José A. Menéndez

University of Valladolid | UVA · Departamento de Estadística e Investigación Operativa

The ability of the human visual system to detect stimuli at low illumination levels provides awareness of potential risks. The influence of age and spectral power distribution on mesopic spectral sensitivity is analyzed. Two typical light sources are used, a high-pressure sodium lamp (HPS), with a higher content of long wavelengths, and a metal hal...

Purpose: To measure the sensitivity of small retinal areas by reducing the influence of the adaptation state of the rest of the retina. To assess the functional behaviour of the retina of several patients affected by different types of retinitis pigmentosa (RP). Methods: A prospective study was performed. Five eyes of patients with retinal disease...

This work discusses the relative significance of optical and neural mechanisms in letter contrast sensitivity under different conditions of environmental lighting. A study was carried out on 26 eyes with normal ocular health. Sixteen lighting conditions were obtained by combining different test luminances (from 10cd/m(2) to 600cd/m(2)) and surround...

There is a growing interest in studying mesopic since in this range rods and cones are simultaneously active. It has been suggested that rods cone interactions could be responsible for alterations in temporal and spatial visual response. By employing a two-channel Maxwellian view optical system we measured thresholds luminance at a steady adapting...

The influence of lighting of different spectral power distribution on letter contrast sensitivity has been studied. The different spectral power distributions were obtained by filtering or dimming tungsten halogen lamps. Measurements were made on 20 young and healthy individuals (25 eyes) whose monocular contrast sensitivities were measured with a...

Night driving is a complex visual task with important ramifications for driver and pedestrian safety. It is usually performed under mesopic or scotopic conditions and frequently, in the presence of transient glare sources that can adapt parts of the central retina. The objective of this work was to analyze the time response of adaptation for the ce...

This paper proposes a new model-based approach to estimate small areas that extends the Fay–Herriot methodology. The new model is additive, with a random term to characterize the inter-area variability and a nonparametric mean function specification, defined using the information on an auxiliary variable. The most significant advantage of the propo...

To determine the influence of surround luminance on the letter contrast sensitivity function. The binocular contrast sensitivities of 31 young and ocularly healthy individuals were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c deg(-1), respectively; with surround luminances from 1 to...

In this article we consider general mixed models to derive small area estimators. The fixed part of the models links the area parameters to the auxiliary variables using a shrinkage region. We show how the selection of the shrinkage region depends on two main factors: the inter-area variation and the correlation coefficient of the auxiliaries with...

The aim of this work is to analyse the simultaneous influence of test and surround luminance's on letter contrast sensitivity measurements. The final issue is to find environmental lighting conditions under which this psychophysical magnitude shows maximum invariance relative to luminance changes in the surround nearest the test. The clinical study...

The aim of this work is to analyse the simultaneous influence of test and surround luminance's on letter contrast sensitivity measurements. The final issue is to find environmental lighting conditions under which this psychophysical magnitude shows maximum invariance relative to luminance changes in the surround nearest the test. The clinical study...

Light scattering from cells: The contribution of the nucleus and the effects of proliferative status " , RESUMEN Se presenta las líneas de investigación del grupo de Óptica de la Visión de la Universidad de Valladolid. La primera de las líneas se centra en la medida de la transmitancia y difusión de los tejidos corneales, la segunda, en los cambios...

In the context of a normal model, where the mean is constrained to a polyhedral convex cone, a new methodology has been developed for estimating a linear combination of the mean components. The method is based on an application of adapted parametric bootstrap procedures to reduce the bias of the maximum likelihood estimator. The proposed method is...

It is well known that anomalies are sometimes observed when using the likelihood ratio test (LRT) for testing restricted hypotheses in a normal model. This paper considers a general framework for these anomalies to occur. We provide a condition, that relates the null and the alternative hypotheses, under which the dominance of the LRT is obtained....

This paper shows how in a normal population, when the mean holds restrictions given by a right cone, the likelihood ratio test (LRT) for testing a face of that cone is equivalent to another test which is also the LRT for testing the linear subspace associated to the above face against a right cone defined only by those restrictions taking part in t...

This paper considers a likelihood ratio test for testing hypotheses defined by non-oblique closed convex cones, satisfying the so called iteration projection property, in a set of k normal means. We obtain the critical values of the test using the Chi-Bar-Squared distribution. The obtuse cones are introduced as a particular class of cones which are...

The first anomaly in the L.R.T. for testing restricted hypotheses was observed by Warrack and Robertson. They found the L.R.T. for testing an order restriction in a normal model to be dominated by a different test. In this paper we deal with a more general situation in which the L. R. T. for testing a face of an acute cone is dominated by a differe...

In this paper we give an algorithm for computing the solutions of the Isotonic median regression problem, equivalent to the calculation of the maximum likelihood estimate for the parameter , where θ1 is the location parameter of the bilateral exponential distribution, under the assumption .

In this article we consider the hypotheses testing problem of means from independent normal populations with known variances, in which both the null and the alternative hypotheses impose order restrictions upon of parameters. It is shown that a likelihood ratio test for these two restriction is dominated by other likelihood ratio test for hypothese...

This paper shows the statistics that define the likelihood ratio tests about the mean of ak-dimensional normal population, when the hypotheses to test areH 0: θ=0;H 0*: θ ∈ τφ;H 1: θ∈τ;H 2: θ∈R k , being τ a closed and poliedric convex cone inR k , and τφ the minima dimension face in τ. It is proved that the obtained statistics distributions are ce...