2,040 research outputs found
Outcome Prediction for Unipolar Depression
Although effective drug and non-drug treatment for unipolar depressive illness exist, different individuals respond differently to different treatments. It is not uncommon for a given patient to lw switched several times from one treatment to another until an effective remedy for that particular patient is found. This process is costly in terms of time, money and suffering. It is thus desirable to determine at the outset the likdy response of a patient to the available treatments, so that the optimal one can be selected. Although prior attempts at outcome prediction with linear regression models have failed, recent work on this problem has indicated that the nonlinear predictive techniques of backpropagation and quadratic regression call account for a significant proportion of the variance in the data. The present research applies the nonlinear predictive technique of kernel regression to this problcrn, and employs cross-validation to test the ability of the resulting model to extract, from extremely noisy dinical data, information with predictive value. The importance of comparison with a suitable null hypothesis is illustrated.Office of Naval Research (N00014-95-1-0409
The effect of retinal image slip on peripheral visual acuity
Retinal image slip promoted by fixational eye movements prevents image fading in central vision. However, in the periphery a higher amount of movement is necessary to prevent this fading. We assessed the effect of different levels of retinal image slip in peripheral vision by measuring peripheral visual acuity (VA), with and without crowding, while modulating retinal image slip by using gaze-linked stimuli. Measurements were carried out at four isoeccentric positions at 5 and at 10 degrees eccentricity. Gaze position was monitored throughout using an infrared eyetracker. The target was presented for up to 500 msec, either with no retinal image slip, with reduced retinal slip, or with increased retinal image slip. Without crowding, peripheral visual acuity improved with increased retinal image slip compared with the other two conditions. In contrast to the previous result, under crowded conditions, peripheral visual acuity decreased markedly with increased retinal image slip. Therefore, the effects of increased retinal image slip are different for simple (noncrowded) and more complex (crowded) visual tasks. These results provide further evidence for the importance of fixation stability on complex visual tasks when using the peripheral retina.This study was supported by a grant from Fundação para a Ciência e a Tecnologia (FCT), Portugal, POCTI 2010 & FSE, SRFD/BD/27975/2006
Electronic books as low vision aids
Every year, around 34 000 people in England and Wales are newly registered as sight impaired or severely sight impaired, the majority of whom have some residual vision.1 In order to read books, people with low vision will generally rely on large print books and supplementary optical2 or electronic3 magnifiers. Only about 1.5% of the approximately two million books currently in print are available in large print format.4
Recently, several electronic book readers have become commercially available.5 These consist of a low glare electronic paper screen and internal memory, which can typically hold the full text of between 150 and 2000 full-length novels. Electronic paper has a wide viewing angle of
Investigating unstable fixation in patients with macular disease
To assess the effect on visual acuity of compensating fixation instability by controlling retinal image motion in people with macular disease.
METHODS:
Ten patients with macular disease participated in this study. Crowded and noncrowded visual acuity were measured using an eye tracking system to compensate for fixation instability. Four conditions, corresponding to four levels of retinal image motion, were tested: no compensation (normal motion), partial compensation (reduced motion), total compensation (no motion), and overcompensation (increased motion). Fixation stability and the number of preferred retinal loci were also measured.
RESULTS:
Modulating retinal image motion had the same effect on crowded and noncrowded visual acuity (P = 0.601). When fixation instability was overcompensated, acuity worsened by 0.1 logMAR units (P < 0.001) compared with baseline (no compensation) and remained equal to baseline for all other conditions.
CONCLUSIONS:
In people with macular disease, retinal image motion caused by fixation instability does not reduce either crowded or noncrowded visual acuity. Acuity declines when fixation instability is overcompensated, showing limited tolerance to increased retinal image motion. The results provide evidence that fixation instability does not improve visual acuity and may be a consequence of poor oculomotor control.Fundação para a Ciência e a Tecnologia (FCT), Portugal, POCTI 2010 & FSE, SRFD/BD/27975/2006 (AFM)
Ultra-fine dark matter structure in the Solar neighbourhood
The direct detection of dark matter on Earth depends crucially on its density
and its velocity distribution on a milliparsec scale. Conventional N-body
simulations are unable to access this scale, making the development of other
approaches necessary. In this paper, we apply the method developed in Fantin et
al. 2008 to a cosmologically-based merger tree, transforming it into a useful
instrument to reproduce and analyse the merger history of a Milky Way-like
system. The aim of the model is to investigate the implications of any
ultra-fine structure for the current and next generation of directional dark
matter detectors. We find that the velocity distribution of a Milky Way-like
Galaxy is almost smooth, due to the overlap of many streams of particles
generated by multiple mergers. Only the merger of a 10^10 Msun analyse can
generate significant features in the ultra-local velocity distribution,
detectable at the resolution attainable by current experiments.Comment: 9 pages, 6 figures, accepted for publication in MNRA
Diagnosing Cysts With Correlation Coefficient Images From 2‐Dimensional Freehand Elastography
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135592/1/jum20072691201.pd
Separate Universes Do Not Constrain Primordial Black Hole Formation
Carr and Hawking showed that the proper size of a spherical overdense region
surrounded by a flat FRW universe cannot be arbitrarily large as otherwise the
region would close up on itself and become a separate universe. From this
result they derived a condition connecting size and density of the overdense
region ensuring that it is part of our universe. Carr used this condition to
obtain an upper bound for the density fluctuation amplitude with the property
that for smaller amplitudes the formation of a primordial black hole is
possible, while larger ones indicate a separate universe. In contrast, we find
that the appearance of a maximum is not a consequence of avoiding separate
universes but arises naturally from the geometry of the chosen slicing. Using
instead of density a volume fluctuation variable reveals that a fluctuation is
a separate universe iff this variable diverges on superhorizon scales. Hence
Carr's and Hawking's condition does not pose a physical constraint on density
fluctuations. The dynamics of primordial black hole formation with an initial
curvature fluctuation amplitude larger than the one corresponding to the
maximum density fluctuation amplitude was previously not considered in detail
and so we compare it to the well-known case where the amplitude is smaller by
presenting embedding and conformal diagrams of both types in dust spacetimes.Comment: Updated version corresponds to the published version
10.1103/PhysRevD.83.124025, 22 pages, 22 figure
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