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.

Haptic devices as a paradigm to enhance learning/function--theory and empirical studies.

Haptics is a modern term employed to describe both afferent and efferent flows of forces with humans. The appropriate design of these force flow fields when coordinated with information to and from computers and other devices to physically challenged individuals can empower the performance of certain tasks previously not attainable. Extensive empirical work presented herein has demonstrated that proper augmentation of particular dynamic force fields, synchronised with certain cognitive tasks, can lead to improved functionality.

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).

Characterisation of a phenomenological model for commercial pneumatic muscle actuators.

This study focuses on the parameter characterisation of a three-element phenomenological model for commercially available pneumatic muscle actuators (PMAs). This model consists of a spring, damping and contractile element arranged in parallel. Data collected from static loading, contraction and relaxation experiments were fitted to theoretical solutions of the governing equation for the three-element model resulting in prediction profiles for the spring, damping and contractile force coefficient.

Characterisation of a pneumatic muscle test station with two dynamic plants in cascade.

Pneumatic muscle actuators (PMAs) offer significant advantages over more traditional actuators, which make them prime candidates in rehabilitation devices. A dynamic test station (DTS) is modified to demonstrate the use of a PMA for this application. The DTS includes two dynamic systems: a PMA and a DC servomotor.

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.

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.

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).

Adaptive displays and controllers using alternative feedback.

Investigations on the design of haptic (force reflecting joystick or force display) controllers were conducted by viewing the display of force information within the context of several different paradigms. First, using analogies from electrical and mechanical systems, certain schemes of the haptic interface were hypothesized which may improve the human-machine interaction with respect to various criteria. A discussion is given on how this interaction benefits the electrical and mechanical system.

Biomimetic model of skeletal muscle isometric contraction: II. A phenomenological model of the skeletal muscle excitation-contraction coupling process.

This paper describes a new macroscopic, phenomenological model of the skeletal muscle excitation-contraction coupling process, as represented by four principal and consecutive compartments (biophysical, biochemical, and biomechanical phases) characteristic of isometric excitation-contraction coupling in mammalian skeletal muscle, and coupled by a system of simultaneous, first-order linear ordinary differential equations. The model is based upon biological compartmental transport kinetics and irreversible thermodynamic energy transformation, and represents a distinct improvement over other biomimetic models. The model was derived using physiological parameter data published in the literature, and validated using MATLAB R12.

Biomimetic model of skeletal muscle isometric contraction: I. an energetic-viscoelastic model for the skeletal muscle isometric force twitch.

This paper describes a revision of the Hill-type muscle model so that it will describe the chemo-mechanical energy conversion process (energetic) and the internal-element stiffness variation (viscoelastic) during a skeletal muscle isometric force twitch contraction. The derivation of this energetic-viscoelastic model is described by a first-order linear ordinary differential equation with constant energetic and viscoelastic coefficients. The model has been implemented as part of a biomimetic model, which describes the excitation-contraction coupling necessary to drive the energetic-viscoelastic model.

Effects of haptic feedback and turbulence on landing performance using an immersive cave automatic virtual environment (CAVE).

An investigation was conducted in which subjects had to land a simulated F-16 aircraft using a CAVE (Cave Automatic Virtual Environment) facility. This was a three-dimensional virtual setting consisting of multiple mirrors, 3-D video-projected displays in a highly stressful environment employing a haptic joystick. 6 subjects learned a task which required landing in wind turbulence with a reduced visual scene.

Modeling the dynamic characteristics of pneumatic muscle.

A pneumatic muscle (PM) system was studied to determine whether a three-element model could describe its dynamics. As far as the authors are aware, this model has not been used to describe the dynamics of PM. A new phenomenological model consists of a contractile (force-generating) element, spring element, and damping element in parallel.

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.

Design of a haptic stick interface as a pilot's assistant in a high turbulence task environment.

A study involving 8 Air Force pilots was conducted to examine the efficacy of a force-reflecting joystick to improve performance during a simulated landing task in wind turbulence. By adding certain force characteristics to a joystick, it was of interest to see if performance may change, different control effort may be utilized, and workload measures may be altered based on the joystick utilized. The main results show that certain performance measures significantly improved by having the force reflection condition on.

Microprocessor based spatial TENS (transcutaneous electric nerve stimulator) designed with waveform optimality for clinical evaluation in a pain study.

A microprocessor based TENS device is developed which utilizes a spatial procedure in the administration of electrical fields to actively interfere with pain signals reaching the brain. This unusual design also has the advantage of requiring the frequency characteristics of the electrical waveform produced to be optimally tuned to the mechanical impedance properties of the skin/tissue. Hence a much more efficient procedure for the transfer of electrical energy from the TENS device to the human tissue is provided.

The acceleration-velocity relationship: identification of normal and spastic upper extremity movement.

This study defines and evaluates a non-invasive technique that will identify a spasm as an uncommanded movement (U) from a normally commanded movement (C). Upper arm function during a tracking task is recognized as non-linear and characterized by a phase plane with acceleration (second derivative of stick position) plotted on the ordinate and velocity (first derivative of stick position) plotted on the abscissa. An acceleration time constant (tau A) is defined as (VA/AM) where AM is the maximal acceleration and VA is the velocity at AM.

Performance study involving a force-reflecting joystick for spastic individuals performing two types of tracking tasks.

10 upper-extremity spastic subjects and 10 normal subjects were studied with a force-reflecting joystick in the performance of a continuous time-tracking task as well as an acquisition task termed, "Fitts' Law." Certain force-reflection paradigms, in a spatial sense, allowed the spastic subjects to obtain performance proficiency near levels of the normal subjects as measured by a capacity metric.

The intentional spring: a strategy for modeling systems that learn to perform intentional acts.

In motor task learning by instruction, the instructor's skill and intention, which, initially, are extrinsic constraints on the learner's perceiving and acting, eventually become internalized as intrinsic constraints by the learner. How is this process to be described formally? This process takes place via a forcing function that acts both as an anticipatory (informing) influence and a hereditary (controlling) influence. A mathematical strategy is suggested by which such intentions and skills might be dynamically learned.

Objective antihistamine side effects are mitigated by evening dosing of hydroxyzine.

First-generation antihistamines have potency, pharmacokinetic, and cost advantages compared with nonsedating second-generation antihistamines. Bedtime dosing of hydroxyzine was investigated as a dosing strategy to minimize reaction time degradation and adverse subjective symptoms previously documented for hydroxyzine in divided doses. Hydroxyzine, 50 mg qhs, was compared with terfenadine, 60 mg bid, in this double-blind, placebo-controlled crossover study of 15 healthy, asymptomatic adults.

Mass discrimination under Gz acceleration.

The purpose of this study was to assess how the perception of mass discrimination is affected by elevated Gz acceleration. Previous experiments studied mass discrimination under weightless conditions. Ten subjects were tested with the Dynamic Environment Simulator (DES) at Wright-Patterson Air Force Base.

Prolongation of simple and choice reaction times in a double-blind comparison of twice-daily hydroxyzine versus terfenadine.

Newer, nonsedating antihistamines provide a therapeutic alternative for the patient with allergy whose work is impaired by the side effects of traditional H1 antihistamines. To assess the differential effect of these antihistamines on reaction times and subjective symptoms, we compared terfenadine, 60 mg twice daily, to hydroxyzine, 25 mg twice daily, in a double-blind, placebo-controlled, crossover study of 16 healthy, asymptomatic adults. Simple reaction time and choice reaction time were measured with a computer-based, eye-hand, reaction-time testing apparatus.

Quantification of reaction time and time perception during Space Shuttle operations.

A microprocessor-based test battery containing simple reaction time, choice reaction time, and time perception tasks was flown aboard a 1985 Space Shuttle flight. Data were obtained from four crewmembers. Individual subject means indicate a correlation between change in reaction time during the flight and the presence of space motion sickness symptoms.

Study of neuromotor reaction times under the influence of thyrotropin-releasing hormone.

Neuromotor reaction times (simple, choice, and decision) were measured when Thyrotropin-releasing hormone (TRH) was administered intravenously to nine healthy men in a double-blind study. Measurements were made of simple reaction time, choice reaction time, and decision time for each subject at various intervals over a 54-hr. period.