Peripheral arterial tone as an on-line measure of load in a simulated flight task.

Variations in continuous and discrete flight demands were investigated in a simulated flight mission measuring peripheral arterial tone (PAT) from the tip of the finger. A total of 12 participants performed a computer-simulated agricultural flight task. They were required to fly over a specific lane of a simulated corn field (continuous task) and change lanes in response to flags, which appeared at varying intervals (discrete task). The difficulty of the flight task was manipulated by varying the airplane control (single- vs. dual-axis control), while the difficulty of the discrete task was manipulated by varying the amount of lateral change signalled by the flag. PAT amplitude was lower in the difficult level of the continuous task and was further attenuated following the appearance of the flag only when a change in the flight position was required. These results suggest the potential utility of PAT as an on-line measure of the joint continuous and discrete demands of a flight mission.

On the potential value and limitations of emphasis change and other exploration-enhancing training methods.

Two experiments are presented that examine the efficiency of training methods that force trainees to explore the possible strategy space. Both experiments used a 2-dimensional search task. Experiment 1 studies a method that enforces exploration by preventing repetitions within short sequences. It shows that the effect of this "enhanced exploration" method in the abstract setting is similar to the effect of "emphasis change" training (see D. Gopher, 1993) in high cognitive workload tasks. This finding appeared only in strategic spaces where intuitive exploration converges to a local optimum. Experiment 2 compares the effect of exploration enhancement with the effect of guided instruction. The results of the experiments, which are captured well by a generalization of I. Erev and D. A. Gopher's (1999) model of the conditions for the success of emphasis change training, shed light on the limitations and potential of exploration-enhancing training methods.

Switching tasks and attention policies.

The determinants and costs of control were studied in 6 experiments examining the performance costs of changing stimulus dimension (digit value/number of elements) or attention strategies (speed/accuracy) on the first trial after task transition. Costs were compared for task shift and reconsideration only. Preparation ability was studied by presenting all transition information at the beginning of a 2-part block or only prior to each part. Results showed pronounced first-trial transition costs. Different factors were associated with stop-start and task-switching requirements. Transition costs were separate from those of basic task performance. Costs were sensitive to global control considerations and were larger for task dimension changes than for attention strategy shifts. Costs involving task dimension change, but not strategy shifts, were reduced with advanced preparation. These results are discussed in relation to contemporary models of control. A new distinction is proposed between activation and execution of control strategies.

The effect of shared responsibility and competition in perceptual games: a test of a cognitive game-theoretic extension of signal-detection theory.

Perceptual decisions are often made in complex social settings in which distinct observers can affect each other. To address such situations, I. Erev, D. Gopher, R. Itkin, and Y. Greenshpan (1995) proposed a formal extension of signal-detection theory and a descriptive modification of the extended theory. The current article presents 2 experiments that were designed to test these models in the context of repeated 2-person perceptual safety games. In both experiments, pairs of participants performed a simulation of an industrial-production process under distinct payoff rules. Each participant had to try to produce as much as possible while avoiding costly accidents. In line with the descriptive model's predictions, the results showed a slow adjustment to the incentive structure that can be approximated by a reinforcement learning process among different perceptual cutoff strategies. Providing players with prior information about the game had an initial effect but did not alter the pattern of the results.

Task coordination and aging: explorations of executive control processes in the task switching paradigm.

A number of models of cognitive aging suggest that older adults exhibit disproportionate performance decrements on tasks which require executive control processes. In a series of three studies we examined age-related differences in executive control processes and more specifically in the executive control processes which underlie performance in the task switching paradigm. Young and old adults were presented with rows of digits and were required to indicate whether the number of digits (element number task) or the value of the digits (digit value task) were greater than or less than five. Switch costs were assessed by subtracting the reaction times obtained on non-switch trials from trials following a task switch. Several theoretically interesting results were obtained. First, large age-related differences in switch costs were found early in practice. Second, and most surprising, after relatively modest amounts of practice old and young adults switch costs were equivalent. Older adults showed large practice effects on switch trials. Third, age-equivalent switch costs were maintained across a two month retention period. Finally, the main constraint on whether age equivalence was observed in task switching performance was memory load. Older adults were unable to capitalize on practice under high memory loads. These data are discussed in terms of their implications for both general and process specific cognitive aging models.

Information structure and the relative efficacy of tables and graphs.

Users and system designers often prefer to display information with graphs rather than with tables. However, empirical studies that compared task performance with the two display types frequently revealed either an advantage of tables over graphs or no differences between the displays. This apparent contradiction may result from previous studies in which the importance of the structure that usually exists in displayed information is overlooked. We predict that graphic displays will have an advantage over tables when the displayed information has structure and when this structure is relevant for the task. These conditions generally exist in the actual use of information displays, but have seldom been assessed in experiments. In the present study participants in an experiment performed an information extraction task and a prediction task with unstructured or structured data and with different levels of prior information about the structure. The results showed that the information structure and prior knowledge about the existence of structure affected the advantage of graphic displays over tables when task performance depended on the use of structure. Existing approaches to the study of displays were analyzed in view of these findings. Actual or potential applications of this research include the development of better displays for process control and decision support and better operator training programs.

Attention control: explorations of the work of an executive controller.

This contribution reviews three lines of studies set to investigate attention control and executive operations, in the general context of the interplay between bottom-up and top-down processes in the conduct of proficient behavior. One line of studies focused on the act of switching attention between tasks and the mental costs associated with it. A second group of experiments investigated attention strategies and resource management in coping with high load and concurrent task demands. A third line of studies examined the influence of enhanced knowledge and accumulated experience on coping with malfunctions and mishaps in system response. The experimental results of all studies lend strong support to the existence and influence of executive control processes. These types of processes operate on the established representations and knowledge bases of tasks, to make the best use of processing and response facilities. The experiments shed light on the nature of the processes and the variables that influence them. It is shown that proficient performance is far from being exclusively guided by automatic processing and response routines triggered directly by events in the environment. Instead it is a joint and non-trivial product of these two types of processes. Executive control is required not only in early stages of training, but also at high levels of mastery and proficiency. Automatism does not eliminate or reduce the importance of executive control and strategic behavior. A new and powerful class of processes comes into play at this level of expertise, with strong influence on modes of behavior and the overall efficiency of performance.

A look into the nature and causes of human errors in the intensive care unit.

OBJECTIVES: The purpose of this study was to investigate the nature and causes of human errors in the intensive care unit (ICU), adopting approaches proposed by human factors engineering. The basic assumption was that errors occur and follow a pattern that can be uncovered. DESIGN: Concurrent incident study. SETTING: Medical-surgical ICU of a university hospital. MEASUREMENTS AND MAIN RESULTS: Two types of data were collected: errors reported by physicians and nurses immediately after an error discovery; and activity profiles based on 24-hr records taken by observers with human engineering experience on a sample of patients. During the 4 months of data collection, a total of 554 human errors were reported by the medical staff. Errors were rated for severity and classified according to the body system and type of medical activity involved. There was an average of 178 activities per patient per day and an estimated number of 1.7 errors per patient per day. For the ICU as a whole, a severe or potentially detrimental error occurred on the average twice a day. Physicians and nurses were about equal contributors to the number of errors, although nurses had many more activities per day. CONCLUSIONS: A significant number of dangerous human errors occur in the ICU. Many of these errors could be attributed to problems of communication between the physicians and nurses. Applying human factor engineering concepts to the study of the weak points of a specific ICU may help to reduce the number of errors. Errors should not be considered as an incurable disease, but rather as preventable phenomena.

Performance under dichoptic versus binocular viewing conditions: effects of attention and task requirements.

Three experiments investigated subjects' ability to allocate attention and cope with task requirements under dichoptic versus binocular viewing conditions. Experiments 1 and 2 employed a target detection task in compound and noncompound stimuli, and Experiment 3 employed a relative-proximity judgment task. The tasks were performed in a focused attention condition in which subjects had to attend to the stimulus presented to one eye or field (under dichoptic and binocular viewing conditions, respectively) while ignoring the stimulus presented to the other eye or field, and in a divided attention condition in which subjects had to attend the stimuli presented to both eyes or fields. Subjects' performance was affected by the interaction of attention conditions with task requirements, but it was generally the same under dichoptic and binocular viewing conditions. The more dependent the task was on finer discrimination, the more performance was impaired by divided attention. These results suggest that at least with discrete tasks and relatively short exposure durations, performance when each eye is presented with a separate stimulus is the same as when the entire field of stimulation is viewed by both eyes.

On separability of and interference between tracking dimensions in dual-axis tracking.

Time-shared tasks may conceivably be separable or integral. A case in which the question of separability seems quite relevant is dual-axis tracking. To test the interaction between tracking dimensions, we first studied whether they interfere with each other. Practiced subjects performed tracking on one or two axes, with or without feedback indicators and with or without a requirement to allocate resources unevenly between axes. They also performed with or without a concurrent binary classification of visually presented digits which were presented within a moving square that served as the target for tracking. Small deficits were found in the performance of both tracking and digit classification when performed together. However, the conditions of tracking did not have a discernible effect on either tracking or digit classification. Hence, the introduction of a second tracking axis probably does not have harmful consequences either on tracking itself or on any other task time-shared with tracking. Further studies were conducted to examine whether the absence of an effect of number of tracking axes is dues to their integrality. Ordinary position tracking was paired either with another similar task on the other axis or with a novel sort of tracking in which subjects had to continually match sizes of moving rectangles. Tasks were paired under both divided-attention and focused-attention instructions. No interference on position tracking was observed even when the types of task on the two axes differed, and no other evidence for integrality of the homogeneous task pairs was found.

Different difficulty manipulations interact differently with task emphasis: evidence for multiple resources.

To test the notion of multiple resources, a two-dimensional pursuit tracking task was paired with a letter-typing task, the difficulty of which was manipulated by varying cognitive (size of stimulus set) and motor (repetitiveness of finger chords) factors. In addition, task priority was manipulated. The latter factor had a large effect on the performance of the two tasks, which indicates that they compete for resources. Both types of typing difficulty manipulations affected typing performance, but only motor difficulty interacted with priorities. Since difficulty manipulations that tap resources common to both tasks are predicted to interact with priorities, the results are interpreted to indicate that in joint performance, typing and tracking compete mainly for motor-related concept, the letter-typing task is argued to require at least two kinds of resources.

Short-term rhythms in the performance of a simple motor task.

Following the discovery of short-term rhythmicities In physiological processes, a study was conducted to investigate existence of similar rhythms in motor behavior. Two groups of eight subjects each were tested every 10 or 20 min respectively in the performance of a linear positioning task with augmented auditory and proprioceptive feedback, for 10 consecutive hr. Each testing sample consisted of five trials with knowledge of results (KR), followed by five trials without knowledge of results (NKR). Between tests subjects drank constant amounts of fluids and urine flow was measured. Movement accuracy in the NKR condition varied rhythmically with periodicities centered at 100 min/ cycle. No comparable rhythms were found in the KR trials or in movement time. Urine flow also varied rhythmically with similar dominant periodicities, but these rhythms were unrelated to rhythms in error. The findings are interpreted to indicate rhythmic modulations in the efficiency of short-term storage and information processing from movement execution. Significance of these results to current views of motor control is discussed.

Varying the type and number of adaptive variables in continuous tracking.

To investigate the effectiveness of various types and numbers of adaptive variables, 48 subjects performed a two-dimensional pursuit tracking task for five 3-min training sessions. In the factorial design resulting in eight experimental conditions, three variables (frequency of the forcing function, ratio of acceleration to rate control, and control stick sensitivity) were either fixed or adaptive. A transfer and retention task in which the tracking situation changed periodically was used to evaluate the ability of subjects to adjust to change. Each adaptive variable was analyzed separately in training. The highest rate of adaptation in frequency occurred when frequency was the only adaptive variable. The rate of adaptation in acceleration was greater early in training when frequency also adapted. More adaptation occurred in gain when another variable also adapted. During transfer subjects trained adaptively generally showed more stable performance in the changing task situation. No reliable differences among conditions appeared in retention. Results are discussed in terms of stimulus and response similarity, the optimum number of adaptive variables, and the appropriateness of a changing task to evaluate adaptive training.