Karl F. Van Orden

Eye Activity Correlates of Workload during a Visuospatial Memory Task

Changes in six measures of eye activity were assessed as a function of task workload in a target identification memory task. Eleven participants completed four 2hr blocks of a mock anti-air-warfare task, in which they were required to examine and remember target classifications (friend/enemy) for subsequent prosecution (fire upon/allow to pass), while targets moved steadily toward two centrally located ship icons. Target density served as the task workload variable; between one and nine targets were simultaneously present on the display. For each participant, moving estimates of blink frequency and duration, fixation frequency and dwell time, saccadic extent, and mean pupil diameter, integrated over periods of 10 to 20 s, demonstrated systematic changes as a function of target density. Nonlinear regression analyses found blink frequency, fixation frequency, and pupil diameter to be the most predictive variables relating eye activity to target density Participant-specific artificial neural network models, developed through training on two or three sessions and subsequently tested on a different session from the same participant, correlated well with actual target density levels (mean R = 0.66). Results indicate that moving mean estimation and artificial neural network techniques enable information from multiple eye measures to be combined to produce reliable near-real-time indicators of workload in some visuospatial tasks. Potential applications include the monitoring of visual activity of system operators for indications of visual workload and scanning efficiency.

Combined Eye Activity Measures Accurately Estimate Changes in Sustained Visual Task Performance

Five concurrent eye activity measures were used to model fatigue-related changes in performance during a visual compensatory tracking task. Nine participants demonstrated considerable variations in performance level during two 53-min testing sessions in which continuous video-based eye activity measures were obtained. Using a trackball, participants were required to maneuver a target disk (destabilized by pseudorandom wind forces) within the center of an annulus on a CRT display. Mean tracking performance as a function of time across 18 sessions demonstrated a monotonic increase in error from 0 to 11 min, and a performance plateau thereafter. Individual performance fluctuated widely around this trend - with an average root mean square (RMS) error of 2.3 disk radii. For each participant, moving estimates of blink duration and frequency, fixation dwell time and frequency, and mean pupil diameter were analyzed using non-linear regression and artificial neural network techniques. Individual models were derived using eye and performance data from one session and cross-validated on data from a second session run on a different day. A general regression model (based only on fixation dwell time and frequency) trained on data from both sessions from all participants produced a correlation of estimated to actual tracking performance of R=0.68 and an RMS error of 1.55 (S. D.=0.26) disk radii. Individual non-linear regression models containing a general linear model term produced the cross-session correlations of estimated to actual tracking performance of R=0.67. Individualized neural network models derived from the data of both experimental sessions produced the lowest RMS error (mean=1.23 disk radii, S.D.=0.13) and highest correlation (R=0.82) between eye activity-based estimates and actual tracking performance. Results suggest that information from multiple eye measures may be combined to produce accurate individualized real-time estimates of sub-minute scale performance changes during sustained tasks.

Redundant Use of Luminance and Flashing with Shape and Color as Highlighting Codes in Symbolic Displays

Three visual search experiments evaluated the benefits and distracting effects of using luminance and flashing to highlight subclasses of symbols coded by shape and color. Each of three general shape/color classes (circular/blue, diamond/red, square/yellow) was divided into three subclasses by presenting the upper half, lower half, or entire symbol. Increasing the luminance of a subclass by a factor of two did not result in a significant improvement in search performance. Flashing a subclass at a rate of 3 Hz resulted in a significantly shorter mean search time (48% improvement). Increasing the luminance of one subclass (by a factor of five) while simultaneously flashing another significantly improved search times by 31% and 43% respectively, compared with nonhighlighted search conditions. In each experiment, the search times for nonhighlighted target subclasses were not affected by the presence of brighter and flashing targets. The failure of the initial experiment to find a significant performance improvement caused by increasing symbol luminance suggested that a larger luminance increase was necessary for this code to be effective. The overall results suggest that using luminance and flashing to highlight subclasses of color-and shape-coded symbols can reduce search times for these subclasses without producing a distraction effect by way of a concomitant increase in the search times for unhighlighted symbols.

Effects of Cold Air Stress on the Performance of a Command and Control Task

Performance on a simulated command and control warfare task was examined as a function of cold-air-induced adrenergic stress. Twenty participants who were experienced with naval war fighting systems completed a scripted 54-min scenario task while exposed to room temperatures of either 22°C or 4°C. The combined task and cold-exposure paradigm significantly elevated heart rate and catecholamine levels. Task performance was nearly identical for both groups for the scenario as a whole. During a 12-min portion of the scenario when hostilities were simulated, stressed participants were more liberal with missile fire and more conservative in their responses to commands requiring greater knowledge of the tactical situation. The responses to commands requiring participants to identify symbols with particular attributes were equivalent for both groups during the hostilities phase. The study demonstrates the utility of the task-independent stressor paradigm for the examination of complex task performance under stress.

Eye Activity Correlates of Fatigue during a Visual Tracking Task

Five concurrent eye activity measures were used to model fatigue-related changes in performance during a visual compensatory tracking task. Five subjects demonstrated considerable variations in performance level within two 53-min testing sessions during which continuous video-based eye activity measures were obtained. For each subject, moving estimates of blink duration and frequency, fixation duration and frequency, and mean pupil diameter from one session were used to train an artificial neural network to produce moving estimates of changes in mean tracking performance during the same session. Applied to eye tracking data from a second session, the same networks produced moving estimates of tracking performance that were highly correlated with actual performance changes (R 2=0.65, range 0.30–0.89 across ten sessions). The results suggest that information from multiple eye measures may be combined to produce individualized and accurate estimates of sub-minute scale changes in alertness during continuous task performance.

Key user support technologies to optimize future command crew efficiency

A significant benefit from strenuous efforts to optimally man next-generation Navy combatants is the re-orientation of the manner in which work is accomplished within the command center. The necessary shift from direct control of weapon and sensor systems towards human supervision of semi-automated tasks has profound implications for the workstation design. Task-centered design has emerged as a key component in the development of human-system integration strategies to meet new warfighting requirements. This presentation discusses how new design concepts are enabling greater work efficiency and multi-tasking in command center workstations. Human-interface technology advances will impact team organization and work procedures: Intra- and inter-team coordination is critical to the success of future ships and battlegroups. The impact of task-centric design principles and task management features on team workload and future warfighting procedures is reviewed and extended to demonstrate support of mission health, readiness and resource concerns of higher echelon commanders.

Highlighting with Flicker Some Basic Visual Search Considerations

Previous research has demonstrated that search times are reduced when flicker is used to highlight color coded symbols, but that flicker is not distracting when subjects must search for non-highlighted symbols. This prompted an examination of flicker and other stimulus dimensions in a conjunctive search paradigm. In all experiments, at least 15 subjects completed a minimum of 330 trials in which they indicated the presence or absence of target stimuli on a CRT display that contained either 8, 16 or 32 items. In Experiment 1, subjects searched for blue-steady or red-flickering (5.6 Hz) circular targets among blue-flickering and red-steady distractors. Blue-steady targets produced a more efficient search rate (11.6 msec/item) than red-flickering targets (19.3 msec/item). In Experiment 2, a conjunction of flicker and size (large and small filled circles) yielded the opposite results; the search performance for large-flickering targets was unequivocally parallel. In Experiment 3, conjunctions of form and flicker yielded highly serial search performance. The findings are consistent with the response properties of parvo and magnocellular channels of the early visual system, and suggest that search is most efficient when one of these channels can be filtered completely.