Navegando por Orientadores "SOUZA, Givago da Silva"

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Acesso aberto (Open Access)
Acidentes ofídicos ocorridos no município de Santarém (PA) no período de 2000-2009
(Universidade Federal do Pará, 2012) SINIMBÚ, Valter Pinheiro; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
It surveyed the epidemiological profile of snakebites and risk factors associated with its incidence among residents of the municipality of Santarém (PA) and occurred in the decade of 2000-2009. Approaches the study with a descriptive-analytical methodology, observational and retrospective, with the use of a properly coded database, provided by the National Notifiable Diseases (SINAN) of the Ministry of Health. During the period, there were 2283 cases, accounting an annual incidence ranging between 70 to 105 cases / 100,000 population with a fatality rate of 0.66%. The accidents predominated in rural people (87%) in the months of Amazon rainy (January to June) in male patients (79%) aged 20-29 years. Almost all cases were treated at the emergency room of the county (88%) located in the urban area. Most patients (56%) came to the Health Unit 6 hours after the accident due to difficulties in access by geographic factors and river transport. Were classified as mild in severity (38%), moderate (55%) and severe (6%). Due to the frequency of species of snakes in the region, Bothrops accounted for the majority with 70.9%, followed by laquéticos accidents (11.3%) and more frequent in Amazonian forests, the crotalic (2.1%) and rare Micrurus (0.2%) and 15.3% in the species was not identified. In 91% of these patients the serum therapy was instituted. Unable to determine the occupancy of these patients, nor their level of education due to lack of completion of the case report forms. The lower limbs were the regions mostly affected (82%), which draws attention to the adoption of simple but effective preventive measures. Because of the high incidence of cases (the largest in Brazil), difficulties in patient access to prompt and effective care (increasing the morbidity and mortality), and little importance given by health professionals with regard to whether the information necessary for a better assessment and protection of the residents of this region, concludes that these accidents, although endemic in much of the world, particularly the tropics, remains, according to WHO definition, a problem neglected (by patients, professionals and society). There is need for more research, more ads and more awareness.
Acesso aberto (Open Access)
Análise da variabilidade da frequência cardíaca em pacientes hansenianos: análise linear, simbólica e de complexidade
(Universidade Federal do Pará, 2014) SANTOS, Marcio Clementino de Souza; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Objective: the purpose of this study was to evaluate the heart rate variability (HRV) in patients with multibacillary leprosy clinic history, from dynamic linear and nonlinear analysis. Materials and methods: this is an experimental not randomized, quantitative study with 42 volunteers of both genres, divided into 2 groups of 21. The first group (LG), with 21 leprosy patients, aged 39.14 ±10.58 years, and the second group (CG), with 21 healthy subjects aged 36.24 ± 12.64 years. HR capture was performed by a heart monitor Polar RS800 CX, for a period of 15 min in the supine and 15 min in a sitting position. Analysis of HRV was performed by frequency domain from high frequency spectral indices (HFun), low frequency (LFun) in standard units and reason BF/AF. The nonlinear analysis of HRV was calculated by symbolic analysis (0V indexes%, 1V%, wholesale% and 2ULV%) shannon entropy (SE) and normalized complexity index (NCI). Results: In the spectral analysis of HRV LG presented higher values (p<0.05) of LFun and smaller values (p<0.05) of HFun compared to CG, on bench press position. Both groups showed higher values (p<0.05) of HFun and smaller values (p<0.05) of LFun in supine position in relation to a sitting position. There was no change of reason LF/HF in the comparison between groups and between positions evaluated. Symbolic analysis LG presented higher values (p<0.05) of 0V index% and smaller values (p<0.05) of the 2LV% and 2ULV% index in relation to the CG, in both positions evaluated. The index 1V% was higher (p<0.05) in the LG in relation to the CG just comparing to a sitting position. The CG presented minors values (p<0.05) of 0V index% and higher values (p<0.05) 2ULV% index supine position in relation to a sitting position. The LG presented higher values (p<0.05) 2ULV% index supine position in relation to a sitting position. On the complexity analysis LG presented minors values (p<0.05) of SE and ICN with respect to CG, on bench press position. There were no differences between the groups in SE and NCI analyzed in a sitting position. The CG presented higher values (p<0.05) of ES and ICN on bench press position in relation to a sitting position. Conclusion: The LG present greater sympathetic modulation and less vagal modulation in relation to the CG, indicating less HRV and cardiac modulation with low complexity. In response to postural change, both groups showed increased vagal modulation on position supine, evidencing greater HRV in this condition. Analysis of HRV by linear and non-linear dynamics proved to be a sensitive method and promising for investigation of autonomic dysfunction in patients with multibacillary leprosy.
Acesso aberto (Open Access)
Avaliação da dispersão de luz sobre a retina de pacientes com histórico de hanseníase
(Universidade Federal do Pará, 2012) OLIVEIRA, Iraciane Rodrigues Nascimento; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Leprosy affects the ocular structures e it has the potential to make deficits the image formation on the retina. As the vision has a very important function for the human being, the decrement of the image quality on the retina can get worst the quality of life of the leprosy patients, which already can have somesthesics and motor alterations. This study was performed with leprosy patients in the Edison Lobão city in the Maranhão state from August 2011 and May 2012. The main purpose was to evaluate the straylight in the eye of the leprosy patients. The data was collected using the equipment C-Quant that performs a psychophysical procedure to quantify the straylight in the retina. Questionnaires were used to get clinical history, incapacities, treatment duration and visual complains. It was evaluated 50 eyes from leprosy patients and they were compared to 48 eyes of control subjects. There were no differences between both groups in the comparison of visual acuity. There was statistical difference of the retinal straylight between the control and leprosy patients (one way ANOVA, α = 0.05). There was no difference between the retinal straylight between the clinical forms of leprosy. Twenty seven eyes of the leprosy patients had retinal straylight values above 99% of the retinal straylight distribution of the control group. The retinal straylight values of the control group fitted well to the predictive model to their variation as a function of the age, while the results obtained from leprosy patients had a low fit to that predictive model. The retinal straylight of the leprosy patients were higher in the begging of the treatment (2-6 months) and in cured patients with diagnosis time above to 30 months. Even in normal visual acuity patients, the retinal straylight values could be altered e they can have decreasing of the quality of life across the years. The changes of the retinal straylight showed by leprosy patients must be due alterations in the ocular media or tissues caused by leprosy, or loss of the protective reaction of the eyes due somesthesics losses or even use of drug therapy.
Acesso aberto (Open Access)
Avaliação da sensação posicional de articulações dos membros superiores em sujeitos expostos cronicamente ao metilmercúrio
(Universidade Federal do Pará, 2014-11-29) OLIVEIRA, Alexandre Rodrigo Batista; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The Exposure of mercury in some watersheds in the Amazon has chronic character and a mild and moderate intensity. Communities of the basin in the Tapajos River has been monitored about the levels of mercury in the hair over the past 20 years and it was observed that the concentration of mercury in the hair of these people has high levels when compared with other riparian regions, without gold mining activities. In accidents occurred on Minamata in Japan, one of the most common symptoms was the loss of the somestetic function. Proprioception is a somestetic function that can be used to monitor the effects of prolonged exposure to mercury in populations. This work aims to study the sensation of positional joints of upper limb of subjects chronically exposed to mercury and with high levels in the last 3 years and compare the results of this assessment with those obtained in populations with less exposure to methylmercury. Fifty-seven volunteers have agreed to participate in this study, 23 of which belonged to group subjects chronically exposed to mercury from the community of barriers and 34 subjects belonged to the group with lower exposure to mercury from the community of Alter do Chão. Each subject had the positional sensations of joints of the shoulder, elbow and wrist evaluated by 3 times under conditions of open and closed eye. The evaluation consisted of teaching the subject to move a segment of the upper limb (forearm, hand or arm) from a neutral position to a position to articulate target. Each time the subject ended the movement was photographed the final position with digital photo camera of high resolution spatial and temporal. To calculate the articular amplitude at the end of the movement was used the program KINOVEA®, in which allows you to open the photo and use a digital tool to measure the angulation between the proximal and distal segment of the joint in question. Middle articular amplitude values for the open eye condition were statistically higher in the exposed group than in the control group in all the joints, while for the closed eye condition the values exposed group was statistically lower than in the control group only in the wrist joint. There was no statistical difference for the relative difference of angular joint positioning values between the study groups in all joints examined. The exposed group showed lower coefficient of variation for the test condition with the eye open in the joints of the wrist and elbow. The exposed group showed the highest coefficient of variation for the test condition with the eye closed only in the wrist joint. The angular difference values were sequentially higher proximal joints to the distal articulation in the exposed group, however in the control group the angular difference was similar in all the joints. The subjects chronically exposed to mercury showed slight alterations of the joint position sensation when compared with a control group. Proprioceptive evaluation can be an inexpensive tool for the assessment of the effects of mercury on the health of coastal populations exposed to the metal.
Acesso aberto (Open Access)
Avaliação temporal da exposição humana ao mercúrio no Oeste paraense
(Universidade Federal do Pará, 2015-11-27) ANDRADE, Paulo Douglas de Oliveira; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
In the present study we described mercury (Hg) exposure evolution in two riverside communities of Tapajos River Basin, Brazilian Amazon. These communities are exposed to this metal by the consumption of fishes that they fishing from the contaminated river. The contamination is due to a process that occurs mainly due to the weathering of soil in the area (which is naturally rich in Hg) and gold mining, that uses mercury to isolate the gold. The analysis used a dosimetric database containing values of mercury, wich was generated from hair samples of the riversides from Tapajos. The data collection was conducted for 17 years (1998-2014) and totaled 1.502 (one thousand, five hundred two) samples, which were divided into four groups: adult male, adult female, male child and female child. The results reveled the group with the highest risk of exposure: the adults males. After all the years of study, the adult male group was the group with the highest average Hg levels (14,41 μg/g ± 10 μg/g). On the other hand, all groups showed a trendy to decrease these levels, with the men took more time to start this process of reduction rates. Their levels dropped from 16,61 μg/g in 2007 to 11,23 μg/g in 2013. Women's group reduced from 13,92 μg/g in 2004 to 7,04 μg/g in 2013. Children had more significant reduction, wherein the girls dropped from 15.42 μg/g in 2001 to 3.83 μg/g in 2014, and the boys from 12.96 μg/g to 5.95 μg/g in the same years. The problematic situation involving the adult male group may indicate a more traditional lifestyle (based on a high fish consumption), less contact with professionals and researchers who instruct the population about the risks of poisoning, and more restrict nutrition, without red meat, tropical fruits, etc. In this sense, it is evident the need for greater awareness of this group in particular (adults males), and must the public health policies aimed specifically, must be enhanced in the region.
Acesso aberto (Open Access)
Correlação entre parâmetros estimados pelos testes Colour Assessment and Diagnosis e Cambridge Colour Test na avaliação da discriminação de cores
(Universidade Federal do Pará, 2015-03-31) FARIAS, Letícia Miquilini de Arruda; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The Colour Assessment and Diagnosis (CAD) and Cambridge Colour Test (CCT) tests are widely used in basic and clinic researches, because of high sensibility and specificity of your results. These tests use distinct paradigms of stimulation to estimate the color discrimination thresholds. It is not well known about the relationship of results of each paradigm in the evaluation of color discrimination in these tests. So, the present study aimed to compare the parameters of evaluation of color discrimination estimated from CAD and CCT tests. Fifty-nine trichromat subjects and thirty eight subjects with congenital dyschromatopsia (16 protans, 22 deutans) with mean age of 26,32 ±8,9 years-old were evaluated. 66 subjects were tested in CAD and CCT tests, 29 subjects in the CAD test and 2 subjects in the CCT test. The color vision phenotype of all subjects was determined through a battery of psychophysical tests and the estimative of color discrimination thresholds was evaluated by CAD and CCT tests. The data of color discrimination thresholds was fitted ellipses. The criteria analyzed to each subject were: area of the ellipses, angle of rotation of the ellipses and size of protan, deutan and tritan vectors. For each one of parameters was realized: descriptive statistic, analysis of dispersion of parameters between CAD e CCT tests and the combination of these parameters in each test, ratio between the parameters, correlation of parameters to three mathematical models and analysis of agreement. The parameters of area and size of deutan and tritan vectors of trichromat subgroup, area and size of tritan vector of protan subgroup, and size of protan and tritan vectors of deutan subgroup exhibited equivalence between the results of both tests. The parameters of area, angle of rotation and size of protan and tritan vectors showed agreement of measures between your results. Factors as the distincts localizations of neutral points of CAD and CCT tests and the spatial arrangement of the vectors in the CIE 1976 color space in the CCT test may have influenced the determination of chromatic discrimination thresholds of both tests. Despite using distinct paradigms in configuration of stimulation, the tests CAD and CCT are comparable.
Acesso aberto (Open Access)
Desenvolvimento de aplicativo para realização do finger tapping test e a influência do sexo e da dominância manual no desempenho do finger tapping test baseado em smartphone
(Universidade Federal do Pará, 2023-11) BRITO, Felipe André da Costa; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
The Finger Tapping Test (FTT) is a classical neuropsychological test that assesses motor functioning, and recently it has been employed using smartphones. For classical protocols, it has been observed that sex and handedness influence the performance during the test. By assessing the influence of sex and handedness on the test, it is possible to adjust the performance measurements to ensure the validity of test results and avoid sex- and handedness-related bias. The present study aimed to evaluate the influence of sex and handedness on smartphone-based FTT performance. We developed an Android application for the FTT and recruited 40 males and 40 females to carry out three spatial designs on it (protocols I, II, and III). Participants’ performance was measured using the global, temporal, and spatial parameters of the FTT. We observed that for the performance in protocol I, handedness had a significant influence on global and temporal variables, while the interaction between handedness and sex had a greater influence on spatial variables. For protocols II and III, we observed that handedness had a significant influence on global, temporal, and spatial variables compared to the other factors. We concluded that the smartphone-based test is partly influenced by handedness and sex, and these factors should be considered during the evaluation of the smartphone-based FTT.
Acesso aberto (Open Access)
Diminuição da sensibilidade ao contraste espacial de luminância em sujeitos com história de uso de terapia medicamentosa anti-tuberculose
(Universidade Federal do Pará, 2012) GOMES, Janildes Maria Silva; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The drugs isoniazid and ethambutol, usually administed for tubercolosis treatment, are well known to cause damage in the visual system of the patients that use them. As vision is an important sense for the quality of life and the luminance contrast is considered a good biomarker for visual evaluation, the present study aimed to compare the contrast sensitivity estimated from subjects that used anti-tuberculosis drug therapy and age-matched healthy subjects. The study was performed in Imperatriz city, Balsas city, Davinópolis city and Governador Edson Lobão city, in Maranhão state, Brazil from 2009 to 2012. The current study had a transversal, analytic, and case control profile. Three group of subjects participated from the present study: Control group (n=40), group of subjects treated with isoniazid (n = 19), and group of subjects that used isoniazid associated with ethambutol (n=18). It was used a CRT monitor, 21”, 6 x 5 degrees of visual angle to investigate the contrast sensitivity function. The comparison of the contrast sensitivities at different spatial frequencies among the three studied groups showed statistical differences (Two-way ANOVA, Tukey test, p < 0,05). Control group had higher contrast sensitivity at 10 and 15 cpd than the group that used only isoniazid as drug therapy for tuberculosis treatment and control group had higher contrast sensitivity at 4, 6, 10, 15 and 20 cpd than the group the received isoniazid and ethambutol together. There were no differences between the groups that received anti-tuberculosis therapy.
Acesso aberto (Open Access)
Dimorfismo sexual da espessura da retina: uma análise de aprendizagem de máquina
(Universidade Federal do Pará, 2022-03) FARIAS, Flavia Monteiro; SALOMÃO, Railson Cruz; http://lattes.cnpq.br/9518575270670446; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
The present research compared the accuracy of machine learning algorithms in classifying the thickness and volume measurements of retinal layers as obtained from male and female subjects. The study evaluated the retina of sixty-four healthy participants (38 women and 26 men), with normal vision and without eye or systemic diseases, aged between 20 and 40 years. The data acquisition was obtained with a Spectralis HRA+OCT tomograph in the macular region of the retina and its layers: retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), retinal pigment epithelium (RPE), inner retina (IRL) and outer retina (ORL). The classification accuracy was obtained with the following algorithms: support vector classifier (SVC), logistic regression (LR), linear discriminant analyses (LDA), k-nearest neighbors (kNN), decision tree (DT), gaussian naive bayes (GNB) and random forest (RF). The characteristics attributed to each participant's samples were the thickness values in the nine regions of the macula plus the total macular volume of each retinal layer. The statistical tests Two-way ANOVA and Tukey HSD post-hoc were used in the statistical comparisons between the accuracies for the classifier and retinal layer variables, considering a significance level of < 0.05. All factors (classifier, retinal layer, and their interactions) had significant influences on accuracy (p < 0.05). The main effect of the algorithm type factor resulted in an F ratio of F (6, 630) = 4.527, p = 0.0002. The main effect for the retinal layer produced an F ratio of F (9, 630) = 51.64 and p < 0.0001. The interaction effect was also significant, F(54, 630) = 1.741, p = 0.0012. All algorithms classified with high accuracy (> 0.70) the innermost layers of the retina (total retina, inner retina, RNFL, GCL, INL) according to the gender of the participants, where we observed significant differences between genders in thickness and measurements volume. The SVC, LDA, and LR algorithms produced high accuracy (>0.70) when thickness and volume data came from the RNFL compared to the outermost layers of the retina. The KNN, RF and DT algorithms performed better in correctly classifying the total retina data in relation to the outermost layers. The thickness and volume of the retina and the innermost layers of the retina allow machine learning algorithms to be more accurate in separating data from different sexes.
Acesso aberto (Open Access)
O efeito do ruído espacial de cor sobre a discriminação limiar de luminância: investigação básica e aplicada em populações expostas ao mercúrio
(Universidade Federal do Pará, 2018-05-22) FARIAS, Letícia Miquilini de Arruda; CÔRTES, Maria Izabel Tentes; http://lattes.cnpq.br/3913689546568227; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Natural images are a complex set of color and luminance contrast that when combined in visual scene helps to create the discrimination of objects from the surrounding visual environment. A series of neural streams transmits the color and luminance information from the retina to the higher cortical centers. Several proposals have been made to study how the visual system processes the stimuli that combining color and luminance contrasts. This thesis has as main proposal to introduce a new stimulus to be used luminance discrimination task under chromatic noise masking. Thus, five experiments were carried out with focus this new paradigm to explore basic and applied questions about its use. Study 1 investigated the effect of color noise saturation on the threshold discrimination of luminance contrast. Study 2 investigated how the mosaic arrangement contributed to the contrast values of luminance contrast thresholds under the chromatic noise masking. Study 3 investigated the influence of the color content of the noise on the threshold discrimination of the luminance contrast. Study 4 investigated the influence of the polarity of the luminance contrast under the chromatic noise masking on the estimated threshold contrasts. Study 5 compared the values of threshold luminance contrasts under chromatic noise masking of two riverine populations of different Amazonian regions of the Pará State and exposed to different levels of mercury by feeding. The main finding of this thesis was that the luminance contrast thresholds varied as a function of the vector length of the chromatic noise values. The higher chromatic noise length, the higher luminance contrast threshold. The contrast threshold estimated by the non-mosaic stimulus exhibited significantly lower values than those estimated with mosaic stimuli (p <0.01). No statistical difference was observed between the contrasts threshold estimated around the five reference chromaticities at different saturation conditions (p> 0.05). The luminance contrasts thresholds estimated in the luminance decrement protocol were xiii significantly lower at all saturation levels than those estimated using the luminance increase protocol (p <0.05). There is no statistical difference between the thresholds of estimated luminance discrimination among riverine communities that were differently exposed to mercury (p> 0.05). The luminance contrasts threshold estimated by the new stimulus, described in this thesis, were influenced by chromatic and spatial noise, and by the polarity of the stimulus of luminance contrast. However, the different chromatic noise compositions did not exhibit any influence on the luminance discrimination. The presence of one or more color-sensitive visual pathways and luminance may be the physiological substrate of the mechanism underlying the luminance contrast perception of this new stimulus.
Acesso aberto (Open Access)
Efeitos da adaptação ao flicker de luminância sobre o potencial cortical provocado visual
(Universidade Federal do Pará, 2015-08-20) LOUREIRO, Terezinha Medeiros Gonçalves de; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Visual Evoked Potential (VEP) has been a useful method to evaluate spatial vision in humans. Sustained observation of a visual stimulus produces several changes in neural responses at different processing levels in visual system. Previous studies has elucidated how primary visual cortex processing spatial information. Many others studies has also suggested about the contribution of parallel pathways M and P activation on the visual cortical responses evoked by a stimuli that excite only one of these pathways. Cortical excitation through a kind of stimulus that promotes one or both preferential adaptation could be a valuable approach to study activity from M and P pathways interactions on the visual responses. The purpose of this study is to evaluate the effects of luminance flicker adaptation on cortical responses elicited under favorable conditions of joint or differential M and P pathways activation, leading to an increase or decrease cortical responses. Eight subjects (20.25 ± 1.5) with normal vision acuity or corrected to 20/20 were tested. VEPs were recorded under three conditions of visual stimulation with no adaptation: sinusoidal gratings at 0.4, 2 and 10cpd presented at 1 Hz pattern-reversal stimulus (test stimuli). Other conditions was elicited by two-dimensional Gaussian mask adaptation stimulus with luminance variation in time domain (flicker) presented at 5 Hz, 10 Hz and 30 Hz temporal modulation. The experiment consisted on VEPs records above occipital scalp elicited by 8 seconds of adaptation stimulus followed by 2 seconds test stimuli. Cortical responses were evaluated in the time and temporal frequencies domain. In the time domain were measured latency and the P1 component amplitude (peak-line), while in the temporal frequency domain were evaluated amplitudes of alpha, beta and gamma frequency bands present in the in the records. VEPs elicited by the test stimuli were compared between flicker adaptation and no adaptation conditions. Main findings consisted on flicker adaptation that occurred differently at spatial frequencies domain. Results showed P1 component in all stimulation conditions and flicker adaptation at lower spatial frequency (0.4 cpd) in all time conditions. It has also showed a reduction at alpha band energy and an increase in the gamma band at same condition. This study concluded that flicker adaptation led to VEP amplitude decreased due to loss of alpha oscillations energy and gamma band energy increased at 0.4 cpd, and it represented a modification on the balance between M and P visual pathways.
Acesso aberto (Open Access)
Entropia conjunta de espaço e reqüência espacial estimada através da discriminação de estímulos espaciais com luminância e cromaticidade moduladas por funções de Gábor: implicações para o processamento paralelo de informação no sistema visual humano
(Universidade Federal do Pará, 2013-12-06) SILVEIRA, Vladímir de Aquino; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The objective of this study was to estimate the joint entropy of the human visual system in the domains of space and spatial frequency by using psychometric functions. The psychometric functions were obtained from stimulus discrimination that had luminance or chromaticity modulated by Gábor functions. The method consisted in evaluating the entropy in the space domain by testing subject capacity to discriminate stimuli that differed only in their spatial extent and in evaluating the entropy in the spatial frequency domain by testing subject capacity to discriminate stimuli that differed only in their spatial frequency. The joint entropy was then estimated from these two individual entropy values. Three visual conditions were studied: achromatic, chromatic without fine tuning correction of equiluminance, and chromatic with full equiluminance correction by using heterochromatic flickker photometry. Four subjects were tested in all conditions, two additional subjects were tested in the chromatic condition without fine equiluminance adjustment and a seventh subject also performed the acrhomatic test. All subjects were examined by an ophthalmologist, their eyes and visual system were considered normals, and presented no report, symptoms or signs of visual dysfunctions or diseases that could have affected their visual system. The subjects had their normal or corrected visual acuity of 20/30 minimum. The work was approved by the Comissão de Ética em Pesquisa (Núcleo de Medicina Tropical, UFPA) and followed the recomendations of the Helsinki Declaration. The Gábor functions used for luminance or chromaticity modulation comprised unidimensional horizontal sinusoidal gratings, modulated in the vertical direction, with bidimensional Gaussian envelopes whose spatial extent was measured by their standard deviation. Stimuli were generated by using a software written in Pascal in a Delphi 7 Enterprise environment. A Dell Precision 390 Workstation was used together with a CRS VSG ViSaGe stimulus generator to display the stimuli in a CRT monitor, 20”, 800 x 600 pixels, 120 Hz, RGB, Mitsubishi Diamond Pro 2070SB. In the achromatic experiments, the stimuli were generated by white luminance modulation (CIE1931: x = 0.270, y = 0.280; CIE1976: u’ = 0.186, v’ = 0.433), 44,5 cd/m2 mean luminance. In the chromatic experiments, mean luminance was kept in 15 cd/m2, and two series of red-green stimuli were used. In the first series, two chromaticities defined on the M-L axes of the DKL color space were used (CIE1976: green, u’=0.131, v’=0.380; red, u’=0.216, v’=0.371). In the second series, two chromaticities were defined along a red-green horizontal axis across the CIE1976 color space (CIE1976: green, u’=0.150, v’=0.480; red, u’=0.255, v’=0.480). Throughout the experiment, the reference stimuli comprised gratings with three different spatial frequencies (0.4, 2, and 10 cycles per degree) and a Gaussian envelope with 1 degree standard deviation. The test stimuli comprised 19 different spatial frequencies in the region of the reference spatial frequency and 21 different Gaussian envelopes in the region of the reference standard deviation. In the achromatic condition, four levels of Michelson contrast were studied: 2%, 5%, 10% e 100%. In the two chromatic conditions, the highest level of pooled cone contrast allowed by the CRT gamut was used, 17%. The procedure consisted of a two interval forced choice with the following steps: i) 1 s display of the reference stimulus; ii) 1 s replacement of the reference stimulus by a background with the same luminance and chromaticity; iii) 1 s display of the test stimulus which differed from the reference stimulus either in spatial frequency or spatial extent, together with a beep to tell the subject that it was now neccessary to provide a response if the two stimuli were equal or different; iv) replacement of the test stimulus by the background. The spatial extent or spatial frequency of the test stimulus was randomly changed from trial to trial by usind the method of constant stimuli. In a series comprising 300 trials, the spatial frequency was changed while in another series also comprising 300 trials, the spatial extent was changed, each test stimulus in each series being displayed at least 10 times. The subject response in every trial was stored as correct or incorrect for further use to estimate the psychometric function. The experimental data of the psychometric functions for spatial extent and spatial frequency at each contrast level, which corresponded to percent of correct responses, were fitted with Gaussian functions using the Least Square Method. For each contrast level, the spatial extent entropy and spatial frequency entropy were estimated from the standard deviations of these Gaussian functions. The joint entropy was then calculated by multiplying the square root of the spatial extent entropy by the spatial frequency entropy. The joint entropy values were compared with the theoretical minimum predicted for linear systems, 1/4π or 0.0796. For low and intermediate spatial frequencies at high contrasts, the joint entropy reached very low levels, below this minimum, suggesting that there were nonlinear interactions between two or more visual mechanisms. This phenomenon occurred in all conditions (achromatic, chromatic, and chromatic with fine equiluminance adjustment) and was more pronounced for spatial frequency 0.4 cycles / degree. A possible explanation for this phenomenon is the occurrence of nonlinear interactions between the retino-geniculo-striate visual pathways, such as the K, M, and P pathways, in the primary visual area or in higher levels of neural processing of visual information.
Acesso aberto (Open Access)
Estudos de mecanismos cromáticos e acromáticos para o potencial cortical provocado visual (VECP) e multifocal (mfVEP)
(Universidade Federal do Pará, 2017-10-06) ARAÚJO, Carolina dos Santos; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Visual evoked potentials (VECPs) and multifocal visual evoked potentials (mfVEPs) are being widely used to investigate cortical information processing in response to stimuli at different sites of the visual field and present the potential for complement information to conventional VEPs on chromatic and achromatic mechanisms of human vision. The objective of this work was to investigate the contribution of chromatic and achromatic mechanisms to VECP and mfVEP from two experiments: in the first, 9 healthy trichromates subjects with normal or corrected to 20/20 visual acuity were submitted to a visual stimulation of 8º of size, formed by achromatic sinusoidal gratings in 7 spatial frequencies (from 0.4 to 10 cpd) and in six contrast levels (from 3.12% to 99%); in the second, a multifocal dartboard with 60 sectors covering 40° of visual angle was shown for 14 healthy subjects (12 trichromates, 1 protan and 1 deutan discromatopsic type) in 7 different ratios of red-green luminance (R/R+G) and in one achromatic condition (99%). The two stimuli were presented as a reverse pattern, temporally controlled by m-sequences. The first slice (K2.1) and the second slice (K2.2) of the second order kernel were extracted. In experiment 1, were analyzed the main components of the waveforms recorded and in experiment 2 the signal-to-noise ratio (SNR) of the waveforms was analyzed to classify them as reliable (SNR> 1.35) or unreliable (SNR <1.35) and the number of reliable waveforms in 6 different rings with the same visual eccentricity (R1 being the central ring and R6 the most peripheral ring) was quantified. The results of experiment 1 indicated that responses in K2.1 were dominated by M pathway, and responses in K2.2 reflected the contribution of P pathway. The results of experiment 2 were similar for K2.1 and K2.2. In the R1-R4 rings, all red-green luminance ratios showed a similar number of reliable waveforms. In the R5-R6 rings, there are more reliable waveforms in the red-green luminance ratios with high luminance contrast, while the equiluminant condition has the fewest reliable responses. Protan and deutan subjects showed inverted results: stimulus conditions with green brighter than red generated more reliable waveforms in the protan subject (0.2-0.4), while the opposite combination generated more reliable waveforms in the deutan subject. The two second-order kernel slices are useful for studying the chromatic and achromatic mfVEP mechanisms. The results in R1-R4 indicated a similar contribution of chromatic and achromatic mechanisms for mfVEP, while R5-R6 show the most pronounced contribution of the achromatic mechanism to mfVEP. The method used allowed to identificate specific characteristics of protan and deutan discromatopsic type from obtained data. discromatopsic type from obtained data.
Acesso aberto (Open Access)
Função de sensibilidade ao contraste de luminância e de cor para estímulos de mosaico
(Universidade Federal do Pará, 2017) SANTOS, Patricia Seixas Alves; GOULART, Paulo Roney Kilpp; http://lattes.cnpq.br/7800966999068746; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
Natural images are compound of different blends of color and luminance. In the visual system, there are processing channels of color and luminance that have distinct sensitivities for both information. The parvocellular pathway has high sensitivity to red-green color contrast and low sensitivity to luminance contrast, and the magnocellular pathway has low sensitivity to red-green color contrast and high sensitivity to luminance contrast. Mosaic stimuli which combines color and luminance information may help us to understand how the visual system processes the information of color and luminance. This study aims to investigate the luminance and color contrast sensitivity function using stimuli that combine both information. Fifteen normal trichromats and 1 congenital dyschromatopsic participant were evaluated. To estimate the color contrast sensitivity function, we used stimuli with a pseudoisochromatic setting in which the test stimulus consists of a mosaic with size and luminance spatial noise. The target was compound by a red-green chromatic grating that differed from the background only by the chromaticity. To estimate the luminance contrast sensitivity function, we used stimuli with size and color spatial noise. The target was compound of a luminance contrast grating that differed from the background by the luminance. We used 9 spatial frequencies between 0,1 and 5,4 cpg. It was applied a twointerval forced choice method. The threshold was estimated by using a staircase of 20 reversions with a rule of2 hits to 1 error. The threshold was estimated with the last 14 reversions. To compare both functions, the thresholds estimated in each test were relativized in function of the higher sensitivity of each participant within each test. The observed color contrast sensitivity function showed a low-pass tuning, with higher contrast sensitivities on the medium and low spatial frequencies, while the luminance contrast sensitivity function presented a band-pass tuning, with decrease of the contrast sensitivity on the spatial frequencies that were higher and lower than 2,7 cpg. The results suggest that the threshold perception of both stimuli may have as physiological substrate, the activation of the parvocellular pathway or P pathway
Acesso aberto (Open Access)
Ganho de contraste do potencial cortical provocado visual multifocal: efeitos da excentricidade e do modo de estimulação
(Universidade Federal do Pará, 2016-11-29) SILVA, Veronica Gabriela Ribeiro da; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
This study evaluated effects of eccentricity and mode presentation on the multifocal visual evoked potential (mfVEPS) recordings extracted by second-order kernels and its possible contributions from parallel visual pathways. Nine subjects (22.5 ± 3.7 years-old) were studied. All the subjects had 20/20 or corrected visual acuity and no previous history of neuro-ophtahlmic diseases or degenerative diseases. The subjects were tested with non dilated pupil in a monocular way. All the experimental procedures agreed to the tenets of Helsinki and were approved by Committee for Ethic in Research of Nucleus of Tropical Medicine (023/2011 protocol, Federal University of Pará, Belém, PA, Brazil). A CRT monitor displayed a 22º radius, 60 sectors dartboard, each sector with 16 checks (8 white and 8 black), pattern mean luminance of 40 cd/m2. The pattern selection to be shown in each sector was temporally modulated according to a binary pseudorandom m-sequence. Two stimulation protocols were used and we called them as pattern reversal and pattern pulse. Stimulus was presented at five Michelson contrast levels (100%, 50%, 25%, 12.5%, and 6.25%) in two trials with increasing and decreasing contrast order. The subject was instructed to keep the eye in a red cross (1º) placed at the center of the screen. Veris 6.01 was used to configure the stimuli. mfVEPs were recorded with gold cup electrodes: the reference electrode was placed at the inion; the recording electrodes were placed at, 4 cm above the inion (channel 1), 1 cm above and 4 cm to the right of the inion (channel 2), 1 cm above and 4 cm to the left of the inion (channel 3). Ground surface electrode was placed at the forehead. Skin impedance was kept below 5 KOhm. Recordings were amplified 100.000x, band-pass filtered between 3 and 100 Hz. The Veris 6.1 performed an offline low-pass filtering at 35 Hz. Veris 6.1 was used to extract first (K2.1) and second (K2.2) slices from second-order kernels data from original channels. Using MATLAB routines three additional channels were computed from the subtraction of the three original channels. For each subject, a signal-to-noise ratio (SNR) evaluation was performed over the averaged data of two trials in each one of the 6 channels. We measured the RMS amplitude of signal and noise interval of each recording. Finally, we analyzed the waveforms with best SNR for each sector. Mean RMS amplitude for each of six eccentric rings (R1 and R6 are the inner and outer rings, respectively) and for all rings together as a function of stimulus contrast was modeled using Michaelis-Menten functions. Semi-saturation constant (C50) of the contrast-response function was used as indicator of response contrast gain. For pattern reversal protocol contrast-response functions from K2.1/K2.2 had the following C50 values: R1: 35,5% ± 9,3; R2: 26,5% ± 6,5; R3: 22,4% ± 8,8; R4: 18,4% ± 4,4; R5: 20,6% ± 9,3; R6: 26,7% ± 12 / R1: 38,4% ± 4,2; R2: 27,4% ± 7,4; R3: 20,2% ± 4,9; R4: 22,4% ± 4,2; R5: 18,7% ± 3,2; R6: 23,1% ± 8,9. For pattern pulse protocol contrast-response functions from K2.1/K2.2 had the following C50 values: R1: 0; R2: 44,7% ± 10,5; R3: 38,3% ± 12,1; R4: 45,8% ± 12,1; R5: 49,4% ± 16,1; R6: 47,8% ± 14,7 / R1: 0; R2: 50,2% ± 10,3; R3: 48,2% ± 11,1; R4: 28,5% ± 4,2; R5: 54,3% ± 16,2; R6: 0. Two contrast sensitivity mechanisms contribute to mfVEPs elicited by stimuli located in the central visual field, one mechanism with higher contrast gain (pattern reversal mfVEP) and other mechanism with low contrast gain (pattern pulse). For stimulus at the periphery visual field, mechanism with high contrast gain contributed to the generation of mfVEPs elicited by all stimulation modes.
Acesso aberto (Open Access)
Influência da luminância de fundo em estímulos pseudoisocromáticos sobre a discriminação de cores
(Universidade Federal do Pará, 2017) MOREIRA, Rodrigo Canto; GOULART, Paulo Roney Kilpp; http://lattes.cnpq.br/7800966999068746; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
Color perception is one of the most complex attributes of the human sensory system and contributes to survival in the expression of eating, reproductive, sexual, surveillance, and other behaviors. Pseudo-isochromatic stimuli are widely used for color vision assessment of humans and other primates. Despite the pervasive use, there are no norms for its application, each developer of these tests using varied stimulus configurations. The present study aims to evaluate the effects of background luminance on color discrimination in humans using pseudo-isochromatic stimuli. Ten trichromatic subjects of both sexes, aged 26 to 54 years (32.3 ± 8.3 years of age), normal visual acuity and no history of previous diseases that potentially affected the visual apparatus and / or nervous system were tested. To evaluate the influence of background luminance on color discrimination, a pseudo-isochromatic stimulus with spatial noise of size and luminance (luminance noise between 5 and 35 cd / m2) was used, with a background of 0 cd/m² illumination, 7.5 cd/m², 15 cd/m², 22.5 cd/m² and 30 cd/m 2. The target was composed of a set of central circles that formed a letter C, which presented different chromaticity in relation to the mosaic field in eight different chromatic axes (0º, 45º, 90º, 135º, 180º, 225º, 270°, 315°) around a chromaticity point of the CIE 1976 diagram (u '= 0.219; v' = 0.48). The color discrimination thresholds on each axis were estimated using a 4-alternative forced choice method and a staircase of 21 reversals, with a 2-hit rule for 1 error, and the threshold was calculated as the average of the last 15 reversals. The variation of color discrimination thresholds as a function of background luminance was dependent on the angle being studied. At angles 0°, 45°, 180° and 225°, the size of vectors in threshold perception were higher at 0 cd/m² and decreased sharply by 7.5 cd/m², where they reached their lowest values and remained low in conditions with higher background luminances. At angle 90°, the vector size was minimal in background luminance condition of 7.5 cd/m² and increased to higher and lower background luminance values. On vectors of angle 135°, 270° and 315° the color discrimination did not change significantly as a function of change background luminance. The area of color discrimination ellipse varied as a function of luminance stimulus background with a minimum value of 7.5 cd/m². The results show that the color discrimination is influenced by modification of luminance background of pseudoisochromatic stimulus. Activation of a red-green opposing mechanism and two blueyellow opposing mechanisms may explain the different influences of background variation in stimulus on discrimination of chromaticity in different axes. The results are important in understanding the physiology of perception of pseudo-isochromatic stimuli and search for a standardization use of these stimuli in clinical practice to facilitate comparison of results between different studies.
Acesso aberto (Open Access)
Influência de parâmetros espaciais sobre potenciais corticais provocados visuais gerados por estimulação pseudoaleatória
(Universidade Federal do Pará, 2013-03-08) ARAÚJO, Carolina dos Santos; GOMES, Bruno Duarte; http://lattes.cnpq.br/4932238030330851; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECP. Single stimulation with spatial contrast temporally controlled by msequences was not extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by a pseudo-random binary m-sequence at seven spatial frequencies (0.4-10 cpd) and three stimulus sizes (4º, 8º, and 16º of visual angle). At 8º of visual angle, it was also used six contrasts levels (3.12-99%). First order kernel had not provided a consistent measurable signal across spatial frequencies and contrasts that were tested – signal was very small or absent – while the second order kernel first and second slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the first and second slices of the second order kernel were the shape of the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that the second order kernel first slice was dominated by M pathway, but for some stimulus condition some P pathway contribution could be found, while the second order kernel second slice reflected the P pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudo-random stimulation for a wider range of spatial frequencies.
Acesso aberto (Open Access)
Mascaramento por ruído de luminância sobre a discriminação de cor e luminância
(Universidade Federal do Pará, 2019-03-13) LOUREIRO, Terezinha Medeiros Gonçalves de; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Several psychophysical experiments were developed using pseudoisochromatics stimuli to evaluate color vision. It was observed that the color perception depends on the characteristics of the luminance noise present in the stimulus. In this thesis were developed two sets of experiments that study how the effects of spatial noise of luminance influence in the visual perception. In the first experiment we investigated the effect of the change in luminance noise amplitude in color discrimination. Eighteen trichromates and ten congenital discromatopics had their color vision evaluated by stimuli adapted from the Cambridge Colour Test and were genetically tested to diagnose mutations associated with congenital color vision deficiency. The stimuli were composed of mosaics of circles in a circular field of 5 ° of visual angle. A subset of the circles differed from the remaining field by chromaticity. The color discrimination was estimated in 4 stimulus conditions that differed in the amplitude of the luminance noise: (i) between 6-20 cd/m²; (ii) between 8 and 18 cd/m²; (iii) between 10 and 16 cd/m²; and (iv) between 12 and 14 cd/m². Six equidistant luminance values were used between the luminance noise limits and the mean luminance of the stimulus maintained in all four conditions. The color discrimination thresholds were estimated through a staircase procedure in 8 different chromatic axes. An ellipse function was fitted to the chromaticity data. The indicators of color discrimination were the area of the ellipse and the values of the eight thresholds of color discrimination. The rate of change of these indicators as a function of the luminance noise amplitude values was calculated as the value of the derivative of the linear function that best fit the function. In the second experiment, a subset of the circles differed from the remaining field by the luminance noise difference, forming the perception of a letter C. In this experiment we tried to evaluate the luminance discrimination in different luminance noise conditions (levels of 2, 4, 6, 10 and 14). Thirty healthy subjects were tested. A ladder procedure was used to control the average luminance of the luminance noise of the target. The luminance discrimination ranges between the mean luminance of the target and the background were the visual functional indicators. The results of the first experiment showed that the rate of variation of the ellipse area as a function of the luminance amplitude in dichromates was higher than in trichromates (p <0.05). It was observed that the low amplitude of the luminance noise (condition of 2 cd/m²) improves the color discrimination of the trichrome and dichromate subjects. Regarding chromatic axes, it was observed that there was a significant difference between the rates of variation of the threshold vector size as a function of the amplitude of the luminance noise of trichromates and dichromates in the axes 0º, 45º, 90º and 135º. The results of the second experiment showed that at lower luminance levels, noise significantly impaired the luminance discrimination (p <0.05) compared to the conditions of higher levels of luminance noise. It was also observed that the higher the luminance contrast present within the noise the worse the luminance discrimination. It is concluded that the modification of luminance noise can lead to significant modifications of the luminance discrimination for color discrimination.
Acesso aberto (Open Access)
Opencards: uma nova proposta de ferramenta para estimava de limiares psicofísicos
(Universidade Federal do Pará, 2017-01-27) CAMPOS, Yuri Sobral; GOULART, Paulo Roney Kilpp; http://lattes.cnpq.br/7800966999068746; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
The knowledge the value of psychophysical thresholds is essential for any sensory study. In order to define a threshold value, before knowing the limits of sensitivity and the results are produced with the same, it is necessary a use of methodologies and tests to obtain them. Currently, it is comprehensive and use of computerized and non-computerized tests for a visual evaluation, however, the standards of advantages and disadvantages. In general, all tests are done with methodologies around you. The present study proposes the development of a printed test for a visual evaluation of discrimination. For this was sought a product of easy portability and application. The OpenCards consists of a set of boards printed in high spatial resolution and high color quality. On the plates with a mosaic of randomly colored circles within 16 color options with a target that differs from the background by a luminance difference. Targets have a shape of square, triangle, circle and letter X. Targets differed from the background by 90%, 80%, 70%, 60%, 50%, 40%, 35%, 35%, 30%, 25% , 20%, 15%, 10%, 5% of luminance contrast. There was still no sign without the target. To show the use of the OpenCards two methods of application have been elaborated. The first method was performed in an environment with controlled lighting and standard for studies in visual system. Plates were shown in subjects in random order and a task of the subject to identify a shape of the object. The subject's response was recorded and the procedure repeated 8 times. The second method was performed in an ambient light environment. The experimenter showed the plates with the same target ordered in descending contrast and how they shuffled along with a blank plate and asked the subject tested how to order in decreasing contrasts using a higher contrast plate as a reference. The test was performed with all two-stroke sets. The response of the subject tested was recorded in both methods applied and a taxon of subject was adjusted to a Gaussian model for an estimate of the psychophysical threshold. The threshold was the value of the luminance contrast in which the Gaussian model estimated the accuracy of 50% accuracy for the first applied method and 75% for the second applied method. Eight subjects were evaluated in both methods and three subjects. The estimated average threshold with the first method was 23.5 ± 3 and the mean estimated method with the second method was 30.1 ± 6.5. The mean difference between the results obtained by the two methods was 7.3% ± 3. The statistical difference between the thresholds estimated by two methods (p <0.05). Since the following stations are to be used for different types of work, and especially for them, they are applied in each method. OpenCards proved to be easy to apply by the experimenter, portability and understanding of the task by the subject tested.
Acesso aberto (Open Access)
Perda de sensibilidade ao contraste espacial de luminância em sujeitos com história clínica de hipovitaminose B1
(Universidade Federal do Pará, 2012) LOBATO, Jaisane Santos Melo; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718
Vitamin B1 acts directly in the energetic metabolism and its deficiency causes several deficits to the nervous system, including those that occurs in vision that is an important and fundamental sense in the quality of life of the human beings. Studies have been shown that the contrast sensitivity estimative is a good biomarker for evaluation of the visual system and the own nervous system. The present study purposed to compare the contrast sensitivity of subjects with history of hypovitaminosis B1 with healthy subjects living in the cities of Imperatriz and João Lisboa in the Maranhão state from 2006 to 2009. This is a transversal, analytic, and case control study. It was investigated 18 patients with history of hypovitaminosis B1 (13 males, 5 females) with mean age 33.77 ± 9.33 years-old, whose had 35 eyes. The control group was composed by 40 subjects (80 eyes) from both sexes, and mean age 33.25 ± 9.3 years-old. Both groups had similar way of life. For psychophysical evaluation, it was used cathodic ray tubes, 21”, 6 x 5 degrees of visual angle. It was performed a nutritional evaluation of all investigated subjects, further visual acuity and contrast sensitivity evaluation. There were statistical differences between the contrast sensitivity of the control group and the group of the subjects with history of hypovitaminosis B1 at 4, 10, 15 e 20 cpd (two-way ANOVA, α = 0,05, Tukey post-hoc test). Most of the subjects with changes in healthy nutritional condition had changes in the visual evaluation. Clinical complains also had important relationship with visual losses.