Shigeko Takahashi

Inconsistency and uncertainty of the human visual area loci following surface‐based registration: Probability and Entropy Maps

Here we created two different multisubject maps (16 subjects) to characterize interindividual variability in the positions of human visual areas (V1, dorsal and ventral parts of V2/3, V3A, V3B, V7, LOc, MT+, and hV4 [or V4v and V8]), which were localized using fMRI and coregistered using a surface‐based method. The first is a probability map representing the degree of alignment inconsistency for each area, in which each point in space is associated with the probability affiliated with a given area. The second, a novel map termed an entropy map in which each point is associated with Shannon entropy computed from the probabilities, represents the degree of uncertainty regarding the area that resides there, and is maximal when all areas are equally probable. The overall average probability and entropy values were about 0.27 and 1.15 bits, respectively, with dependencies on the visual areas. The probability and entropy maps generated here will benefit any application which requires predictions of areas that are most likely present at an anatomical point and know the uncertainty associated with such predictions. Hum Brain Mapp, 2012.

Visual Perception of Contextual Effect and Its Neural Correlates

We investigated contextual effect in the visual perception using fMRI measurements. First, we examined spatiotemporal pattern of response modulation in human V1, V2 and V3/VP during contextual modulation of perceptual contrast using fMRI. Analysis of the spatial distribution of the response modulation indicated that multiple neural processes underlie the contextual effects. A long-range interaction that is selective to relative orientation may contribute predominantly to the suppressive response modulation in V1 and V2. Second, we examined higher-level contextual effect in the visual perception. We investigated the neural mechanisms of meaning generation from visual inputs, including Rorschach inkblots, using fMRI. Significant activity was observed in the prefrontal cortex together with distributed regions in the parietal and occipital cortices. The activated brain regions included the memory system for visual information and the spatial processing in visually guided eye movement in the brain. The results provide a clue to identify the brain regions responsible for the thought disorders and eye movement abnormalities of schizophrenia.

Spectral sensitivities for illusory contour perception: a manifold linkage of chromatic and achromatic cues with the generation of contours.

Using colored inducing patterns presented as increments upon a white uniform background, the increment thresholds needed for illusory contour perception were measured as a function of the wavelength of inducing pattern. The spectral sensitivity functions were obtained with varying adaptation level and stimulus configuration, high and low background illumination, and line-based and figure-based inducing patterns. The results showed a distinctive feature between the line-based and the figure-based illusory contours. The sensitivity functions for the line-based illusory contours showed the characteristics of non-opponent mechanisms and they were shape invariant with background intensity and spatial variables. On the other hand, the sensitivity functions for the figure-based illusory contours showed non-opponent nature for low background illumination but opponent nature for high background illumination. It is suggested that the generation of illusory contours involves concurrent processing of different cues of luminance and color, and that photopic adaptation level and stimulus configuration control the degree of the contributions of chromatic and achromatic mechanisms to contour formation.

Contextual information processing of brain in art appreciation

A psycho-historical framework for the science of art appreciation will be an experimental discipline that may shed new light on the highest capacities of the human brain, yielding new scientific ways to talk about the art appreciation. The recent findings of the contextual information processing in the human brain make the concept of the art-historical context clear for empirical experimentation.

Neural correlates of the stereokinetic effect revealed by functional magnetic resonance imaging

The stereokinetic effect (SKE) refers to a visual phenomenon in which a two-dimensional figure rotating in the fronto-parallel plane about the visual axis can create the impression of a three-dimensional (3-D) object. Although several characteristics of SKE suggest that the perceptual mechanisms involved in SKE may differ from those of the kinetic depth effect (KDE), the differences between SKE and KDE in neural mechanisms have not yet been investigated. In order to determine the cortical areas involved in SKE, we presented a variety of SKE stimuli in a series of functional magnetic resonance imaging experiments, controlling for motion and contrast energies as well as stimulus presentation paradigm. Cortical activation associated with SKE was observed in the middle temporal complex (hMT+), lateral occipital area (LO), V3B, inferior temporal gyrus (ITG), fusiform gyrus (FG), and dorsal intraparietal sulcus anterior (DIPSA). On the other hand, ITG, FG, and DIPSA were also activated by the static versions of SKE stimuli. hMT+, LO, and V3B are also known to be activated in KDE. These findings suggest that general motion-dependent 3-D object processing may be performed in these areas.

Positioning of retinotopic areas and patterning of cerebral cortex layout.

We examined the positioning of human retinotopic areas, which were considered to be homologous with the macaque visual cortices, by applying computational geometry to MRI and fMRI data sets. We found a similarity between the positional relationship of the retinotopic areas in the human and macaque visual cortex, despite the large difference in brain size. This suggests that area maps in different species may share topological features, probably resulting from broad similarities in the patterning mechanism of cerebral cortex layout.

Modes of Effective Connectivity within Cortical Pathways Are Distinguished for Different Categories of Visual Context: An fMRI Study

Context contributes to accurate and efficient information processing. To reveal the dynamics of the neural mechanisms that underlie the processing of visual contexts during the recognition of color, shape, and 3D structure of objects, we carried out functional magnetic resonance imaging (fMRI) of subjects while judging the contextual validity of the three visual contexts. Our results demonstrated that the modes of effective connectivity in the cortical pathways, as well as the patterns of activation in these pathways, were dynamical depending on the nature of the visual contexts. While the fusiform gyrus, superior parietal lobe, and inferior prefrontal gyrus were activated by the three visual contexts, the temporal and parahippocampal gyrus/Amygdala (PHG/Amg) cortices were activated only by the color context. We further carried out dynamic causal modeling (DCM) analysis and revealed the nature of the effective connectivity involved in the three contextual information processing. DCM showed that there were dynamic connections and collaborations among the brain regions belonging to the previously identified ventral and dorsal visual pathways.

Basic principles of visual functions: mathematical formalism of geometries of shape and space, and the architecture of visual systems

There is growing evidence for homologous mechanisms of recognition/perception and navigation in many species, from insects to humans. This leads to the notion that the core systems of recognition and navigation are shared across species and that the visual environment during motion and/or navigation molds the spatiotemporal properties of the nervous systems across widely separated phyla according to basic common principles. In this study, we propose a mathematical formalism for two distinct geometries of shape and space in the visual images on the retina. The formalism enunciates the relevance of the architecture of the visual system for processing the two geometries and for producing some sort of circulating memory in space-time, i.e., recognition of allocentric space. Correspondence to: Shigeko Takahashi, Psychology Laboratory, Kyoto City University of Arts, Ohe-Kutsukake-cho, 13-6, Nishikyo-ku, Kyoto 601-1197, Japan, Tel: +81-(0)75-334-2265; E-mail: sgtak@kcua.ac.jp