The Experts below are selected from a list of 87 Experts worldwide ranked by ideXlab platform
S Zeki - One of the best experts on this subject based on the ideXlab platform.
-
area v5 of the human brain evidence from a combined study using positron emission tomography and magnetic resonance imaging
Cerebral Cortex, 1993Co-Authors: John D G Watson, John C Mazziotta, Ralph Myers, Richard S J Frackowiak, Joseph V Hajnal, Roger P Woods, S Shipp, S ZekiAbstract:In pursuing our work on the organization of human visual cortex, we wanted to specify more accurately the position of the visual motion area (area V5) in relation to the sulcal and gyral pattern of the cerebral cortex. We also wanted to determine the intersubject variation of area V5 in terms of position and extent of blood flow change in it, in response to the same task. We therefore used positron emission tomography (PET) to determine the foci of relative cerebral blood flow increases produced when subjects viewed a moving checkerboard pattern, compared to viewing the same pattern when it was stationary. We coregistered the PET images from each subject with images of the same brain obtained by magnetic resonance imaging, thus relating the position of V5 in all 24 hemispheres examined to the individual gyral configuration of the same brains. This approach also enabled us to examine the extent to which results obtained by pooling the PET data from a small group of individuals (e.g., six), chosen at random, would be representative of a much larger sample in determining the mean location of V5 after transformation into Talairach coordinates. After stereotaxic transformation of each individual brain, we found that the position of area V5 can vary by as much as 27 mm in the left hemisphere and 18 mm in the right for the pixel with the highest significance for blood flow change. There is also an intersubject variability in blood flow change within it in response to the same visual task. V5 nevertheless bears a consistent relationship, within each brain, to the sulcal pattern of the Occipital lobe. It is situated ventroLaterally, just posterior to the meeting point of the ascending limb of the inferior temporal Sulcus and the Lateral Occipital Sulcus. In position it corresponds almost precisely with Flechsig's Feld 16, one of the areas that he found to be myelinated at birth. © 1993 Oxford University Press.
Cristiana Cavina-pratesi - One of the best experts on this subject based on the ideXlab platform.
-
Dissociable Neural Responses to Hands and Non-Hand Body Parts in Human Left Extrastriate Visual Cortex
Journal of neurophysiology, 2010Co-Authors: Stefania Bracci, Magdalena Ietswaart, Marius V. Peelen, Cristiana Cavina-pratesiAbstract:Accumulating evidence points to a map of visual regions encoding specific categories of objects. For example, a region in the human extrastriate visual cortex, the extrastriate body area (EBA), has been implicated in the visual processing of bodies and body parts. Although in the monkey, neurons selective for hands have been reported, in humans it is unclear whether areas selective for individual body parts such as the hand exist. Here, we conducted two functional MRI experiments to test for hand-preferring responses in the human extrastriate visual cortex. We found evidence for a hand-preferring region in left Lateral occipitotemporal cortex in all 14 participants. This region, located in the Lateral Occipital Sulcus, partially overlapped with left EBA, but could be functionally and anatomically dissociated from it. In experiment 2, we further investigated the functional profile of hand- and body-preferring regions by measuring responses to hands, fingers, feet, assorted body parts (arms, legs, torsos), and non-biological handlike stimuli such as robotic hands. The hand-preferring region responded most strongly to hands, followed by robotic hands, fingers, and feet, whereas its response to assorted body parts did not significantly differ from baseline. By contrast, EBA responded most strongly to body parts, followed by hands and feet, and did not significantly respond to robotic hands or fingers. Together, these results provide evidence for a representation of the hand in extrastriate visual cortex that is distinct from the representation of other body parts.
Guy Orban - One of the best experts on this subject based on the ideXlab platform.
-
human functional magnetic resonance imaging reveals separation and integration of shape and motion cues in biological motion processing
The Journal of Neuroscience, 2009Co-Authors: Jan Jastorff, Guy OrbanAbstract:In a series of human functional magnetic resonance imaging experiments, we systematically manipulated point-light stimuli to identify the contributions of the various areas implicated in biological motion processing (for review, see Giese and Poggio, 2003). The first experiment consisted of a 2 × 2 factorial design with global shape and kinematics as factors. In two additional experiments, we investigated the contributions of local opponent motion, the complexity of the portrayed movement and a one-back task to the activation pattern. Experiment 1 revealed a clear separation between shape and motion processing, resulting in two branches of activation. A ventral region, extending from the Lateral Occipital Sulcus to the posterior inferior temporal gyrus, showed a main effect of shape and its extension into the fusiform gyrus also an interaction. The dorsal region, including the posterior inferior temporal Sulcus and the posterior superior temporal Sulcus (pSTS), showed a main effect of kinematics together with an interaction. Region of interest analysis identified these interaction sites as the extrastriate and fusiform body areas (EBA and FBA). The local opponent motion cue yielded only little activation, limited to the ventral region (experiment 3). Our results suggest that the EBA and the FBA correspond to the initial stages in visual action analysis, in which the performed action is linked to the body of the actor. Moreover, experiment 2 indicates that the body areas are activated automatically even in the absence of a task, whereas other cortical areas like pSTS or frontal regions depend on the complexity of movements or task instructions for their activation.
-
The Extraction of 3D Shape from Texture and Shading in the Human Brain
Cerebral cortex (New York N.Y. : 1991), 2008Co-Authors: Svetlana S. Georgieva, James T. Todd, Ronald R. Peeters, Guy OrbanAbstract:We used functional magnetic resonance imaging to investigate the human cortical areas involved in processing 3-dimensional (3D) shape from texture (SfT) and shading. The stimuli included monocular images of randomly shaped 3D surfaces and a wide variety of 2-dimensional (2D) controls. The results of both passive and active experiments reveal that the extraction of 3D SfT involves the biLateral caudal inferior temporal gyrus (caudal ITG), Lateral Occipital Sulcus (LOS) and several biLateral sites along the intraparietal Sulcus. These areas are largely consistent with those involved in the processing of 3D shape from motion and stereo. The experiments also demonstrate, however, that the analysis of 3D shape from shading is primarily restricted to the caudal ITG areas. Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues. These results underscore the importance of the posterior part of the Lateral Occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions.
-
Color Discrimination Involves Ventral and Dorsal Stream Visual Areas
Cerebral cortex (New York N.Y. : 1991), 2004Co-Authors: Kristl G. Claeys, Patrick Dupont, Luc Cornette, Stefan Sunaert, Paul Van Hecke, Erik De Schutter, Guy OrbanAbstract:We used positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) in human subjects to investigate whether the ventral and dorsal visual stream cooperate when active judgements about color have to be made. Color was used as the attribute, because it is processed primarily in the ventral stream. The centrally positioned stimuli were equiluminant shades of brown. The successive color discrimination task was contrasted to a dimming detection task, in which retinal input was identical but with double the number of motor responses. The stimulus presentation rate was parametrically varied and a constant performance level was obtained for all conditions. The visual activation sites were identified by retinotopic mapping and cortical flattening. In addition, one psychophysical and two fMRI experiments were performed to control for differences in visuospatial attention and motor output. Successive color discrimination involved early visual areas, including V1 and VP and the ventral color-responsive region, as well as anterior and middle dorsal intraparietal Sulcus, dorsal premotor cortex and pre-SMA. Cortical regions involved in dimming detection and motor output included area V3A, hMT/V5+, Lateral Occipital Sulcus, posterior dorsal intraparietal Sulcus, primary motor cortex and SMA. These experiments demonstrated that even with color as the attribute, successive discrimination, in which a decision process has to link visual signals to motor responses, involves both ventral and dorsal visual stream areas.
Chantal E. Stern - One of the best experts on this subject based on the ideXlab platform.
-
Cerebral Cortex doi:10.1093/cercor/bhm197 Where Vision Meets Memory: Prefrontal-- Posterior Networks for Visual Object Constancy during Categorization and Recognition
2016Co-Authors: Haline E. Schendan, Chantal E. SternAbstract:Objects seen from unusual relative to more canonical views require more time to categorize and recognize, and, according to object model verification theories, additionally recruit prefrontal processes for cognitive control that interact with parietal processes for mental rotation. To test this using functional magnetic resonance imaging, people categorized and recognized known objects from unusual and canonical views. Canonical views activated some components of a default network more on categorization than recognition. Activation to unusual views showed that both ventral and dorsal visual pathways, and prefrontal cortex, have key roles in visual object constancy. Unusual views activated object-sensitive and mental rotation (and not saccade) regions in ventrocaudal intraparietal, transverse Occipital, and inferotemporal sulci, and ventral premotor cortex for verification processes of model testing on any task. A colLateral--lingual sulci ‘‘place’ ’ area activated for mental rotation, working memory, and unusual views on correct recognition and categorization trials to accomplish detailed spatial matching. VentroLateral prefrontal cortex and object-sensitive Lateral Occipital Sulcus activated for mental rotation and unusual views on categorization more than recognition, supporting verifi-cation processes of model prediction. This visual knowledge framework integrates vision and memory theories to explain how distinct prefrontal--posterior networks enable meaningful interac-tions with objects in diverse situations
-
Where Vision Meets Memory: Prefrontal–Posterior Networks for Visual Object Constancy during Categorization and Recognition
Cerebral cortex (New York N.Y. : 1991), 2007Co-Authors: Haline E. Schendan, Chantal E. SternAbstract:Objects seen from unusual relative to more canonical views require more time to categorize and recognize, and, according to object model verification theories, additionally recruit prefrontal processes for cognitive control that interact with parietal processes for mental rotation. To test this using functional magnetic resonance imaging, people categorized and recognized known objects from unusual and canonical views. Canonical views activated some components of a default network more on categorization than recognition. Activation to unusual views showed that both ventral and dorsal visual pathways, and prefrontal cortex, have key roles in visual object constancy. Unusual views activated object-sensitive and mental rotation (and not saccade) regions in ventrocaudal intraparietal, transverse Occipital, and inferotemporal sulci, and ventral premotor cortex for verification processes of model testing on any task. A colLateral--lingual sulci ‘‘place’’ area activated for mental rotation, working memory, and unusual views on correct recognition and categorization trials to accomplish detailed spatial matching. VentroLateral prefrontal cortex and object-sensitive Lateral Occipital Sulcus activated for mental rotation and unusual views on categorization more than recognition, supporting verification processes of model prediction. This visual knowledge framework integrates vision and memory theories to explain how distinct prefrontal--posterior networks enable meaningful interactions with objects in diverse situations.
John D G Watson - One of the best experts on this subject based on the ideXlab platform.
-
area v5 of the human brain evidence from a combined study using positron emission tomography and magnetic resonance imaging
Cerebral Cortex, 1993Co-Authors: John D G Watson, John C Mazziotta, Ralph Myers, Richard S J Frackowiak, Joseph V Hajnal, Roger P Woods, S Shipp, S ZekiAbstract:In pursuing our work on the organization of human visual cortex, we wanted to specify more accurately the position of the visual motion area (area V5) in relation to the sulcal and gyral pattern of the cerebral cortex. We also wanted to determine the intersubject variation of area V5 in terms of position and extent of blood flow change in it, in response to the same task. We therefore used positron emission tomography (PET) to determine the foci of relative cerebral blood flow increases produced when subjects viewed a moving checkerboard pattern, compared to viewing the same pattern when it was stationary. We coregistered the PET images from each subject with images of the same brain obtained by magnetic resonance imaging, thus relating the position of V5 in all 24 hemispheres examined to the individual gyral configuration of the same brains. This approach also enabled us to examine the extent to which results obtained by pooling the PET data from a small group of individuals (e.g., six), chosen at random, would be representative of a much larger sample in determining the mean location of V5 after transformation into Talairach coordinates. After stereotaxic transformation of each individual brain, we found that the position of area V5 can vary by as much as 27 mm in the left hemisphere and 18 mm in the right for the pixel with the highest significance for blood flow change. There is also an intersubject variability in blood flow change within it in response to the same visual task. V5 nevertheless bears a consistent relationship, within each brain, to the sulcal pattern of the Occipital lobe. It is situated ventroLaterally, just posterior to the meeting point of the ascending limb of the inferior temporal Sulcus and the Lateral Occipital Sulcus. In position it corresponds almost precisely with Flechsig's Feld 16, one of the areas that he found to be myelinated at birth. © 1993 Oxford University Press.
