577 research outputs found
Modelling, Measuring and Compensating Color Weak Vision
We use methods from Riemann geometry to investigate transformations between
the color spaces of color-normal and color weak observers. The two main
applications are the simulation of the perception of a color weak observer for
a color normal observer and the compensation of color images in a way that a
color weak observer has approximately the same perception as a color normal
observer. The metrics in the color spaces of interest are characterized with
the help of ellipsoids defined by the just-noticable-differences between color
which are measured with the help of color-matching experiments. The constructed
mappings are isometries of Riemann spaces that preserve the perceived
color-differences for both observers. Among the two approaches to build such an
isometry, we introduce normal coordinates in Riemann spaces as a tool to
construct a global color-weak compensation map. Compared to previously used
methods this method is free from approximation errors due to local
linearizations and it avoids the problem of shifting locations of the origin of
the local coordinate system. We analyse the variations of the Riemann metrics
for different observers obtained from new color matching experiments and
describe three variations of the basic method. The performance of the methods
is evaluated with the help of semantic differential (SD) tests.Comment: Full resolution color pictures are available from the author
Adaptive Methods for Color Vision Impaired Users
Color plays a key role in the understanding of the information in computer environments. It
happens that about 5% of the world population is affected by color vision deficiency (CVD),
also called color blindness. This visual impairment hampers the color perception, ending up by
limiting the overall perception that CVD people have about the surrounding environment, no
matter it is real or virtual. In fact, a CVD individual may not distinguish between two different
colors, what often originates confusion or a biased understanding of the reality, including web
environments, whose web pages are plenty of media elements like text, still images, video,
sprites, and so on.
Aware of the difficulties that color-blind people may face in interpreting colored contents,
a significant number of recoloring algorithms have been proposed in the literature with the
purpose of improving the visual perception of those people somehow. However, most of those
algorithms lack a systematic study of subjective assessment, what undermines their validity, not
to say usefulness. Thus, in the sequel of the research work behind this Ph.D. thesis, the central
question that needs to be answered is whether recoloring algorithms are of any usefulness and
help for colorblind people or not.
With this in mind, we conceived a few preliminary recoloring algorithms that were published in
conference proceedings elsewhere. Except the algorithm detailed in Chapter 3, these conference
algorithms are not described in this thesis, though they have been important to engender
those presented here. The first algorithm (Chapter 3) was designed and implemented for people
with dichromacy to improve their color perception. The idea is to project the reddish hues onto
other hues that are perceived more regularly by dichromat people.
The second algorithm (Chapter 4) is also intended for people with dichromacy to improve their
perception of color, but its applicability covers the adaptation of text and image, in HTML5-
compliant web environments. This enhancement of color contrast of text and imaging in web
pages is done while keeping the naturalness of color as much as possible. Also, to the best of our
knowledge, this is the first web recoloring approach targeted to dichromat people that takes
into consideration both text and image recoloring in an integrated manner.
The third algorithm (Chapter 5) primarily focuses on the enhancement of some of the object
contours in still images, instead of recoloring the pixels of the regions bounded by such contours.
Enhancing contours is particularly suited to increase contrast in images, where we find adjacent
regions that are color indistinguishable from dichromat’s point of view. To our best knowledge,
this is one of the first algorithms that take advantage of image analysis and processing techniques
for region contours.
After accurate subjective assessment studies for color-blind people, we concluded that the CVD
adaptation methods are useful in general. Nevertheless, each method is not efficient enough to
adapt all sorts of images, that is, the adequacy of each method depends on the type of image
(photo-images, graphical representations, etc.).
Furthermore, we noted that the experience-based perceptual learning of colorblind people
throughout their lives determines their visual perception. That is, color adaptation algorithms must satisfy requirements such as color naturalness and consistency, to ensure that dichromat
people improve their visual perception without artifacts. On the other hand, CVD adaptation
algorithms should be object-oriented, instead of pixel-oriented (as typically done), to select
judiciously pixels that should be adapted. This perspective opens an opportunity window for
future research in color accessibility in the field of in human-computer interaction (HCI).A cor desempenha um papel fundamental na compreensão da informação em ambientes computacionais.
Porém, cerca de 5% da população mundial é afetada pela deficiência de visão de
cor (ou Color Vision Deficiency (CVD), do Inglês), correntemente designada por daltonismo. Esta
insuficiência visual dificulta a perceção das cores, o que limita a perceção geral que os indivÃduos
têm sobre o meio, seja real ou virtual. Efetivamente, um indivÃduo com CVD vê como iguais
cores que são diferentes, o que origina confusão ou uma compreensão distorcida da realidade,
assim como dos ambientes web, onde existe uma abundância de conteúdos média coloridos,
como texto, imagens fixas e vÃdeo, entre outros.
Com o intuito de mitigar as dificuldades que as pessoas com CVD enfrentam na interpretação de
conteúdos coloridos, tem sido proposto na literatura um número significativo de algoritmos de
recoloração, que têm como o objetivo melhorar, de alguma forma, a perceção visual de pessoas
com CVD. Porém, a maioria desses trabalhos carece de um estudo sistemático de avaliação
subjetiva, o que põe em causa a sua validação, se não mesmo a sua utilidade. Assim, a principal
questão à qual se pretende responder, como resultado do trabalho de investigação subjacente
a esta tese de doutoramento, é se os algoritmos de recoloração têm ou não uma real utilidade,
constituindo assim uma ajuda efetiva às pessoas com daltonismo.
Tendo em mente esta questão, concebemos alguns algoritmos de recoloração preliminares que
foram publicados em atas de conferências. Com exceção do algoritmo descrito no CapÃtulo 3,
esses algoritmos não são descritos nesta tese, não obstante a sua importância na conceção
daqueles descritos nesta dissertação. O primeiro algoritmo (CapÃtulo 3) foi projetado e implementado
para pessoas com dicromacia, a fim de melhorar a sua perceção da cor. A ideia consiste
em projetar as cores de matiz avermelhada em matizes que são melhor percebidos pelas pessoas
com os tipos de daltonismo em causa.
O segundo algoritmo (CapÃtulo 4) também se destina a melhorar a perceção da cor por parte de
pessoas com dicromacia, porém a sua aplicabilidade abrange a adaptação de texto e imagem,
em ambientes web compatÃveis com HTML5. Isto é conseguido através do realce do contraste
de cores em blocos de texto e em imagens, em páginas da web, mantendo a naturalidade da
cor tanto quanto possÃvel. Além disso, tanto quanto sabemos, esta é a primeira abordagem de
recoloração em ambiente web para pessoas com dicromacia, que trata o texto e a imagem de
forma integrada.
O terceiro algoritmo (CapÃtulo 5) centra-se principalmente na melhoria de alguns dos contornos
de objetos em imagens, em vez de aplicar a recoloração aos pixels das regiões delimitadas por
esses contornos. Esta abordagem é particularmente adequada para aumentar o contraste em
imagens, quando existem regiões adjacentes que são de cor indistinguÃvel sob a perspetiva dos
observadores com dicromacia. Também neste caso, e tanto quanto é do nosso conhecimento,
este é um dos primeiros algoritmos em que se recorre a técnicas de análise e processamento de
contornos de regiões.
Após rigorosos estudos de avaliação subjetiva com pessoas com daltonismo, concluiu-se que os
métodos de adaptação CVD são úteis em geral. No entanto, cada método não é suficientemente
eficiente para todos os tipo de imagens, isto é, o desempenho de cada método depende do tipo de imagem (fotografias, representações gráficas, etc.).
Além disso, notámos que a aprendizagem perceptual baseada na experiência das pessoas daltónicas
ao longo de suas vidas é determinante para perceber aquilo que vêem. Isto significa que os
algoritmos de adaptação de cor devem satisfazer requisitos tais como a naturalidade e a consistência
da cor, de modo a não pôr em causa aquilo que os destinatários consideram razoável
ver no mundo real. Por outro lado, a abordagem seguida na adaptação CVD deve ser orientada
aos objetos, em vez de ser orientada aos pixéis (como tem sido feito até ao momento), de
forma a possibilitar uma seleção mais criteriosa dos pixéis que deverão ser sujeitos ao processo
de adaptação. Esta perspectiva abre uma janela de oportunidade para futura investigação em
acessibilidade da cor no domÃnio da interacção humano-computador (HCI)
Sensorimotor Control of 3D Arm Movement and Stability in Post-Stroke Hemiparesis
Deficits of the affected arm in people with post-stroke hemiparesis have been generally associated with decreased strength and increased spasticity. These deficits are varied in proximal (shoulder) and distal (elbow) joints which results in an overall impairment during movement or during stabilization of hand position in space. In this study, reaching of the hemiparetic arm in 3D workspace was characterized by a curved and non-smooth endpoint trajectory and a reduced functional range of motion, compared to the unimpaired arm. Smoother trajectories were observed in the acceleration phase more than the deceleration phase, which was common to both the stroke subjects and the neurologically intact controls. Decreased range of motion of the paretic arm in the proximal joint was associated with shoulder weakness, whereas limited range of motion in the elbow appeared to be due to increased antagonist muscle activation. In a task requiring subjects to stabilize their hand at different positions in space, arm weakness and movement synergy constraints may have contributed to stroke survivors generally decreasing the plane of elevation in order to maintain stable arm postures during movement and then stabilize the hand in space. The degree of decreased plane of elevation was negatively correlated with the Fugl-Meyer score. For a task when fine control movement was required simultaneously with a stable arm posture, stroke subjects demonstrated an inability to grade fine muscle control, resulting in larger range of the plane of elevation movements and larger endpoint error. These findings suggest that shoulder strength training might have important implications to the recovery of movement and ability to stabilize the hemiparetic arm during functional tasks
The 4D Einstein-Gauss-Bonnet theory of gravity: a review
57 pages, 2 figures57 pages, 2 figure
The impact of Joint Hypermobility Syndrome in adults: A quantitative exploration of neuromuscular impairments, activity limitations and participation restrictions
Abstract:Introduction: Joint hypermobility syndrome (JHS) is a heritable connective tissue disorder associated with multiple joint laxity and pain. JHS is severe and disabling condition with a prevalence reaching 55% of patients attended physiotherapy with musculoskeletal symptoms. However, the literature is limited in quantity and quality to support the assessment and management strategies for people with JHS. Therefore, impairment, activity and participation were explored to identify the underlying problems. Methods: A cross-section design was employed to compare a group of adults with JHS against a matched control group. Neuromuscular impairments were explored through five domains: 1) pain intensity in the lower-limb joints was measured using visual analogue scales. 2) Achilles tendon stiffness was measured using the diagnostic ultrasound with strain-gauge myometer. 3) the plantar flexors strength was measured using the strain-gauge myometer. 4) knee proprioception was explored using the angle reproduction test. 5) gastrocnemius medius (GM) elasticity was quantified using the sonoelastography (SEG). Regarding the activity domain, both gait and vertical jump were analysed in terms of spatiotemporal, kinematics and kinetics using the Qualisys motion capture system, synchronised with the Kistler platform. The participation domain was assessed using the 12-item Short Form Health Survey (SF-12) and the Bristol Impact of Hypermobility questionnaire (BIoH). Additionally, the feasibility of the SEG was explored, and the intra-rater reliabilities for examining the Achilles tendon stiffness and gait kinematics were determined. Statistical Package for Social Sciences (SPSS) was used to conduct the statistical analysis. Results: The JHS group included 29 women and two men aged 38.52 ± 14.14 years (mean ± SD), while the control group included 29 women and two men aged 39.06 ± 12.43 years (mean ± SD). Various statistically significant differences were identified in the JHS group when compared to the control group, including increased pain intensity (all p ≤ 0.001), reduced Achilles tendon stiffness (p = 0.03), reduced plantar flexors strength (p = 0.01) and reduced non-dominant knee proprioception (p range 0.001 – 0.04). The gait and jump kinematics in the JHS group were mostly comparable to the control (p ≥ 0.05), with statistically significant reductions in moments (p ranged from 0.001 - 0.04) and power generation and absorption (p ranged from 0.001- 0.04) in the JHS group. Significant reductions in the participation level were evidenced in the JHS group, obtained from SF-12 (p ranged from 0.001 - 0.002), with significant impact from JHS (211.51 ± 39.28)/360 (mean ± standard deviation) obtained from the BIoH. Sonoelastography seems a feasible tool in terms of training, examination time, patient tolerance, and image analysis. High intra-rater reliability was demonstrated for examining the Achilles tendon stiffness (ICC ranged from 0.981 – 0.984), and moderate-high intra-rater reliability was demonstrated for examining gait kinematics (ICC ranged from 0.625 – 0.996). Conclusion: JHS has a multi-dimensional impact, causing neuromuscular impairment, activity limitations and participation restrictions. Assessment strategies should consider this multi-dimensional impact of the condition, and management strategies should be multi-disciplinary, aiming to target the problems identified in the current study.Key words: Joint hypermobility syndrome, impairment, activity, participation
Investigating the effect of rivastigmine on postural control in Parkinson's disease dementia
Objectifs : Comparer l’efficacité et l'aspect sécuritaire de la rivastigmine sous forme orale et transdermique destinée au traitement des symptômes liés aux instabilités posturales de patients atteints de la démence de la maladie de Parkinson (PDD) et qui sont des candidats pour un inhibiteur de l’acétylcholinestérase. La principale variable de l'étude était le changement de vitesse moyenne du centre de pression (CoP) en position debout après 6 mois de traitement. Les variables secondaires étaient les paramètres structuraux de posturographie dynamique, des échelles d’évaluation cliniques et les effets secondaires nécessitant une réduction de la dose. Méthodes: Des patients avec PDD ont été randomisé dans un ratio de 1 :1 impliquant une prise de rivastigmine orale ou transdermique avec des doses cibles de 6 mg deux fois par jour et 9,5 mg/10 cm2 par jour, respectivement. Les variables dépendantes ont été comparées au départ de l’étude et après 6 mois (comparaisons intra-groupes), de même qu'entre les groupes. Résultats: Dix-neuf patients ont complété l’étude (n=8 orale; n=11 transdermique). Des doses quotidiennes moyennes de 9,4 mg (± 1,5 mg) et 16,4 mg (± 3,6 mg) ont été administrées aux groupes oral et transdermique, respectivement. Le groupe transdermique a démontré une réduction significative de la vitesse moyenne du CoP de 15.8% (timbre: p=0,02; orale: réduction de 10,0%, p=0,16) lors de la condition d'équilibre la plus difficile (yeux fermés en maintenant l'équilibre sur une plateforme mobile synchronisée avec les déplacements du corps). Aucune différence n’a été trouvée entre les groupes (p=0,27). Concernant les paramètres structuraux, des améliorations significatives ont été observées au niveau de la durée moyenne des pics de stabilité de l'équilibre (timbre) et de la distance entre les pics de stabilité (orale) dans la condition d'équilibre la plus difficile. Aucun changement n’a été observé par rapport aux échelles cliniques. Six patients ont eu des effets secondaires mineurs nécessitant une réduction de dose (n=5 orale; n=1 transdermique). Conclusions: La rivastigmine pourrait améliorer certains éléments du contrôle postural de patients atteints de PDD, notamment la vitesse moyenne du CoP en position debout. Les bienfaits sont plus évidents sous les conditions qui challengent davantage l'équilibre.Objectives: To compare the efficacy and safety of oral and transdermal rivastigmine for postural instability in patients with Parkinson’s disease dementia (PDD) who were candidates for a cholinesterase inhibitor. The primary outcome was the change in mean velocity of the centre of pressure (CoP) after 6 months. Secondary outcomes included structural parameters of dynamic posturography, clinical rating scales and adverse events requiring dose reduction. Methods: Patients with PDD were randomized in a 1:1 ratio to oral or transdermal rivastigmine with target doses of 6 mg twice daily and 9.5 mg/10 cm2 daily, respectively. Outcomes were assessed at baseline and 6 months. Results were compared within and between groups. Results: Nineteen patients completed the study (n=8 oral, n=11 transdermal). Mean daily doses of 9.4 mg (± 1.5 mg) and 16.4 mg (± 3.6 mg) were achieved in the oral and transdermal groups, respectively. The transdermal group demonstrated a significant 15.8% decrease in mean velocity of CoP (patch: p <0.05; oral: 10.0% decrease, p=0.16) in the most difficult scenario (eyes closed with sway-referenced support). There was no difference between groups (p=0.27). For structural parameters, significant improvements were seen in the mean duration of peaks (patch) and inter-peak distance (oral) in the most difficult condition. No changes were observed in clinical rating scales. Six patients experienced non-serious adverse events requiring dose reduction (n= 5 oral; n=1 transdermal). Conclusions: Rivastigmine may improve certain elements of postural control, notably the mean velocity of CoP. Benefits appear to be more obvious under more taxing sensory conditions
Searching for Continuous Gravitational Waves from Unknown Isolated Neutron Stars in Advanced LIGO Data
With the advent of the advanced gravitational wave detector era, the Laser Interferometer Gravitational-wave Observatory (LIGO) has made several detections of gravitational waves from coalescing binary black holes and binary neutron stars, but other sources are also predicted to exist. Among these are continuous waves from isolated neutron stars. This type of signal is expected to be significantly weaker than the sources observed so far, but to last for years. In this work we discuss the efforts and obstacles involved in searching for continuous gravitational waves. In particular, we give details of the PowerFlux analysis pipeline and evaluate its performance compared to other pipelines. We also discuss searches in the first observing run of Advanced LIGO, including methods for mitigating the effects of the many spectral noise lines present at low frequencies. Finally, we discuss approximations to the barycentering routines used by LIGO to account for the Earth's motion, approximations that provide justification for more computationally efficient loosely coherent searches.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147561/1/osauter_1.pd
- …