VTechWorks Repository :: Browsing by Author "Casali, John G."

Browsing by Author "Casali, John G."

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Active noise reduction headphone measurement: Comparison of physical and psychophysical protocols and effects of microphone placement
Perala, Chuck H. (Virginia Tech, 2006-04-10)
Currently in the United States, Active Noise Reduction (ANR) headphones cannot be tested and labeled as hearing protection devices (HPDs) due to inherent limitations with the existing psychophysical headphone testing standard, real-ear attenuation at threshold (REAT). This research focused on the use of a standard, for physical, microphone-in-real-ear testing, (MIRE, ANSI S12.42-1995), to determine if MIRE may be appropriately used to measure the total attenuation (i.e., passive + active) of ANR headphones. The REAT " Method B, Subject-Fit protocol," ANSI S12.6-1997(R2002), was also used to assess passive attenuation (and used for comparison with the MIRE data), as this is the current standard for passive Headphone attenuation testing. The MIRE protocol currently does not specify a standardized location for measurement microphone placement. Prior research is mixed as to the potential benefits and shortcomings of placing the measurement microphone outside versus inside the ear canal. This study captured and compared acoustic spectral data at three different microphone locations: in concha, in ear canal-shallow depth, and in ear canal-deep depth (with a probe tube microphone positioned near the tympanic membrane), using human test participants and five ANR headphones of differing design. Results indicate that the MIRE protocol may be used to supplant the REAT protocol for the measurement of passive attenuation, although differences were observed at the lowest-tested frequency of 125 Hz. Microphone placement analysis revealed no significant difference among the three locations specified, with a noted caveat for the probe tube microphone location at the highest tested frequency of 8000 Hz. Overall findings may be useful to standards-making committees for evaluating a viable solution and standardized method for testing and labeling ANR headphones for use as hearing protection devices. Microphone placement results may assist the practitioner in determining where to place measurement microphones to best suit their particular needs when using MIRE. Discussion includes an in-depth interpretation of the data, comparisons within and between each protocol, and recommendations for further avenues to explore based on the data presented.
Active Noise Reduction Versus Passive Designs in Communication Headsets: Speech Intelligibility and Pilot Performance Effects in an Instrument Flight Simulation
Valimont, Robert Brian (Virginia Tech, 2006-04-20)
Researchers have long known that general aviation (GA) aircraft exhibit some of the most intense and potentially damaging sound environments to a pilot's hearing. Yet, another potentially more ominous result of this noise-intense environment is the masking of the radio communications. Radio communications must remain intelligible, as they are imperative to the safe and efficient functioning of the airspace, especially the airspace surrounding our busiest airports, Class B and Class C. However, the high amplitude, low frequency noise dominating the GA cockpit causes an upward spreading of masking with such inference that it renders radio communications almost totally unintelligible, unless the pilot is wearing a communications headset. Even with a headset, some researchers have stated that the noise and masking effects overcome the headset performance and still threaten the pilot's hearing and overall safety while in the aircraft. In reaction to this situation, this experiment sought to investigate the effects which active noise reduction (ANR) headsets have on the permissible exposure levels (PELs), speech intelligibility, workload, and ultimately the pilot's performance inside the cockpit. Eight instrument-rated pilot participants flew through different flight tasks of varying levels and types of workload embedded in four 3.5 hour flight scenarios while wearing four different headsets. The 3.5 hours were considered long duration due the instrument conditions, severe weather conditions, difficult flight tasks, and the fatiguing effects of a high intensity noise environment. The noise intensity and spectrum in the simulator facility were specifically calibrated to mimic those of a Cessna 172. Speech intelligibility of radio communications was modified using the Speech Transmission Index (STI), while measures of flight performance and workload were collected to examine any relationships between workload, speech intelligibility, performance, and type of headset. It is believed that the low frequency attenuation advantages afforded by the ANR headset decreased the signal-to-noise ratio, thereby increasing speech intelligibility for the pilot. This increase may positively affect workload and flight performance. Estimates of subjective preference and comfort were also collected and analyzed for relevant relationships. The results of the experiment supported the above hypotheses. It was found that headsets which incorporate ANR technology do increase speech intelligibility which has a direct inverse influence on workload. For example, an increase in speech intelligibility is seen with a concomitant decrease in pilot workload across all types and levels of workload. Furthermore, flight task performance results show that the pilot's headset can facilitate safer flight performance. However, the factors that influence performance are more numerous and complex than those that affect speech intelligibility or workload. Factors such as the operational performance of the communications system in the headset, in addition to the ANR technology, were determined to be highly influential factors in pilot performance. This study has concluded that the pilot's headset has received much research and design attention as a noise attenuation device. However, it has been almost completely overlooked as a tool which could be used to facilitate the safety and performance of a general aviation flight. More research should focus on identifying and optimizing the headset components which contribute most to the results demonstrated in this experiment. The pilot's headset is a component of the aviation system which could economically improve the safety of the entire system.
Ambulatory Fall Event Detection with Integrative Ambulatory Measurement (IAM) Framework
Liu, Jian (Virginia Tech, 2008-08-29)
Injuries associated with fall accidents pose a significant health problem to society, both in terms of human suffering and economic losses. Existing fall intervention approaches are facing various limitations. This dissertation presented an effort to advance indirect type of injury prevention approach. The overall objective was to develop a new fall event detection algorithm and a new integrative ambulatory measurement (IAM) framework which could further improve the fall detection algorithm's performance in detecting slip-induced backward falls. This type of fall was chosen because slipping contributes to a major portion of fall-related injuries. The new fall detection algorithm was designed to utilize trunk angular kinematics information as measured by Inertial Measurement Units (IMU). Two empirical studies were conducted to demonstrate the utility of the new detection algorithm and the IAM framework in fall event detection. The first study involved a biomechanical analysis of trunk motion features during common Activities of Daily Living (ADLs) and slip-induced falls using an optical motion analysis system. The second study involved collecting laboratory data of common ADLs and slip-induced falls using ambulatory sensors, and evaluating the performance of the new algorithm in fall event detection. Results from the current study indicated that the backward falls were characterized by the unique, simultaneous occurrence of an extremely high trunk extension angular velocity and a slight trunk extension angle. The quadratic form of the two-dimensional discrimination function showed a close-to-ideal overall detection performance (AUC of ROCa = 0.9952). The sensitivity, specificity, and the average response time associated with the specific configuration of the new algorithm were found to be 100%, 95.65%, and 255ms, respectively. The individual calibration significantly improved the response time by 2.4% (6ms). Therefore, it was concluded that slip-induced backward fall was clearly distinguishable from ADLs in the trunk angular phase plot. The new algorithm utilizing a gyroscope and orientation sensor was able to detect backward falls prior to the impact, with a high level of sensitivity and specificity. In addition, individual calibration provided by the IAM framework was able to further enhance the fall detection performance.
An analytic model to predict detection threshold and performance data for misconvergence on a shadow-mask CRT
DeVilbiss, Carita Allene (Virginia Tech, 1990-04-15)
This research was conducted to achieve four objectives. The first objective was to develop an analytic model to predict the expected luminance distribution through the shadow mask structure on a color CRT display system. The model incorporates functions to describe the unique features of a color CRT, that is, the discrete sampling imposed by the shadow mask/ phosphor-dot arrangement as well as the electron beam phase relationships. The model also includes a flexible beam profile which allows the user to specify the desired shape of the beam profile, that is, whether the profile is described with a Gaussian, leptokurtic, or platykurtic distribution. This objective was fully satisfied with a computer program written in Lightspeed C which runs efficiently on Macintosh computers. The second objective was to determine detection thresholds for various levels of misconvergence of the three electron guns. When the three guns are properly registered, the luminance profiles converge and one perceives a color combination rather than the separate red, green, and blue luminances. Misconvergence is perceived by a change in the overall color or by color fringes, for example, a red edge to a yellow line. Past research has shown that threshold detection of misconvergence occurs when the primary beams are misconverged by 1 to 2 visual arcminutes of separation. This finding was replicated in this research for the two-color beam combinations which have previously been investigated, as well as for a white pixel, which involves all three guns. The third objective was to demonstrate the effect of misconvergence on the performance of a visual task and on subjective estimates of image quality. While subjective quality and threshold detection have previously been investigated for some color combinations, the three tasks (i.e., threshold detection, visual task performance, and subjective estimates) have not been systematically combined within the same data set for a variety of misconvergence conditions. This research provides such a composite data set. The subjective quality estimates were significantly correlated with the threshold detection data. In other words, as misconvergence of the display image increased, the probability of detection of misconvergence increased and the subjective quality rating decreased. However, the selected visual task (a short reading task with average reading time of 6.5 s) was not significantly affected by very large levels of misconvergence. Rather than conclude that the levels of misconvergence used in this research do not affect reading task performance, a more comprehensive visual task (e.g., a longer editing task, a random search task, or a map reading task) should be evaluated. The final objective was to evaluate the ability of selected image quality metrics which are computed from the model to predict threshold detection, subjective quality ratings, or visual task performance. The three metrics computed in this model (MTF Area, MTFA, and SQRI) are all based upon the modulation transfer function (MTF) of the display. These three computed metrics were for all practical purposes constant across the range of misconvergence. While this result was unexpected, it does suggest (1) that a model based only on luminance may be deficient because of the omission of chromaticity, and (2) that MTF-based metrics may not be an appropriate representation because misconvergence does not change the display’s ability to transmit information, but is a phase shift along the shadow mask. As summarized, this research successfully met three of the stated objectives. Further, it points toward future research opportunities to further this type of modelling effort and to successfully develop image quality metrics for color displays.
Assessing Negative Side Effects in Virtual Environments
McGee, Michael K. (Virginia Tech, 1998-01-26)
Virtual environment (VE) systems have been touted as exciting new technologies with many varied applications. Today VEs are used in telerobotics, training, simulation, medicine, architecture, and entertainment. The future use of VEs seems limited only by the creativity of its designers. However, as with any developing technology, some difficulties need to be overcome. Certain users of VEs experience negative side effects from being immersed into the graphically rendered virtual worlds. Some side effects that have been observed include: disorientation, headaches, and difficulties with vision. These negative side effects threaten the safety and effectiveness of VE systems. Negative side effects have been found to develop in a variety of environments. The research focus on VE side effects thus far has been on the symptoms and not the causes. The main goals of this research is fourfold: 1) to compare a new measure for side effects with established ones; 2) begin analyzing the causes of side effects with an analysis of head-tracking; 3) to examine any adaptation that may occur within a session and between days of a session; and, 4) to examine possible predictors for users who may experience side effects. An experiment was conducted using two different VEs with either head-tracking on or head-tracking off over four days. A questionnaire, a balance test, a vision test, and magnitude estimations of side effects were used to assess the incidence and severity of sickness experienced in the VEs. Other assessments, including a mental rotation test, perceptual style, and a questionnaire on pre-existing susceptibility to motion sickness were administered. All factors were analyzed to determine what their relationships were with the incidence and severity of negative side effects that result from immersion into the VEs. Results showed that head-tracking induces more negative side effects than no head-tracking. The maze task environment induces more negative side effects than the office task environment. Adaptation did not occur from day to day throughout the four testing sessions. The incidence and severity of negative side effects increased at a constant rate throughout the 30 minute immersive VE sessions, but did not show any significant changes from day to day. No evidence was found for a predictor that would foretell who might be susceptible to motion sickness in VEs.
Attentional demand evaluation for an automobile moving-map navigation system
Dingus, Thomas A. (Virginia Tech, 1987)
A study was undertaken to test and evaluate the human factors design aspects of an automobile moving-map navigation system. The primary objective of the study was to assess the driver attentional demand required by the navigation system during vehicle operation. A secondary objective of the study was to assess design specifics and determine whether or not the design was optimal in terms of efficiency of use in an automotive environment. Thirty-two driver-subjects drove a specially instrumented 1985 Cadillac Sedan de Ville on public roadways for this research. A cross-section of driver-subjects (both genders, ages 18 to 73, and driving experience from 2,000 to 40,000 miles per year) participated, and a cross·section of roadway types (residential, two-lane state route, and limited·access four-lane) and traffic conditions (light and moderate) were used as part of this research. The driver-subjects were asked to perform a variety of tasks while operating the research vehicle. These tasks included navigation tasks normally performed while using the navigation system, as well as a wide variety of conventional automotive tasks (e.g., tuning the radio or reading the speedometer) normally performed during vehicle operation. The purpose of asking the driver-subjects to perform a variety of conventional automotive tasks was so that direct comparisons in attentional demand could be made between tasks performed daily in an automotive environment and the navigation tasks. Twenty-one performance and behavioral measures were collected and analyzed for this research. These measures included eye—scanning and dwell-time measures, task-completion-time measures, and a variety of measures indicating driver performance and behavior. The data analyses for these measures focused on two major goals. First, the analyses determined which tasks (both navigator and conventional) required the highest attentional demand. Second, the analyses were used to determine groups of tasks which, for all practical purposes, required equivalent attentional demand. The results of the analyses indicated that the navigation system is a relatively effective device, useful for its intended purpose. The results also indicated that a number of design improvements are required, however, to optimize the safety and efficiency of the device. An iterative process of design improvement and further research into the effects of improved design on required attentional demand is therefore recommended.
Automobile navigation methods: effectiveness, efficiency, and strategy
Antin, Jonathan F. (Virginia Polytechnic Institute and State University, 1987)
A study was performed to evaluate the effectiveness, efficiency, and strategy associated with three navigation methods: memorized route, conventional paper map, and a moving-map navigational display (the navigator). Thirty-two driver-subjects of both genders, and wide ranges of age (18-73) and driving experience (2,000 to 40,000 miles per year) navigated along public roadways for this research using a specially instrumented automobile. A variety of different roadway conditions were also used for this research including limited access four-lane highways, two-lane state routes, and city streets. In addition, the research was conducted under conditions of both light and moderate traffic densities. Measures taken include eye movement, navigation effectiveness, and driving performance measures. Results showed that the paper map took longer to study at the beginning of a run than the navigator. Even with this handicap, the total time taken when using the paper map was not significantly different from the time taken to use the navigator. Also, there were no differences in the directness or quality of routes selected when using either the paper map or the navigator to navigate. These findings were a result of the strategies adopted in the use of the various methods of navigation. During the initial study phase the paper map was essentially used to plan the entire route from start to finish. After the initial phase, the map was used only as an occasional reference. In contrast, effective use of the navigator could only be accomplished by repetitively glancing at the display to acquire important information as it was updated and presented. As a result, subjects spent more driving time glancing to the navigator than the paper map, and it substantially drew the subjects' gaze away from the driving task relative to the norm established in the memorized route condition, as well as in comparison to the paper map. Still, driving performance did not greatly change as a function of navigation method indicating that the additional visual attentional demand associated with the navigator was drawn primarily from spare driver resources. It is also very likely that the novelty of the navigator was responsible for some portion of the glance time spent on it.
Azimuthal Localization and Detection of Vehicular Backup Alarms Under Electronic and Non-Electronic Hearing Protection Devices in Noisy and Quiet Environments
Alali, Khaled Ahmed (Virginia Tech, 2011-03-29)
Objective assessment for the effect of hearing protectors, background noise levels, and backup alarm acoustic features on listeners' abilities to localize backup alarm signals in the horizontal dimension, as well as on their ability to detect backup alarm signals in the distance dimension, is lacking in the acoustics and safety literature. Accordingly, two research experiments were conducted for this dissertation. In the first experiment, the effect of seven hearing protectors, two background pink noise levels (60 dBA and 90 dBA), and two backup alarm signals (standard and spectrally-modified) on the ability of normal hearing listeners to localize backup alarm signals in the horizontal dimension was investigated. Results indicated that a diotic sound transmission earmuff significantly degraded localization accuracy as compared to all other hearing protectors and the open ear condition. In addition, no significant difference existed between the open ear condition and the other hearing protectors in localization accuracy in most of the conditions tested. However, the E-A-R/3M HiFiTM earplug was advantageous in localization performance since it provided a significantly higher percentage correct localization than the Moldex foam earplug, the diotic earmuff, and the dichotic earmuff in 90 dBA pink noise. As for main effects of the other independent variables, the 90 dBA pink noise significantly degraded localization performance as compared to the quiet condition of 60 dBA, and a spectrally-modified backup alarm significantly improved localization performance as compared to the standard (narrowband) backup alarm. Potential application of these results includes the revision of backup alarm standards. In addition, these results provide clear advice for safety professionals to avoid the application of diotic sound transmission earmuffs for workers if localizing backup alarms is important. In the first experiment, listeners' feeling of comfort for each hearing protector was assessed subjectively by using a comfort rating scale. In addition, a subjective assessment for listeners' confidence in their localization decisions was established. Results indicated no significant difference between the hearing protectors in terms of comfort. However, in terms of listeners' confidence in localization decisions, their confidence was significantly degraded when they were fitted with the diotic earmuff. By contrast, they showed significantly more confidence in their localization decisions when they were fitted with the E-A-R/3M HiFi™ earplug as compared to when they were fitted with the Moldex foam earplug, the E-A-R/3M Ultrafit™ earplug, and the Bilsom passive earmuff. In the second experiment, listeners' performance in detecting a stationary backup alarm signal, including both a standard (narrowband) and broadband (pulsed white noise) alarm, was determined while they were equipped with various passive and electronic hearing protection devices. Listeners' performance was quantified by detection distance, which was defined as the distance between the stationary backup alarm device and the position where the listener detected the backup alarm signal. The resultant data demonstrated that normal hearing listeners detected a standard (narrowband) backup alarm signal at significantly longer distances as compared to the broadband (Brigade™) backup alarm signal, thus indicating the earlier forewarning by the standard alarm. In addition, passive hearing protection devices characterized with high attenuation significantly reduced the detection distance. These results may be applied to assist safety professionals in selecting hearing protectors and backup alarm signals that provide on-foot workers with ample time to react to an approaching backing vehicle, thus improving their safety.
Combat aircraft scenario tradeoff models for conceptual design evaluation
Cabrera, Antonio Trani (Virginia Polytechnic Institute and State University, 1988)
The purpose of this research is to apply engineering-based knowledge to the field of combat aircraft survivability, and to create scenario-specific models in order to estimate the tradeoff between aircraft survivability and lethality metrics at the encounter and sortie levels. The development of scenario-specific models serves to identify and quantify technological changes that have Ieverage on the overall performance of the aircraft from a survivability point of view. Also, the models focus on the fighter aircraft susceptibility assessment and are capable of incorporating outputs from offline studies as inputs, such as in the area of vulnerability assessment where extensive databases are available. The mission scenario models are microscopic in nature and relate important conceptual aircraft design parameters such as thrust-to-mass ratio, wing loading, empty mass, maneuverability, etc. and operational parameters (e.g., weapon payload, range, loiter time, flight profiles, etc.) to the aircraft sortie survivability and lethality under various threat scenarios. This research proposes a methodology to estimate survivability and lethality aircraft performance at the sortie level where aircraft parameters can be implemented into scenario-specific models to assess their impact upon survivability-related metrics. While the project was conceived with naval aircraft in mind, the methodology, to the extent possible, is not to be aircraft-specific and thus could be applied to any particular design at the conceptual stage.
A comparison of human performance on computer text editing tasks using windowed and non-windowed strategies
O'Keefe, Timothy J. (Virginia Polytechnic Institute and State University, 1987)
Software packages which use windows have become increasingly popular in the last two years. Their popularity derives from the belief that windows will improve productivity by decreasing task completion time. However, two studies (Silver, 1985 and Davies, Bury and Darnell, 1985) have found this not to be the case. In fact, one of the studies (Davies at al., 1985) found that task completion time was increased when using windows. It is thought that performance using window systems is a function of the number of responses required to be executed as well as the amount of information which must be found and used to complete a task. The purpose of the present study was to determine under what conditions, in terms of memory load and task complexity, performance using windows and non-window strategies differed. Forty-eight subjects were placed in one of four environments and each performed six editing tasks which varied on complexity and memory load level. Human performance in one windowed environment was compared to three non-window strategies. These three strategies, note-taking, memorizing, or switching between files, were included to allow comparisons in terms of working memory and number and types of responses executed. The tasks required subjects to locate information from a supplementary file and type it into a main file. The three memory load levels which were used required subjects to find either 2, 4 or 8 pieces of information. The two complexity levels referred to the placement of needed information in the supplementary file; whether or not information was located in close proximity to other needed information. Results indicated that it made little difference which system was used in the low memory load condition. However, as memory load increased, more subjects were found to make errors in the non-window conditions. More responses were executed in the Switch condition than in the Window or Memorization conditions in the high memory load condition. Mental workload was also found to be higher in the Memorization and Switch conditions than in the Window and Notes conditions as memory load increased. Nevertheless, there was no significant interaction for task completion times between Memory Load and Environment. This was thought to be due to a failure to adequately load working memory as well as a failure of a test of verbal and spatial ability to account for individual differences. It was concluded that the benefits of windows are not apparent until one°s working memory capacity is exceeded. As memory load increases beyond this point, it is thought that memorization will quickly become an inefficient strategy due to limitations of memory capacity. As memory load continues to increase, a switching strategy should become inefficient due to limitations of both memory and response capacities. A strategy of note taking should not become inefficient until a large memory load is placed upon the user. This is because note taking is a well learned uncomplicated response. The benefits of windows include a reduction in the number of responses, errors, and mental workload due to their ability to reduce the amount of mental resources required by providing the user with a very efficient and accurate memory aid.
A comparison of three subsidiary tasks used as driver drowsiness countermeasures
Hardee, Helen Lenora (Virginia Polytechnic Institute and State University, 1985)
Two previous studies performed at Virginia Tech have shown that it is feasible to detect drowsy drivers using driving performance and physiological measures. Therefore, assuming that drowsiness can be detected, it becomes important to develop methods (countermeasures) by which drivers can regain and maintain alertness. The current study was thus undertaken in an attempt to evaluate three subsidiary tasks which differed only in regard to input modality (auditory, tactual, or visual) in terms of: 1) the degree to which they aided the driver by maintaining or restoring alertness; and 2) the degree to which the responses to these tasks could be used to detect drowsiness. Subjective measures of drowsiness were also obtained to provide an additional source of verification of level of drowsiness. To accomplish these objectives, a total of 12 male and female driver-subjects drove a moving-base simulator continuously from 12:30 a.m. to 3:00 a.m. During this time, the subjects performed each of the subsidiary tasks for a 30-minute period; they also drove for a 30-minute period during which no subsidiary task was performed. During the simulated, nighttime, highway driving scenario, 20 driving performance, behavioral, and physiological measures were collected for each 3-minute driving interval, along with 5 subsidiary task measures and subjective alertness ratings. The experimental results indicated that none of the three subsidiary tasks provided an effective means of maintaining driver alertness. However, the results of a second series of discriminant analyses did indicate that driver impairment due to drowsiness could be reliably detected with linear combinations of subsidiary task and driving measures. In fact, promising discriminant models for the auditory and visual tasks were identified which employed a subsidiary task response measure of the number of correct responses to the subsidiary task during each 6-minute driving interval as well as a physiological measure of the subject's heart rate variance; these models showed overall classification error percentages as low as 3% and 8%. Finally, the analyses of the subjective alertness ratings indicated that subjects' ratings were not significantly affected by either the type of subsidiary task performed or time-on-task.
Custom-fitting earplug formed in situ using foaming action
(United States Patent and Trademark Office, 1992-07-21)
A custom-fitting earplug (18) for hearing protection or other ear applications, or in-ear communications device mounting (40) is fabricated in situ by depositing a foaming material (14 or 24) within the person's ear (10 or 42, respectively) and allowing the foaming material (14 or 24) to expand therein to form foam (16 or 44, respectively). By applying slight pressure from outside the person's ear (10 or 42) through the stem (13) and/or keeper (11) during expansion, the foam (16 or 44, respectively) will be tightly packed in and conform to the ear canal. An optional sheath (15 or 36) positioned over the foaming material (14 or 24, respectively) serves to provide a smooth outer surface for the earplug (18) or communications device (40) produced and can aid in defining and limiting the expansion of the foam (14 or 24, respectively).
Design and evaluation of CNC-user interfaces
Torres-Chazaro, Octavio F. (Virginia Tech, 1992)
Computer Numerically Controlled (CNC) machines are common pieces of equipment in manufacturing plants. In recent years, CNC-user interfaces have been evolving from CNC command languages to menu based and direct manipulation interfaces. However, there have been few efforts to evaluate CNC-user interfaces and to identify those interface features that have major effects on the usability of CNC machines. Thus, an objective assessment of the improvement achieved from different user interface technologies is needed. Two experiments compared the effectiveness of two types of CNC-user interfaces: command-language and direct manipulation interfaces. Two command language interfaces and one object oriented interface were designed and evaluated in terms of human performance and preferences. Experiment 1 compared two command-language interfaces: Layout 1 was a simulation of the original control panel of a CNC-Dyna machine, and Layout 2 was a modified user interface based on the analysis of the Dyna control language. Four factors were manipulated: (1) users’ level of expertise, (2) layouts, (3) tasks, and (4) trials. It was found that both groups of subjects completed the tasks faster using Layout 2 than Layout 1. Modification tasks were performed faster than copy tasks. Subjects’ responses to a questionnaire indicated that Layout 2 was preferred over Layout 1 in several categories. In Experiment 2 subjects used a command-language interface and a direct-manipulation interface. Four factors were manipulated: (1) experimental sessions (two sessions with a one-week interval between them), (2) users’ level of expertise, (3) tasks, and (4) trials. The interval between sessions had a significant effect on task completion time when the command-language interface was used, but there was not a significant effect of this factor when the direct-manipulation interface was used. Subjects’ subjective responses indicated a stable preference for the direct-manipulation interface in several categories of usability.
Design and Testing of a Quick-Connect Wheelchair Power Add-On Unit
Clark, Laura L. (Virginia Tech, 1997-12-04)
A quick-connect wheelchair power add-on unit (PAU) has been developed at the Human Factors Engineering Center of Virginia Tech. The objective of the new invention is to provide an inexpensive, highly portable product which can quickly convert a manual wheelchair into a power-operated wheelchair. This dissertation details the three year research and design effort to develop the new wheelchair PAU. Results are presented from a series of evaluations conducted to identify performance and user-interaction characteristics of the PAU. Interpretation of the results provides a prioritized list of identified design deficiencies along with wheelchair expert and design team suggestions for the next generation of design alterations. The three evaluations conducted with the second generation PAU prototype include a series of wheelchair expert interviews, a PAU performance evaluation, and a usability evaluation which utilized wheelchair operators as subjects. Also included in the dissertation is an explanation of the need for a new PAU, a description of the most recent design iteration, a literature review containing information about the history of wheelchairs, the condition of the current PAU market, and an analysis of wheelchair PAU consumers. The new invention was conceived and patented by Dr. John G. Casali of the Industrial and Systems Engineering (ISE) Department at Virginia Tech. This research was supported jointly by Southwestern Applied Technologies, L. C., of Roanoke, Virginia and Virginia's Center for Innovative Technology in Herndon, Virginia.
The Detection of Warning Signals While Wearing Active Noise Reduction and Passive Hearing Protection Devices
Christian, Erika (Virginia Tech, 1999-07-15)
The research described herein was undertaken to determine how masked thresholds changed when individuals wore an active noise reduction (ANR) hearing protection device (HPD), a passive HPD, or no HPD. An ANR earmuff, a passive earmuff, and a user-molded foam earplug were tested in two types of noises (pink and red) at two different noise levels (85 dBA and 100 dBA). The signal used was an industry-standard backup alarm. The experimental design was completely within-subjects. An ascending method of limits was used to obtain 15-20 correct positive responses, which were then averaged to obtain the masked thresholds for each treatment condition. A visual probability monitoring task was incorporated in the experimental design to provide a loading task for the participants. In addition to masked thresholds, comfort and mental workload were assessed. Finally, participants were asked to rank each of the three HPDs with respect to their perceived ability to facilitate hearing the signal in noise. Results indicated that in 85 dBA noise, masked thresholds were lower when hearing protection devices were worn, compared to the unoccluded condition. Additionally, the results indicated that the ANR device provided a significant advantage (lower masked thresholds) over the passive earmuff in the low-frequency biased red noise (across both noise levels) and the 100 dBA noise level (across both noise spectra). However, the ANR earmuff exhibited no significant advantage over the user-molded foam earplug in any of the conditions. Rather, the user-molded foam earplug produced significantly lower masked thresholds at 100 dBA. The results also indicated that there was no difference between the three devices in their perceived ability to facilitate detection of the signal. There was also not a significant difference in comfort ratings between the three HPDs, although there were several complaints about the comfort of the ANR earmuff during the experiment.
Determination of Backup Alarm Masked Threshold in Construction Noise
Muchenje, Lovejoy (Virginia Tech, 2008-05-01)
Sound transmission devices have advanced filtering abilities that theoretically protect the ear from harmful Masking noise while amplifying the sounds that need to be heard, such as backup alarms. Therefore, such devices should provide improved signal detection in noise when compared to their passive counterparts. The masked threshold of a vehicular backup alarm was determined for audiometrically normal and non-normal hearers using two types of sound transmission devices and their passive counterparts within pink noise and milling machine noise at intensities of 75, 85, 95 and 105 dBA. Results indicated that the sound transmission devices did not have any statistically significant advantages over the passive devices with respect to masked threshold of a backup alarm. Therefore, it cannot be concluded that these devices offer advantage over similar passive devices with respect to signal detection. Additionally, ratings of comfort and the ability to detect the alarm for each device were gathered. Both scales did not show any significant differences between the two device types.
Development and Human Factors Evaluation of a Portable Auditory Localization Acclimation Training System
Thompson, Brandon Scott (Virginia Tech, 2020-06-19)
Auditory situation awareness (ASA) is essential for safety and survivability in military operations where many of the hazards are not immediately visible. Unfortunately, the Hearing Protection Devices (HPDs) required to operate in these environments can impede auditory localization performance. Promisingly, recent studies have exhibited the plasticity of the human auditory system by demonstrating that training can improve auditory localization ability while wearing HPDs, including military Tactical Communications and Protective Systems (TCAPS). As a result, the U.S. military identified the need for a portable system capable of imparting auditory localization acquisition skills at similar levels to those demonstrated in laboratory environments. The purpose of this investigation was to develop and validate a Portable Auditory Localization Acclimation Training (PALAT) system equipped with an improved training protocol against a proven laboratory grade system referred to as the DRILCOM system and subsequently evaluate the transfer-of-training benefit in a field environment. In Phase I, a systems decision process was used to develop a prototype PALAT system consisting of an expandable frame housing 32-loudspeakers operated by a user-controlled tablet computer capable of reproducing acoustically accurate localization cues similar to the DRILCOM system. Phase II used a within-subjects human factors experiment to validate whether the PALAT system could impart similar auditory localization training benefits as the DRILCOM system. Results showed no significant difference between the two localization training systems at each stage of training or in training rates for the open ear and with two TCAPS devices. The PALAT system also demonstrated the ability to detect differences in localization accuracy between listening conditions in the same manner as the DRILCOM system. Participant ratings indicated no perceived difference in localization training benefit but significantly preferred the PALAT system user interface which was specifically designed to improve usability features to meet requirements of a user operable system. The Phase III investigation evaluated the transfer-of-training benefit imparted by the PALAT system using a broadband stimulus to a field environment using gunshot stimulus. Training under the open ear and in-the-ear TCAPS resulted in significant differences between the trained and untrained groups from in-office pretest to in-field posttest.
Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. I. Research of Working Group 11, Accredited Standards Committee S12, noise
Royster, Julia D.; Berger, Elliott H.; Merry, Carol J.; Nixon, Charles W.; Franks, John R.; Behar, Alberto; Casali, John G.; Dixon-Ernst, Christine; Kieper, Ronald W.; Mozo, Ben T.; Ohlin, Doug; Royster, Larry H. (Acoustical Society of America, 1996-03-01)
This paper describes research conducted by Working Group 11 of Accredited Standards Committee S12, Noise, to develop procedures to estimate the field performance of hearing protection devices (HPDs). Current standardized test methods overestimate the attenuation achieved by workers in everyday use on the job. The goal was to approximate the amount of attenuation that can be achieved by noise-exposed populations in well-managed real-world hearing conservation programs, while maintaining acceptable interlaboratory measurement variability. S12/WG11 designed two new laboratory-based protocols for measuring real-ear attenuation at threshold, with explicit procedures for subject selection, training, supervision, and HPD fitting. After pilot-testing, S12/WG11 conducted a full-scale study of three types of earplugs and one earmuff tested by four independent laboratories using both protocols. The protocol designated as ''subject-fit'' assessed the attenuation achieved by subjects who were experienced in threshold audiometry, but naive with respect to the use of hearing protection, when they fit HPDs by following manufacturers' instructions without any experimenter assistance. The attenuation results from the subject-fit method corresponded more closely to real-world data than results from the other protocol tested, which allowed the experimenter to coach subjects in HPD use, Comparisons of interlaboratory measurement variability for the subject-fit procedure to previous interlaboratory studies using other protocols indicated that the measurements with the new procedure are at least as reproducible as those obtained with existing standardized methods. Therefore, the subject-fit protocol was selected for consideration for use in future revisions of HPD attenuation test standards.
Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. the validity of using subject-fit data
Berger, Elliott H.; Franks, John R.; Behar, Alberto; Casali, John G.; Dixon-Ernst, Christine; Kieper, Ronald W.; Merry, Carol J.; Mozo, Ben T.; Nixon, Charles W.; Ohlin, Doug; Royster, Julia D.; Royster, Larry H. (Acoustical Society of America, 1998-02-01)
The mandate of ASA Working Group S12/WG11 has been to develop "laboratory and/or field procedure(s) that yield useful estimates of field performance" of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an, interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et al., "Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise," J. Acoust. Soc. Am. 99, 1506-1526 (1996); ANSI S12.6-1997, "American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors" (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with Listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-a-vis attenuation values achieved by workers in practice, Twenty-two field studies were reviewed to develop a data base for comparison purposes, Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings. (C) 1998 Acoustical Society of America. [S0001-4966(98)03001-X].
Display spatial luminance nonuniformities: effects on operator performance and perception
Decker, Jennie Jo (Virginia Polytechnic Institute and State University, 1989)
This dissertation examined the effects of display spatial luminance nonuniformities on operator performance and perception. The objectives of this research were to develop definitions of nonuniformity, develop accurate measurement techniques, determine acceptable levels of nonuniformities, and to develop a predictive model based on user performance data. Nonuniformities were described in terms of spatial frequency, amplitude, display luminance, gradient shape, and number of dimensions. Performance measures included a visual random search task and a subjective measure to determine users' perceptions of the nonuniformities. Results showed that users were able to perform the search task in the presence of appreciable nonuniformities. lt was concluded that current published recommendations for acceptable levels of nonuniformities are adequately specified. Results from the subjective task showed that users were sensitive to the presence of nonuniformities in terms of their perceptions of uniformity. Specifically, results showed that as spatial frequency increased, perceived uniformity ratings increased. That is, users rated nonuniformities to be less noticeable. As amplitude and display luminance increased, the users' ratings of perceived uniformity decreased; that is, they rated the display as being farther from a uniform field. There were no differences in impressions between a sine and triangle gradient shape, while a square gradient shape resulted in lower ratings of perceived uniformity. Few differences were attributed to the dimension (1-D versus 2- D) of the nonuniformity and results were inconclusive because dimension was confounded with the display luminance. Nonuniformities were analyzed using Fourier techniques to determine the amplitudes of the coefficients for each nonuniformity pattern. These physical descriptors were used to develop models to predict users' perceptions of the nonuniformities. A few models yielded good fits of the subjective data. lt was concluded that the method for describing and measuring nonuniformities was successful. Also, the results of this research were in strong concurrence with previous research in the area of spatial vision.

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