What information is used by the visual system to detect patterns? A standard model hypothesizes that both spatial frequency and orientation information are processed by independent channels, meaning there is no summation among channels. Despite consensus among researchers on how the visual system sums spatial frequency and orientation information there are data in the literature (Kersten, 1987) that ostensibly contradict the standard model. To resolve this conflict, we measured the efficiency of spatial frequency and orientation of filtered noise. To learn what information the visual system uses when detecting filtered noise, we applied a technique that can determine the information used to detect and discriminate filtered visual noise. In Chapter 2 the detection of spatial frequency filtered noise is not only efficient but remains so with stimulus uncertainty and extremely brief (10ms) stimulus duration. When the spatial frequency channel used was measured, we found a fixed bandwidth channel as the spatial frequency of the pattern was increased. To test the standard model, we implemented simulations of the standard model and contrary to the interpretation, the standard model could predict detection of spatial frequency filtered noise. Chapter 3 used spatial frequency filtered noise to relate the detection and discrimination of filtered visual noise. A simple rule relates what information observers use to detect and discriminate spatial frequency filtered noise. Chapter 4 extends the work of Chapter 2 to orientation information and found that orientation filtered noise is detected efficiently. We again measured what information observers used and found that, unlike SF filtered noise, observers use orientation in a flexible or adjustable manner. / Thesis / Doctor of Philosophy (PhD)

Over the past several decades, experimental studies of the organisation of spatial frequency (SF) preference in mammalian visual cortex (V1) have reported a wide variety of conflicting results. A consensus now appears to be emerging that in the superficial layers SF is mapped continuously across the cortical surface. However, other evidence suggests that SF may differ systematically with cortical depth, at least in layer 4, where the magnocellular (M) and parvocellular (P) pathway afferents terminate in different sublaminae. It is not yet clear whether the topographic organisation for SF observed in the superficial layers is maintained throughout the input layers as well, or whether there is a switch from a laminar to a topographic organisation along the vertical dimension in V1. I present results from two alternative self-organising computational models of V1 that receive natural image inputs through multiple SF channels in the LGN, differing in whether they develop laminar or topographic organisation in layer 4. Both models lead to topographic organisation for orientation (OR) and SF preference in upper layers, consistent with current experimental evidence. The results suggest that in either case separate sub-populations of neurons are required to obtain a wide range of SF preference from Hebbian learning of natural images. These models show that a laminar organisation for SF preference can coexist with a topographic, columnar organisation for orientation, and that the columnar organisation for orientation is dependent upon inter-laminar feedback. These results help clarify and explain the wide range of SF results reported in previous studies.

Retinal blur experienced by myopes during near work has been linked to myopia development and progression. Whether poor responses to blur signals are due to poor perceptual blur sensitivity (subjective depth of focus), poor neural accommodation responses (objective depth of focus) to blur or optical differences such as higher order aberrations making blur detection difficult is yet unclear. This study investigates whether myopes respond to blur differently compared to emmetropes and whether filtering spatial frequencies in reading text influence accommodation responses. Accommodative functions were investigated using spatial frequency filtered text targets of two different sizes (N10 and N20). Monocular objective depth of focus (DOF), accommodative microfluctuations, and dynamic accommodation were measured. Subjective DOF after cycloplegia was also recorded with the same targets. Higher order aberration measurements explored optical contributions to blur. Peripheral refraction and accommodative lag were also measured to consider how in combination they might increase peripheral retinal blur for near tasks. Results showed that myopes demonstrated larger subjective DOF. Subjective DOF was larger when viewing the peak text spatial frequency in both refractive error groups. The optimum focus was more myopic for text peak spatial frequencies. Levels of spherical aberration were correlated with the point of optimum focus. Objective DOF and accommodative microfluctuations were larger in myopes when viewing the peak text spatial frequencies. Dynamic accommodation showed that while myopes were not poorer at initiating accommodation responses they had longer positive response times. Accommodative lag, although not different in myopes, increases the peripheral hyperopic blur experienced for near tasks. Conclusion: Myopes were poorer at using retinal blur cues to refine accommodation responses especially when viewing peak text spatial frequencies. Larger positive response times, DOF and accommodative microfluctuations in myopes resulted in accommodative error and hyperopic blur for near tasks. Spherical aberration, previously thought to provide a myopigenic stimulus, was not different between refractive groups and is unlikely to be large enough to enhance DOF during naturalistic viewing. Blur adaptation studies might consider using peak text spatial frequencies as adaptation targets to reduce accommodation differences in myopes and emmetropes. Optical treatment strategies aimed at correcting peripheral refraction to control myopia should consider the combined effect of accommodative lag which increases levels of hyperopic peripheral blur experienced by myopes.

The purpose of this thesis was to determine whether asymmetry in metric and topological spatial judgments could be attributed to the spatial frequency of the stimulus or the size of the attended receptive field. A left hemisphere advantage has been found for topological judgments and a right hemisphere advantage for metric judgments. This asymmetry has been attributed to asymmetrical processing of input conditions, namely size of attended receptive field (called the attentional bin) and spatial frequency of the stimulus. The larger a stimulus, the higher the proportion of low spatial frequencies, so large stimuli are thought to facilitate the extraction of lower spatial frequencies while small stimuli are thought to facilitate the extraction of higher spatial frequencies. A left hemisphere advantage has been reported for high spatial frequencies and small attentional bins and a right hemisphere advantage has been reported for low spatial frequencies and large attentional bins. A method for pitting asymmetrically distributed input conditions against each other using asymmetrically distributed tasks was developed. Three studies were conducted. In the first study, a lack of hemisphere effects suggested bilateral processing of the stimuli. Using an eye tracker, participants were easily able to saccade to the stimulus as was shown in Experiment 2. In Experiment 3, effective exposure duration was reduced so that unilateral viewing was ensured. Under these conditions, bin size and spatial frequency were not dissociable due to a lack of hemisphere effects for spatial frequency and because of task dependency for bin size and spatial frequency processing. Although the assumptions of the double double dissociation were not met, asymmetry in spatial judgments under conditions comparable to those used by Kosslyn et al.(1989) was attributable to a right hemisphere advantage for processing through small attentional bins.

The purpose of this thesis was to determine whether asymmetry in metric and topological spatial judgments could be attributed to the spatial frequency of the stimulus or the size of the attended receptive field. A left hemisphere advantage has been found for topological judgments and a right hemisphere advantage for metric judgments. This asymmetry has been attributed to asymmetrical processing of input conditions, namely size of attended receptive field (called the attentional bin) and spatial frequency of the stimulus. The larger a stimulus, the higher the proportion of low spatial frequencies, so large stimuli are thought to facilitate the extraction of lower spatial frequencies while small stimuli are thought to facilitate the extraction of higher spatial frequencies. A left hemisphere advantage has been reported for high spatial frequencies and small attentional bins and a right hemisphere advantage has been reported for low spatial frequencies and large attentional bins. A method for pitting asymmetrically distributed input conditions against each other using asymmetrically distributed tasks was developed. Three studies were conducted. In the first study, a lack of hemisphere effects suggested bilateral processing of the stimuli. Using an eye tracker, participants were easily able to saccade to the stimulus as was shown in Experiment 2. In Experiment 3, effective exposure duration was reduced so that unilateral viewing was ensured. Under these conditions, bin size and spatial frequency were not dissociable due to a lack of hemisphere effects for spatial frequency and because of task dependency for bin size and spatial frequency processing. Although the assumptions of the double double dissociation were not met, asymmetry in spatial judgments under conditions comparable to those used by Kosslyn et al.(1989) was attributable to a right hemisphere advantage for processing through small attentional bins.

No / Current models of short-term visual perceptual memory invoke mechanisms that are closely allied to low-level perceptual discrimination mechanisms. The purpose of this study was to investigate the extent to which human visual perceptual memory for spatial frequency is based upon multiple, spatially tuned channels similar to those found in the earliest stages of visual processing. To this end we measured how performance on a delayed spatial frequency discrimination paradigm was affected by the introduction of interfering or ‘memory masking’ stimuli of variable spatial frequency during the delay period. Masking stimuli were shown to induce shifts in the points of subjective equality (PSE) when their spatial frequencies were within a bandwidth of 1.2 octaves of the reference spatial frequency. When mask spatial frequencies differed by more than this value, there was no change in the PSE from baseline levels. This selective pattern of masking was observed for different spatial frequencies and demonstrates the existence of multiple, spatially tuned mechanisms in visual perceptual memory. Memory masking effects were also found to occur for horizontal separations of up to 6 deg between the masking and test stimuli and lacked any orientation selectivity. These findings add further support to the view that low-level sensory processing mechanisms form the basis for the retention of spatial frequency information in perceptual memory. However, the broad range of transfer of memory masking effects across spatial location and other dimensions indicates more long range, long duration interactions between spatial frequency channels that are likely to rely contributions from neural processes located in higher visual areas. / V.N. supported by a Ph.D. studentship funded by the Federation of Ophthalmic and Dispensing Opticians.

No description available.

O sinal de entrada na retina é decomposto em termos de frequência espacial (FE), variações periódicas de luminância ao longo do espaço. Existe vasta literatura sobre o processamento de FE no córtex visual primário. No entanto, não se sabe ao certo como esta informação sensorial básica é processada e integrada numa visão de alto nível. Esta tese aborda este tema ao investigar lateralidade cerebral, tempo de processamento e contexto cognitivo em três diferentes seções com objetivos específicos. Estas seções investigaram comportamentalmente visão de alto nível tendo a face humana como estímulo, dado sua relevância biológica e social. Na primeira seção (Theoretical Review), uma revisão apresenta estudos clínicos e neuropsicológicos que mostram áreas cerebrais envolvidas na percepção de faces e como os hemisférios esquerdo e direito realizam um processamento holístico e analítico baseado em informações de FEs. A especialização hemisférica de FE no reconhecimento de faces é então revisada e discutida. Concluiu-se que assimetrias sensoriais podem ser a base para assimetrias cognitivas de alta ordem. Ademais, foi destacado a influência do tempo de processamento. Na segunda seção (Study 1), foi investigado por método psicofísico a lateralidade de baixas e altas FEs no reconhecimento de faces em diferentes tempos de exposição. Faces com filtragem de FE foram apresentadas em campo visual dividido em alta e baixa restrição temporal em duas tarefas: reconhecimento facial (Experimento 1) e reconhecimento do sexo facial (Experimento 2). No Experimento 1, informações faciais de baixas e altas FEs foram mais eficientemente processadas no hemisfério direito e esquerdo, respectivamente, sem efeito do tempo de exposição das faces. Os resultados do Experimento 2 mostraram uma assimetria do hemisfério direito para baixas FEs em baixa restrição temporal. Conclui-se que o processamento de altas e baixas FEs é lateralizado nos hemisférios cerebrais no reconhecimento de faces. No entanto, a contribuição de altas e baixas FEs é dependente da tarefa e do tempo de exposição. Na terceira seção (Study 2) foi investigado qual estratégia temporal, coarse-to-fine (de baixas para altas FEs) ou fine-to-coarse, cada hemisfério cerebral utiliza para integrar informação de FE de faces humanas numa tarefa de categorização facial homem-mulher. Sequências dinâmicas breves coarse-to-fine e fine-to-coarse de faces foram apresentadas no campo visual esquerdo, direito e central. Os resultados do tempo de resposta e do score de eficiência invertida mostraram uma prevalência geral de um processamento coarse-to-fine, independente do campo visual de apresentação. Ainda, os dados da taxa de erro ressaltam o processamento coarse-to-fine realizado pelo hemisfério direito. No geral, esta tese fornece insights sobre assimetria cerebral funcional, integração de alto nível e curso temporal do processamento de FEs, principalmente para aqueles interessados na percepção de faces. Também foi mostrado que operações lateralizadas, tarefa-dependente e coarse-to-fine podem coexistir e interagir no cérebro para processar informação de FE. / Retinal input is decomposed in terms of spatial frequency (SF), i.e., periodic variations of luminance through space. There is extensive literature on the processing of SF in the primary visual cortex. However, it is still unclear how SF information is processed and integrated in high-level vision. This thesis addressed this issue in terms of laterality effects, processing time-course, and the cognitive context in three different sections with specific purposes. These sections behaviorally tackle high-level vision using human faces as stimuli due to their biological and social relevance. In the first section (Theoretical Review) a literature review presented clinical and neurophysiological studies that show brain areas that are involved in face perception and how the right and left hemispheres perform holistic and analytic processing, depending on SF information. The SF hemispheric specialization in face recognition is then reviewed and discussed. Our conclusion is that functional sensorial asymmetries may be the basis for high-level cognitive asymmetries. In addition, we highlighted the role of the processing time. In the second section (Study 1), we psychophysically investigated laterality of low and high SF in face recognition at different exposure times. The SF filtered faces were presented in a divided visual field at high and low temporal constraint in two tasks: face recognition (Experiment 1) and face gender recognition (Experiment 2). In Experiment 1, low and high SF facial information were more efficiently processed in the right and in the left hemisphere, respectively, with no effect of exposure time. In Experiment 2, results showed a right hemisphere asymmetry for low SF faces at low temporal constraint. We concluded that the processing of low and high SF is lateralized in the brain hemispheres for face recognition. However, low and high SF contribution is dependent on the task and the exposure time. In the third section (Study 2), we aimed to investigate which temporal strategy, i.e., coarse-to-fine (from low to high SF) or fine-to-course, each brain hemisphere performs to integrate SF information of human faces in a male-female categorization task. Coarse-to-fine and fine-to-course brief dynamic sequences of faces were presented in the left, right and central visual field. Results of the correct response time and the inverse efficiency score showed an overall advantage of coarse-to-fine processing, irrespective of the visual field of presentation. Data of the error rate also highlights the role of the right hemisphere in the coarse-to-fine processing. All in all, this thesis provided some insights on functional brain asymmetry, high-level integration, and processing time-course of SF information, mainly for those interested in face perception. It was also shown that lateralized, diagnostic-oriented, and coarse-to-fine operations may coexist and interact in the human brain to process SF information.

Mice have emerged as a popular model of cortical visual processing due to their genetic manipulability. Compared to traditional animal models of visual processing there is less research describing the visual system of mice. Before we can use the genetic techniques available in mice, we must examine the similarity between their visual processing, and that of common animal models used in vision research. One useful method to characterize the way information about form and motion is processed is to examine the interaction between selectivity for spatial and temporal frequency of sine-wave gratings in a given visual area. In experiment 1, we investigated spatiotemporal tuning in neurons of mouse primary visual cortex (V1). Tuning for stimulus speed can readily be extracted from the spatiotemporal profile of a neuron, and we were interested in whether recently described differences in the degree of speed tuning in mouse V1 and macaque V1 were due to methodology. We confirm that speed tuning is rare in mouse V1, demonstrating a difference between motion processing in the striate cortex of mice and macaques. In experiment 2, we examined the spatiotemporal dependence of contrast adaptation in mouse V1 neurons. Little is known about the underlying cellular mechanisms of contrast adaptation, so the mouse provides an attractive model in which to study this phenomenon. We characterized the spatial and temporal frequency dependence of contrast adaptation in mouse V1 neurons simultaneously using a dynamic contrast ramp. We found that for most mouse V1 neurons there was often a difference between the grating that elicited maximal firing, and the grating where adaptation was most pronounced, such that adaptation was usually stronger at higher spatial frequencies.

O sinal de entrada na retina é decomposto em termos de frequência espacial (FE), variações periódicas de luminância ao longo do espaço. Existe vasta literatura sobre o processamento de FE no córtex visual primário. No entanto, não se sabe ao certo como esta informação sensorial básica é processada e integrada numa visão de alto nível. Esta tese aborda este tema ao investigar lateralidade cerebral, tempo de processamento e contexto cognitivo em três diferentes seções com objetivos específicos. Estas seções investigaram comportamentalmente visão de alto nível tendo a face humana como estímulo, dado sua relevância biológica e social. Na primeira seção (Theoretical Review), uma revisão apresenta estudos clínicos e neuropsicológicos que mostram áreas cerebrais envolvidas na percepção de faces e como os hemisférios esquerdo e direito realizam um processamento holístico e analítico baseado em informações de FEs. A especialização hemisférica de FE no reconhecimento de faces é então revisada e discutida. Concluiu-se que assimetrias sensoriais podem ser a base para assimetrias cognitivas de alta ordem. Ademais, foi destacado a influência do tempo de processamento. Na segunda seção (Study 1), foi investigado por método psicofísico a lateralidade de baixas e altas FEs no reconhecimento de faces em diferentes tempos de exposição. Faces com filtragem de FE foram apresentadas em campo visual dividido em alta e baixa restrição temporal em duas tarefas: reconhecimento facial (Experimento 1) e reconhecimento do sexo facial (Experimento 2). No Experimento 1, informações faciais de baixas e altas FEs foram mais eficientemente processadas no hemisfério direito e esquerdo, respectivamente, sem efeito do tempo de exposição das faces. Os resultados do Experimento 2 mostraram uma assimetria do hemisfério direito para baixas FEs em baixa restrição temporal. Conclui-se que o processamento de altas e baixas FEs é lateralizado nos hemisférios cerebrais no reconhecimento de faces. No entanto, a contribuição de altas e baixas FEs é dependente da tarefa e do tempo de exposição. Na terceira seção (Study 2) foi investigado qual estratégia temporal, coarse-to-fine (de baixas para altas FEs) ou fine-to-coarse, cada hemisfério cerebral utiliza para integrar informação de FE de faces humanas numa tarefa de categorização facial homem-mulher. Sequências dinâmicas breves coarse-to-fine e fine-to-coarse de faces foram apresentadas no campo visual esquerdo, direito e central. Os resultados do tempo de resposta e do score de eficiência invertida mostraram uma prevalência geral de um processamento coarse-to-fine, independente do campo visual de apresentação. Ainda, os dados da taxa de erro ressaltam o processamento coarse-to-fine realizado pelo hemisfério direito. No geral, esta tese fornece insights sobre assimetria cerebral funcional, integração de alto nível e curso temporal do processamento de FEs, principalmente para aqueles interessados na percepção de faces. Também foi mostrado que operações lateralizadas, tarefa-dependente e coarse-to-fine podem coexistir e interagir no cérebro para processar informação de FE. / Retinal input is decomposed in terms of spatial frequency (SF), i.e., periodic variations of luminance through space. There is extensive literature on the processing of SF in the primary visual cortex. However, it is still unclear how SF information is processed and integrated in high-level vision. This thesis addressed this issue in terms of laterality effects, processing time-course, and the cognitive context in three different sections with specific purposes. These sections behaviorally tackle high-level vision using human faces as stimuli due to their biological and social relevance. In the first section (Theoretical Review) a literature review presented clinical and neurophysiological studies that show brain areas that are involved in face perception and how the right and left hemispheres perform holistic and analytic processing, depending on SF information. The SF hemispheric specialization in face recognition is then reviewed and discussed. Our conclusion is that functional sensorial asymmetries may be the basis for high-level cognitive asymmetries. In addition, we highlighted the role of the processing time. In the second section (Study 1), we psychophysically investigated laterality of low and high SF in face recognition at different exposure times. The SF filtered faces were presented in a divided visual field at high and low temporal constraint in two tasks: face recognition (Experiment 1) and face gender recognition (Experiment 2). In Experiment 1, low and high SF facial information were more efficiently processed in the right and in the left hemisphere, respectively, with no effect of exposure time. In Experiment 2, results showed a right hemisphere asymmetry for low SF faces at low temporal constraint. We concluded that the processing of low and high SF is lateralized in the brain hemispheres for face recognition. However, low and high SF contribution is dependent on the task and the exposure time. In the third section (Study 2), we aimed to investigate which temporal strategy, i.e., coarse-to-fine (from low to high SF) or fine-to-course, each brain hemisphere performs to integrate SF information of human faces in a male-female categorization task. Coarse-to-fine and fine-to-course brief dynamic sequences of faces were presented in the left, right and central visual field. Results of the correct response time and the inverse efficiency score showed an overall advantage of coarse-to-fine processing, irrespective of the visual field of presentation. Data of the error rate also highlights the role of the right hemisphere in the coarse-to-fine processing. All in all, this thesis provided some insights on functional brain asymmetry, high-level integration, and processing time-course of SF information, mainly for those interested in face perception. It was also shown that lateralized, diagnostic-oriented, and coarse-to-fine operations may coexist and interact in the human brain to process SF information.