Engineering topics

Hancock, P. A.

Publications and source records attributed to Hancock, P. A..

11 records

NASA NTRS1993

Effect of task load and task load increment on performance and workload

The goal of adaptive automated task allocation is the 'seamless' transfer of work demand between human and machine. Clearly, at the present time, we are far from this objective. One of the barriers to achieving effortless human-machine symbiosis is an inadequate understanding of the way in which operators themselves seek to reallocate demand among their own personal 'resources.' The paper addresses this through an examination of workload response, which scales an individual's reaction to common levels of experienced external demand. The results indicate the primary driver of performance is the absolute level of task demand over the increment in that demand.

Hancock, P. A.↗

NASA NTRS1991

On operator strategic behavior

Deeper and more detailed knowledge as to how human operators such as pilots respond, singly and in groups, to demands on their performance which arise from technical systems will support the manipulation of such systems' design in order to accommodate the foibles of human behavior. Efforts to understand how self-autonomy impacts strategic behavior and such related issues as error generation/recognition/correction are still in their infancy. The present treatment offers both general and aviation-specific definitions of strategic behavior as precursors of prospective investigations.

Hancock, P. A.↗

NASA NTRS1990

Age and the elderly internal clock - Further evidence for a fundamentally slowed CNS

Age-related differences in accuracy of time estimation have been studied. It is found that compared to the younger subjects (mean age 25 years), the older adults (mean age 70 years) consistently overestimated the target 10-sec interval when they had to simultaneously perform an interpolating task (i.e., count backwards by subtractions of three).

Cann, Michael T.↗

NASA NTRS1990

Workload and strategic adaptation under transformations of visual-coordinative mappings

A study involving a bimanual pursuit-tracking task is conducted to examine strategic exploration of differing visual and motor coordination patterns emphasizing workload as an indicator of strategic behavior. The mappings are conducted for 16 possible variations of order, speed, and combination. Performance is assessed by means of the rms and percent time-on-target, and the NASA task-load index is used to classify subjective reports on workload. The results are broken down into four primary performance mappings and four hybrid mappings called contradictory conditions. The order of difficulty of the conditions is apparently determined by the workload, except that in the case of the three most difficult decoupled conditions some dissociation is reported.

Caird, J. K.↗

NASA NTRS1989

A dynamic model of stress and sustained attention

Arguments are presented that an integrated view of stress and performance must consider the task demanding a sustained attention as a primary source of cognitive stress. A dynamic model is developed on the basis of the concept of adaptability in both physiological and psychological terms, that addresses the effects of stress on vigilance and, potentially, a wide variety of attention-demanding performance tasks. The model provides an insight into the failure of an operator under the driving influences of stress and opens a number of potential avenues through which solutions to the complex challenge of stress and performance might be posed.

Hancock, P. A.↗

NASA NTRS1989

The effects of control order, feedback, practice, and input device on tracking performance and perceived workload

The present experiment examined the influence of several task-related factors on tracking performance and concomitant workload. The manipulated factors included tracking order, the presence or absence of knowledge of performance, and the control device. Summed root mean square error (rmse) and perceived workload were measured at the termination of each trial. Perceived workload was measured using the NASA Task Load Index (TLX) and the Subjective Workload Assessment Technique (SWAT). Results indicated a large and expected effect for track order on both performance and the perception of load. In general, trackball input was more accurate and judged for lower load than input using a mouse. The presence or absence of knowledge of performance had little effect on either performance or workload. There were a number of interactions between factors shown in performance that were mirrored by perceived workload scores. Results from each workload scale were equivalent in terms of sensitivity to task manipulations. The pattern of results affirm the utility of these workload measures in assessing the imposed load of multiple task-related variables.

Hancock, P. A.↗

NASA NTRS1989

The effects of practice on tracking and subjective workload

Six college-age male subjects performed one hundred, two-minute trials on a second-order tracking task. After each trial, subjects estimated perceived workload using both the NASA TLX and SWAT workload assessment procedures. Results confirmed an expected performance improvement on the tracking task which followed traditional learning curves within the performance of each individual. Perceived workload also decreased for both scales across trials. While performance variability significantly decreased across trials, workload variability remained constant. One month later, the same subjects returned to complete the second experiment in the sequence which was a retention replication of the first experiment. Results replicated those for the first experiment except that both performance error and workload were at reduced overall levels. Results in general affirm a parallel workload reduction with performance improvement, an observation consistent with a resource-based view of automaticity.

Hancock, P. A.↗

NASA NTRS1988

Estimation of duration and mental workload at differing times of day by males and females

Two experiments are reported which investigated whether male and female operator duration estimation and subjective workload followed conventional circadian fluctuation. In the first experiment, twenty-four subjects performed a filled time-estimation task in a constant blacked-out, noise-reduced environment at 0800, 1200, 1600, and 2000 h. In the second experiment, twelve subjects performed an unfilled time estimation task in similar conditions at 0900, 1400, and 1900 h. At the termination of all experimental sessions, participants completed the NASA TLX workload assessment questionnaire as a measure of perceived mental workload. Results indicated that while physiological response followed an expected pattern, estimations of duration and subjective perception of workload showed no significant effects for time-of-day. In each of the experiments, however, there were significant differences in durational estimates and mental workload response depending upon the gender of the participant. Results are taken to support the assertion that subjective workload is responsive largely to task-related factors and indicates the important differences that may be expected due to operator gender.

Hancock, P. A.↗

NASA NTRS1986

Knowledge-based load leveling and task allocation in human-machine systems

Conventional human-machine systems use task allocation policies which are based on the premise of a flexible human operator. This individual is most often required to compensate for and augment the capabilities of the machine. The development of artificial intelligence and improved technologies have allowed for a wider range of task allocation strategies. In response to these issues a Knowledge Based Adaptive Mechanism (KBAM) is proposed for assigning tasks to human and machine in real time, using a load leveling policy. This mechanism employs an online workload assessment and compensation system which is responsive to variations in load through an intelligent interface. This interface consists of a loading strategy reasoner which has access to information about the current status of the human-machine system as well as a database of admissible human/machine loading strategies. Difficulties standing in the way of successful implementation of the load leveling strategy are examined.

Chignell, M. H.↗

NASA NTRS1986

The effects of stress on attentional resources

A new perspective is presented from which to view the action of stress on human behavior. At a behavioral level, the action of stress is related to notions of human attention and an indication of an isomorphic relationship between modes of control at a physiological and behavioral level is presented. Examples of this phenomenon are extracted from performance under heat stress, since this is one of the most simple stress circumstances. It is suggested that stress sufficient to overcome adaptive capability, that is efficient homeostasis, acts to drain attentional resources. The manner in which such resources fail approximates that function typical of a positive feedback system, which also characterizes the breakdown of physiological response under severe environmental stress. The end point of this draining sequence is the absence of all attentional resources, which is taken to be unconsciousness, to be rapidly followed by the failure of physiological adaptability upon which life sustaining functions depend. This overall picture preserves the inverted-U shaped relationship between stress and performance, yet is in distinct contrast to the traditional arousal account of such behavior. The theoretical and practical ramifications of these observations are explored.

Hancock, P. A.↗

NASA NTRS1984

An Analysis of Kinetic Response Variability

Studies evaluating variability of force as a function of absolute force generated are synthesized. Inconsistencies in reported estimates of this relationship are viewed as a function of experimental constraints imposed. Typically, within-subject force variability increases at a negative accelerating rate with equal increments in force produced. Current pulse-step and impulse variability models are unable to accommodate this description, although the notion of efficiency is suggested as a useful construct to explain the description outlined.

Hancock, P. A.↗