Thesis (Ph. D.)--University of California, San Diego, 2004. / Vita. Includes bibliographical references.

Understanding how the human visual system recognizes objects is one of the key challenges in neuroscience. Inspired by a large body of physiological evidence (Felleman and Van Essen, 1991; Hubel and Wiesel, 1962; Livingstone and Hubel, 1988; Tso et al., 2001; Zeki, 1993), a general class of recognition models has emerged which is based on a hierarchical organization of visual processing, with succeeding stages being sensitive to image features of increasing complexity (Hummel and Biederman, 1992; Riesenhuber and Poggio, 1999; Selfridge, 1959). However, these models appear to be incompatible with some well-known psychophysical results. Prominent among these are experiments investigating recognition impairments caused by vertical inversion of images, especially those of faces. It has been reported that faces that differ “featurally” are much easier to distinguish when inverted than those that differ “configurally” (Freire et al., 2000; Le Grand et al., 2001; Mondloch et al., 2002) – a finding that is difficult to reconcile with the aforementioned models. Here we show that after controlling for subjects’ expectations, there is no difference between “featurally” and “configurally” transformed faces in terms of inversion effect. This result reinforces the plausibility of simple hierarchical models of object representation and recognition in cortex.

Traditionally, human texture perception has been studied using artificial textures made of random-dot patterns or abstract structured elements. At the same time, computer algorithms for the synthesis of natural textures have improved dramatically. The current study seeks to unify these two fields of research through a psychophysical assessment of a particular computational model, thus providing a sense of what image statistics are most vital for representing a range of natural textures. We employ Portilla and Simoncelli’s 2000 model of texture synthesis for this task (a parametric model of analysis and synthesis designed to mimic computations carried out by the human visual system). We find an intriguing interaction between texture type (periodic v. structured) and image statistics (autocorrelation function and filter magnitude correlations), suggesting different processing strategies may be employed for these two texture families under pre-attentive viewing.

Avaliar a dispersão de luz intraocular em participantes com olhos saudáveis, moradores da Grande São Paulo e de San Miguel de Tucuman, Argentina, e pacientes que realizariam cirurgia refrativa (LASIK), utilizando o metodo psicofísico da Comparacão da Compensação presente no aparelho C-Quant (Oculus Optikgerate, Alemanha). Método: Foi utilizado o aparelho C-Quant, desenvolvido por Franssen, Coppens e van den Berg. (IOVS, 47:768,2006), disponivel comercialmente, para avaliar de maneira objetiva a dispersão de luz intraocular atraves de metodo psicofisico. Foram testados 261 voluntarios, de ambos os sexos, com idades variando entre 10 e 78 anos, divididos em tres grupos experimentais: grupo 1: n= 209, idade: 33,74 } 15,87 anos, moradores da Grande Sao Paulo; grupo 2: n=29, idade: 39,72}13,28 anos, moradores de San Miguel de Tucuman, Argentina; grupo 3: n=23, idade: 30,52}4,94 anos, moradores da Grande Sao Paulo e pacientes de cirurgia refrativa (LASIK). Cada voluntario realizou 6 testes, 3 em cada olho (olhos alternados), e os valores obtidos do parametro de dispersao foram comparados entre si e com as normas do equipamento. Os voluntarios do grupo 3 realizaram tres sessoes de testagem, antes da cirurgia, apos 60 dias da cirurgia e apos 120 dias da cirurgia. Resultados: Observou-se que, apesar da variacao entre respostas do mesmo participante e de diferentes participantes da mesma idade, nao houve significancia estatistica (ANOVA medidas pareadas, grupo 1: t=1,501, Wilcoxon, grupo 2: Z=-2,422, p-level 0,015) entre os dados, e em todos os grupos experimentais houve alta correlacao (grupo 1: Pearson: R=0,7101, grupo 2: Spearman = 0,942, grupo 3: Spearman = 0,958) entre olho direito e esquerdo. Comparando-se com as normas do aparelho atualizadas, nao foi encontrada diferenca estatistica para os tres grupos experimentais. No grupo 3, os resultados de dispersao pre-operatorio foram ligeiramente maiores que os obtidos com 60 e 120 dias de pos-operatorio, porem nao houve diferenca estatistica entre tais dados. Discussão: Os valores de dispersao de luz intraocular foram compativeis com as normas atualizadas do aparelho, o que se deve, principalmente, a grande variacao dos dados coletados, levando a um desvio padrao grande, que impossibilita qualquer diferenca estatistica. Observamos que entre os mais jovens (entre 10 e 20 anos), tais variacoes de valores de dispersao tambem ocorrem, levantando duvidas sobre a constancia da dispersao de luz nessa faixa etaria, fato predito na literatura. Observamos tambem uma diminuicao nos valores de dispersao no pos-operatorio a niveis normais, indicando recuperacao dos meios opticos apos a cirurgia. Nao foram observadas diferencas significativas entre a populacao brasileira e a argentina, nem entre participantes de olhos de cores diferentes, o que vai contra a literatura, que prediz valores maiores de dispersao para olhos claros / Purpose: Evaluate retinal straylight in healthy eyes of people living in Sao Paulo and San Miguel de Tucuman, Argentina, and in patients of refractive surgery (LASIK), using the psychophysical method Compensation Comparison as presented in the Oculus C-Quant (Oculus Optikgerate, Germany). Methods: Oculus C-Quant was used to access the retinal straylight, as developed by Franssen, Coppens and van den Berg (IOVS, 47:768,2006), using a psychophysical method to quantify retinal straylight. For this study 261 subjects were tested, both sexes, ages between 10 and 78 years old, arranged in three experimental groups: group 1, n=209, age: 33,74 } 15,87 years, all living in Sao Paulo; group 2: n=29, age: 39,72}13,28 years, living in San Miguel de Tucuman, Argentina; group 3: n=23, age: 30,52}4,94 years, living in Sao Paulo and all refractive surgery (LASIK) patients. Each subject performed the test 6 times, 3 times each eye (alternating eyes), and the straylight values were compared between measures on the same subject and with the updated standard norms of the C-Quant. Group 3 subjects were tested three times, one previously the refractive surgery, one 60 days after surgery and the last one 120 days after surgery. Results: As a result, there were no statistic differences between measures on the same subject and when comparing different subjects same age (Paired Measures ANOVA, group 1, t=1,501, Wilcoxon, group 2: Z=-2,422, p-level 0,015), and there were high correlation between right and left eyes for all three groups (group 1: Pearson: R=0,7101, group 2: Spearman = 0,942, group 3: Spearman = 0,958). The standard norms of the C-Quant were also compared with the straylight values for the subjects in all three groups, and also there was no statistical significance between them. At group 3, the pre-op results were slightly higher than the post-op (both 60 and 120 days), but no statistical difference was found. Discussion: The straylight values obtained were similar to those on the updated standard norms of the test, due mainly to data scatter and therefore high standard deviation values. Among the younger subjects (ages between 10 and 20 years) the straylight values also vary and didnt remain constant as predicted by literature. At group 3, straylight values on postop (60 and 120 days) were similar those from updated norms, indicating a recovery of the eye media after surgery. No statistical differences were found between Brazilian and Argentinean subjects, neither between dark and light eyes subjects, although the literature predicts higher straylight values for light eyes

O objetivo geral deste estudo foi avaliar a dor crônica advinda de diferentes tipos de cânceres. Os objetivos específicos foram descrever as características sociais dos participantes, caracterizar a dor percebida por meio de indicadores específicos e identificar os 10 descritores de dor crônica de maior e menor atribuição conforme a percepção da amostra. Participaram do estudo 45 mulheres com câncer de mama, 45 homens com câncer de próstata e 60 indivíduos de ambos os sexos com câncer de sistema digestivo. Para a mensuração da dor foram utilizados os 50 descritores de dor crônica que compõem a Escala Multidimensional de Avaliação de Dor (EMADOR), utilizando-se o método psicofísico de estimação de categorias. Os resultados da caracterização social das 3 amostras foram: a média de idade foi de 60 anos, 54% eram do gênero masculino, 58,7% casados, 65,3% pertencentes à religião católica e 50,6% tinham ensino fundamental completo. Na caracterização da dor foi evidenciado que, referente ao sítio primário do tumor, 30% estavam localizados na mama, 30% na próstata e 14,7% no estômago. O início da queixa dolorosa ocorreu em 40,7% dos participantes antes do diagnóstico da doença, 52,7% relataram somente 1 sítio de dor e 55,4% relataram que a mesma era intermitente. A intensidade da dor atribuída nas 3 amostras, considerando a média aritmética, demonstrou que os participantes com tumores de sistema digestivo reportaram os maiores escores (7,58 ± 2,59) e 26,6% desta amostra relataram escores acima de 8 para todos os descritores apresentados. Na avaliação dos descritores 10 descritores de maior atribuição foi observado que, 5 estavam presentes nas 3 amostras: -dolorosa?, -desconfortável?, -chata?, -desagradável? e o descritor -incômoda?, o qual foi o mais atribuído tanto pelos participantes com câncer de sistema digestivo quanto pelos participantes com câncer de próstata, demonstrando a similaridade da linguagem da dor nos diferentes grupos. Sobre a dimensão dos descritores de maior atribuição nas 3 amostras houve predomínio de descritores de dor crônica que caracterizaram a dimensão afetiva (50%), seguido pelos de dimensão cognitiva (26,6%) e pelos de dimensão sensitiva (23,3%). Concluímos que, mesmo sendo a dor oncológica um fenômeno considerado individual, multidimensional com comprometimento em diversos domínios da vida, a sua linguagem apresenta semelhança independente do sítio do tumor e do gênero e a dimensão afetiva da dor deve ser melhor explorada nas avaliações clínicas. / The aim general of this study was to evaluate chronic pain arising from different types of cancers. The specific objectives were to describe the social characteristics of the participants, to characterize the pain perceived by specific indicators and descriptors to identify the 10 major and minor award chronic cancer pain as perceived in the sample. The study included 45 women with breast cancer, 45 men with prostate cancer and 60 individuals of both sexes with cancers of the digestive system. For the measurement of pain were used 50 descriptors of chronic pain comprising the Multidimensional Pain Evaluation Scale (EMADOR), using the psychophysical method of category estimation. The results of the social characterization of the 3 samples were mean age was 60 years, 54% were male, 58.7% married, 65.3% belonging to the Catholic area and 50.6% had completed elementary education as schooling. The characterization of pain was evident that, for the primary tumor site 30% were located in the breast, prostate 30% and 14.7% in the stomach. The onset of pain complaint occurred in 40.7% of the participants before the diagnosis of disease, 52.7% reported only one site of pain and 55.4% reported that it was intermittent. Pain intensity given in three samples, considering the arithmetic mean, showed that participants with tumors of the digestive system report higher scores (7.58 ± 2.59) and 26.6% of this sample reported scores above average in 8 arithmetic mean of all the descriptors presented. In the evaluation of the descriptors was seen observed that among the 10 descriptors with higher scores, five were present in three samples: \"painful,\" \"uncomfortable\", \"boring,\" \"unpleasant,\" and the descriptor \"incommode? that was the longer assigned by both the participants with cancer of the digestive system and by the participants with prostate cancer, demonstrating the similarity of the language of pain in different groups. The dimension of descriptors with higher scores in three groups, there was a predominance of chronic pain descriptors that characterize the affective dimension (50%), followed by the cognitive dimension (26.6%) and size sensitive (23.3%). We conclude that even though cancer pain phenomenon considered an individual, multidimensional impairment in several areas of life, their language has similarities regardless of tumor site and gender, and affective dimension of pain should be further explored in the clinical ratings.

Conceitos e fenômenos subjetivos, como a dor, sempre foram difíceis de serem medidos com precisão. A metodologia psicofísica, especialmente os procedimentos de estimativa de magnitude desenvolvidos por S.S. Stevens (1950), tem contribuído para o desenvolvimento de técnicas, para a criação de instrumentos, para escalonar fenômenos subjetivos. O objetivo do trabalho foi de construir uma escala psicofísica de medida da dor, utilizando julgamentos subjetivos de dor provocada por diferentes eventos. O trabalho foi realizado com 40 sujeitos adultos (30 mulheres e 10 homens) com idades entre 20 e 79 anos, para o grupo experimental e com 24 sujeitos do grupo controle com características de sexo, faixa etárias, estado conjugal e escolaridades semelhantes às do grupo experimental. Todos os sujeitos do grupo experimental eram doentes com dor crônica que se encontrava em tratamento, no ambulatório de dor da Clínica Neurológica do Instituto Central do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo. Investigou-se a concordância dos julgamentos obtidos entre o grupo experimental (com dor) e o controle (sem dor), procurando-se averiguar se existe ou não concordâncias entre os grupos, no que diz respeito à forma de avaliação da dor. Os dados coletados foram obtidos mediante entrevistas individuais, em que os sujeitos faziam julgamentos da magnitude de cada evento doloroso apresentado. Para obter uma escala objetiva de dor, utilizou-se de três listas com três conjuntos distintos de eventos dolorosos: dores do cotidiano (dor de cabeça, dor nas costas, etc.), dores por doenças físicas (lombalgia, câncer, etc.), dores por eventos dolorosos de vida ou eventos psicossociais (morte de filho, diagnóstico grave, perda de emprego, etc.). A partir dessas estimativas da sensação da dor, procurou-se encontrar a magnitude física da dor estimada, aplicando-se a função de Stevens (S=kIn). Os resultados permitiram observar que existe coerência entre os sujeitos desta população, nos julgamentos da magnitude do fenômeno doloroso, sendo possível se construir uma escala geral de dor a partir desses julgamentos. O conjunto de dores no qual houve maior correlação foi o de dores do cotidiano. Trata-se de situações que a maioria das pessoas conhece e já experienciou, encontrando, portanto, maior facilidade para dimensionar e estimar a magnitude. Por serem as dores do cotidiano, situações já vivenciadas, acredita-se que estas formam o conjunto de dores mais confiáveis para serem utilizadas numa escala geral de dor. / Concepts and subjective phenomena such as pain have always been difficult to measure accurately. The psychophysical methodology, mainly the magnitude estimation method developed by S.S. Stevens (1950), provides techniques for the development of precise scaling instruments for subjective phenomena. The present study intends to build a tool for the measure of pain using the psychophysical method of subjective magnitude estimation. Forty subjects (30 women and 10 men) with ages between 20 and 79 years were selected for the experimental group and twenty-four subjects with similar characteristics (sex, age, education and marital status) for the control group. Subjects from the experimental group were under treatment in the Pain Clinic of the University of São Paulo (Clínica Neurológica do Instituto Central do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo). The differences between the judgements made by the experimental group (with pain) and the judgements made by the control group (without pain) were studied in order to investigate if those groups had different ways of estimating the pain aroused by different painful situations. Data was collected individually by means of written forms. Three different forms were used for each subject containing three different sets of painful situations grouped as follows: pain due to common situations (headache, back pain, a.s.o.); pain due to severe illness (back pain, cancer, a.s.o); pain aroused by emotional or psychosocial situations (death of the son/daughter, diagnostic of severe illness, lost of the job, a.s.o.). From these judgement, the physical magnitude of the pain was calculated using the reverse of the psychophysical function of S. S. Stevens (S=kIn). The results demonstrated that there is agreement between the magnitude judgements of pain by both groups, making it possible to construct a pain-measuring tool by this means. Highest correlation was obtained for pain due to common situations (r=0,896), probably because most of the subjects had experienced these situations before and could give an accurate estimation of the aroused pain. It is concluded, that a pain-measuring tool should use these kind of painful situations as references for the pain felt by the patients.

A opacificação do cristalino presente ao nascimento ou nos primeiros meses de vida é denominada de Catarata Congênita (CC). As primeiras semanas de vida são importantes no desenvolvimento visual, já que há diferença significativa no desempenho visual de crianças que passaram pela cirurgia até seis semanas de vida (com melhor desempenho visual) em relação às crianças que realizaram a cirurgia após seis semanas de vida. Crianças que tiveram privação visual durante a primeira infância por catarata bilateral apresentam redução da visão espacial. O objetivo deste trabalho foi verificar o impacto na Função de Sensibilidade ao Contraste (FSC) em crianças de tratamento cirúrgico de Catarata Congênita, durante a fase de desenvolvimento visual. Foram avaliados três grupos: 11 crianças do grupo controle (média idade =6,83; DP=1,38), 9 crianças do grupo CC (média idade =6,87; DP=2,03) e 15 indivíduos adultos (média idade =27,63; DP=4,16). Foi utilizado o software Metropsis para avaliação da sensibilidade ao contraste de luminância de grade senoidal nas frequências espaciais de 0,2 cpg; 0,5 cpg; 1,0 cpg; 2,0 cpg; 4,2 cpg e 8,9 cpg e luminância média de 34,4 cd/m². Houve redução em toda a curva de sensibilidade ao contraste (SC) do grupo CC quando comparado ao grupo controle e não houve relação entre o tempo de privação e a redução da SC / The opacification of the lens present at birth is called Congenital Cataract (CC). The first weeks of life are important in visual development since there is not any significant difference in visual performance of children who had surgery within six weeks of life (with better visual performance) compared with children who underwent surgery after this period. Children who have visual deprivation during infancy due to bilateral cataracts have reduced spatial vision. The aim of this study was to assess the impact on Contrast Sensitivity Function (CSF) in children with Congenital Cataract surgery during the visual development age range. We evaluated three groups: 11 control children (mean age = 6.83, SD = 1.38), 9 children in the CC group (mean age = 6.87, SD = 2.03) and 15 adults (mean age = 27.63, SD = 4.16). Metropsis software was used to evaluate sensitivity to luminance contrast of the sinusoidal grating spatial frequencies of 0.2 cpd, 0.5 cpd, 1.0 cpd, 2.0 cpd, 4.2 cpd and 8.9 cpd with an average luminance of 34.4 cd / m². There was a reduction in the contrast sensitivity function (CSF) of the CC group compared to the control group and there was no correlation between the duration of deprivation and the impairment in the SC

Visual target acquisition is performed during several daily tasks, often requmng time¬dependent behavioural responses towards stimuli. Information processing during such tasks is subject to bottom-up as well top-down influences, which results in an integrated processing mechanism. It follows that if the underlying neural mechanisms can be elucidated, behaviour towards visual stimuli will be better understood, allowing for the development of visual environments that facilitates desired behavioural response. The current study aimed to develop a systems-level approach according to which the mechanisms that underlie visual target acquisition can be understood, by interpreting psychophysical data in terms of the structural and functional organization of the visual system. Empirical work entailed psychophysical experiments and elaborated on previous studies regarding conspicuity areas around and response time towards visual targets. The rationale was that these two measures can be used as an indication of the conspicuity of a target within a specific background, which in turn can be related to the nature of information processing during a target acquisition task. Results showed that a proportional relationship exists between the size of the conspicuity area and a target's perceived conspicuity, with the most conspicuous targets being associated with the largest conspicuity areas. Response time trends showed that target detectability at different positions within the conspicuity area is equal, but that detection performance at positions outside the conspicuity area is greatly influenced by the nature of the background surrounding the target. Interpretation of the results points to the importance of visual attention during target acquisition, which in turn is supported by the structural and functional organization of the visual system. Findings from the psychophysical study presented here, along with the proposed framework of information processing, emphasise that behavioural outcome during visual target acquisition cannot be explained without considering the structural and functional organization of the visual system. / Dissertation (MSc (Human Physiology))--University of Pretoria, 2006. / Physiology / unrestricted

Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Motion perception is critical to navigation within the environment and has been studied primarily in the unisensory visual domain. However, the real world is not unisensory, but contains motion information from several modalities. With the billions of sensory stimuli our brains receive every second, many complex processes must be executed in order to properly filter relevant motion related information. In transparent motion, when there are more than one velocity fields within the same visual space, our brains must be able to separate out conflicting forms of motion utilizing environmental cues. But even in unimodal visual situations, one often uses information from other modalities for guidance. We studied this phenomenon in psychophysics with cross-modal (visual and auditory) cues and their role in detecting transparent motion. To further examine these ideas, using a single subject we explored the spatiotemporal characteristics of the neural substrates involved in utilizing these different cues in motion detection during magnetoencephalography (MEG). Another dimension of motion perception is involved when the observer is moving and, therefore, must deal with self-motion and changing environmental cues. To better understand this idea we used a visual search psychophysical task that has been well studied in our lab to determine whether subjects use a simple relative-motion computation to detect moving objects during self-motion or whether they utilize scene context when detecting object motion and how this might change when given a cross-modal auditory cue. To find the spatiotemporal neural characteristics involved in this process, functional magnetic resonance imaging (fMRI) and MEG were performed separately in elderly subjects (healthy and a stroke patient) and compared with previous studies of young healthy subjects doing the same task. / 2031-01-01

The brain is highly efficient at processing complicated patterns of information, filtering ambiguous input it receives from the senses. Competition between these representations is regulated by multiple mechanisms, together forming a coherent percept of our environment. One approach to regulating incoming sensory information is the recruitment of a canonical neural computation: divisive normalization. Another approach to further steer processing towards behaviorally relevant goals is by means of cognitive influences. In this project I examined the degree to which cognitive processes interact with normalization to shape human visual perception. First, a set of fMRI experiments (Exps 1-3: n=6) examined the hypothesis that attention-driven gain modulation within human visual cortex is dependent on the magnitude of normalization. Leveraging the fact that normalization is modulated by similarity of visual features, my results illustrated that attentional modulation of BOLD responses is larger when visual cortex is put under stronger normalization. These results suggest that the degree to which a subpopulation exhibits normalization plays a role in dictating its potential for attentional benefits. Second, I examined how attention modulates visual population responses (n=7). Neurons within visual cortex exhibit a well-characterized relationship between stimulus intensity and the neural response, known as a contrast response function. While animal and psychophysical studies suggest that attention improves visual processing by multiplicatively increasing the gain of the contrast response, human fMRI studies instead report additive attentional effects, which act independently of stimulus contrast. Consistent with prior work, I demonstrated using a fMRI model-based analysis that attentional modulation indeed appears additive within early visual cortex. Lastly, I examined whether perceptual and memory representations are distinct from one another (Exp 1: n=12, Exp 2: n=10). A prevailing theory posits that the retention of visual memories involves maintenance of information within visual cortices. I tested the degree to which representations in visual memory undergo contrast normalization, by leveraging a classic demonstration: center- surround suppression. I obtained psychophysical measurements of perceived contrast and found robust normalization in perception, yet no signature of normalization occurring between visual memory representations. Taken together, this work helps unravel the underlying neural mechanisms by which cognitive influences shape visual perception.