3438 3 AE Welchman A Deubelius V Conrad HH Bülthoff Z Kourtzi 2005-05-00 6 8 820 827 Nature Neuroscience Our perception of the world&lsquo;s three-dimensional (3D) structure is critical for object recognition, navigation and planning actions. To accomplish this, the brain combines different types of visual information about depth structure, but at present, the neural architecture mediating this combination remains largely unknown. Here, we report neuroimaging correlates of human 3D shape perception from the combination of two depth cues. We measured fMRI responses while observers judged the 3D structure of two sequentially presented images of slanted planes defined by binocular disparity and perspective. We compared the behavioral and fMRI responses evoked by changes in one or both of the depth cues. fMRI responses in extrastriate areas (hMT+/V5 and lateral occipital complex), rather than responses in early retinotopic areas, reflected differences in perceived 3D shape, suggesting &lsquo;combined-cue&lsquo; representations in higher visual areas. These findings provide insight into the neural circuits engaged when the human brain combines different information sources for unified 3D visual perception. no notspecified http://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf3438.pdf published 7 15017 15422 2415 3 CF Altmann A Deubelius Z Kourtzi 2004-06-00 5 16 794 804 Journal of Cognitive Neuroscience Visual context influences our perception of target objects in natural scenes. However, little is known about the analysis of context information and its role in shape perception in the human brain. We investigated whether the human lateral occipital complex (LOC), known to be involved in the visual analysis of shapes, also processes information about the context of shapes within cluttered scenes. We employed an fMRI adaptation paradigm in which fMRI responses are lower for two identical than for two different stimuli presented consecutively. The stimuli consisted of closed target contours defined by aligned Gabor elements embedded in a background of randomly oriented Gabors. We measured fMRI adaptation in the LOC across changes in the context of the target shapes by manipulating the position and orientation of the background elements. No adaptation was observed across context changes when the background elements were presented in the same plane as the target elements. However, adaptation was observed when the grouping of the target elements was enhanced in a bottom-up (i.e., grouping by disparity or motion) or top-down (i.e., shape priming) manner and thus the saliency of the target shape increased. These findings suggest that the LOC processes information not only about shapes, but also about their context. This processing of context information in the LOC is modulated by figure–ground segmentation and grouping processes. That is, neural populations in the LOC encode context information when relevant to the perception of target shapes, but represent salient targets independent of context changes. no notspecified http://www.kyb.tuebingen.mpg.de/ published 10 15017 15422 ShmuelDSL2005 7 A Shmuel A Deubelius T Steudel NK Logothetis Washington, DC, USA2005-11-00 35th Annual Meeting of the Society for Neuroscience (Neuroscience 2005) Functional brain imaging and physiology studies of the visual cortex often utilize fixation on a spot as their baseline condition. It is not clear, however, whether fixation per se causes changes in activity in early retinotopic visual areas. To investigate possible changes in activity in V1 and V2 during fixation, we conducted fMRI experiments in alert monkeys. Monkeys were trained to stay still for 20 s long trials. Each trial began with 3 s in which a blank dark image was presented, followed by the presentation of a fixation spot (0.15 degrees radius) for 7 s. The animals fixated within 1 degree from the spot. A blank dark image was presented during the last 10 s of each trial. A surface coil (40 mm diameter) was positioned in proximity to the lateral part of the operculum. fMRI was conducted in a 7T vertical bore Bruker magnet, using a GE-EPI sequence. Cross-correlation analysis revealed increased activity in response to fixation, in the central visual field representation of V1 and V2 (eccentricities 0 to 2 degrees). To verify this response using a model-free analysis, a rotating checkers pattern bound between eccentricities of 0 and 1 degree was used as a localizer stimulus. In response to the localizer stimulus, increased activity (2.5%) was observed in the foveal representation of V1 and V2. The map obtained using the localizer was used as a region of interest to sample the time-course during trials in which only the fixation spot was presented. An increased activity was detected in these trials in V2 (~1%) and in V1 (~0.5%). To check whether this increased activity could be caused by the small fixation spot, we varied the luminance of the fixation spot and its contrast relative to the dark background. The amplitude of the response was largely invariant to differences in the contrast of the fixation point relative to the background, whether it was 90%, 50%, or 10%. These findings indicate the involvement of attentional mechanisms in early visual cortex during fixation. no notspecified http://www.kyb.tuebingen.mpg.de/ published 0 15017 15421 DeubeliusSLS2005 7 A Deubelius T Steudel NK Logotethis A Shmuel Washington, DC, USA2005-11-00 35th Annual Meeting of the Society for Neuroscience (Neuroscience 2005) Previous studies demonstrated negative BOLD response beyond the stimulated regions in V1, V2 and V3 in humans and anesthetized monkeys. Here we demonstrate negative BOLD response in alert monkey early visual areas. Monkeys were trained to stay still during 20 s long trials. Each trial began with 3 s in which a blank gray image was presented, followed by the presentation of a fixation spot (0.15 degrees radius) for 3 s, and a stimulus for 4 s. The stimulus consisted of rotating checkers pattern bound between eccentricities of 2 and 4 degrees. The animals fixated within 1 degree from the fixation spot. A blank gray image was presented during the last 10 s of each trial. A surface coil (40 mm diameter) was positioned in proximity to the operculum of one hemisphere. fMRI was conducted in a vertical bore Bruker 7T magnet, using a GE-EPI sequence. Increased activity (2.5%) was observed within the V1, V2, and V3 representations of the stimulated regions in the visual space. Negative BOLD response was detected in these areas in regions corresponding to more peripheral eccentricities. We are currently conducting experiments to further characterize this negative BOLD response. no notspecified http://www.kyb.tuebingen.mpg.de/ published 0 15017 15421 DeubeliusLS2005 7 A Deubelius NK Logothetis A Shmuel A Coruña, Spain2005-08-00 91 28th European Conference on Visual Perception Recent fMRI studies demonstrated negative BOLD response beyond the stimulated regions within retinotopic visual areas (Shmuel et al, 2002 Neuron 36 1195 - 1210). It has been suggested that this negative BOLD response is a reflection of automatic withdrawal of attention when a large stimulus is presented in the visual field (Smith et al, 2004 NeuroReport 11 271 - 277). We investigated psychophysically whether stimulating large parts of the visual field significantly impairs the detection of a small target stimulus in the non-stimulated parts of the visual field. In half of the trials subjects had to detect a Gabor patch (target) of full contrast, presented either centrally (2 - 4 deg) or peripherally (8 - 10 deg) relative to a rotating checkerboard ring (stimulus) with an eccentricity of 4.5 - 7.5 deg. In the other half of the trials, the subjects had to detect the target in the central or peripheral region in the absence of the stimulus. Fixation had to be maintained on a spot in the centre of the screen. The target was presented at random orientation, time, and location within the central or peripheral region. Subjects indicated the detection of the target by pressing a button. We observed that the reaction times in both the central and the peripheral region are higher when a stimulus is presented than when no stimulus is presented (centre: p < 0.001, two-tailed paired t-test; periphery: p < 0.001, two-tailed paired t-test). Our results suggest that stimulating a large part of the visual field might cause automatic withdrawal of attention from the non-stimulated parts of the visual field. no notspecified http://www.kyb.tuebingen.mpg.de/ published -91 15017 15421 2384 7 A Deubelius AE Welchman Z Kourtzi NK Logothetis New Orleans, LA, USA2003-11-00 33rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003) Humans can perceive object shape based on a range of different sources of visual information (or cues). Two cues to shape, that the visual system appears to be especially sensitive to, are horizontal binocular disparity and geometric perspective. This study examined the relationship between fMRI activity in the human brain and the perception of shape from perspective and disparity cues. Observers viewed open book stimuli consisting of a hinged plane receding symmetrically in depth. We parametrically varied the dihedral angle between the planes. Observers were required to judge which dihedral angle was larger (or more open) of two sequentially-presented stimuli. Stimuli were rear-projected inside a 3T scanner. Psychophysical judgments were made whilst fMRI responses were collected concurrently. We employed an event-related fMRI adaptation paradigm in which stimulus changes result in increased fMRI responses (rebound effect) compared with repeated presentation of the same stimuli. Psychophysical data were fit using Probit analysis and the perceptual discriminability of different stimuli was calculated. We examined fMRI responses in early retinotopic visual areas, higher object-related (Lateral Occipital Complex-LOC) and motion-related (hMT+/V5) areas. We observed significant fMRI rebound effects, that is increased responses compared with repeated presentation of the same stimulus, in early and higher visual areas. These rebound effects were consistent with the discriminability of the perceived shape in areas LOC hMT+/V5. These results suggest that both object and motion-related visual areas are involved in the perception of 3D shapes from multiple visual cues. no notspecified http://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2384.pdf published 0 15017 1542115017 15422 2349 7 AE Welchman A Deubelius Z Kourtzi New Orleans, LA, USA2003-11-00 33rd Annual Meeting of the Society for Neuroscience (Neuroscience 2003) The visual system is sensitive to multiple visual cues indicating the shape of objects; these cues are combined by the brain to result in unified shape perception. The goal of this study was to examine whether different visual areas are involved in the analysis of individual cues versus the representation of the perceived shape based on combined cues. We manipulated horizontal binocular disparity and geometric perspective cues to the shape of test stimuli (hinged planes). Disparity and perspective cues could indicate the same shape (consistent cues) or different shapes (inconsistent cues). Psychophysical judgments about the angle between the hinged planes of two sequentially-presented stimuli were collected concurrently with fMRI responses. A sequential-presentation fMRI adaptation paradigm was employed, in which stimulus changes result in increased fMRI responses (rebound effect) compared with repeated presentation of the same stimuli. We used conditions in which either individual cues changed, or both cues changed. We tested for fMRI responses in early retinotopic visual areas, higher object-related (Lateral Occipital Complex-LOC) and motion-related (hMT+/V5) areas. We observed significant fMRI rebound effects in early and higher visual areas. These rebound effects followed similar patterns to psychophysical discrminiability (d prime) of the perceived shape in areas LOC and hMT+/V5. However, rebound effects in areas V3 and V3a were consistent with changes in each of the individual cues rather than the perceived shape per se. These results suggest that early visual areas are involved in cue-based representations, while representations based on a combination of cues appear to be encoded in higher object-related (LOC) and motion-related (hMT+/V5) areas. no notspecified http://www.kyb.tuebingen.mpg.de/ published 0 15017 15422 2109 7 AE Welchman A Deubelius SJ Maier HH Bülthoff Z Kourtzi Sarasota, FL, USA2003-10-00 850 Third Annual Meeting of the Vision Sciences Society (VSS 2003) Recent models of cue combination (e.g. Landy et al., 1995, Vis Res, 35, 389) suggest that the perception of an object’s 3D shape is mediated by the combination of different depth cues (e.g. disparity and texture). We used fMRI to investigate the neural substrates of this process. Methods: Vertical cylinders defined by binocular disparity and texture cues were rear-projected inside a 3T scanner. We studied cylinders in which both disparity and texture specified the same curvature (consistent cues), and cylinders in which the two cues specified different curvatures (inconsistent cues). Prior to conducting fMRI experiments, subjects adjusted the curvature of consistent cue cylinders so that their perceived curvature was similar to that of the inconsistent ones. Performance in this task was used to define stimuli with consistent cues that were perceived to have similar curvature to the inconsistent cue stimuli. We employed a sequential-presentation fMRI adaptation technique, in which stimulus changes result in increased fMRI responses compared with repeated presentation of the same stimuli. Results: We observed increased responses in the Lateral Occipital Complex (LOC) and hMT(V5)+ when the subjects discriminated curvature changes. In contrast, adaptation in these regions was observed when subjects perceived similar curvature. Conclusions: These findings suggest that visual areas LOC and hMT(V5)+ are involved in the processing of perceived 3D shape based on the combination of disparity and textures cues. no notspecified http://www.kyb.tuebingen.mpg.de/ published -850 15017 15422 2114 7 E Huberle A Deubelius W Lutzenberger HH Bülthoff Z Kourtzi Sarasota, FL, USA2003-10-00 266 Third Annual Meeting of the Vision Sciences Society (VSS 2003) Recent studies have shown that global information about shapes is processed in both early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral Occipital Complex-LOC). However, the temporal properties of shape processing across visual areas in the human brain are not known. We addressed this question in a combined fMRI and MEG study that made use of the complimentary spatial and temporal resolution of the two techniques. We used an event-related adaptation paradigm in which lower neural responses are observed for two identical than two different consecutively-presented stimuli. The stimuli were closed contours that consisted of collinear Gabor elements. We manipulated the interstimulus interval (ISI: 100 vs. 400 msec) between the two consecutively-presented stimuli. The fMRI results showed adaptation for both the short and the long ISI in the LOC but only for the short ISI in early visual areas. The MEG data showed similar patterns of response amplitude to the fMRI data and differences in latencies for the different ISIs across visual areas. These findings suggest sustained shape processing in higher visual areas compared to more transient visual analysis in early visual areas. Further studies test the analysis of local vs. global shape features across areas with different temporal processing properties. no notspecified http://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/pdf2114.pdf published -266 15017 15422 2106 7 CF Altmann A Deubelius Z Kourtzi HH Bülthoff Kiel, Germany2003-03-00 158 45. Tagung Experimentell Arbeitender Psychologen (TeaP 2003) Aktuelle Modelle der visuellen Objekterkennung schlagen eine hierarchische Verarbeitung visueller Informationen vor. Wenig geklärt ist jedoch, inwieweit höhere visuelle Areale bei der Figur-Grund- Segmentierung auch Kontextinformation repräsentieren. Um dieser Fragestellung nachzugehen, untersuchten wir den lateral okzipitalen Komplex (LOC), eine kortikale Struktur, die an der Verarbeitung von Objektinformation beteiligt ist, mithilfe eines fMRI-Adaptations-Paradigmas. Dieses macht sich zunutze, dass das fMRI-Signal bei visueller Stimulation nach mehrmaliger Präsentation gleichen Reizmaterials zurückgeht. Für den LOC irrelevante Reizänderungen sollten zu fMRI-Adaptation in dieser Struktur führen. Wir konnten beobachten, dass Kontextänderungen nicht in Adaptation resultierten, d.h. der visuelle Kontext beeinflusst das fMRI-Signal im LOC. Dieser Kontexteffekt liess sich durch Modulation der Figur-Grund-Trennung beeinflussen. Hierzu führten wir zusätzliche räumliche Information, Bewegungsinformation beziehungsweise Priming der Figur ein. Die beobachteten Ergebnisse führen zu dem Schluss, dass der LOC Informationen über den Kontext einer Figur erhält, dieser Kontexteffekt jedoch durch Figur-Grund-Segmentierungsprozesse moduliert wird. no notspecified http://www.kyb.tuebingen.mpg.de/ published -158 15017 15422 HuberleDLBK2003 7 E Huberle A Deubelius W Lutzenberger HH Bülthoff Z Kourtzi Tübingen, Germany2003-02-00 151 6. Tübinger Wahrnehmungskonferenz (TWK 2003) Recent studies have shown that global information about shapes is processed in both early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral Occipital Complex-LOC). However, the temporal properties of shape processing across visual areas in the human brain are largely unknown. We addressed this question in a combined fMRI and MEG study that made use of the high spatial resolution of fMRI and the temporal resolution of MEG. We used an event-related adaptation paradigm in which lower neural responses are observed for two identical than two different consecutively-presented stimuli. The stimuli were closed contours that consisted of collinear Gabor elements. We manipulated the interstimulus interval (ISI: 100 vs. 400 msec) between the two consecutively-presented stimuli in each trial. To ensure comparability between fMRI and MEG results, subjects participated in both parts of the study. The fMRI results for 11 subjects showed adaptation for both the short and the long ISI in the LOC but only for the short ISI in early visual areas. The MEG data showed similar patterns of response amplitude to the fMRI data and dierences in latencies for the dierent ISIs across visual areas ranging between 70 and 160 ms. These ndings suggest sustained shape processing in higher visual areas compared to more transient visual analysis in early visual areas. Further studies test the analysis of local vs. global shape features across areas with dierent temporal processing properties. no notspecified http://www.kyb.tuebingen.mpg.de/ published -151 15017 1542215017 15421