Thesis (Ph. D.)--New York University, School of Education. / Also on film. eContent provider-neutral record in process. Description based on print version record.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 89-108).

Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed on Sept. 3, 2009). Includes bibliographical references (p. 45-52).

While three decades of intensive cortical electrophysiology using a variety of sustained visual stimuli has made a significant contribution to many aspects of visual function, it has not supported the existence of intracortical circuit operations in cortical processing. This study investigated cortical processing by a comparison of the response of primary visual cortical neurones to transient electrical and strobe-flash stimulation. Experiments were performed on 74 anaesthetised Long Evans rats. Standard stereotaxic and extracellular electrophysiological techniques were employed. Continuous (on-line) raster plots and peri-stimulus time histograms (PSTHs) of the extracellular spikes from 81 visual cortical and 55 lateral geniculate nucleus (LGN) neurones were compiled. The strobe-flash stimuli (0.05 ms) were applied to the contralateral eye while the monopolar or bipolar electrical stimuli (0.2 ms, 80-400 μA) were applied to the ipsilateral LGN. 60 of the 81 (74%) tested cortical units were found to be responsive to visual stimuli. A distinct and consistent difference in the cortical response to the two types of transient stimuli was found: (a) Electrical stimulation evoked a prolonged period (197 ± 61 ms) of inhibition in all cortical neurones tested (n=20). This was the case even in those cortical units that were completely unresponsive to visual stimulation. The protracted inhibition was usually followed by a 100-200 ms phase of rebound excitation. (b) Flash stimulation evoked a prominent excitatory discharge (5-30 ms duration) after a latency of 30-60 ms from the onset of the stimulus (n = 59). This was followed by either moderate inhibition or return to a firing rate similar to control activity, for a maximum of 40 ms. Thereafter, cortical neurones showed a sustained increased level of activity with superimposed secondary excitatory phases. The duration of this late re-excitatory phase was 200-300 ms. In 17 of 20 (85%) tested units, the temporal profile of the cortical response to flash stimulation was modulated by small changes in the level of background illumination. In 16 of the 17 units, this sensitivity was reflected primarily as an emergence of a brief secondary inhibitory phase at the lowest level of background illumination (0 lux). Only 1 of the 17 cortical units displayed a flash-evoked primary inhibitory phase at O lux. We explored the possibility that neurones in the lateral geniculate nucleus (LGN) of the thalamus were responsible for the late phase of cortical reexcitation. 49 of the 55 (89%) LGN neurones could be classified as either of the "ON type" i.e. excited by visual stimuli, or the "OFF type" i.e. inhibited by visual stimuli. The response of ON-like LGN neurones to strobe-flash stimulation of the contralateral eye was characterised by a primary excitatory or early discharge (ED) phase after a latency of 25-40 ms. Thereafter, a 200- 400 ms period of inhibition was observed. In 57% of the sample, a rebound excitatory or late discharge (LD) phase completed the response. OFF-like LGN neurones were inhibited by the strobe-flash stimuli after a latency of 30- 35 ms. This flash-evoked inhibition was maintained for 200-400 ms. The sensitivity of the flash-evoked LGN response to the level of background illumination was tested in 11 ON-like and 10 OFF-like neurones. No sustained secondary excitatory events, as observed in visual cortical neurones, were found in any of the ON- and OFF-like LGN neurones, irrespective of the level of background illumination. In conclusion, the data show that the late re-excitatory phase evoked in cortical neurones upon strobe-flash stimulation, is not due to sustained LGN (thalamic) input. Rather, it suggests that these re-excitatory phases are due to intracortical processing of the transient stimuli. These findings emphasize the independent role of the cortex in computing the response to visual stimuli, and cast doubt on traditional theories that have emphasised the role of the thalamus in shaping cortical responses. The difference in the flash and electrically evoked cortical response suggests that even though substantial inhibition is available to the cortex, only a small fraction of this inhibitory capacity is utilised during natural stimulation.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

The aim of this study was to investigate the intra- and intermodal impact of different kinds of early sensory experience on the development of specific neural/perceptual systems. The manipulations of the rats' early experience involved a combination of early binocular deprivation through dark-rearing, somatosensory restriction through cauterization of mystacial vibrissae, and multimodal enrichment through rearing in a complex environment. Specific lesions to somatosensory (Parl) and visual (Oc2M) cortex in differentially reared animals were included in an attempt to gain further insight into the plasticity surrounding manipulations of early stimulation history. Five tasks were used to assess these effects of early rearing condition in combination with later cortical lesions. Behavioral assessment focused on the ability of the animals to encode, abstract, and remember specific relationships between stimuli within the deprived modality itself, their ability to do so with information presented in other modalities, and on the basic species specific behavior. The only effect found was a main effect for rearing condition. Basically, complex-reared rats were more competent on several of the behavioral tasks than were dark-reared rats. However, this result provided little behavioral support for ideas of modality interdependence. Dendritic proliferation is considered to be a general mechanism supporting behavioral change. The subsequent neuroanatomical assessment focused on dendritic branching of neurons in specific cortical areas thought to be most affected by early environmental manipulations. Animals that were raised in a complex environment, but had experienced early tactile restriction through cauterization of vibrissae, showed significantly more dendritic branching than animals from all other rearing conditions in all cortical areas measured. This finding is consistent with ideas of both intra- and intermodal compensation following damage to an early developing modality, as well as behavioral demand acting as a significant factor in determining the impact of early somatosensory restriction. It is reasonable to assume that anatomical changes should be manifested behaviorally. Suggestions for smaller, more restricted studies, that would be more effective in describing the behavioral impact of early manipulations of the environment, were outlined. / Arts, Faculty of / Psychology, Department of / Graduate

Orientadores: Keila Miriam Monteiro de Carvalho, Rodrigo Pessoa Cavalcanti Lira / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-22T10:04:39Z (GMT). No. of bitstreams: 1 Zimmermann_Anita_D.pdf: 2614474 bytes, checksum: 1d6ddd4b27c92b25dfed8b28ff8b7940 (MD5) Previous issue date: 2013 / Resumo: Objetivo: Avaliar a Visão Funcional de crianças de zero a 5 anos e 11 meses de idade, após diagnóstico oftalmológico de Baixa Visão, para identificar a necessidade de Estimulação Visual no grupo estudado do Serviço de Estimulação Visual/VSN/OFTALMOLOGIA/HC/FCM/UNICAMP. Materiais e Métodos: Trata-se de estudo transversal analítico, aprovado pelo Comitê de Ética em Pesquisa, nº 1025/2010. Foi utilizado instrumento de Avaliação da Visão Funcional Infantil, organizado após estudos na literatura de autores nacionais e internacionais, na busca por avaliações da visão funcional que contemplassem a necessidade do serviço. Considerando-se as diferentes faixas etárias infantis propostas neste estudo, com n = 143, ponderou-se sobre a efetividade de algumas avaliações pesquisadas, organizando-se instrumento avaliatório, com tópicos, desenvolvidos de maneira a se obter respostas visuais eficientes para determinar condutas em Estimulação Visual. O Instrumento de Avaliação da Visão Funcional Infantil foi aplicado em grupo controle, com mesmo n (n=143) para sua validação. Resultados: As afecções oftalmológicas, responsáveis pelas deficiências visuais do grupo estudado foram: Retinopatia da Prematuridade, Afecções de Nervo Óptico, Deficiência Visual Cortical, Coriorretinite Macular Infecciosa, Malformações Oculares, Catarata Infantil, Degenerações Primárias da Retina, Glaucoma Congênito, Ceratopatias e Trauma Ocular ou Orbitário. A distribuição por idades foi determinada pela proximidade de respostas visuais esperadas para cada faixa etária deste estudo. Em relação ao Desenvolvimento Neuro Psico Motor (DNPM), 44 (30%) crianças apresentavam Bom desenvolvimento Neuro Psico Motor (BDNPM) e 99 (70%) Retardo no Desenvolvimento Neuro Psico Motor (RDNPM). No grupo controle, 2 crianças (1,4%) apresentaram RDNPM. Após aplicação do Instrumento de Avaliação da Visão Funcional Infantil, Parte 1 e Parte 2 (Teste com Cartões de Teller), das 143 crianças estudadas, 107, representando 74% do total, receberam indicação para Estimulação Visual. No grupo controle, independente do DNPM, nenhuma criança recebeu indicação para estimulação visual. Conclusão: O Instrumento de Avaliação da Visão Funcional Infantil, em sua composição com o teste com Cartões de Teller, foi eficiente para determinar condutas em estimulação visual / Abstract: Objective: To evaluate the Functional Vision in children between zero and 5 years and 11 months old, after ophthalmological diagnosis of Low Vision, in order to identify the necessity of Visual Stimulation in the studied group from the Visual Stimulation Service/VSN/OPHTHALMOLOGY/HC/FCM/UNICAMP. Materials and Methods: This is a transversal analytical study, approved by the Research Ethics Committee, nº 1025/2010. It was used an Instrument for Functional Vision Evaluation for Children, organized after studies in the literature of national and international authors, in the search for functional vision evaluations which addressed the need for the service. Considering the different infant ages proposed on this study, with n = 143, the effectiveness of some evaluations surveyed were pondered, resulting in the organization of an evaluation instrument, with topics, developed in order to obtain efficient visual answers to determine Visual Stimulation conducts. The Instrument for Functional Vision Evaluation was applied in the Control Group, with similar n (n=143) for its validation. Results: The ophthalmologic diseases, responsible for the visual deficiencies of the studied group were: Retinopathy of Prematurity, Optical Nerve Disorder, Cortical Visual Deficiency, Infectious Macular Chorioretinitis, Ocular Malformations, Child Cataract, Retinal Primary Degenerations, Congenital Glaucoma, Ceratopatias and Ocular or Orbital Trauma. The age distribution was determined by the proximity of visual responses expected for each group age on this study. Regarding to the Psycho Neuro Motor Development (PNMD), 44 (30%) of the children presented Good Psycho Neuro Motor Development (GPNMD) and 99 (70%) presented Retardation of Psycho Neuro Motor Development (RPNMD). After the application of the Instrument for Functional Vision Evaluation for Children, Part 1 and Part 2 (Test with Teller Cards), on the 143 evaluated children, 107, representing 74% of the total, received indication for Visual Stimulation. In the control group, independently from the PNMD, no children has received indication for visual stimulation. Conclusion: The Instrument for Functional Vision Evaluation for Children, in its composition with the Test with Teller Cards, was efficient to identify conducts in Visual Stimulation / Doutorado / Ciencias Biomedicas / Doutora em Ciências Médicas

The luminance and colour gradients across an image are the result of complex interactions between object shape, material and illumination. Using such variations to infer object shape or surface colour is therefore a difficult problem for the visual system. We know that changes to the shape of an object can affect its perceived colour, and that shading gradients confer a sense of shape. Here we investigate if the visual system is able to effectively utilise these gradients as a cue to shape perception, even when additional cues are not available. We tested shape perception of a folded card object that contained illumination gradients in the form of shading and more subtle effects such as inter-reflections. Our results suggest that observers are able to use the gradients to make consistent shape judgements. In order to do this, observers must be given the opportunity to learn suitable assumptions about the lighting and scene. Using a variety of different training conditions, we demonstrate that learning can occur quickly and requires only coarse information. We also establish that learning does not deliver a trivial mapping between gradient and shape; rather learning leads to the acquisition of assumptions about lighting and scene parameters that subsequently allow for gradients to be used as a shape cue. The perceived shape is shown to be consistent for convex and concave versions of the object that exhibit very different shading, and also similar to that delivered by outline, a largely unrelated cue to shape. Overall our results indicate that, although gradients are less reliable than some other cues, the relationship between gradients and shape can be quickly assessed and the gradients therefore used effectively as a visual shape cue.

Precortical vision is mediated by three opponent mechanisms that combine receptoral outputs to form a luminance channel (L + M) and two chromatic channels, red-green (L/M) and blue-yellow (S/L + M). Here we ask the extent to which these basic color opponent mechanisms interact in the phenomenon of crowding, where nearby targets interfere with the processing of a central test target. The task was to identify the orientation of a Gabor patch while an annular plaid surrounded the patch. The radius of the annulus was varied in order to produce different separations of the test and flanker. The chromatic content of the Gabor and the annulus could be varied independently along the (L + M), (L/M), and (S/L + M) cardinal axes. For all targets, when the target and flanker shared the same chromaticity, performance decreased with decreasing separation of the target and annulus, i.e., a typical crowding effect was seen. When the test and flanker isolated different chromatic mechanisms, very little crowding was observed, even at the minimum separation of test target and annulus. In addition to this, intermediate chromaticities were found to produce intermediate levels of crowding. Finally, crowding effects using "half-wave rectified" stimuli suggest a locus for crowding effects beyond the level of color opponent mechanisms.

The parallel processing of information forms an important organisational principle of the primate visual system. Here we describe experiments which use a novel chromatic-achromatic temporal compound stimulus to simultaneously identify colour and luminance specific signals in the human electroretinogram (ERG). Luminance and chromatic components are separated in the stimulus; the luminance modulation has twice the temporal frequency of the chromatic modulation. ERGs were recorded from four trichromatic and two dichromatic subjects (1 deuteranope and 1 protanope). At isoluminance, the fundamental (first harmonic) response was elicited by the chromatic component in the stimulus. The trichromatic ERGs possessed low-pass temporal tuning characteristics, reflecting the activity of parvocellular post-receptoral mechanisms. There was very little first harmonic response in the dichromats' ERGs. The second harmonic response was elicited by the luminance modulation in the compound stimulus and showed, in all subjects, band-pass temporal tuning characteristic of magnocellular activity. Thus it is possible to concurrently elicit ERG responses from the human retina which reflect processing in both chromatic and luminance pathways. As well as providing a clear demonstration of the parallel nature of chromatic and luminance processing in the human retina, the differences that exist between ERGs from trichromatic and dichromatic subjects point to the existence of interactions between afferent post-receptoral pathways that are in operation from the earliest stages of visual processing.