No description available.

Whether humans form cognitive maps is controversial. One view is that the ability to generate detours and shortcuts demonstrates retention of direction and distance information integrated within a common frame of reference. Another view is that spatial representations are not Euclidean, given findings of biases, distortions, and lack of recognition of impossible spaces in VR. A compromise comes from an individual-differences perspective, suggesting that some people in some environments may integrate across routes. We created Virtual Copetown to examine within-route knowledge, integration between routes with experienced connections, and integration between routes requiring inference. We also examined cognitive correlates of the ability to make these judgments. Our results indicated that some people were more accurate across all kinds of pointing judgments including inferred relations, along with ability to construct an overall map of Copetown. A second group of people were less accurate overall, and less accurate for between-route relations than within-route relations; they also had worse mapping scores. Variability was related to self-reports of navigation strategy use. / Psychology

No description available.

Based on the principle of sequential lessons for teaching orienteering, the program is a center that teaches navigation to people who are blind, located in the remains of the Chesapeake and Ohio Canal in Harpers Ferry, West Virginia. Through the use of materials, light, and this program of sequential patterns, the architecture focuses on heightening the working senses of the occupants using the progression throughout the building. This connection of the body and mind to architecture creates an awareness of space, unifying a perception of place, while bridging the old life to the new. / Master of Architecture

For humans, walking is the principle means of locomotion, or moving from one point to another. While upright locomotion is a human characteristic, the way humans direct their locomotion has not been studied extensively. Prior to the late 1940's, little research or scholarly thought was published regarding locomotion. In 1950, J. J. Gibson published one of the first texts on visual perception, which included theories and research on how humans interpret and react to a world of movement, even as they move within that world. Published research on the topic has been sporadic since then, especially when compared to the volume of work on eye-hand coordination and other eye-brain perception issues. Very little work has been documented on humans moving in a "real world" setting, not laboratory settings or under very specific timing requirements. This study begins by proposing a heuristic framework of human navigation, a description of how humans move from point to point, navigating over and across navigation hazards in the walking path. The heuristic model provides an engineering perspective for the safe design of pedestrian areas, allowing sufficient area for visual recognition of hazards. Two observational studies were performed, one with four different navigation hazards humans come in contact with and the other one with two different hazards that humans pass without contacting. These two classes of hazards involve different perceptual principles. The studies examined the effects of ambient lighting available affected the time required for high attention, fine navigation when approaching a navigation hazard. Specific comparisons between types of navigation hazards were not contemplated, since the perceptual and motor requirements varied considerably among the hazards. Low ambient light levels, representing twilight and night conditions, increase the amount of time required for fine navigation. Analysis of variance (ANOVA) showed a statistically significant difference in the fine navigation time to contact a navigation hazard for stairs travelling down, a 900 turn in the path, and walking downhill with a step midway. ANOVA also showed a significant difference in the fine navigation time to pass a navigation hazard for two different hazards. Under all conditions, post hoc analysis showed Night lighting levels were different from Day lighting levels. Practical applications of this research are in the facilities planning and safety design fields. The individual's locomotion speed combined with the fine navigation time required determines the distance needed for visual recognition of the hazard and preparatory locomotor changes. With extensive research, formalized guidelines and standards can be developed for the safe planning, design and redesign of pedestrian walkways. The human factors engineer could interact knowledgeably with other professional designers to assure that walking paths are designed to meet the human's requirements for safe locomotion. / Master of Science

Community colleges serve a diverse population of learners including many older students counting on the community college for enhanced skills or personal enrichment. Many of these colleges target this population with programs designed specifically to meet the needs and goals of the older adult but may not consider this population when designing a website. Older users of a community college website have similar needs to the traditional student; however, little was known about the impact of the typical navigational links on the successful completion of tasks and obtaining information for this type of user. It is essential for educational institution website designers to understand which navigational links will provide the best usability for older adults with differing levels of experience. Previous research has found that usage-oriented links and pages that offer both usage and subject-oriented links yield statistically higher performance than subject-oriented links. Other research has found that presenting navigational links in the form of an action enhances usability. For this study, three websites were created utilizing navigational links in the form of usage-oriented links, subject-oriented navigational links, and then a combination of both to conduct a usability study to expand on previous work. This study was designed to determine the impact of such navigation on obtaining the correct answer, time on task, and the user's perception of the navigation. The research question, Does website usability and the user's perception of usability vary for older users based on navigational links, task type, and audience type? was addressed through two hypotheses and data which were obtained during the study. The first hypothesis: Website navigation, task type, and audience type significantly affect usability, was based on performance, and was measured on the two components, correct answer ratio (CAR) and navigation time (NT). The results indicated that the older user's ability to complete tasks faster and more accurately depended on the user's experience level, the difficulty of the task, and the types of navigational links presented, with usage-based navigation being the more effective solution. The second hypothesis: Website navigation, task type, and audience type significantly affect perceptions of usability, was based on perception questions presented after task completion and was measured by a four question post-test questionnaire, which used a 7-point Likert scale. This study found the older user's perception of usability varied based on the navigational links presented, but the experience level of the participant or the task type did not have a significant effect on the perception of usability. Therefore, it is recommended that designers of educational sites present navigational links in a goal-oriented, action-based format to support the end users of all ages and to enhance usability of the institution's website. This research found that if developers emphasize accuracy and the need to navigate quickly as a goal of an educational website for the older user, the website should be designed using a usage-based navigation structure. This research provides the detail to support a better understanding of which navigation type results in higher usability for the older user and enhances the guidelines of website design for this population.

Ants typically use path integration and vision for navigation when the environment precludes the use of pheromones for trails. Recent simulations have been able to accurately mimic the retinotopic navigation behaviour of these ants using simple models of movement and memory of unprocessed visual images. Naturally it is interesting to test these navigation algorithms in more realistic circumstances, particularly with actual route data from the ant, in an accurate facsimile of the ant world and with visual input that draws on the characteristics of the animal. While increasing the complexity of the visual processing to include skyline extraction, inhomogeneous sampling and motion processing was conjectured to improve the performance of the simulations, the reverse appears to be the case. Examining closely the assumptions about motion, analysis of ants in the field shows that they experience considerable displacement of the head which when applied to the simulation leads to significant degradation in performance. The family of simulations rely upon continuous visual monitoring of the scene to determine heading and it was decided to test whether the animals were similarly dependent on this input. A field study demonstrated that ants with only visual navigation cues can return the nest when largely facing away from the direction of travel (moving backwards) and so it appears that ant visual navigation is not a process of continuous retinotopic image matching. We conclude ants may use vision to determine an initial heading by image matching and then continue to follow this direction using their celestial compass, or they may use a rotationally invariant form of the visual world for continuous course correction.

As NASA prepares to return humans to the moon and establish a long-term presence on the surface, technologies must be developed to access previously unvisited terrain regardless of the condition. Among these technologies is a guidance, navigation and control (GNC) system capable of safely and precisely delivering a spacecraft, whether manned or robotic, to a predetermined landing area. This thesis presents detailed research of both terrain-relative navigation using a terrain-scanning instrument and beacon-relative radiometric navigation using beacons in lunar orbit or on the surface of the moon. The models for these sensors are developed along with a baseline sensor suite that includes an altimeter, IMU, velocimeter, and star camera. Linear covariance analysis is used to rapidly perform the trade studies relevant to this problem and to provide the navigation performance data necessary to determine which navigation method is best suited to support a 100 m 3-σ navigation requirement for landing anytime and anywhere on the moon.

Today the area of high-cost and high-performance navigation for vehicles is a well-developed field. The challenge now is to develop high-performance navigation systems using low-cost sensortechnology. This development involves problems spanning from signal processing of the dirty measurements produced by low-costsensors via fusion and synchronization of information produced by a large set of diverse sensors, to reducing the size and energyconsumption of the systems. This thesis examines and proposessolutions to four of these problems. The first problem examined is the time synchronizing of the sensordata in a global positioning system aided inertial navigationsystem in which no hardware clock synchronization is possible. A poor time synchronization results in an increased mean squareerror of the navigation solution and expressions for calculating this mean square error are presented. A method to solve the timesynchronization issue in the data integration software is proposed. The potential of the method is illustrated with tests onreal-world data that are subjected to timing errors. The second problem examined is the achievable clocksynchronization accuracy in a sensor network employing a two-waymessage exchange model. The Cramer-Rao bound for the estimation of the clock parameters is derived and transformed in to a lower bound on the mean square error of the clock offset.Further, an approximate maximum likelihood estimator for the clockparameters is proposed. The estimator is shown to be of low complexity and to have a mean square error in the vicinity of the Cramer-Rao bound. The third problem examined is the detection of the time epochswhen zero-velocity updates can be applied in a foot-mountedpedestrian navigation system. Four general likelihood ratio testsfor detecting when the navigation system is stationary based onthe inertial measurement data are studied. The performance of thefour detectors is evaluated using levelled ground, forward-gaitdata. The results show that the signals from the gyroscopes holdthe most reliable information for the zero-velocity detection. The fourth problem examined is the calibration of a low-costinertial measurement unit. A calibration procedure that relaxesthe accuracy requirements of the orientation angles the inertialmeasurement unit must be placed in during the calibration isstudied. The proposed calibration method is compared with theCramer-Rao bound for the case when the inertial measurementunit is rotated into precisely controlled orientations. Simulationresults show that the mean square error of the estimated sensormodel parameters reaches the Cramer-Rao bound within fewdecibels. Thus, the proposed method may be acceptable for a widerange of low-cost applications. / QC 20100810

Durch die Entwicklung moderner Technologien konnte die Unfallchirurgie in der vergangenen Dekade enorme Fortschritte in der operativen Behandlung von Frakturen im Bereich der zervikalen, thorakalen und lumbalen Wirbelsäule verzeichnen. In allen operativen Behandlungsverfahren ist der Einsatz der computergestützten Navigationstechnik möglich. Anhand der vorliegenden Arbeit wird die Wertigkeit der CT-gestützten Navigation bei der operativen Behandlung thorakolumbaler Wirbelkörperfrakturen hinsichtlich der klinischen Bedeutsamkeit in der alltäglichen Anwendung untersucht. Als wesentliche Aspekte wurden dabei Genauigkeit, Reproduzierbarkeit, mögliche Risiken und Fehlerquellen sowie Anforderungen an das behandelnde Personal integriert. Im Rahmen einer retrospektiv-deskriptiven Studie wurden im Zeitraum März 2002 und Juli 2004 insgesamt 97 (64 männliche, 33 weibliche) Patienten an der Klinik für Unfall-, Wiederherstellungs- und Plastische Chirurgie des Universitätsklinikums Leipzig operativ mit CT-gestützter Navigationstechnik mit Frakturen der thorakolumbalen Wirbelsäule versorgt und hinsichtlich des perioperativen und poststationären Verlaufes einschließlich potentieller Komplikationen nachuntersucht. Sowohl traumatisch (n= 83) als auch nichttraumatisch bedingte (n= 14) Frakturen der Wirbelsäule sind mit Einsatz der genannten Techniken versorgt worden. Während der größere Teil der Patienten im Alter bis 65 Jahren männlich ist, überwiegen im Alter ab 65 Jahren weibliche Patienten. Am häufigsten ist der Bereich 12. BWK und 1. LWK (70,3%) betroffen. Als Frakturursachen dominieren Stürze aus der Höhe. Unter den pathologischen Frakturen kommen vor allem Wirbelkörpermetastasen vor. Die Klassifizierung der Frakturen erfolgte anhand der Einteilung nach Magerl et al. OP-Indikationen liegen für Frakturen A2.3 - A3.3 sowie für alle B – und C-Frakturen vor. Ausnahmen stellten stark kyphosierte A1.2-Frakturen (>15-20° Kyphosewinkel, hier wurde die operative Stabilisierung vorgenommen) und wenig kyphosierte A3.1-Frakturen dar (hier wurde das konservative Vorgehen bevorzugt). Die operativen Möglichkeiten zur Stabilisierung reichen von isoliert dorsaler Versorgung mittels Fixateur interne (n=14) über isoliert ventrale (n=26) bis hin zu kombiniert dorsoventralen (n=57) Verfahren. Die am häufigsten durchgeführten dorsoventralen Operationen wurden überwiegend zweizeitig (70,2% der dorsoventralen OP´s ) durchgeführt. Postoperativ wurden die Patienten ab dem 1. postoperativen Tag mobilisiert. Anhand von Scoresystemen (Visuelle Analogskala, Hannover Wirbelsäulenscore, Frankel-Score (ASIA), Kraftgradeinteilung nach Janda, SF-36-Fragebogen) konnte der postoperative Verlauf im Rahmen der Nachuntersuchung nachvollzogen und dokumentiert werden. Röntgenbilder und CT-Aufnahmen ermöglichten ebenfalls eine Verlaufsbeobachtung. Die Integration der Navigation in etablierte OP- Verfahren stellte einen erhöhten Aufwand im Rahmen der OP- Vorbereitung als auch bei Durchführung der Operation selbst dar. Besonders in anatomisch kritischen Regionen und speziellen anatomischen Gegebenheiten zeigte sich der Nutzen dieser neuen Methode durch die zusätzliche vom Chirurgen nutzbare axiale Bildebene. Verschiedene Einflussfaktoren können dazu führen, dass eine Weiterverwendung des Navigationssystems für den Fortlauf der Operation nicht möglich und ein Umstieg auf konventionelle Verfahren notwendig ist. In der vorliegenden Arbeit lagen Ungenauigkeiten durch technische Probleme vor allem beim Matching (n=4) vor, seltener eine auffällige Fehllage bei der Pedikelschraubenimplantation (n=2), sowie intrapleurale Verwachsungen im Rahmen ventraler navigationsgestützter Eingriffe bei 2 Patienten. Navigationsbedingte Komplikationen traten bei der ventralen Versorgung nicht auf. Besonderes Augenmerk lag auf der Präzision bei der Implantation von Pedikelschrauben. Vor allem im mittleren und oberen BWS-Bereich zeigte sich die dorsale Navigation aufgrund der besonderen anatomischen Situation mit engen Pedikeln hilfreich. Aber auch im unteren BWS- und im gesamten LWS-Bereich kann die Navigation die hohen Ansprüche an die Präzision und Sicherheit für den Operateur und den Patienten steigern. Von 124 Pedikelschrauben bei traumatisch bedingten Frakturen wurden 98 optimal zentral eingebracht. 19 Schrauben davon ließen B-Perforation und 7 Schrauben eine C-Perforation erkennen. Unter den 24 eingebrachten Pedikelschrauben bei pathologischen Frakturen waren 19 in zentraler Lage. Somit können zwar Perforationen nicht gänzlich vermieden werden, jedoch wird die Wahrscheinlichkeit für das Auftreten von Pedikelperforationen durch den Einsatz der modernen Technik insbesondere an der oberen BWS gesenkt. Zu beachten ist allerdings die nicht zu vernachlässigende verlängerte Vorbereitungszeit für die Operation (Erstellung des Datensatzes), die verlängerte OP-Dauer (Matching, initialisieren der Technik) und der erhöhte Material- und Personalaufwand. Die Durchleuchtungszeit bei der Insertion von Pedikelschrauben war an der oberen BWS (BWK 1-8) signifikant länger als an der unteren BWS und LWS. Im Vergleich zwischen navigierten und nicht navigiert implantierten Pedikelschrauben zeigte sich im beobachteten Zeitraum kein signifikanter Unterschied. Nahezu allen Patienten wurden ambulante oder stationäre Rehabilitationsmaßnahmen bewilligt. Bei polytraumatisierten Patienten war die Rehabilitationsdauer im Vergleich zu Monoverletzungen verlängert. Mit guten Behandlungsergebnissen steigt die Wahrscheinlichkeit für eine zeitnahe Wiedereingliederung ins Arbeitsleben. Die kürzeste Krankheitsdauer wurde unter den isoliert ventral versorgten Patienten festgestellt. Insgesamt waren 2 Jahre postoperativ 69% aller präoperativ arbeitstätigen Patienten wieder in den alten Beruf zurückgekehrt. Von den übrigen 31% wurden 14,3 % in andere Berufe umgeschult, 4,8 % wurden berufsunfähig, 2,4 % waren noch krankgeschrieben und 9,5 % waren arbeitslos. Lag ein Arbeitsunfall vor, war die Krankheitsdauer tendenziell verlängert. Betrachtet man das Schmerzempfinden, gaben überwiegend die isoliert dorsal versorgten Patienten auch postoperativ einen hohen Schmerzmittelbedarf an. Die Zugangsstelle an sich war davon eher nicht betroffen. Durch die Anwendung der Minithorakotomie beim ventralen Zugang wurden Postthorakotomiesyndrome nicht beobachtet. Durch den SF-36-Bogen wurde auch die Patientenzufriedenheit abgebildet. Am zufriedensten schnitt dabei die Gruppe der isoliert ventral versorgten Patienten ab. Mit der Entwicklung von OP-Techniken mit möglichst kleinem minimal invasivem Zugang wurde die Zufriedenheit gesteigert und das Schmerzempfinden der Patienten gesenkt. Weitere Möglichkeiten zur Steigerung der Patientenzufriedenheit bestehen durch begleitende psychosoziale Therapien. Zusammenfassend stellt die Anwendung der Navigationstechnik eine interessante neue Facette im Bereich der Wirbelsäulenchirurgie dar. Zu beachten ist jedoch, dass bei der CT- basierten Technik die Abbildungen auf dem Monitor nur einer virtuellen Welt entsprechen aber dem Operateur eine sinnvolle und zuverlässige Unterstützung bieten können. Den entscheidenden Einfluss auf den Verlauf der Operation hat auch weiterhin allein der Operateur. Daher gehört die moderne Technik in die Hände erfahrener Operateure und sollte nicht von Anfängern allein bedient werden. Anhand evidenzbasierter Untersuchung ist auch weiterhin eine Überprüfung auf Effektivität und Nutzen neu etablierter Behandlungsverfahren erforderlich um die hohe Behandlungsqualität aufrecht zu erhalten. Interessante Neuerungen stellen die nächste Generation der 3D-Bildwandler mit Flat- Panel-Technologie als auch das intraoperative CT mit Navigationsanbindung dar.