Vitrina, design e emoção: uma investigação sobre a percepção visual feminina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Division of labor between M and P visual pathways: different visual pathways minimize joint entropy differently

Visual perception and action are strongly linked with parallel processing channels connecting the retina, the lateral geniculate nucleus, and the input layers of the primary visual cortex. Achromatic vision is provided by at least two of such channels formed by the M and P neurons. These cell pathways are similarly organized in primates having different lifestyles, including species that are diurnal, nocturnal, and which exhibit a variety of color vision phenotypes. We describe the M and P cell properties by 3D Gábor functions and their 3D Fourier transform. The M and P cells occupy different loci in the Gábor information diagram or Fourier Space. This separation allows the M and P pathways to transmit visual signals with distinct 6D joint entropy for space, spatial frequency, time, and temporal frequency. By combining the M and P impacts on the cortical neurons beyond V1 input layers, the cortical pathways are able to process aspects of visual stimuli with a better precision than it would be possible using the M or P pathway alone. This performance fulfils the requirements of different behavioral tasks.

Efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia

Purpose: To verify the efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia. Methods: The participants were 20 students from third to fifth grade of a public elementary school in Marília, São Paulo, aged from 8 years to 11 years and 11 months, distributed into the following groups: Group I (GI; 10 students with developmental dyslexia) and Group II (GII; 10 students with good academic performance). A perceptual and visual-motor intervention program was applied, which comprised exercises for visual-motor coordination, visual discrimination, visual memory, visual-spatial relationship, shape constancy, sequential memory, visual figure-ground coordination, and visual closure. In pre- and post-testing situations, both groups were submitted to the Test of Visual-Perceptual Skills (TVPS-3), and the quality of handwriting was analyzed using the Dysgraphia Scale. Results: The analyzed statistical results showed that both groups of students had dysgraphia in pretesting situation. In visual perceptual skills, GI presented a lower performance compared to GII, as well as in the quality of writing. After undergoing the intervention program, GI increased the average of correct answers in TVPS-3 and improved the quality of handwriting. Conclusion: The developed intervention program proved appropriate for being applied to students with dyslexia, and showed positive effects because it provided improved visual perception skills and quality of writing for students with developmental dyslexia.

A percepção visual visando a continuação gráfica na repetição modular do design de superfície

This article narrates from experiences in the classroom, the use of visual perception in the search for the solution of a basic problem of modular repetition, embodied by the lack of continuity in the elements that shape the design surface. Although Wong (1998) approach emphasizes the intuitive and intellectual approach as different parameters for building visual compositions, we list both as participants in the same focus, where the solution starts from the sensory stimulation.

Construção e Evidências Psicométricas de uma Escala de Avaliação da Percepção Visual

Este estudo teve como objetivo construir e conhecer os parâmetros psicométricos de um instrumento para análise da percepção visual de adultos. Para a construção da escala participaram 295 adultos saudáveis, sem déficits cognitivos ou perceptivo-visuais. Nesta etapa foi formulada uma escala tetrafatorial constituída por 20 itens que avaliam quatro dimensões referentes à percepção visual: constância da forma, figurafundo, posição e relação espacial. Para obter evidências de validade foi utilizada uma amostra de 183 voluntários com boa saúde física e mental e acuidade visual normal ou corrigida. Os dados obtidos relatam a existência de concordância interjuízes, adequação semântica e significância no teste-reteste do instrumento. Os coeficientes de fidedignidade variaram de 0,84 a 0,93. Os quatro fatores esperados foram encontrados, cada um contendo 5 itens, e juntos explicaram 57,52% da variância do constructo. O instrumento apresentou parâmetros psicométricos adequados, o que pode justificar sua utilidade em pesquisas básicas e na prática clínica.

Construção e evidências psicométricas de uma escala de avaliação da percepção visual

Este estudo teve como objetivo construir e conhecer os parâmetros psicométricos de um instrumento para análise da percepção visual de adultos. Para a construção da escala participaram 295 adultos saudáveis, sem déficits cognitivos ou perceptivo-visuais. Nesta etapa foi formulada uma escala tetrafatorial constituída por 20 itens que avaliam quatro dimensões referentes à percepção visual: constância da forma, figura-fundo, posição e relação espacial. Para obter evidências de validade foi utilizada uma amostra de 183 voluntários com boa saúde física e mental e acuidade visual normal ou corrigida. Os dados obtidos relatam a existência de concordância interjuízes, adequação semântica e significância no teste-reteste do instrumento. Os coeficientes de fidedignidade variaram de 0,84 a 0,93. Os quatro fatores esperados foram encontrados, cada um contendo 5 itens, e juntos explicaram 57,52% da variância do constructo. O instrumento apresentou parâmetros psicométricos adequados, o que pode justificar sua utilidade em pesquisas básicas e na prática clínica.

Reliability and consistency affect the integration of visual depth cues

Abstract Originalsprache (englisch) Visual perception relies on a two-dimensional projection of the viewed scene on the retinas of both eyes. Thus, visual depth has to be reconstructed from a number of different cues that are subsequently integrated to obtain robust depth percepts. Existing models of sensory integration are mainly based on the reliabilities of individual cues and disregard potential cue interactions. In the current study, an extended Bayesian model is proposed that takes into account both cue reliability and consistency. Four experiments were carried out to test this model's predictions. Observers had to judge visual displays of hemi-cylinders with an elliptical cross section, which were constructed to allow for an orthogonal variation of several competing depth cues. In Experiment 1 and 2, observers estimated the cylinder's depth as defined by shading, texture, and motion gradients. The degree of consistency among these cues was systematically varied. It turned out that the extended Bayesian model provided a better fit to the empirical data compared to the traditional model which disregards covariations among cues. To circumvent the potentially problematic assessment of single-cue reliabilities, Experiment 3 used a multiple-observation task, which allowed for estimating perceptual weights from multiple-cue stimuli. Using the same multiple-observation task, the integration of stereoscopic disparity, shading, and texture gradients was examined in Experiment 4. It turned out that less reliable cues were downweighted in the combined percept. Moreover, a specific influence of cue consistency was revealed. Shading and disparity seemed to be processed interactively while other cue combinations could be well described by additive integration rules. These results suggest that cue combination in visual depth perception is highly flexible and depends on single-cue properties as well as on interrelations among cues. The extension of the traditional cue combination model is defended in terms of the necessity for robust perception in ecologically valid environments and the current findings are discussed in the light of emerging computational theories and neuroscientific approaches.

Seeing and identifying with a virtual body decreases pain perception

Pain and the conscious mind (or the self) are experienced in our body. Both are intimately linked to the subjective quality of conscious experience. Here, we used virtual reality technology and visuo-tactile conflicts in healthy subjects to test whether experimentally induced changes of bodily self-consciousness (self-location; self-identification) lead to changes in pain perception. We found that visuo-tactile stroking of a virtual body but not of a control object led to increased pressure pain thresholds and self-location. This increase was not modulated by the synchrony of stroking as predicted based on earlier work. This differed for self-identification where we found as predicted that synchrony of stroking increased self-identification with the virtual body (but not a control object), and positively correlated with an increase in pain thresholds. We discuss the functional mechanisms of self-identification, self-location, and the visual perception of human bodies with respect to pain perception.

The neurophysiological time pattern of illusionary visual perceptual transitions: a simultaneous EEG and fMRI study

Several divergent cortical mechanisms generating multistability in visual perception have been suggested. Here, we investigated the neurophysiologic time pattern of multistable perceptual changes by means of a simultaneous recording with electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Volunteers responded to the subjective perception of a sudden change between stable patterns of illusionary motion (multistable transition) during a stroboscopic paradigm. We found a global deceleration of the EEG frequency prior to a transition and an occipital-accentuated acceleration after a transition, as obtained by low-resolution electromagnetic tomography analysis (LORETA) analysis. A decrease in BOLD response was found in the prefrontal cortex before, and an increase after the transitions was observed in the right anterior insula, the MT/V5 regions and the SMA. The thalamus and left superior temporal gyrus showed a pattern of decrease before and increase after transitions. No such temporal course was found in the control condition. The multimodal approach of data acquisition allows us to argue that the top-down control of illusionary visual perception depends on selective attention, and that a diminution of vigilance reduces selective attention. These are necessary conditions to allow for the occurrence of a perception discontinuity in absence of a physical change of the stimulus.

The feeling of fluent perception: A single experience from multiple asynchronous sources

Zeki and co-workers recently proposed that perception can best be described as locally distributed, asynchronous processes that each create a kind of microconsciousness, which condense into an experienced percept. The present article is aimed at extending this theory to metacognitive feelings. We present evidence that perceptual fluency-the subjective feeling of ease during perceptual processing-is based on speed of processing at different stages of the perceptual process. Specifically, detection of briefly presented stimuli was influenced by figure-ground contrast, but not by symmetry (Experiment 1) or the font (Experiment 2) of the stimuli. Conversely, discrimination of these stimuli was influenced by whether they were symmetric (Experiment 1) and by the font they were presented in (Experiment 2), but not by figure-ground contrast. Both tasks however were related with the subjective experience of fluency (Experiments 1 and 2). We conclude that subjective fluency is the conscious phenomenal correlate of different processing stages in visual perception.

One session of repeated parietal theta burst stimulation trains induces long-lasting improvement of visual neglect

BACKGROUND AND PURPOSE: Visual neglect is a frequent disability in stroke and adversely affects mobility, discharge destination, and length of hospital stay. It is assumed that its severity is enhanced by a released interhemispheric inhibition from the unaffected toward the affected hemisphere. Continuous theta burst transcranial magnetic stimulation (TBS) is a new inhibitory brain stimulation protocol which has the potential to induce behavioral effects outlasting stimulation. We aimed to test whether parietal TBS over the unaffected hemisphere can induce a long-lasting improvement of visual neglect by reducing the interhemispheric inhibition. METHODS: Eleven patients with left-sided visual neglect attributable to right hemispheric stroke were tested in a visual perception task. To evaluate the specificity of the TBS effect, 3 conditions were tested: 2 TBS trains over the left contralesional posterior parietal cortex, 2 trains of sham stimulation over the contralesional posterior parietal cortex, and a control condition without any intervention. To evaluate the lifetime of repeated trains of TBS in 1 session, 4 trains were applied over the contralesional posterior parietal cortex. RESULTS: Two TBS trains significantly increased the number of perceived left visual targets for up to 8 hours as compared to baseline. No significant improvement was found with sham stimulation or in the control condition without any intervention. The application of 4 TBS trains significantly increased the number of perceived left targets up to 32 hours. CONCLUSIONS: The new approach of repeating TBS at the same day may be promising for therapy of neglect.

Relationship between threshold and suprathreshold perception of position and stereoscopic depth.

We seek to determine the relationship between threshold and suprathreshold perception for position offset and stereoscopic depth perception under conditions that elevate their respective thresholds. Two threshold-elevating conditions were used: (1) increasing the interline gap and (2) dioptric blur. Although increasing the interline gap increases position (Vernier) offset and stereoscopic disparity thresholds substantially, the perception of suprathreshold position offset and stereoscopic depth remains unchanged. Perception of suprathreshold position offset also remains unchanged when the Vernier threshold is elevated by dioptric blur. We show that such normalization of suprathreshold position offset can be attributed to the topographical-map-based encoding of position. On the other hand, dioptric blur increases the stereoscopic disparity thresholds and reduces the perceived suprathreshold stereoscopic depth, which can be accounted for by a disparity-computation model in which the activities of absolute disparity encoders are multiplied by a Gaussian weighting function that is centered on the horopter. Overall, the statement "equal suprathreshold perception occurs in threshold-elevated and unelevated conditions when the stimuli are equally above their corresponding thresholds" describes the results better than the statement "suprathreshold stimuli are perceived as equal when they are equal multiples of their respective threshold values."

The Neuroscience of Visual Hallucinations

Each year, some two million people in the United Kingdom experience visual hallucinations. Infrequent, fleeting visual hallucinations, often around sleep, are a usual feature of life. In contrast, consistent, frequent, persistent hallucinations during waking are strongly associated with clinical disorders; in particular delirium, eye disease, psychosis, and dementia. Research interest in these disorders has driven a rapid expansion in investigatory techniques, new evidence, and explanatory models. In parallel, a move to generative models of normal visual function has resolved the theoretical tension between veridical and hallucinatory perceptions. From initial fragmented areas of investigation, the field has become increasingly coherent over the last decade. Controversies and gaps remain, but for the first time the shapes of possible unifying models are becoming clear, along with the techniques for testing these. This book provides a comprehensive survey of the neuroscience of visual hallucinations and the clinical techniques for testing these. It brings together the very latest evidence from cognitive neuropsychology, neuroimaging, neuropathology, and neuropharmacology, placing this within current models of visual perception. Leading researchers from a range of clinical and basic science areas describe visual hallucinations in their historical and scientific context, combining introductory information with up-to-date discoveries. They discuss results from the main investigatory techniques applied in a range of clinical disorders. The final section outlines future research directions investigating the potential for new understandings of veridical and hallucinatory perceptions, and for treatments of problematic hallucinations. Fully comprehensive, this is an essential reference for clinicians in the fields of the psychology and psychiatry of hallucinations, as well as for researchers in departments, research institutes and libraries. It has strong foundations in neuroscience, cognitive science, optometry, psychiatry, psychology, clinical medicine, and philosophy. With its lucid explanation and many illustrations, it is a clear resource for educators and advanced undergraduate and graduate students.

Cathodal HD-tDCS on the right V5 improves motion perception in humans

Brain lesions in the visual associative cortex are known to impair visual perception, i.e., the capacity to correctly perceive different aspects of the visual world, such as motion, color, or shapes. Visual perception can be influenced by non-invasive brain stimulation such as transcranial direct current stimulation (tDCS). In a recently developed technique called high definition (HD) tDCS, small HD-electrodes are used instead of the sponge electrodes in the conventional approach. This is believed to achieve high focality and precision over the target area. In this paper we tested the effects of cathodal and anodal HD-tDCS over the right V5 on motion and shape perception in a single blind, within-subject, sham controlled, cross-over trial. The purpose of the study was to prove the high focality of the stimulation only over the target area. Twenty one healthy volunteers received 20 min of 2 mA cathodal, anodal and sham stimulation over the right V5 and their performance on a visual test was recorded. The results showed significant improvement in motion perception in the left hemifield after cathodal HD-tDCS, but not in shape perception. Sham and anodal HD-tDCS did not affect performance. The specific effect of influencing performance of visual tasks by modulating the excitability of the neurons in the visual cortex might be explained by the complexity of perceptual information needed for the tasks. This provokes a "noisy" activation state of the encoding neuronal patterns. We speculate that in this case cathodal HD-tDCS may focus the correct perception by decreasing global excitation and thus diminishing the "noise" below threshold.