condition) for three minutes. On some task trials, the startle eyeblink reflex was elicited by a noise burst. Results showed that startle eyeblink was attenuated during both tasks and that the attenuation was greater during the multiple-task condition than during the single-task condition. Subjective ratings, endogenous eyeblink rate, heart period, and heart period variability provided convergent validity of the workload manipulations. The findings suggest that the startle eyeblink is sensitive to the workload demands associated with a continuous visual task. The application of startle eyeblink modulation as a workload metric and the possibility that it may be diagnostic of workload demands in different stimulus modalities is discussed.     

Effect of varying levels of mental workload on startle eyeblink modulation

Previous research using punctuate reaction time and counting tasks has found that the startle eyeblink reflex is sensitive to attentional demands. The present experiment explored whether startle eyeblink is also modulated during a complex continuous task and is sensitive to different levels of mental workload. Participants (N = 14) performed a visual horizontal tracking task either alone (single-task condition) or in combination with a visual gauge monitoring task (multiple-task condition) for three minutes. On some task trials, the startle eyeblink reflex was elicited by a noise burst. Results showed that startle eyeblink was attenuated during both tasks and that the attenuation was greater during the multiple-task condition than during the single-task condition. Subjective ratings, endogenous eyeblink rate, heart period, and heart period variability provided convergent validity of the workload manipulations. The findings suggest that the startle eyeblink is sensitive to the workload demands associated with a continuous visual task. The application of startle eyeblink modulation as a workload metric and the possibility that it may be diagnostic of workload demands in different stimulus modalities is discussed.     

The comparison of accommodative response and ocular movements in viewing 3D and 2D displays

Some people often appear asthenopia symptoms of eye fatigue, double vision, nausea, and dizziness while viewing 3D movies. By testing the changes of accommodation function and ocular movements during watching 3D and 2D movies, the factors in visual discomfort are confirmed in this study.20 subjects with normal visual acuity and binocular vision function view 3D and 2D movies with the same content for 30 min, and the amplitude of accommodation, binocular vergence ability, stereo-acuity, and tear break-up time of the subjects before and after viewing the films are measured. Furthermore, an open-field auto-refractor is utilized for synchronously testing the change of accommodative response while viewing 3D and 2D films, and Skalar IRIS tracking system is applied to record ocular movements through infrared positioning.In comparison with viewing 2D movies, the accommodative response and ocular movements reveal obvious changes while viewing 3D movies. The accommodation ability and binocular vergence ability obviously drop after viewing 3D movies; moreover, the stability of stereo-acuity and tear film also gets worse. The changes of such physiological factors might be the major cause of asthenopia.     

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.     

Windows环境下脑机接口视觉刺激器的设计

给出了基于视觉诱发电位的脑-机接口模式的方案,该方案的关键部分是视觉刺激器的实现,它提供了用户利用脑电信号识别字符所需的多种刺激模式。在Windows环境下,以闪烁的不同小块代表多种可能的选择,受试者注视其中一个目标,分析诱发电位可判别受试者所注视的目标。实测显示,视窗中的目标图像同时运动时,平滑稳定、无抖动现象,时间精度达到设计要求的1ms,实时向并口输出数据,该方案能有效地诱发出可识别的具有特征性的视觉诱发电位。     

Accommodation,cognition, and virtual image displays: A review of the literature

This paper reviews the literature on factors that influence the visual (ocular) accommodation response when using see-through virtual image displays (VIDs) such as head-up and helmet-mounted displays. This review suggests that the overall accommodation response is determined by a complex interaction of many factors, some of which are associated with the visual stimulus (such as blur and chromatic aberration) and some of which are cognitive in nature (such as workload and attention). When using VIDs, the effects of these different influences on the accommodation response may not be congruent, leading to the level of accommodation being inappropriate for the task.     

Cardiovascular state changes during performance of a simulated ambulance dispatchers' task: Potential use for adaptive support

Adaptive support has the potential to keep the operator optimally motivated, involved, and able to perform a task. In order to use such support, the operator's state has to be determined from physiological parameters and task performance measures. In an environment where the task of an ambulance dispatcher was simulated, two studies have been carried out to evaluate the feasibility of using cardiovascular measures for adaptive support. During performance of this 2–3 h lasting planning task, a pattern of results is found that can be characterized by an initial increase of blood pressure and heart rate and a decrease of heart rate variability (defense reaction pattern) followed by an ongoing increase of blood pressure counteracted by a decrease in heart rate. This pattern can be explained by an augmented short-term blood pressure control (baroreflex), which is reflected in an increase of baroreflex sensitivity. Additionally, in this latter phase heart rate variability (HRV) increases as a function of time, while blood pressure variability decreases. In the two studies performed, the baroreflex pattern was consistent for all the relevant variables.In both studies there were periods with high and low workload. Effects of task load are mainly reflected in the variability measures, while in the second study, additionally, blood pressure level was higher during periods with high task demands.The conclusion of the studies is that consistent cardiovascular response patterns can be recognized during this semi-realistic planning task, where variability measures are most sensitive to task demand changes, while blood pressure and baroreflex sensitivity are most informative with respect to cardiovascular state changes. These findings can be seen as a great potential benefit for future use in adaptive support applications.     

Psychophysiological changes during a VDU repetitive task

Abstract

A simulated realistic data-entry task on a visual display unit (VDU) was employed to study the relationships between performance and various physiological indices of arousal. After several training sessions on separate days, subjects performed the data-entry task which lasted 120 min. All the components of the workplace were adjusted in order to provide each subject with suitable ergonomic conditions. Performance (correct entries, errors, omissions) and physiological parameters (spectral analysis of the electroencephalogram (EEG) and heart rate (HR)) were recorded continuously. Three functional tests were performed before and after the data-entry task: an eye muscle balance test, a visual reaction time task (RT) and an attentional-perceptual task (AP) displayed on the terminal. Data-entry task performance showed a progressive decline, reaching minimal values after 45-60 min of work, followed by a significant rebound. This pattern characterized 80% of the subjects and was not dependent on the individual average level of performance. Behavioural responses were found to be associated with corresponding EEG arousal changes: i.e. with a parallel trend of beta activity and an opposite one of theta and alpha activities, whereas average HR decreased from the beginning to the end. There is some evidence that different EEG frequency bands are more sensitive to selective attentional requirements than HR which is rather related to diffuse arousal changes. The before/after tests showed a more pronounced esophoria, an increase of RT and of errors percentage in the AP task after 2 hours of work. The EEG did not show any significant difference after work but the average HR level was significantly lower compared with the before-work values. The EEG pattern accompanying the rebound of the performance during the data-entry task supports the auto-arousal hypothesis which assumes that a cerebral compensatory effort intervenes in a mental repetitive task.     

Effects of display technologies on operation performances and visual fatigue

The use of 3D stereoscopic display technology in all aspects of life has attracted considerable research attention. However, only few studies have simultaneously considered the effects of stereoscopic display technologies on visual fatigue and operating performances. This study with 36 participants (50% females; mean age = 23.17 years, SD = 3.3) analyzed the effects of display technologies, task complexity, and use time on operation performances, subjective and objective visual fatigue. Results indicated that display technology did not significantly affect the operation performances, whereas task complexity did. However, no interaction took place between them. Display technology had no significant effects on subjective visual fatigue and near-point accommodation (NPA) but affected critical fusion frequency (CFF) significantly. Use time had significant effects on both subjective and objective visual fatigue.     

Air-to-ground training missions: a psychophysiological workload analysis

Psychophysiological measures are used to assess the workload of F4 Phantom aircraft pilots and weapon systems officers (WSOs) during air-to-ground training missions and during the performance of two levels of difficulty of a laboratory tracking task. The bombing range portion of the missions was associated with the highest pilot workload, while the WSO flying the aircraft was the highest workload segment for the WSOs. The pilots' data were found to have a wider range of values for the physiological measures than were found in the WSO data. The different levels of tracking task difficulty produced significant physiological effects but the range of values found for most of the flight segments were much greater. These data demonstrate that extrapolating laboratory data to the flight environment is risky at best. The various physiological measures were differentially sensitive to the different demands of the various flight segments.     

基于虚拟仪器LabVIEW的脑—机接口系统

给出了基于瞬态视觉诱发电位的脑-机接口系统在LabVIEW环境下的实现方案。该方案的关键部分是视觉刺激器的设计和脑电信号的提取两部分。不同的刺激模块代表了多种可能的选择,受试者注视屏幕上其中一个目标,分析诱发电位可判别试者所注视的目标。采用累加平均和滤波的方法提高信噪比,用于提取微弱的脑电信号。该方案能有效地诱发出可识别的具有特征性的视觉诱发电位,并且通过离线的信号处理能够提取出所诱发的视觉诱发电位。     

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.     

Human interaction with robotic systems: performance and workload evaluations

Abstract

We first tested the effect of differing tactile informational forms (i.e. directional cues vs. static cues vs. dynamic cues) on objective performance and perceived workload in a collaborative human–robot task. A second experiment evaluated the influence of task load and informational message type (i.e. single words vs. grouped phrases) on that same collaborative task. In both experiments, the relationship of personal characteristics (attentional control and spatial ability) to performance and workload was also measured. In addition to objective performance and self-report of cognitive load, we evaluated different physiological responses in each experiment. Results showed a performance–workload association for directional cues, message type and task load. EEG measures however, proved generally insensitive to such task load manipulations. Where significant EEG effects were observed, right hemisphere amplitude differences predominated, although unexpectedly these latter relationships were negative. Although EEG measures were partially associated with performance, they appear to possess limited utility as measures of workload in association with tactile displays.

Practitioner Summary: As practitioners look to take advantage of innovative tactile displays in complex operational realms like human–robotic interaction, associated performance effects are mediated by cognitive workload. Despite some patterns of association, reliable reflections of operator state can be difficult to discern and employ as the number, complexity and sophistication of these respective measures themselves increase.     

Utilizing slope method as an alternative data analysis for functional near-infrared spectroscopy-derived cerebral hemodynamic responses

The purpose was to propose an alternative data analysis for functional near-infrared spectroscopy (fNIRS)-derived hemodynamics as a function of cortical activation changes. We evaluated hemodynamic responses from the prefrontal cortex region while 38 participants performed a cognitive task. The task consisted of an arithmetic calculation with three levels of complexity (i.e., easy, medium and difficult). These task-dependent hemodynamic responses were analyzed by the slope method (i.e. using a linear regression through the cognitive task) and were compared with the corresponding responses obtained with a traditional approach of the amplitude method. Subjective scales of task loading (assessed by DP15 and NASA-TLX) and behavioral outcomes (performance and reaction time) were also recorded in response to the task complexity. Results revealed that the proposed slope method allowed a better discrimination in terms of cortical activation among all levels of mental workload. There was no significant increase in cortical activation between the medium and difficult levels (p = .30; d = 0.09) with the amplitude method while the slope coefficient was sensitive to the different levels (p < .01; d = 0.32). These preliminary results from a large sample size demonstrated that the slope method appears suitable for discriminating the changes in cortical activation with respect to the mental workload.Relevance to industryIn this work, we proposed an optimum way of quantifying the mental workload of participants in terms of fNIRS-derived cerebral hemodynamic responses.     

Assessment and monitoring of mental workload in subway train operations using physiological,subjective, and performance measures

Subway train operation is a complex, sociotechnical system that involves a variety of cognitively demanding tasks. The train operators are responsible for continuously monitoring the surrounding environment, maintaining awareness, processing information, and making decisions under risk. The resulting mental strain on operators can negatively affect their performance and the interaction of the human–machine system. The objective of this study was to evaluate if physiological, subjective, and performance measures could identify the level of mental workloads arising from routine and nonroutine operations in the subway system. A total of 11 subway train operators underwent different driving scenarios in a high‐fidelity simulator. The simulated tasks were divided into two categories: routine operations (preparing to drive and driving between stations without interruptions or emergencies) and nonroutine operation (responding to a tunnel fire, dealing with a high density of passengers, encountering a passenger/technician on the track, and responding to train failure). The mental workload was monitored and evaluated in these tasks using an electrocardiogram, subjective self‐rating scales, and driving performance. Both heart rate variability and performance measures (including reaction time and error rate) detected mental workload variations in the different operations. On the other hand, the subjective ratings (including NASA‐TLX) assessed the overall mental workload associated with a task, without explaining the mental demand variations within the task over time. Subway train drivers experienced different levels of mental workload during routine and nonroutine driving conditions. The findings of this study can be used to extract mental workload limits to optimize workload levels during train operations.