Barbara Sweet

The role of the professoriate in influencing future community college leadership

New Directions for Community Colleges, 1996

... Cannon, LW Fostering Positive Race, Class, and Gender Dynamics in the Classroom. In K ... S... more

Designing and Developing an Image Generator for the Operational Based Vision Assessment Simulator

AIAA Modeling and Simulation Technologies Conference, 2012

Many factors affect the suitability of an out-the-window simulator visual system. Contrast, brigh... more Many factors affect the suitability of an out-the-window simulator visual system. Contrast, brightness, resolution, field-of-view, update rate, scene content and a number of other criteria are common factors often used to define requirements for simulator visual systems. For the past several years, NASA has worked with the United States Air Force (USAF) on the Operational Based Vision Assessment Program (OBVA). The purpose of this program has been to provide the USAF School of Aerospace Medicine (USAFSAM) with a scientific testing laboratory to study human vision and testing standards in an operationally relevant environment (i.e., a research simulator). Requirements for the visual system include high luminance, a large field-of-view, a large color gamut capable of reproducing aviation red, green, and blue, a limited development budget, and a flexible design to support future technology insertion and upgrades. One of the more challenging requirements in designing the reconfigurable image generator was the resolution requirementapproximately 0.5 arc-minutes per pixel, roughly equivalent to 20/10 visual acuity. In addition to static resolution, dynamic resolution (i.e., the perceived resolution of moving imagery) was also investigated to determine how best to minimize motion artifacts in the visual system. In this paper, we will describe how the simulator specifications were developed in order to meet the vision research objectives of USAFSAM, the various design considerations, and the resulting architecture. In particular, we will discuss the image generator architecture and describe the latest performance results along with the unique challenges of developing a visual system that provides eye limited resolution.

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Estimation of Time-Varying Pilot Model Parameters

AIAA Modeling and Simulation Technologies Conference, 2011

Human control behavior is rarely completely stationary over time due to fatigue or loss of attent... more Human control behavior is rarely completely stationary over time due to fatigue or loss of attention. In addition, there are many control tasks for which human operators need to adapt their control strategy to vehicle dynamics that vary in time. In previous studies on the identification of time-varying pilot control behavior wavelets were used to estimate the time-varying frequency response functions. However, the estimation of time-varying pilot model parameters was not considered. Estimating these parameters can be a valuable tool for the quantification of different aspects of human time-varying manual control. This paper presents two methods for the estimation of time-varying pilot model parameters, a two-step method using wavelets and a windowed maximum likelihood estimation method. The methods are evaluated using simulations of a closed-loop control task with time-varying pilot equalization and vehicle dynamics. Simulations are performed with and without remnant. Both methods give accurate results when no pilot remnant is present. The wavelet transform is very sensitive to measurement noise, resulting in inaccurate parameter estimates when considerable pilot remnant is present. Maximum likelihood estimation is less sensitive to pilot remnant, but cannot detect fast changes in pilot control behavior.

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Estimation of Time-Varying Pilot Model Parameters

Human control behavior is rarely completely stationary over time due to fatigue or loss of attent... more Human control behavior is rarely completely stationary over time due to fatigue or loss of attention. In addition, there are many control tasks for which human operators need to adapt their control strategy to vehicle dynamics that vary in time. In previous studies on the identification of time-varying pilot control behavior wavelets were used to estimate the time-varying frequency response functions. However, the estimation of time-varying pilot model parameters was not considered. Estimating these parameters can be a valuable tool for the quantification of different aspects of human time-varying manual control. This paper presents two methods for the estimation of time-varying pilot model parameters, a two-step method using wavelets and a windowed maximum likelihood estimation method. The methods are evaluated using simulations of a closed-loop control task with time-varying pilot equalization and vehicle dynamics. Simulations are performed with and without remnant. Both methods give accurate results when no pilot remnant is present. The wavelet transform is very sensitive to measurement noise, resulting in inaccurate parameter estimates when considerable pilot remnant is present. Maximum likelihood estimation is less sensitive to pilot remnant, but cannot detect fast changes in pilot control behavior.

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Identification of Time-Varying Pilot Control Behavior in Multi-Axis Control Tasks

AIAA Modeling and Simulation Technologies Conference, 2012

Recent developments in fly-by-wire control architectures for rotorcraft have introduced new inter... more Recent developments in fly-by-wire control architectures for rotorcraft have introduced new interest in the identification of time-varying pilot control behavior in multi-axis control tasks. In this paper a maximum likelihood estimation method is used to estimate the parameters of a pilot model with time-dependent sigmoid functions to characterize timevarying human control behavior. An experiment was performed by 9 general aviation pilots who had to perform a simultaneous roll and pitch control task with time-varying aircraft dynamics. In 8 different conditions, the axis containing the time-varying dynamics and the growth factor of the dynamics were varied, allowing for an analysis of the performance of the estimation method when estimating time-dependent parameter functions. In addition, a detailed analysis of pilots' adaptation to the time-varying aircraft dynamics in both the roll and pitch axes could be performed. Pilot control behavior in both axes was significantly affected by the time-varying aircraft dynamics in roll and pitch, and by the growth factor. The main effect was found in the axis that contained the time-varying dynamics. However, pilot control behavior also changed over time in the axis not containing the time-varying aircraft dynamics. This indicates that some cross coupling exists in the perception and control processes between the roll and pitch axes.

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Image processing and fusion for landing guidance

SPIE Proceedings, 1996

The use of various imaging sensors which can penetrate obscuring visual phenomena (such as fog, s... more The use of various imaging sensors which can penetrate obscuring visual phenomena (such as fog, snow, smoke, etc.) has been proposed to enable aircraft landings in low visibility conditions. In this paper, we examine the use of two particular sensors, infrared and millimeter wave imaging radar, to aid in the landing task. Several image processing strategies are discussed and demonstrated which could improve the efficacy of an operational concept in which an image is presented to the pilot on a Head-Up Display. The possible strategies include the use of aircraft navigation information to help improve image quality, warping of the images to be geometrically conformal with the pilot's eye-point, use of a priori knowledge about the landing geometry to aid with sensor registration and processing, and fusion of multiple image sources.

Effects of Visual Spatio-Temporal Aliasing on Pilot Performance in Active Control Tasks

Visual display systems such as the out-the-window or head-down displays of a simulator present a ... more Visual display systems such as the out-the-window or head-down displays of a simulator present a visual scene that is sampled in both the spatial domain (by the display resolution) and the time domain (by the display refresh rate). For a given human visual temporal sensitivity, spatial-frequency content of the scene, and speed of the image motion, spatiotemporal aliasing can occur when the image is sampled at a rate that is too low. The effects of spatio-temporal aliasing on visual perception are understood to some extend. However, not much is known about the effects on pilot performance in active control tasks. This paper presents the results of an experiment to determine the effects of spatio-temporal aliasing on pilot performance and control behavior in a target-tracking task. To induce different levels of spatio-temporal aliasing, the refresh rate of the experimental display was varied among five different levels. The results indicate that pilots adopt a different control strategy when the display refresh rate is increased from 60 to 120 Hz. The visual gain and neuromuscular frequency of the identified pilot model increase, while the visual time delay decreases. This change in control strategy allows for a higher tracking performance at higher display refresh rates as indicated by a decrease in root mean square of the error signal and an increase in crossover frequency.

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T h e application of quadratic optimal cooperative control synthesis to a CH-47 he-licopter

Information integration in judgements of time to contact

Http Dx Doi Org 10 1080 02724980343000053, Sep 24, 2010

Time to contact (TTC) is specified optically by tau, and studies suggest that observers are sensi... more Time to contact (TTC) is specified optically by tau, and studies suggest that observers are sensitive to this information. However, TTC judgements also are influenced by other sources of information, including pictorial depth cues. Therefore, it is useful to identify these sources of information and to determine whether and how their effects combine when multiple sources are available. We evaluated the effect of five depth cues on TTC judgements. Results indicate that relative size, height in field, occlusion, and motion parallax influence TTC judgements. When multiple cues are available, an integration (rather than selection) strategy is used. Finally, the combined effects of multiple cues are not always consistent with a strict additive model and may be task dependent.

The Impact of Motion-Induced Blur on Out-The-Window Visual System Performance

All visual display system technologies have visual artifacts, or perceptual features that would n... more All visual display system technologies have visual artifacts, or perceptual features that would not be present in a naturally-viewed scene. The characteristics of certain light-valve technologies, specifically Liquid Crystal Display (LCD) and Liquid Crystal on Silicon (LCoS), exhibit a blurring artifact with image motion. In this paper, the causes of this artifact will be reviewed. Current knowledge regarding the impact of this artifact on both perception and simulator task performance will also be reviewed, and methods for reducing motioninduced blur will be discussed.

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Choosing Your Poison: Optimizing Simulator Visual System Selection as a Function of Operational Tasks

120 Hertz – the New 60 for Flight Simulation?

Recent advances in technology have led to the development of out-the-window (OTW) scene generator... more Recent advances in technology have led to the development of out-the-window (OTW) scene generators with unprecedented levels of realism; attainable levels of resolution, database detail, color, contrast, and luminance have significantly increased for flight simulation applications. These aforementioned characteristics describe the static qualities of the image. These characteristics, and other factors, also affect the dynamic qualities of not only the out-the-window scene, but also the overall performance of the simulator. Aspects of simulator performance affected by update rate will be discussed.

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Modeling of Depth Cue Integration in Manual Control Tasks

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Evaluating Stereo Displays for Manual Control

A Model of Manual Control with Perspective Scene Viewing

AIAA Modeling and Simulation Technologies (MST) Conference, 2013

A model of manual control during perspective scene viewing is presented, which combines the Cross... more A model of manual control during perspective scene viewing is presented, which combines the Crossover Model with a simplified model of perspective-scene viewing and visualcue selection. The model is developed for a particular example task: an idealized constantaltitude task in which the operator controls longitudinal position in the presence of both longitudinal and pitch disturbances. An experiment is performed to develop and validate the model. The model corresponds closely with the experimental measurements, and identified model parameters are highly consistent with the visual cues available in the perspective scene.

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Effects of Spatio-Temporal Aliasing on Out-The-Window Visual Systems

Designers of out-the-window visual systems face a challenge when attempting to simulate the outsi... more Designers of out-the-window visual systems face a challenge when attempting to simulate the outside world as viewed from a cockpit. Many methodologies have been developed and adopted to aid in the depiction of particular scene features, or levels of static image detail. However, because aircraft move, it is necessary to also consider the quality of the motion in the simulated visual scene. When motion is introduced in the simulated visual scene, perceptual artifacts can become apparent. A particular artifact related to image motion, spatiotemporal aliasing, will be addressed. The causes of spatio-temporal aliasing will be discussed, and current knowledge regarding the impact of these artifacts on both motion perception and simulator task performance will be reviewed. Methods of reducing the impact of this artifact are also addressed.

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59.5L: Late-News Paper: Evaluation of a Prototype Grating-Light-Valve Laser Projector for Flight Simulation Applications

SID Symposium Digest of Technical Papers, 2008

An evaluation of a prototype grating light valve laser projector indicates it has properties well... more An evaluation of a prototype grating light valve laser projector indicates it has properties well-suited to flight-simulation applications. Full-field luminance and contrast, spatial resolution, temporal resolution, and color stability were equal to or better than those of CRT projectors typically used in flight-simulator applications. In addition, this projector is capable of providing refresh rates greater than 60 Hz. The higher refresh rates eliminate perceived flicker, and greatly reduce (120 Hz) or eliminate (240 Hz) motion artifacts over the range of target speeds tested.

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The Human Visual System and its Role in Motion Perception

AIAA Modeling and Simulation Technologies Conference, 2011

Design of an Eye Limiting Resolution Visual System Using Commercial-off-the-Shelf Technology

AIAA Modeling and Simulation Technologies Conference and Exhibit, 2008

A feasibility study was conducted to determine if a flight simulator with an eye-limiting resolut... more A feasibility study was conducted to determine if a flight simulator with an eye-limiting resolution out-the-window (OTW) visual system could be built using commercial off-theshelf (COTS) technology and used to evaluate the visual performance of Air Force pilots in an operations context. Results of this study demonstrate that an eye limiting OTW visual system can be built using COTS technology. Further, a series of operationally-based tasks linked to clinical vision tests can be used within the synthetic environment to demonstrate a correlation and quantify the level of correlation between vision and operational aviation performance.

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Integration of Size and Binocular Disparity Visual Cues in Manual Depth-Control Tasks

AIAA Modeling and Simulation Technologies Conference and Exhibit, 2006

Humans rely on a plethora of visual cues to inform judgments of the depth or range of a particula... more Humans rely on a plethora of visual cues to inform judgments of the depth or range of a particular object or feature. One source of information is binocular (or stereo) vision, enabled by the slight differences in the images between the two eyes. Another source of information is the size, in visual angle, of the feature or object. Although it is possible to provide binocular disparity in a display, it typically implies increased system cost or lower update rates; therefore it is useful to determine how critical it is to provide binocular disparity to the user. This paper describes the results of several experiments investigating the integration of stereo and size cues in performing manual control tasks. In the first experiment, a visual cue integration model was developed for two types of manual control tasks (rate-control and acceleration-control) and different levels of cue salience. The results of this experiment were that stereo disparity dominated judgments of depth position, while size dominated judgment of depth rate. From this experiment, it was hypothesized that stereo disparity would do more to improve performance on rate-control tasks more than on acceleration-control tasks. Two additional experiments were conducted, with and without stereo display, to test this hypothesis at different update rates. The results confirmed that while stereo disparity improved performance on rate-control tasks, it did not improve performance on acceleration-control tasks; in fact, performance was reduced with stereo disparity when the display method reduced update rate below a particular threshold.

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