Perceptual integration for qualitatively different 3-D cues in the human brain.

The visual system's flexibility in estimating depth is remarkable: We readily perceive 3-D structure under diverse conditions from the seemingly random dots of a "magic eye" stereogram to the aesthetically beautiful, but obviously flat, canvasses of the Old Masters. Yet, 3-D perception is often enhanced when different cues specify the same depth. This perceptual process is understood as Bayesian inference that improves sensory estimates. Despite considerable behavioral support for this theory, insights into the cortical circuits involved are limited. Moreover, extant work tested quantitatively similar cues, reducing some of the challenges associated with integrating computationally and qualitatively different signals. Here we address this challenge by measuring fMRI responses to depth structures defined by shading, binocular disparity, and their combination. We quantified information about depth configurations (convex "bumps" vs. concave "dimples") in different visual cortical areas using pattern classification analysis. We found that fMRI responses in dorsal visual area V3B/KO were more discriminable when disparity and shading concurrently signaled depth, in line with the predictions of cue integration. Importantly, by relating fMRI and psychophysical tests of integration, we observed a close association between depth judgments and activity in this area. Finally, using a cross-cue transfer test, we found that fMRI responses evoked by one cue afford classification of responses evoked by the other. This reveals a generalized depth representation in dorsal visual cortex that combines qualitatively different information in line with 3-D perception

The matching rule of Panum’s limiting case and its influencing factors

IntroductionPanum’s limiting case is one of the typical configurations of monocular occlusion region. The matching rule of Panum’s limiting case is the key to understanding how monocular occlusion region produces stereopsis. There are currently two main views on the matching rule of Panum’s limiting case, namely double fusion and uniqueness constraint. This paper further discusses its matching mechanism on the basis of previous studies.MethodsIn this study, fold line Panum’s stimuli were used to study the matching rule of Panum’s limiting case. In Experiment 1, fixation position was adopted to present the stimulus in a short time to explore the matching rules in Panum’s limiting case. In Experiment 2, the effect of fixation position on Panum’s limiting case matching results was further investigated.ResultsThe results of Experiment 1 show that when stimuli are presented in a short period of time, the reported result that a single feature in one eye may be matched alternately with two features in the other eye. This matching rule is called “fast alternative matching” in this article. The results of Experiment 2 results show that the position of the fixation could affect the matching result of participants.ConclusionIn conclusion, the matching rule of Panum’s limiting case is fast alternative matching, and the matching result is related to the attention state of the participant. These results not only provide a new perspective for matching rules in Panum’s limiting case, but also show that depth perception results in stereopsis can be influenced by top-down cognitive processing. This study provides a theoretical basis for studying the formation of stereopsis in the monocular region to a certain extent. In summary, the matching rule of Panum’s limiting case is fast alternative matching. In previous studies, the perceived result of double fusion may be caused by fast alternative matching. Also, the matching results are related to the participant’s state of attention, which suggests that the depth perception results of stereopsis are influenced by top-down cognitive processing

Areal differences in depth cue integration between monkey and human.

Electrophysiological evidence suggested primarily the involvement of the middle temporal (MT) area in depth cue integration in macaques, as opposed to human imaging data pinpointing area V3B/kinetic occipital area (V3B/KO). To clarify this conundrum, we decoded monkey functional MRI (fMRI) responses evoked by stimuli signaling near or far depths defined by binocular disparity, relative motion, and their combination, and we compared results with those from an identical experiment previously performed in humans. Responses in macaque area MT are more discriminable when two cues concurrently signal depth, and information provided by one cue is diagnostic of depth indicated by the other. This suggests that monkey area MT computes fusion of disparity and motion depth signals, exactly as shown for human area V3B/KO. Hence, these data reconcile previously reported discrepancies between depth processing in human and monkey by showing the involvement of the dorsal stream in depth cue integration using the same technique, despite the engagement of different regions

Perceptual integration for qualitatively different 3-D cues in the human brain.

The visual systemʼs flexibility in estimating depth is remarkable: We readily perceive 3-D structure under diverse conditions from the seemingly random dots of a “magic eye” stereogram to the aesthetically beautiful, but obviously flat, canvasses of the Old Masters. Yet, 3-D perception is often enhanced when different cues specify the same depth. This perceptual process is understood as Bayesian inference that improves sensory estimates. Despite considerable behavioral support for this theory, insights into the cortical circuits involved are limited. Moreover, extant work tested quantitatively similar cues, reducing some of the challenges associated with integrating computationally and qualitatively different signals. Here we address this challenge by measuring fMRI responses to depth structures defined by shading, binocular disparity, and their combination. We quantified information about depth configurations (convex “bumps” vs. concave “dimples”) in different visual cortical areas using pattern classification analysis. We found that fMRI responses in dorsal visual area V3B/KO were more discriminable when disparity and shading concurrently signaled depth, in line with the predictions of cue integration. Importantly, by relating fMRI and psychophysical tests of integration, we observed a close association between depth judgments and activity in this area. Finally, using a cross-cue transfer test, we found that fMRI responses evoked by one cue afford classification of responses evoked by the other. This reveals a generalized depth representation in dorsal visual cortex that combines qualitatively different information in line with 3-D perception

Visual Anxiolytics: developing theory and design guidelines for abstract affective visualizations aimed at alleviating episodes of anxiety

Visual Anxiolytics is a novel term proposed to describe affective visualizations of which affective quality is predetermined and designed to alleviate anxiety and anxious pathology. This thesis presents ground theory and visual guidelines to inform the design of screen-based interfaces to give users aspects of a restorative and anxiolytic environment at a time when attention restoration is least likely and anxiety highly probable; during sedentary screen-time. Visual Anxiolytics are introduced as an affective layer of the interface capable of communicating affect through aesthetic, abstract, ambient emotion visualizations existing in the periphery of the screen and users’ vision. Their theory is brought into the field of Visual Communication Design from a number of disciplines; primarily Affective Computing, Human-Computer Interaction, Psychology, and Neuroscience. Visual Anxiolytics attempt to alleviate anxiety through restoration of attentional cognitive resources by rendering the digital environment restorative and by elicitation of positive emotions through affect communication. Design guidelines analyse and describe properties of anxiolytic affective visual attributes color, shape, motion, and visual depth, as well as compositional characteristics of Visual Anxiolytics. Potential implications for future research in emotion visualization and affect communication are discussed

The neural basis of visual material properties in the human brain

Three independent studies with human functional magnetic resonance imaging (fMRI) measurements were designed to investigate the neural basis of visual glossiness processing in the human brain. The first study is to localize brain areas preferentially responding to glossy objects defined by specular reflectance. We found activations related to gloss in the posterior fusiform (pFs) and in area V3B/KO. The second study is to investigate how the visual-induced haptic sensation is achieved in our brain. We found that in secondary somatosensory area (S2) was distinguishable between glossy and rough surfaces, suggesting that visual information about object surfaces may be transformed into tactile information in S2. In the third study we investigate how the brain processes surface gloss information conveyed by disparity of specular reflections on stereo mirror objects and compared it with the processing of specular reflectance. We found that both dorsal and ventral areas were involving in this processing. The result implicates that in this region the processing of stereoscopic gloss information has a pattern of activation that is additional to the representation of specular reflectance. Overall, the three studies contribute to our understanding about the neural basis of visual glossiness and material processing in the human brain

Shape-from-shading and light source estimation in humans

Light source estimation is very important for the interpretation of shape-fromshading by humans. We used a range of methods to characterise the way in which the type, and position of the light source can influence observers’ performance in shape-from-shading tasks. Firstly, we used classification images to discover people’s priors for light source position using noise only stimuli. This cue-free approach uncovered the weakness of the light-from-above prior. We also examined the effect of varying the light source elevation on the perceived shape of isotropic and anisotropic surfaces, the impacts of lighting ambiguities on shape-from-shading and, finally, the interpretation of shadow regions. We found that lighting priors are weighted by the visual system in a way that is inversely proportional to the strength of lighting cues in the stimuli, revealing that knowledge about the light source position is critical to perceiving shapefrom- shading. Where ambiguous cues to lighting direction are present human vision seems to favour local cues over distal ones. We also showed that perceived surface shape varies with light elevation only in so far as elevation alters contrast. Finally we show that human vision does not treat shadows in the same way as objects

Seeing 3D surfaces: neural stimulation, learning and masking

In the present dissertation, I assessed the visual hierarchy stages that support the visual perception of three-dimensional (3D) surfaces. In the first experimental chapter, I used fMRI-guided rTMS to probe the cortical areas involved in the perception of slanted surfaces. Results hint at a functional contribution of the dorso-parietal visual stream (posterior parietal cortex; PPC) to slant estimation, however, further work is needed to fully understand the nature of its involvement. I then showed that fMRI-guided rTMS-induced disruption of the ventral stream (area LO) eliminates the facilitation observed, in 3D surface discrimination, when disparity and motion cues congruently inform depth. This finding indicates that LO encodes signals for the integration of depth cues. Then, I showed rTMS evidence that disparity and orientation signal-in-noise discriminations causally relate to PPC’s function. Interestingly, this relation diminishes after training on a visual feature other than the one employed during rTMS testing. This finding indicates that training, even across visual features, can influence neuronal organization. Finally, I used backward masking to show that brightness masking incorporates the 3D information of disparity-defined slant. This finding suggests that brightness estimation is mediated by mid-level neuronal mechanisms, at a cortical stage where binocular signals have been combined

Neural mechanisms for reducing uncertainty in 3D depth perception

In order to navigate and interact within their environment, animals must process and interpret sensory information to generate a representation or ‘percept’ of that environment. However, sensory information is invariably noisy, ambiguous, or incomplete due to the constraints of sensory apparatus, and this leads to uncertainty in perceptual interpretation. To overcome these problems, sensory systems have evolved multiple strategies for reducing perceptual uncertainty in the face of uncertain visual input, thus optimizing goal-oriented behaviours. Two available strategies have been observed even in the simplest of neural systems, and are represented in Bayesian formulations of perceptual inference: sensory integration and prior experience. In this thesis, I present a series of studies that examine these processes and the neural mechanisms underlying them in the primate visual system, by studying depth perception in human observers. Chapters 2 & 3 used functional brain imaging to localize cortical areas involved in integrating multiple visual depth cues, which enhance observers’ ability to judge depth. Specifically, we tested which of two possible computational methods the brain uses to combine depth cues. Based on the results we applied disruption techniques to examine whether these select brain regions are critical for depth cue integration. Chapters 4 & 5 addressed the question of how memory systems operating over different time scales interact to resolve perceptual ambiguity when the retinal signal is compatible with more than one 3D interpretation of the world. Finally, we examined the role of higher cortical regions (parietal cortex) in depth perception and the resolution of ambiguous visual input by testing patients with brain lesions