Evaluation of eye metrics as a detector of fatigue.

OBJECTIVES: This study evaluated oculometrics as a detector of fatigue in Air Force-relevant tasks after sleep deprivation. Using the metrics of total eye closure duration (PERCLOS) and approximate entropy (ApEn), the relation between these eye metrics and fatigue-induced performance decrements was investigated. BACKGROUND: One damaging effect to the successful outcome of operational military missions is that attributed to sleep deprivation-induced fatigue. Consequently, there is interest in the development of reliable monitoring devices that can assess when an operator is overly fatigued. METHOD: Ten civilian participants volunteered to serve in this study. Each was trained on three performance tasks: target identification, unmanned aerial vehicle landing, and the psychomotor vigilance task (PVT). Experimental testing began after 14 hr awake and continued every 2 hr until 28 hr of sleep deprivation was reached. RESULTS: Performance on the PVT and target identification tasks declined significantly as the level of sleep deprivation increased.These performance declines were paralleled more closely by changes in the ApEn compared to the PERCLOS measure. CONCLUSION: The results provide evidence that the ApEn eye metric can be used to detect fatigue in relevant military aviation tasks. APPLICATION: Military and commercial operators could benefit from an alertness monitoring device.

Pneumatic muscle actuator for resistive exercise in microgravity: test with a leg model.

INTRODUCTION: A proof-of-concept demonstration is described in which a DC servomotor (simulating the quadriceps of a human operator) rotated a pulley 90 degrees (simulating knee extension). A pneumatic muscle actuator (PMA) generated an opposing force (antagonist) to the rotating pulley. One application of such a device is for use in microgravity environments because the PMA is compact, simple, and of relatively small mass (283 g). In addition, the operator can set a computer-controlled force-level range in response to individual user changes in exercise conditioning over time. METHODS: A PMA was used in this study and interacted with a DC servomotor. For each trial, the PMA contracted in response to internal pressure. An input voltage profile activated the DC servomotor, resulting in the following three phases: an isokinetic counterclockwise pulley rotation of 90 degrees over 5 s (Phase I), the position was held for 5 s (Phase II), and an isokinetic clockwise rotation of 90 degrees over 5 s (Phase III). Root mean square error (RMSE) values were used to evaluate the pulley rotation. RESULTS: For Phase I, when the PMA pressures (in kPa) were 300, 450, and 575, the percent RMSE, respectively, were 5.24, 6.23, and 4.59. For Phase II, the percent RMSE were 2.81, 2.57, and 5.63, respectively. For Phase III, the percent RMSE were 5.69, 2.63, and 3.30, respectively. DISCUSSION: This study presents a demonstration of a PMA device that can enhance exercise by providing a wide range of resistive loads.

A computational simulated control system for a high-force pneumatic muscle actuator: system definition and application as an augmented orthosis.

High-force pneumatic muscle actuators (PMAs) are used for force assistance with minimal displacement applications. However, poor control due to dynamic nonlinearities has limited PMA applications. A simulated control system is developed consisting of: (1) a controller relating an input position angle to an output proportional pressure regulator voltage, (2) a phenomenological model of the PMA with an internal dynamic force loop (system time constant information), (3) a physical model of a human sit-to-stand task and (4) an external position angle feed-back loop. The results indicate that PMA assistance regarding the human sit-to-stand task is feasible within a specified PMA operational pressure range.

Complexity of visual icons studied via signal detection theory.

Two investigations on how humans perceive information from visually rendered complex objects, such as military icons (glyphs) were conducted. A signal detection theory framework was employed to evaluate the sensitivity and specificity of human subject performance. The 6 adults tested showed that as complexity increased, their accuracy in performance decreased. Study 1 showed that complex dimensions (features) could not be assigned arbitrarily. Study 2 developed a rank ordering for features of an iconic object.

A quantitative model of the human-machine interaction and multi-task performance: a strategy function and the unity model paradigm.

A human-machine-interaction (HMI) model is developed for the human operator (HO) performing five simultaneous tasks and characterized by a strategy function. Five levels of total machine-initiated baud rate (B(IN)) are generated by the multi-attribute task battery (MATB) and five HO baud rates (B(O)) are then recorded. Total baud ratio (B ) is defined as the ratio of B(O) to B(IN). Results indicate that with increasing B(IN) levels: (1) there is an overall increase in B(O), and (2) there is an overall decrease in B . These results are due to a decreasing HMI performance and divergence of the strategy function from a unity model paradigm.

Physiological state model for human ergonomic workload.

Twenty ergonomic tasks were evaluated in which human operators performed mixed static work and dynamic work. Steady-state physiological data are the input into a model as regressor variables, which are then multiplied by the respective regressor coefficients. The resultant physiological state model output is a single response variable that represents the workload. Mixed stepping regression techniques were utilized to calculate the regressor coefficients. Ten physiological state model equations resulted. A lower order equation (with three regressor variables) accounted for 80% of the observed variance. The highest order equation (with ten regressor variables) accounted for 89% of the variance.