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.     

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.     

Human performance in a multiple-task environment: Effects of automation reliability on visual attention allocation

Diagnostic automation has been posited to alleviate the high demands of multiple-task environments; however, mixed effects have been found pertaining to performance aid success. To better understand these effects, attention allocation must be studied directly. We developed a multiple-task environment to study the effects of automation on visual attention. Participants interacted with a system providing varying levels of automation and automation reliability and then were transferred to a system with no support. Attention allocation was measured by tracking the number of times each task was viewed. We found that participants receiving automation allocated their time according to the task frequency and that tasks that benefited most from automation were most harmed when it was removed. The results suggest that the degree to which automation affects multiple-task performance is dependent on the relative attributes of the tasks involved. Moreover, there is an inverse relationship between support and cost when automation fails.     

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.     

External and internal attentional environments I. The utilization of cardiac deceleratory and acceleratory response data for evaluating differences in mental workload between machine-paced and self-paced work ∗

Previous evidence has suggested that self-paced (SP) task performance may constitute a higher mental workload than machine-paced (MP) performance. These differences in mental workload were thought to be due to the presence, when working SP, of an internal pacing mechanism serving to maintain the worker's rhythm. In MP tasks, this function would be maintained externally by the machine. The present investigation attempted to directly test this hypothesis. For this purpose, Lacey's psychophysiological model relating changes in heart rate (HR) to attentional demands was employed. Differences in cardiac deceleratory and acceleratory activity between MP and SP performance were evaluated for each of two tasks. In one task, the emphasis was predominantly on visual detection. Based on the suspected direction of attentional demands, this task was characterized as external. The other task required mental solution to arithmetic problems and was categorized accordingly as internal. Psychophysiological findings were consistent with Lacey's basic model and offered no support for the existence of an internal pacing mechanism under SP conditions. Instead, they suggested the presence of uncertainty factors reflecting higher mental workload during the MP performance of both tasks. Performance data, however, did not support the causal interpretation given by Lacey for his psychophysiological model, and were explained in terms of a complex interplay between HR level and HR change.     

Age-related performance in a multiple-task environment.

Younger and older adult participants performed a dynamic multiple-task requiring concurrent processing of 4 independent tasks. Component-task performance emphasis (i.e., task priorities) was biased by differential point allocations across task components. After training, the point structure was modified. Older adults exhibited larger multiple-task performance deficits compared with younger adults; however, the age-related gap in multiple-task performance decreased with practice. The age-related performance difference increased again when task emphasis was changed, but not when demands were changed. Consistent with the training data, the age-related differences diminished again with additional experience on this new task-component emphasis. The data suggest that higher-order, strategic processing may be an important source of age-related differences in complex multiple-task performance. Actual or potential applications of this research include the facilitation of techniques for age-related comprehensive usability testing for products of even moderate complexity.     

Divided attention in experienced young and older drivers: lane tracking and visual analysis in a dynamic driving simulator.

A simulated driving task that required the simultaneous execution of two continuous visual tasks was administered to 12 healthy young (mean age 26.1 years) and 12 healthy older (mean age 64.4 years) experienced and currently active drivers. The first task was a compensatory lane-tracking task involving a three-dimensional road display. The second task was a timed, self-paced visual analysis task involving either a vocal or manual binary response to dot patterns projected within the road display. Using adaptive tasks, single-task difficulty was individually adjusted for each subject. To control for individual differences in attention allocation strategy, the dual task was performed according to three different sets of instructions based on the relative importance of each task. Compared with young adults, older adults showed a significantly decreased ability to divide attention. This effect was apparent in lane tracking and in the accuracy of visual analysis. The impairment of divided attention was less pronounced in the vocal condition than in the manual one. This suggests that difficulty in integrating responses may be an important determinant of poor dual-task performance in old age.     

The physical demands upon (Dutch) fire-fighters in relation to the maximum acceptable energetic workload

The aim of this study was to assess the tasks and activities that make physical demands on Dutch fire-fighters and to compare them with a guideline related to the development of excessive fatigue. The occupational physical demands on Dutch fire-fighters were assessed by conducting a task analysis during 85 24-h shifts. While workplace observations on the duration and frequency of physical tasks and activities were recorded, the heart rate was measured. This was then used to calculate the heart rate reserve percentage (%HRR) for predefined working periods, tasks and activities during 24-h shifts. The findings indicate that actual fire-fighting during 24-h shifts is characterised by a low frequency of incidents, a short ‘turn-out’ time, short tasks, and activities with a moderate to occasionally high energetic workload. Two tasks which sometimes occur in actual fire-fighting exceeded the guideline on energetic workload. The conclusion was that, though the number of incidents and the occupational demands are low during 24-h shifts, the peak loads for these two tasks are energetically high and could lead to excessive fatigue. Consequently, attention may need to be paid to health surveillance for persons exposed to such energetic peak loads, the development of physical and medical selection procedures, training, and workplace adjustments.     

Frontal midline theta rhythm and eyeblinking activity during a VDT task and a video game: useful tools for psychophysiology in ergonomics

The necessity of psychophysiological research in ergonomics has gradually been recognized in Japan. In this paper, frontal midline theta rhythm (Fm-theta) and eyeblinking are recommended as tools in this field, especially for assessing workers' attention concentration, mental workload, fatigue, and interest during VDT work at the workplace and playing video games at home. In experiment 1, Fm-theta and eyeblink rates were measured in 10 Japanese abacus experts (Group E) and 10 normal students (Group C) during a visual search task with VDT. Memory load affected all measures. The amount of Fm-theta appeared more in Group E than Group C, but blink rate was lower in Group E than in Group C. As abacus experts have such highly developed skills in concentration, the result indicates that the amount of Fm-theta would be a good index of attention concentration in VDT workers. The second experiment was done with 10 schoolaged children as subjects during three visual tasks: video game, mental test and animation. Amounts of Fm-theta and the degree of blink inhibition were maximum while playing the video game, which all subjects reported they most preferred, and minimum while watching animation, which eight subjects reported to be most boring. An interesting task would seem to provoke Fm-theta and inhibit eyeblink activity. From these two experiments, Fm-theta and eyeblink rate would appear to be good indices of attention concentration and task pleasantness of a mental task using VDT.     

The physical demands upon (Dutch) fire-fighters in relation to the maximum acceptable energetic workload

The aim of this study was to assess the tasks and activities that make physical demands on Dutch fire-fighters and to compare them with a guideline related to the development of excessive fatigue. The occupational physical demands on Dutch fire-fighters were assessed by conducting a task analysis during 85 24-h shifts. While workplace observations on the duration and frequency of physical tasks and activities were recorded, the heart rate was measured. This was then used to calculate the heart rate reserve percentage (%HRR) for predefined working periods, tasks and activities during 24-h shifts. The findings indicate that actual fire-fighting during 24-h shifts is characterised by a low frequency of incidents, a short 'turn-out' time, short tasks, and activities with a moderate to occasionally high energetic workload. Two tasks which sometimes occur in actual fire-fighting exceeded the guideline on energetic workload. The conclusion was that, though the number of incidents and the occupational demands are low during 24-h shifts, the peak loads for these two tasks are energetically high and could lead to excessive fatigue. Consequently, attention may need to be paid to health surveillance for persons exposed to such energetic peak loads, the development of physical and medical selection procedures, training, and workplace adjustments.     

Pupil responses to continuous aiming movements

Pupillary response is associated with perceptual and cognitive loads in visual and cognitive tasks, but no quantitative link between pupil response and the task workload in visual−motor tasks has been confirmed. The objective of this study is to investigate how the changes of task requirement of a visual−motor task are reflected by the changes of pupil size. In the present study, a simple continuous aiming task is performed and the task requirement is manipulated and measured by Fitts’ Index of Difficulty (ID), calculated for different combinations of the target size and movement distance. Pupil response is recorded using a remote eye-tracker. The results show that event-triggered pupil dilations in continuous aiming movements respect Fitts’ Law, such that higher task difficulty evokes higher peak pupil dilation and longer peak duration. These findings suggest that pupil diameter can be employed as a physiological indicator to task workload evoked by the task requirement in visual−motor tasks.     

Dual-task performance in multimodal human-computer interaction: a psychophysiological perspective

This paper examines the psychophysiological effects of mental workload in single-task and dual-task human-computer interaction. A mental arithmetic task and a manual error correction task were performed both separately and concurrently on a computer using verbal and haptic input devices. Heart rate, skin conductance, respiration and peripheral skin temperature were recorded in addition to objective performance measures and self-report questionnaires. Analysis of psychophysiological responses found significant changes from baseline for both single-task and dual-task conditions. There were also significant psychophysiological differences between the mental arithmetic task and the manual error correction task, but no differences in questionnaire results. Additionally, there was no significant psychophysiological difference between performing only the mental arithmetic task and performing both tasks at once. These findings suggest that psychophysiological measures respond differently to different types of tasks and that they do not always agree with performance or with participants’ subjective feelings.     

Tactile interruption management: tactile cues as task-switching reminders

Tactile cuing has been suggested as a method of interruption management for busy visual environments. This study examined the effectiveness of tactile cues as an interruption management strategy in a multi-tasking environment. Sixty-four participants completed a continuous aircraft monitoring task with periodic interruptions of a discrete gauge memory task. Participants were randomly assigned to two groups; one group had to remember to monitor for interruptions while the other group received tactile cues indicating an interruption’s arrival and location. As expected, the cued participants evidenced superior performance on both tasks. The results are consistent with the notion that tactile cues transform the resource-intensive, time-based task of remembering to check for interruptions into a simpler, event-based task, where cues assume a portion of the workload, permitting the application of valuable resources to other task demands. This study is discussed in the context of multiple resource theory and has practical implications for systems design in environments consisting of multiple, visual tasks and time-sensitive information.     

Using cerebral hemovelocity to measure workload during a spatialised auditory vigilance task in novice and experienced observers

This experiment was designed to assess cognitive load using transcranial Doppler sonography during the performance of a 40-min communication vigilance task in which messages were presented in different spatial locations or across a single monaural radio channel. In addition, some observers received 14 hours of practice to determine whether the neurophysiological measure was sensitive to a potential attenuation of workload. Critical messages were detected more frequently in the spatialised audio presentation mode condition, but there were no performance differences between experienced and novice observers. Neurophysiological data show that activation was greater in the novice condition than in the experienced condition, suggesting that novice observers expended greater effort. Furthermore, the neurophysiological measure showed more activation in the monaural radio condition than in the spatialised audio condition. The results support a resource account of vigilance and suggest that cerebral blood flow velocity can be used to diagnose the degree of attentional resource utilisation during vigilance tasks.

Practitioner Summary: Due to high workload experienced during vigilance tasks, displays and methods are sought which enhance performance. This study shows that spatialising auditory communications in a monitoring task enhances performance and attenuates mental workload. Also, experience mitigates excessive workload, and cerebral hemovelocity can be used to diagnose attentional resource utilisation.     

Mental workload and cognitive task automaticity: an evaluation of subjective and time estimation metrics

Abstract

The evaluation of mental workload is becoming increasingly important in system design and analysis. The present study examined the structure and assessment of mental workload in performing decision and monitoring tasks by focusing on two mental workload measurements: subjective assessment and time estimation. The task required the assignment of a series of incoming customers to the shortest of three parallel service lines displayed on a computer monitor. The subject was either in charge of the customer assignment (manual mode) or was monitoring an automated system performing the same task (automatic mode). In both cases, the subjects were required to detect the non-optimal assignments that they or the computer had made. Time pressure was manipulated by the experimenter to create fast and slow conditions. The results revealed a multi-dimensional structure of mental workload and a multi-step process of subjective workload assessment. The results also indicated that subjective workload was more influenced by the subject's participatory mode than by the factor of task speed. The time estimation intervals produced while performing the decision and monitoring tasks had significantly greater length and larger variability than those produced while either performing no other tasks or performing a well practised customer assignment task. This result seemed to indicate that time estimation was sensitive to the presence of perceptual/cognitive demands, but not to response related activities to which behavioural automaticity has developed.     

The effect of distractor modality and processing code on human-automation interaction

We examined the effect of distractor characteristics (modality and processing code) on visual search performance and interaction with an automated decision aid. Multiple Resource Theory suggests that concurrent tasks that are processed similarly (e.g. two visual tasks) will cause greater interference than tasks that are not (e.g., a visual and auditory task). The impact of tasks that share processing and perceptual demands and their interaction with human-automation interaction is not established. In order to examine this, participants completed two blocks of a luggage screening simulation with or without the assistance of an automated aid. For one block, participants performed a concurrent distractor task drawn from one of four combinations of modality and processing code: auditory-verbal; auditory-spatial; visual-verbal; visual-spatial. We measured sensitivity, criterion setting, perceived workload, system trust, perceived system reliability, compliance, reliance, and confidence. Participants demonstrated highest sensitivity when performing with an auditory-spatial secondary task. Automation compliance was higher when the auditory-spatial distraction was present versus absent; however, system trust was highest in the auditory-verbal condition. Confidence (when disagreeing with the aid) was also highest when the distractor was auditory. This study indicates that some forms of auditory ‘distractors’ may actually help performance; these results further contribute to understanding how distractions influence performance when operators interact with automation and have implications for improved work environment and system design.     

Mental workload measurement for emergency operating procedures in digital nuclear power plants

Mental workload is a major consideration for the design of emergency operation procedures (EOPs) in nuclear power plants. Continuous and objective measures are desired. This paper compares seven mental workload measurement methods (pupil size, blink rate, blink duration, heart rate variability, parasympathetic/sympathetic ratio, total power and (Goals, Operations, Methods, and Section Rules)-(Keystroke Level Model) GOMS-KLM-based workload index) with regard to sensitivity, validity and intrusiveness. Eighteen participants performed two computerised EOPs of different complexity levels, and mental workload measures were collected during the experiment. The results show that the blink rate is sensitive to both the difference in the overall task complexity and changes in peak complexity within EOPs, that the error rate is sensitive to the level of arousal and correlate to the step error rate and that blink duration increases over the task period in both low and high complexity EOPs. Cardiac measures were able to distinguish tasks with different overall complexity. The intrusiveness of the physiological instruments is acceptable. Finally, the six physiological measures were integrated using group method of data handling to predict perceived overall mental workload.

Practitioner Summary: The study compared seven measures for evaluating the mental workload with emergency operation procedure in nuclear power plants. An experiment with simulated procedures was carried out, and the results show that eye response measures are useful for assessing temporal changes of workload whereas cardiac measures are useful for evaluating the overall workload.     

Effects of different physical workload parameters on mental workload and performance

The design and evaluation of an occupational task should include an assessment of mental workload, since excessive levels of mental workload can cause errors or delayed information processing. Physically demanding work that is performed concurrently with a cognitive task may impact mental workload by impairing mental processing or decreasing performance. The primary objective of this study was to determine whether there is a differential effect of various types of physical activity on both mental workload and cognitive performance. Objective and subjective assessment tools (heart rate variability and visual analog scale) were used as indicators of mental workload, while correct responses during an arithmetic task reflected levels of performance. Thirty participants (ages 18-24 years) performed a combination of tasks inducing both physical and mental workload. Type of physical effort, frequency of movement, and force exertion level were manipulated to alter the workload associated with the physical activity. Changes in subjective ratings generally corresponded to changes in both performance on the arithmetic task and objective mental workload assessment. Some discrepancies occurred at the highest physical force exertion level as participants perceived an increase in effort to maintain the same level of performance. Further research is needed to determine the force exertion threshold, beyond which the physical effort required interferes with mental workload and/or cognitive performance.

Relevance to industry

Technological advancements have increased the requirement for many workers to execute cognitive tasks concurrently with physical activity. When designing and evaluating such situations it is important to determine the interactive effects of these activities. A simple, uni-dimensional tool is suggested as a screening tool to identify situations requiring excessive or increased mental workload that many degrade performance or place additional stress on the individual.     

Vigilance requires hard mental work and is stressful

OBJECTIVE: We describe major discoveries and developments in vigilance research. BACKGROUND: Vigilance tasks have typically been viewed as undemanding assignments requiring little mental effort. The vigilance decrement function has also been considered to result from a decline in arousal brought about by understimulation. METHODS: Recent research in vigilance is reviewed in four areas: studies of task type, perceived mental workload during vigilance, neural measures of resource demand in vigilance, and studies of task-induced stress. RESULTS: Experiments comparing successive and simultaneous vigilance tasks support an attentional resource theory of vigilance. Subjective reports also show that the workload of vigilance is high and sensitive to factors that increase processing demands. Neuroimaging studies using transcranial Doppler sonography provide strong, independent evidence for resource changes linked to performance decrement in vigilance tasks. Finally, physiological and subjective reports confirm that vigilance tasks reduce task engagement and increase distress and that these changes rise with increased task difficulty. CONCLUSIONS: Converging evidence using behavioral, neural, and subjective measures shows that vigilance requires hard mental work and is stressful. APPLICATION: This research applies to most human-machine systems that require human monitoring, particularly those involving automated subsystems.     

Predicting dual-task performance with the Multiple Resources Questionnaire (MRQ)

OBJECTIVE: The objective was to assess the validity of the Multiple Resources Questionnaire (MRQ) in predicting dual-task interference. BACKGROUND: Subjective workload measures such as the Subjective Workload Assessment Technique (SWAT) and NASA Task Load Index are sensitive to single-task parameters and dual-task loads but have not attempted to measure workload in particular mental processes. An alternative is the MRQ. METHOD: In Experiment 1, participants completed simple laboratory tasks and the MRQ after each. Interference between tasks was then correlated to three different task similarity metrics: profile similarity, based on r(2) between ratings; overlap similarity, based on summed minima; and overall demand, based on summed ratings. Experiment 2 used similar methods but more complex computer-based games. RESULTS: In Experiment 1 the MRQ moderately predicted interference (r = +.37), with no significant difference between metrics. In Experiment 2 the metric effect was significant, with overlap similarity excelling in predicting interference (r = +.83). Mean ratings showed high diagnosticity in identifying specific mental processing bottlenecks. CONCLUSION: The MRQ shows considerable promise as a cognitive-process-sensitive workload measure. APPLICATION: Potential applications of the MRQ include the identification of dual-processing bottlenecks as well as process overloads in single tasks, preparatory to redesign in areas such as air traffic management, advanced flight displays, and medical imaging.