Elisa Margarita Colombo - Academia.edu (original) (raw)

Papers by Elisa Margarita Colombo

Intra-specific color variation is often underestimated by researchers, and among mammalian specie... more Intra-specific color variation is often underestimated by researchers, and among mammalian species, intra-specific differences in coloration are poorly documented for most species. The main goal of this study was to apply an objective color measurement methodology to the study of a specific problem: the detection, if any, of patterns of changes in the fur color of specimens of Akodon budini in relation to biological (i.e., sex) and environmental (i.e., season) variables. We hypothesize that male coat color will be more homogeneous than that of females and that the winter coat color will be darker than that of summer, the latter being orange. We measured the pelage color on five points over the dorsal surface of 26 A. budini museum specimens region using a spectroradiometer and a diffuse illumination cabin. We used Principal Component Analysis to describe the association between the color variables, sex and season, and each of the observations. We then used general linear models of A...

Light originated at a glare source and entering the eye, produces a veiling luminance that causes... more Light originated at a glare source and entering the eye, produces a veiling luminance that causes contrast decrease in retinal images and this effect could differ if the subject wears lenses or not. In this work the glare effects in subjects wearing lenses is studied inducing ammetropies in emmetropes. Contrast thresholds of sinusoidal patterns of 2 cpd and 0.5 cd/m2 are evaluated without and with glare, the glare source being steady, at 12o and producing 60 lx at the cornea. To exemplify the use of this methodology, 2 emmetropes under 8 different conditions are considered: naked eye; 3 control conditions (wearing neutral lenses) and 4 ammetropic conditions, inducing low (2 D) and medium (5 D) myopia and hyperopia with positive and negative contact lenses and correcting them with adequate ophthalmic lenses. The contrast threshold differences between the naked eye and the other 7 conditions are statistically not significant without glare and significant (up to more than 100%) with gl...

Cuando un ojo miope o hipermétrope utilizando una lente oftálmica mira un estímulo y, además, rec... more Cuando un ojo miope o hipermétrope utilizando una lente oftálmica mira un estímulo y, además, recibe luz de un punto periférico, la lente modifica el ángulo de excentricidad con el cual la luz originada en dicho punto llega al ojo. En aproximación paraxial, el aumento visual de la lente (cociente entre los ángulos subtendidos en el vértice corneal por el punto y por su imagen a través de lente) puede evaluarse como es usual, considerando o bien lente gruesa o delgada. En el primer caso, el cálculo requiere datos (no siempre disponibles) referentes a ubicación de la fuente, parámetros constructivos de la lente y distancia de vértice mientras que, en el segundo, los resultados son imprecisos para lentes gruesas empleadas por pacientes con hipermetropía severa. Para evitar estos inconvenientes, en el presente artículo obtenemos una formula para el aumento visual promedio de una lente oftálmica estándar de caras esféricas como función solo de su potencia. Proponemos utilizar esta fórmul...

Fil: Aguirre, Rolando Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro ... more Fil: Aguirre, Rolando Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman. Instituto de Investigacion en Luz, Ambiente y Vision. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Instituto de Investigacion en Luz, Ambiente y Vision; Argentina

F1000Research, 2011

A Transitional Space (TS)-from exterior to interior-becomes in "lighting barrier" due to the extr... more A Transitional Space (TS)-from exterior to interior-becomes in "lighting barrier" due to the extreme lighting conditions involved. Considering the increasing of the adaptation time becoming with ageing, strong illumination change effects will depend on people age. An experiment was performed to test this dependency. We measured the time required to identify the orientation of the aperture of two rings when the person moves from the outdoor to the indoor of a building. The adaptation of the subjects was determined by the outdoor conditions (sunny) and the change of adaptation luminance was about 4 magnitude orders. Contrast stimuli-0.45 and size aperture 0.7 degree. Thirteen older adults (60^67), nine younger ones (30^52) and eight young adults (20^30 years) with healthy vision participated of this experiment. All subjects repeated the task five times. The oldest group needed 4 times the time required by the youngest group and the middle group needed an intermediate value, to perform the task. Applying a Multilevel Model, which considers the observations dependency, we found that the efficiency differences between age groups are statistically significant (p<0.001). These outcomes point out the importance of adequately addressing the TS to support the daily life activities of older adults.

Energy and Buildings, 2018

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  A new equation was proposed for evaluating glare in offices with direct sunlight  Absolute and relative glare values were evaluated in real working conditions  Percentage of central and near FOV over 2000cd/m2 was tested as absolute glare factor

Attention, perception & psychophysics, Jan 30, 2018

The ability of the human visual system to detect stimuli at low illumination levels provides awar... more 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 halide lamp (MH), with a higher content of short wavelengths. Two experiments were performed, using a two-channel Maxwellian-view optical system to measure contrast threshold under different experimental conditions. In Experiment 1, three age groups (young, middle-aged and old, n = 2 each), two retinal locations (on-axis and off-axis vision), four background luminances (0.01, 0.07, 0.45, and 3.2 cd/m), and two photometry systems (photopic and the MES2 systems) were considered. In Experiment 2, contrast threshold measurement was performed with two age groups (young and old, n = 11 each), one retinal location (off-axis vision), one background l...

Anais da Academia Brasileira de Ciências, 2016

The role of color in taxonomic and systematic studies of several taxa is central. Color data are ... more The role of color in taxonomic and systematic studies of several taxa is central. Color data are more valuable if they permit comparisons. We aimed to provide pelage objective color measurements of a series of Akodon budini and to use those color data to test and to quantitatively analyze the influence of both the lighting source and the measuring point, in the determination of pelage color of museum skins. We used a spectroradiometer to measure the pelage color at five points over the dorsal midline of 54 Akodon budini museum skins. PCAs and ANOVAs were conducted over the color data. The characteristics of the studied series also allowed us to include and assess the potential effects of some main sources of intra-specific variation. Determinations of fur color strongly depend on the lighting source, and therefore it is essential that lighting conditions are controlled during color measurements and then made explicit when communicating the color characterization of particular taxono...

Optica Applicata

In a previous work (Opt. Appl. 39(2), 2009, pp. 415-428) we established the characteristics that ... more In a previous work (Opt. Appl. 39(2), 2009, pp. 415-428) we established the characteristics that a computer-based contrast sensitivity function (CSF) measurement system has to be used in the opthalmological clinic. In order to obtain a generalized use of CSF in clinics and as a screening tool, the necessity to incorporate a normality range by age was also suggested. It will also be important to establish how many reference curves are necessary, because in the last decades, different ranges have been presented in the literature. In the present work, our purpose was to show how to distribute the observers in terms of the statistical variations of CSF as a function of age in a normal population of healthy eyes. We then evaluated the utility of these curves in the detection of vision problems and, finally, the possibility of using them as a screening tool considering a reduced number of spatial frequencies. We used a computer-based CSF measurement system to present sinusoidal gratings w...

Optica Pura y Aplicada, 2013

Journal of Light & Visual Environment, 2007

SPIE Proceedings, 1995

The aim of the actual paper is to enhance achievements of the text Optica FIsica Básica: estructu... more The aim of the actual paper is to enhance achievements of the text Optica FIsica Básica: estructurada airededor del concepto de coherencia luminosa" (1) (in English Basic Physical Optics centred in the concept of coherence'). We consider that this book is a very worth tool when one has to learn or to teach some fundamental concepts ofphysical optics. It is well known that the topics of physical optics present not easy understanding for students. Even more they also present some difficulties for the teachers when they have to introduce them to the class. First, we think that different phenomena like diffraction and polarization could be well understood if the starting point is a deep comprehension of the concept of interference of light and, associated with this, the fundamental and nothing intuitive concept of coherence of the light. In the reference text the authors propose the use of expression "stable

SPIE Proceedings, 1995

Most ofthe time, in the teaching ofgeometrical and physical optics, the visual system is not cons... more Most ofthe time, in the teaching ofgeometrical and physical optics, the visual system is not considered in the analysis of different phenomena. This situation is often reflected in the physic texts and is responsible of a limited comprehension of physic concepts involved. It is so natural for us to see that it is sometimes difficult for the physic teachers to give up intuitive conceptions about what and how we see. The authors propose that the common sense is not enough. It is necessary to start from a scientific point of view considering contributions from diverse fields of analysis, avoing the tentation of reducing the behaviour of the vision system to a photgraphic camera. To see is much more than just to record images. Vision seems effortless. Objects are recognised in the environment and actions are carried out accordingly. However, current thinking suggest that the task is performed by the cooperative action of many different modules, each with specific task. Theses modules may represent different parts ofthe brain, or different routines in a computer program. This article stands out significant contributions from different approaches: * Theory of information processing * fificial vision * Computational vision * Cognitive psychology theory of learning These interdisciplinary contributions lead to the conclusion that the vision is an intended process. It is also able to make use of light propagation in the environment. This energy is processed constructing useflill visual representations and symbols. The conclusion is that the vision is a cognitive process.

Psychology and Neuroscience, 2013

In this work we introduce a new category of barriers that we call "functional vision barriers." T... more In this work we introduce a new category of barriers that we call "functional vision barriers." This expression refers to lighting and visual elements that may complicate or hinder functional vision and may make life even more difficult for people with visual defects. These barriers appear as a consequence of certain negative effects caused by the poor design of the visual stimulus or visual environment that surrounds it in which lighting is one of the main factors. We use the term "functional vision" because this expression refers to the ability of the visual system to perform everyday tasks. We analyzed some of our previous results with regard to situations that can be considered "functional vision barriers": (1) stimuli with low luminance contrast information in which the addition of chromatic contrast improves visual performance and (2) tasks that are performed in the presence of a glare source in the visual field, diminishing visual performance and reducing brightness perception.

Psicologia USP, 2011

El objetivo de este estudio fue comparar el desempeño de dos test psicofísicos de sensibilidad al... more El objetivo de este estudio fue comparar el desempeño de dos test psicofísicos de sensibilidad al contraste, uno basado en un sistema informatizado - FVC 100 - y otro en láminas impresas - VCTS 6500, ambos empleando la discriminación de redes sinusoidales en condiciones de adaptación fotópica. Fueron medidos 45 ojos de 23 personas con edades entre 28 y 70 años. Los sujetos fueron reclutados en un Servicio de Oftalmología al cual concurrieron tanto por consulta como por control. A partir de tomar el criterio clínico como referencia, los resultados muestran que, de los 23 sujetos, en 16 casos ambos sistemas detectaron correctamente su estado visual, en cinco casos (10 ojos) sólo el FVC 100 consiguió hacerlo, mientras que en dos casos este sistema no detectó el problema visual y sí lo hizo el VCTS 6500. Considerando los datos obtenidos se aprecia un mejor desempeño del test informatizado, destacándose la necesidad de continuar trabajando para conseguir un atlas con información de la fu...

Vision Research, 2001

To examine how the time course of rapid events of adaptation affect motion vision, the lower thre... more To examine how the time course of rapid events of adaptation affect motion vision, the lower threshold of motion (LTM) was measured for suprathreshold sinusoidal gratings in presence of transient and steady glare. In the case of the transient condition, glare and stimulus were presented separated in time by a variable extent (SOA: 50-450 ms). A two alternative forced choice paradigm using the method of constant stimuli was adopted to measure the LTM. It was found that LTM follows the characteristic Crawford's time course of adaptation. Results are similar for two stimulus duration (300 and 500 ms). It was proposed that the increment of contrast threshold for displacing gratings (C tq) due to the loss of sensitivity produced by the sudden onset of the glare source can explain the results.

Vision Research, 1995

Reversals in perceived direction of motion of a grating when its spatial frequency exceeds half t... more Reversals in perceived direction of motion of a grating when its spatial frequency exceeds half that of the sampling mosaic provide a potential tool for estimating sampling frequency in peripheral retina. We used two-alternative forced-choice tasks to measure performance of three observers detecting or discriminating direction of motion of high contrast horizontal or vertical sinusoidal luminance gratings presented either 20 or 40 deg from the fovea along the horizontal meridian. A foveal target at a comfortable viewing distance aided fixation and accommodation. A Maxwellian view optometer with 3 mm artificial pupil was used to correct the refraction of the peripheral grating, which was presented in a circular patch, 1.8 deg in diameter, in a surround of similar colour and mean luminance (47.5 cd-m-2). The refractive correction at each eccentricity was measured by recording the aerial image of a point after a double pass through the eye. The highest frequency which can reliably be detected (7-14 c/deg at 20 deg, 5.5-7.5 c/deg at 40 deg) depends critically on refraction. Refraction differs by up to 5 D from the fovea to periphery, and by up to 6 D from horizontal to vertical. Direction discrimination performance shows no consistent reversals, and depends less on refraction. It falls to chance at frequencies as low as one-third of the highest that can be detected. Gratings which can be detected but whose direction of motion cannot be discriminated appear as irregular speckle patterns whose direction of motion varies from trial to trial. The absence of motion reversals may reflect irregularity of sampling, and suggests that reversals are not a simple tool for studying sampling in peripheral vision.

Vision Research, 2009

We present a series of experiments exploring the effect of the stimulus spatial configuration on ... more We present a series of experiments exploring the effect of the stimulus spatial configuration on speed discrimination and two different types of segmentation, for random dot patterns. In the first experiment, we find that parsing the image produces a decrease of speed discrimination thresholds such as was first shown by Verghese and Stone [Verghese, P., & Stone, L. (1997). Spatial layout affects speed discrimination threshold. Vision Research, 37(4), 397-406; Verghese, P., & Stone, L. S. (1996). Perceived visual speed constrained by image segmentation. Nature, 381, 161-163] for sinusoidal gratings. In the second experiment, we study how the spatial configuration affects the ability of a subject in localizing an illusory contour defined by two surfaces with different speeds. Results show that the speed difference necessary to localize the contour decreases as the stimulus patches are separated. The third experiment involves transparency. Our results show a little or null effect for this condition. We explain the first and second experiment in the framework of the model of Bravo and Watamaniuk [Bravo, M., & Watamaniuk, S. (1995). Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination. Vision Research, 35(12), 1691-1697] who proposed that motion computation consists in, at least, two stages: a first computation of coarse local speeds followed by an integration stage. We propose that the more precise estimate of speed obtained from the integration stage is used to produce a new refined segmentation of the image perhaps, through a feedback loop. Our data suggest that this third stage would not apply to the processing of transparency.

Optics Express, 2000

We measured the lower threshold of motion (LTM) of suprathreshold gratings as a function of spati... more We measured the lower threshold of motion (LTM) of suprathreshold gratings as a function of spatial frequency and contrast, for both transient glare and no-glare conditions. A two alternatives forced choice paradigm, using the method of constant stimuli, was adopted to measure the LTM. The LTM occurs at constant velocity. This velocity threshold is higher for transient glare condition than for no-glare condition. We found that the sudden onset of glare increases LTM over the whole range of contrasts. We believe the effect of transient glare sources on the lower threshold of motion is due to the transient loss of sensitivity.

Optica Applicata, 2009

We discuss the characteristics a system to measure the contrast sensitivity function (CSF) in the... more We discuss the characteristics a system to measure the contrast sensitivity function (CSF) in the ophthalmologic clinic has to have. We propose that this system should be computer based in order to assure flexibility and precision. Besides the original calibration, this equipment needs an auxiliary system to keep the working conditions allowing periodical gamma corrections. We try a calibration method based on visual comparisons and show that it is valid and simple. We propose to use an adaptive psychophysical method to obtain contrast thresholds that assure a good compromise between precision and duration of the whole test. Finally, we propose that the system has to have its own normality curves for the different age ranges allowing the practitioner to perform clinical evaluations. Summing up, we can say that taking into account the above issues, the fidelity of the stimuli will be guaranteed and the challenges entailed in its transference to the clinic will be overcome.

Intra-specific color variation is often underestimated by researchers, and among mammalian specie... more Intra-specific color variation is often underestimated by researchers, and among mammalian species, intra-specific differences in coloration are poorly documented for most species. The main goal of this study was to apply an objective color measurement methodology to the study of a specific problem: the detection, if any, of patterns of changes in the fur color of specimens of Akodon budini in relation to biological (i.e., sex) and environmental (i.e., season) variables. We hypothesize that male coat color will be more homogeneous than that of females and that the winter coat color will be darker than that of summer, the latter being orange. We measured the pelage color on five points over the dorsal surface of 26 A. budini museum specimens region using a spectroradiometer and a diffuse illumination cabin. We used Principal Component Analysis to describe the association between the color variables, sex and season, and each of the observations. We then used general linear models of A...

Light originated at a glare source and entering the eye, produces a veiling luminance that causes... more Light originated at a glare source and entering the eye, produces a veiling luminance that causes contrast decrease in retinal images and this effect could differ if the subject wears lenses or not. In this work the glare effects in subjects wearing lenses is studied inducing ammetropies in emmetropes. Contrast thresholds of sinusoidal patterns of 2 cpd and 0.5 cd/m2 are evaluated without and with glare, the glare source being steady, at 12o and producing 60 lx at the cornea. To exemplify the use of this methodology, 2 emmetropes under 8 different conditions are considered: naked eye; 3 control conditions (wearing neutral lenses) and 4 ammetropic conditions, inducing low (2 D) and medium (5 D) myopia and hyperopia with positive and negative contact lenses and correcting them with adequate ophthalmic lenses. The contrast threshold differences between the naked eye and the other 7 conditions are statistically not significant without glare and significant (up to more than 100%) with gl...

Cuando un ojo miope o hipermétrope utilizando una lente oftálmica mira un estímulo y, además, rec... more Cuando un ojo miope o hipermétrope utilizando una lente oftálmica mira un estímulo y, además, recibe luz de un punto periférico, la lente modifica el ángulo de excentricidad con el cual la luz originada en dicho punto llega al ojo. En aproximación paraxial, el aumento visual de la lente (cociente entre los ángulos subtendidos en el vértice corneal por el punto y por su imagen a través de lente) puede evaluarse como es usual, considerando o bien lente gruesa o delgada. En el primer caso, el cálculo requiere datos (no siempre disponibles) referentes a ubicación de la fuente, parámetros constructivos de la lente y distancia de vértice mientras que, en el segundo, los resultados son imprecisos para lentes gruesas empleadas por pacientes con hipermetropía severa. Para evitar estos inconvenientes, en el presente artículo obtenemos una formula para el aumento visual promedio de una lente oftálmica estándar de caras esféricas como función solo de su potencia. Proponemos utilizar esta fórmul...

Fil: Aguirre, Rolando Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro ... more Fil: Aguirre, Rolando Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman. Instituto de Investigacion en Luz, Ambiente y Vision. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Instituto de Investigacion en Luz, Ambiente y Vision; Argentina

F1000Research, 2011

A Transitional Space (TS)-from exterior to interior-becomes in "lighting barrier" due to the extr... more A Transitional Space (TS)-from exterior to interior-becomes in "lighting barrier" due to the extreme lighting conditions involved. Considering the increasing of the adaptation time becoming with ageing, strong illumination change effects will depend on people age. An experiment was performed to test this dependency. We measured the time required to identify the orientation of the aperture of two rings when the person moves from the outdoor to the indoor of a building. The adaptation of the subjects was determined by the outdoor conditions (sunny) and the change of adaptation luminance was about 4 magnitude orders. Contrast stimuli-0.45 and size aperture 0.7 degree. Thirteen older adults (60^67), nine younger ones (30^52) and eight young adults (20^30 years) with healthy vision participated of this experiment. All subjects repeated the task five times. The oldest group needed 4 times the time required by the youngest group and the middle group needed an intermediate value, to perform the task. Applying a Multilevel Model, which considers the observations dependency, we found that the efficiency differences between age groups are statistically significant (p<0.001). These outcomes point out the importance of adequately addressing the TS to support the daily life activities of older adults.

Energy and Buildings, 2018

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  A new equation was proposed for evaluating glare in offices with direct sunlight  Absolute and relative glare values were evaluated in real working conditions  Percentage of central and near FOV over 2000cd/m2 was tested as absolute glare factor

Attention, perception & psychophysics, Jan 30, 2018

The ability of the human visual system to detect stimuli at low illumination levels provides awar... more 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 halide lamp (MH), with a higher content of short wavelengths. Two experiments were performed, using a two-channel Maxwellian-view optical system to measure contrast threshold under different experimental conditions. In Experiment 1, three age groups (young, middle-aged and old, n = 2 each), two retinal locations (on-axis and off-axis vision), four background luminances (0.01, 0.07, 0.45, and 3.2 cd/m), and two photometry systems (photopic and the MES2 systems) were considered. In Experiment 2, contrast threshold measurement was performed with two age groups (young and old, n = 11 each), one retinal location (off-axis vision), one background l...

Anais da Academia Brasileira de Ciências, 2016

The role of color in taxonomic and systematic studies of several taxa is central. Color data are ... more The role of color in taxonomic and systematic studies of several taxa is central. Color data are more valuable if they permit comparisons. We aimed to provide pelage objective color measurements of a series of Akodon budini and to use those color data to test and to quantitatively analyze the influence of both the lighting source and the measuring point, in the determination of pelage color of museum skins. We used a spectroradiometer to measure the pelage color at five points over the dorsal midline of 54 Akodon budini museum skins. PCAs and ANOVAs were conducted over the color data. The characteristics of the studied series also allowed us to include and assess the potential effects of some main sources of intra-specific variation. Determinations of fur color strongly depend on the lighting source, and therefore it is essential that lighting conditions are controlled during color measurements and then made explicit when communicating the color characterization of particular taxono...

Optica Applicata

In a previous work (Opt. Appl. 39(2), 2009, pp. 415-428) we established the characteristics that ... more In a previous work (Opt. Appl. 39(2), 2009, pp. 415-428) we established the characteristics that a computer-based contrast sensitivity function (CSF) measurement system has to be used in the opthalmological clinic. In order to obtain a generalized use of CSF in clinics and as a screening tool, the necessity to incorporate a normality range by age was also suggested. It will also be important to establish how many reference curves are necessary, because in the last decades, different ranges have been presented in the literature. In the present work, our purpose was to show how to distribute the observers in terms of the statistical variations of CSF as a function of age in a normal population of healthy eyes. We then evaluated the utility of these curves in the detection of vision problems and, finally, the possibility of using them as a screening tool considering a reduced number of spatial frequencies. We used a computer-based CSF measurement system to present sinusoidal gratings w...

Optica Pura y Aplicada, 2013

Journal of Light & Visual Environment, 2007

SPIE Proceedings, 1995

The aim of the actual paper is to enhance achievements of the text Optica FIsica Básica: estructu... more The aim of the actual paper is to enhance achievements of the text Optica FIsica Básica: estructurada airededor del concepto de coherencia luminosa" (1) (in English Basic Physical Optics centred in the concept of coherence'). We consider that this book is a very worth tool when one has to learn or to teach some fundamental concepts ofphysical optics. It is well known that the topics of physical optics present not easy understanding for students. Even more they also present some difficulties for the teachers when they have to introduce them to the class. First, we think that different phenomena like diffraction and polarization could be well understood if the starting point is a deep comprehension of the concept of interference of light and, associated with this, the fundamental and nothing intuitive concept of coherence of the light. In the reference text the authors propose the use of expression "stable

SPIE Proceedings, 1995

Most ofthe time, in the teaching ofgeometrical and physical optics, the visual system is not cons... more Most ofthe time, in the teaching ofgeometrical and physical optics, the visual system is not considered in the analysis of different phenomena. This situation is often reflected in the physic texts and is responsible of a limited comprehension of physic concepts involved. It is so natural for us to see that it is sometimes difficult for the physic teachers to give up intuitive conceptions about what and how we see. The authors propose that the common sense is not enough. It is necessary to start from a scientific point of view considering contributions from diverse fields of analysis, avoing the tentation of reducing the behaviour of the vision system to a photgraphic camera. To see is much more than just to record images. Vision seems effortless. Objects are recognised in the environment and actions are carried out accordingly. However, current thinking suggest that the task is performed by the cooperative action of many different modules, each with specific task. Theses modules may represent different parts ofthe brain, or different routines in a computer program. This article stands out significant contributions from different approaches: * Theory of information processing * fificial vision * Computational vision * Cognitive psychology theory of learning These interdisciplinary contributions lead to the conclusion that the vision is an intended process. It is also able to make use of light propagation in the environment. This energy is processed constructing useflill visual representations and symbols. The conclusion is that the vision is a cognitive process.

Psychology and Neuroscience, 2013

In this work we introduce a new category of barriers that we call "functional vision barriers." T... more In this work we introduce a new category of barriers that we call "functional vision barriers." This expression refers to lighting and visual elements that may complicate or hinder functional vision and may make life even more difficult for people with visual defects. These barriers appear as a consequence of certain negative effects caused by the poor design of the visual stimulus or visual environment that surrounds it in which lighting is one of the main factors. We use the term "functional vision" because this expression refers to the ability of the visual system to perform everyday tasks. We analyzed some of our previous results with regard to situations that can be considered "functional vision barriers": (1) stimuli with low luminance contrast information in which the addition of chromatic contrast improves visual performance and (2) tasks that are performed in the presence of a glare source in the visual field, diminishing visual performance and reducing brightness perception.

Psicologia USP, 2011

El objetivo de este estudio fue comparar el desempeño de dos test psicofísicos de sensibilidad al... more El objetivo de este estudio fue comparar el desempeño de dos test psicofísicos de sensibilidad al contraste, uno basado en un sistema informatizado - FVC 100 - y otro en láminas impresas - VCTS 6500, ambos empleando la discriminación de redes sinusoidales en condiciones de adaptación fotópica. Fueron medidos 45 ojos de 23 personas con edades entre 28 y 70 años. Los sujetos fueron reclutados en un Servicio de Oftalmología al cual concurrieron tanto por consulta como por control. A partir de tomar el criterio clínico como referencia, los resultados muestran que, de los 23 sujetos, en 16 casos ambos sistemas detectaron correctamente su estado visual, en cinco casos (10 ojos) sólo el FVC 100 consiguió hacerlo, mientras que en dos casos este sistema no detectó el problema visual y sí lo hizo el VCTS 6500. Considerando los datos obtenidos se aprecia un mejor desempeño del test informatizado, destacándose la necesidad de continuar trabajando para conseguir un atlas con información de la fu...

Vision Research, 2001

To examine how the time course of rapid events of adaptation affect motion vision, the lower thre... more To examine how the time course of rapid events of adaptation affect motion vision, the lower threshold of motion (LTM) was measured for suprathreshold sinusoidal gratings in presence of transient and steady glare. In the case of the transient condition, glare and stimulus were presented separated in time by a variable extent (SOA: 50-450 ms). A two alternative forced choice paradigm using the method of constant stimuli was adopted to measure the LTM. It was found that LTM follows the characteristic Crawford's time course of adaptation. Results are similar for two stimulus duration (300 and 500 ms). It was proposed that the increment of contrast threshold for displacing gratings (C tq) due to the loss of sensitivity produced by the sudden onset of the glare source can explain the results.

Vision Research, 1995

Reversals in perceived direction of motion of a grating when its spatial frequency exceeds half t... more Reversals in perceived direction of motion of a grating when its spatial frequency exceeds half that of the sampling mosaic provide a potential tool for estimating sampling frequency in peripheral retina. We used two-alternative forced-choice tasks to measure performance of three observers detecting or discriminating direction of motion of high contrast horizontal or vertical sinusoidal luminance gratings presented either 20 or 40 deg from the fovea along the horizontal meridian. A foveal target at a comfortable viewing distance aided fixation and accommodation. A Maxwellian view optometer with 3 mm artificial pupil was used to correct the refraction of the peripheral grating, which was presented in a circular patch, 1.8 deg in diameter, in a surround of similar colour and mean luminance (47.5 cd-m-2). The refractive correction at each eccentricity was measured by recording the aerial image of a point after a double pass through the eye. The highest frequency which can reliably be detected (7-14 c/deg at 20 deg, 5.5-7.5 c/deg at 40 deg) depends critically on refraction. Refraction differs by up to 5 D from the fovea to periphery, and by up to 6 D from horizontal to vertical. Direction discrimination performance shows no consistent reversals, and depends less on refraction. It falls to chance at frequencies as low as one-third of the highest that can be detected. Gratings which can be detected but whose direction of motion cannot be discriminated appear as irregular speckle patterns whose direction of motion varies from trial to trial. The absence of motion reversals may reflect irregularity of sampling, and suggests that reversals are not a simple tool for studying sampling in peripheral vision.

Vision Research, 2009

We present a series of experiments exploring the effect of the stimulus spatial configuration on ... more We present a series of experiments exploring the effect of the stimulus spatial configuration on speed discrimination and two different types of segmentation, for random dot patterns. In the first experiment, we find that parsing the image produces a decrease of speed discrimination thresholds such as was first shown by Verghese and Stone [Verghese, P., & Stone, L. (1997). Spatial layout affects speed discrimination threshold. Vision Research, 37(4), 397-406; Verghese, P., & Stone, L. S. (1996). Perceived visual speed constrained by image segmentation. Nature, 381, 161-163] for sinusoidal gratings. In the second experiment, we study how the spatial configuration affects the ability of a subject in localizing an illusory contour defined by two surfaces with different speeds. Results show that the speed difference necessary to localize the contour decreases as the stimulus patches are separated. The third experiment involves transparency. Our results show a little or null effect for this condition. We explain the first and second experiment in the framework of the model of Bravo and Watamaniuk [Bravo, M., & Watamaniuk, S. (1995). Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination. Vision Research, 35(12), 1691-1697] who proposed that motion computation consists in, at least, two stages: a first computation of coarse local speeds followed by an integration stage. We propose that the more precise estimate of speed obtained from the integration stage is used to produce a new refined segmentation of the image perhaps, through a feedback loop. Our data suggest that this third stage would not apply to the processing of transparency.

Optics Express, 2000

We measured the lower threshold of motion (LTM) of suprathreshold gratings as a function of spati... more We measured the lower threshold of motion (LTM) of suprathreshold gratings as a function of spatial frequency and contrast, for both transient glare and no-glare conditions. A two alternatives forced choice paradigm, using the method of constant stimuli, was adopted to measure the LTM. The LTM occurs at constant velocity. This velocity threshold is higher for transient glare condition than for no-glare condition. We found that the sudden onset of glare increases LTM over the whole range of contrasts. We believe the effect of transient glare sources on the lower threshold of motion is due to the transient loss of sensitivity.

Optica Applicata, 2009

We discuss the characteristics a system to measure the contrast sensitivity function (CSF) in the... more We discuss the characteristics a system to measure the contrast sensitivity function (CSF) in the ophthalmologic clinic has to have. We propose that this system should be computer based in order to assure flexibility and precision. Besides the original calibration, this equipment needs an auxiliary system to keep the working conditions allowing periodical gamma corrections. We try a calibration method based on visual comparisons and show that it is valid and simple. We propose to use an adaptive psychophysical method to obtain contrast thresholds that assure a good compromise between precision and duration of the whole test. Finally, we propose that the system has to have its own normality curves for the different age ranges allowing the practitioner to perform clinical evaluations. Summing up, we can say that taking into account the above issues, the fidelity of the stimuli will be guaranteed and the challenges entailed in its transference to the clinic will be overcome.