12,829 research outputs found
Absolutely Continuous Spectrum for Parabolic Flows/Maps
We provide an abstract framework for the study of certain spectral properties
of parabolic systems; specifically, we determine under which general conditions
to expect the presence of absolutely continuous spectral measures. We use these
general conditions to derive results for spectral properties of time-changes of
unipotent flows on homogeneous spaces of semisimple groups regarding absolutely
continuous spectrum as well as maximal spectral type; the time-changes of the
horocycle flow are special cases of this general category of flows. In addition
we use the general conditions to derive spectral results for twisted horocycle
flows and to rederive certain spectral results for skew products over
translations and Furstenberg transformations
Parabolic Flows Renormalized by Partially Hyperbolic Maps
We consider parabolic flows on 3-dimensional manifolds which are renormalized
by circle extensions of Anosov diffeormorphisms. This class of flows includes
nilflows on the Heisenberg nilmanifold which are renormalized by partially
hyperbolic automorphisms. The transfer operators associated to the
renormalization maps, acting on anisotropic Sobolev spaces, are known to have
good spectral properties (this relies on ideas which have some resemblance to
representation theory but also apply to non-algebraic systems). The spectral
information is used to describe the deviation of ergodic averages and solutions
of the cohomological equation for the parabolic flow.Comment: Comments welcom
A method for selecting an efficient diagnostic protocol for classification of perceptive and cognitive impairments in neurological patients
"Published in final edited form as: Conf Proc IEEE Eng Med Biol Soc. 2011 ; 2011: 1129ā1132. doi:10.1109/IEMBS.2011.6090264."An important and unresolved problem in the assessment of perceptual and cognitive deficits in
neurological patients is how to choose from the many existing behavioral tests, a subset that is
sufficient for an appropriate diagnosis. This problem has to be dealt with in clinical trials, as well
as in rehabilitation settings and often even at bedside in acute care hospitals. The need for
efficient, cost effective and accurate diagnostic-evaluations, in the context of clinician time
constraints and concerns for patientsā fatigue in long testing sessions, make it imperative to select
a set of tests that will provide the best classification of the patientās deficits. However, the small
sample size of the patient population complicates the selection methodology and the potential
accuracy of the classifier. We propose a method that allows for ordering tests based on having
progressive increases in classification using cross-validation to assess the classification power of
the chosen test set. This method applies forward linear regression to find an ordering of the tests
with leave-one-out cross-validation to quantify, without biasing to the training set, the
classification power of the chosen tests.R01 NS064100 - NINDS NIH HHS; R01NS064100 - NINDS NIH HHSAccepted manuscrip
Autoimmunity, Autoinflammation, and Infection in Uveitis
Funding/Support: No funding or grant support. Financial Disclosures: John V. Forrester has received an honorarium for lecturing from Janssen (London, UK). Lucia Kuffova has undertaken consultancy work for Abbvie (London, UK). Andrew D. Dick has undertaken consultancy work for Abbvie (London, UK), Roche (London, UK), and Genentech (London, UK) and has received honoraria from Janssen (London, UK) and Abbvie (London, UK). The authors attest that they meet the current ICMJE criteria for authorship.Peer reviewedPublisher PD
The emotional valence of subliminal priming effects perception of facial expressions
We investigated, in young healthy subjects, how the affective content of subliminally
presented priming images and their specific visual attributes impacted conscious
perception of facial expressions. The priming images were broadly categorised as
aggressive, pleasant, or neutral and further subcategorised by the presence of a face and
by the centricity (egocentric or allocentric vantage-point) of the image content. Subjects
responded to the emotion portrayed in a pixelated target-face by indicating via key-press
if the expression was angry or neutral. Priming images containing a face compared to
those not containing a face significantly impaired performance on neutral or angry targetface
evaluation. Recognition of angry target-face expressions was selectively impaired by
pleasant prime images which contained a face. For egocentric primes, recognition of
neutral target-face expressions was significantly better than of angry expressions. Our
results suggest that, first, the affective primacy hypothesis which predicts that affective
information can be accessed automatically, preceding conscious cognition, holds true in
subliminal priming only when the priming image contains a face. Second, egocentric
primes interfere with the perception of angry target-face expressions suggesting that this
vantage-point, directly relevant to the viewer, perhaps engages processes involved in
action preparation which may weaken the priority of affect processing.Accepted manuscrip
Two mechanisms for optic flow and scale change processing of looming
Published in final edited form as: J Vis. ; 11(3): . doi:10.1167/11.3.5.The detection of looming, the motion of objects in depth, underlies many behavioral tasks, including the perception of self-motion and time-to-collision. A number of studies have demonstrated that one of the most important cues for looming detection is optic flow, the pattern of motion across the retina. Schrater et al. have suggested that changes in spatial frequency over time, or scale changes, may also support looming detection in the absence of optic flow (P. R. Schrater, D. C. Knill, & E. P. Simoncelli, 2001). Here we used an adaptation paradigm to determine whether the perception of looming from optic flow and scale changes is mediated by single or separate mechanisms. We show first that when the adaptation and test stimuli were the same (both optic flow or both scale change), observer performance was significantly impaired compared to a dynamic (non-motion, non-scale change) null adaptation control. Second, we found no evidence of cross-cue adaptation, either from optic flow to scale change, or vice versa. Taken together, our data suggest that optic flow and scale changes are processed by separate mechanisms, providing multiple pathways for the detection of looming.We thank Jonathan Victor and the anonymous reviewers of the paper for feedback and suggestions regarding the stimuli used here. This work was supported by NIH grant R01NS064100 to LMV. (R01NS064100 - NIH)Accepted manuscrip
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