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Hans-otto Karnath - One of the best experts on this subject based on the ideXlab platform.
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Simultanagnosia does not affect processes of auditory Gestalt perception
Neuropsychologia, 2017Co-Authors: Johannes Rennig, Anna Lena Bleyer, Hans-otto KarnathAbstract:Simultanagnosia is a neuropsychological deficit of higher visual processes caused by temporo-parietal brain damage. It is characterized by a specific failure of recognition of a global visual Gestalt, like a visual scene or complex objects, consisting of local elements. In this study we investigated to what extend this deficit should be understood as a deficit related to specifically the visual domain or whether it should be seen as defective Gestalt processing per se. To examine if Simultanagnosia occurs across sensory domains, we designed several auditory experiments sharing typical characteristics of visual tasks that are known to be particularly demanding for patients suffering from Simultanagnosia. We also included control tasks for auditory working memory deficits and for auditory extinction. We tested four Simultanagnosia patients who suffered from severe symptoms in the visual domain. Two of them indeed showed significant impairments in recognition of simultaneously presented sounds. However, the same two patients also suffered from severe auditory working memory deficits and from symptoms comparable to auditory extinction, both sufficiently explaining the impairments in simultaneous auditory perception. We thus conclude that deficits in auditory Gestalt perception do not appear to be characteristic for Simultanagnosia and that the human brain obviously uses independent mechanisms for visual and for auditory Gestalt perception.
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Stimulus size mediates Gestalt processes in object perception - evidence from Simultanagnosia.
Neuropsychologia, 2016Co-Authors: Johannes Rennig, Hans-otto KarnathAbstract:Abstract Simultanagnosia caused by posterior temporo-parietal brain damage is characterized through an inability to recognize a global Gestalt from an arrangement of single objects while perception of single objects appears widely intact. We asked whether recognition of single objects in Simultanagnosia is still intact if objects are really large, i.e. if they exceed the size of a usual computer screen. Single objects were presented in three different sizes: ‘regular’, ’medium’, and ‘large’. Simultanagnosia patients demonstrated a decrease of recognition performance with increasing object size; recognition of ‘large’ objects was significantly impaired while perception of ‘regular’ sized objects was unaffected. The results argue against the traditional view of preserved recognition of single objects in Simultanagnosia. They provide evidence for a more general perceptual impairment that emerges irrespective of presenting single or multiple objects, but whenever the visual system has to assemble information over larger spatial distances or other demanding viewing conditions. It appears that perception of large single objects requires intact abilities of dorsal Gestalt processing, in addition to regular functions of ventral object recognition.
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Modeling Simultanagnosia
2016Co-Authors: Anna Belardinelli, Hans-otto Karnath, Johannes M. Kurz, Esther F. Kutter, Heiko Neumann, Martin V. ButzAbstract:Simultanagnosia is a visual cognitive disorder following a bi-lateral lesion in parieto-occipital brain areas. It affects the pa-tients integrative perception so that scenes or hierarchically or-ganized objects cannot be perceived as a whole but just in a piecemeal fashion. Qualitative explanations consider impair-ments of attentional selection mechanisms, feature binding, or global shape processing. Until now, however, no compu-tational model has been used to quantitatively reproduce the performance patients suffering from Simultanagnosia. We fo-cus on modeling the impairment of recognizing hierarchical stimuli (Navon letters), which have been used in several stud-ies with patients and healthy subjects. In particular, we apply the established HMAX model of object recognition, specifi-cally trained on letter recognition, to investigate the role o
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A JOURNAL OF NEUROLOGY Enabling global processing in Simultanagnosia by psychophysical biasing of visual pathways
2015Co-Authors: Cibu Thomas, Hans-otto Karnath, Elisabeth Huberle, Kestutis Kveraga, Moshe BarAbstract:A fundamental aspect of visual cognition is our disposition to see the ‘forest before the trees’. However, damage to the posterior parietal cortex, a critical brain region along the dorsal visual pathway, can produce a neurological disorder called simultanag-nosia, characterized by a debilitating inability to perceive the ‘forest ’ but not the ‘trees ’ (i.e. impaired global processing despite intact local processing). This impairment in perceiving the global shape persists even though the ventral visual pathway, the primary recognition pathway, is intact in these patients. Here, we enabled global processing in patients with Simultanagnosia using a psychophysical technique, which allowed us to bias stimuli such that they are processed predominantly by the intact ventral visual pathway. Our findings reveal that the impairment in global processing that characterizes Simultanagnosia stems from a disruption in the processing of low-spatial frequencies through the dorsal pathway. These findings advance our under-standing of the relationship between visuospatial attention and perception and reveal the neural mechanism mediating the disposition to see the ‘forest before the trees’
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Involvement of the tpj area in processing of novel global forms
Journal of cognitive neuroscience, 2015Co-Authors: Johannes Rennig, Elisabeth Huberle, Marc Himmelbach, Hans-otto KarnathAbstract:The neuropsychological syndrome "Simultanagnosia" is characterized by the inability to integrate local elements into a global entity. This deficit in Gestalt perception is mainly apparent for novel global structures administered in clinical tests or unfamiliar visual scenes. Recognition of familiar complex objects or well-known visual scenes is often unaffected. Recent neuroimaging studies and reports from Simultanagnosia patients suggest a crucial involvement of temporoparietal brain areas in processing of hierarchically organized visual material. In this study, we investigated the specific role of the TPJ in Gestalt perception. On the basis of perceptual characteristics known from Simultanagnosia, we hypothesized that TPJ is dominantly involved in processing of novel object arrangements. To answer this question, we performed a learning study with hierarchical stimuli and tested behavioral and neuronal characteristics of Gestalt perception pre-and posttraining. The study included 16 psychophysical training sessions and two neuroimaging sessions. Participants improved their behavioral performance for trained global stimuli and showed limited transfer to untrained global material. We found significant training dependent neuronal signal modulations in anterior right hemispheric TPJ regions. These activation changes were specific to trained global stimuli, whereas no systematic neuronal response changes were observed for recognition of untrained global stimuli, local elements and regular objects that served as control stimuli. In line with perceptual characteristics in Simultanagnosia, the results argue for an involvement of TPJ in processing of novel global structures. We discuss the signal modulations in the context of a more efficient or different neuronal strategy to process familiar global stimuli.
Alan Kingstone - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Simulating Simultanagnosia: spatially constricted vision mimics local capture and the global processing deficit
2016Co-Authors: David Cameron, Jason J.s. Barton, Alan KingstoneAbstract:Abstract Patients with Simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time. As a result, these patients see the world in a piecemeal fashion, seeing the local components of objects or scenes at the expense of the global picture. To directly test the relationship between the restriction of the attentional window in Simultanagnosia and patients ’ diffi-culty with global-level processing, we used a gaze-con-tingent display to create a literal restriction of vision for healthy participants while they performed a global/local identification task. Participants in this viewing condition were instructed to identify the global and local aspects of hierarchical letter stimuli of different sizes and densities. They performed well at the local identification task, and their patterns of inaccuracies for the global level task were highly similar to the pattern of inaccuracies typically seen with simultanagnosic patients. This suggests that a restricted spatial area of visual processing, combined with normal limits to visual processing, can lead to difficulties with global-level perception
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A world unglued: Simultanagnosia as a spatial restriction of attention
Frontiers in human neuroscience, 2013Co-Authors: Kirsten A. Dalrymple, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention that leaves a patient’s world unglued: scenes and objects are perceived in a piecemeal manner. It is generally agreed that Simultanagnosia is related to an impairment of attention, but it is unclear whether this impairment is object- or space-based in nature. We first consider the findings that support a concept of Simultanagnosia as deficit of object-based attention. We then examine the evidence suggesting that Simultanagnosia results from damage to a space-based attentional system, and in particular a model of Simultanagnosia as a narrowed spatial window of attention. We ask whether seemingly object-based deficits can be explained by space-based mechanisms, and consider the evidence that object processing influences spatial deficits in this condition. Finally, we discuss limitations of a space-based attentional explanation.
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Eyeing the eyes in social scenes: Evidence for top-down control of stimulus selection in Simultanagnosia
Cognitive neuropsychology, 2013Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alexander K. Gray, Brielle L. Perler, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention resulting from bilateral parieto-occipital lesions. Healthy individuals look at eyes to infer people's attentional states, but simultanagnosics allocate abnormally few fixations to eyes in scenes. It is unclear why simultanagnosics fail to fixate eyes, but it might reflect that they are (a) unable to locate and fixate them, or (b) do not prioritize attentional states. We compared eye movements of simultanagnosic G.B. to those of healthy subjects viewing scenes normally or through a restricted window of vision. They described scenes and explicitly inferred attentional states of people in scenes. G.B. and subjects viewing scenes through a restricted window made few fixations on eyes when describing scenes, yet increased fixations on eyes when inferring attention. Thus G.B. understands that eyes are important for inferring attentional states and can exert top-down control to seek out and process the gaze of others when attentional states are of interest.
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Reviewed by:
2013Co-Authors: Alan Kingstone, Jason J.s. Barton, Pascal Molenberghs, Kirsten A. DalrympleAbstract:doi: 10.3389/fnhum.2013.00145 A world unglued: Simultanagnosia as a spatial restriction of attentio
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Experiencing Simultanagnosia through windowed viewing of complex social scenes.
Brain research, 2010Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention, defined as an inability to see more than one object at once. It has been conceived as being due to a constriction of the visual "window" of attention, a metaphor that we examine in the present article. A simultanagnosic patient (SL) and two non-simultanagnosic control patients (KC and ES) described social scenes while their eye movements were monitored. These data were compared to a group of healthy subjects who described the same scenes under the same conditions as the patients, or through an aperture that restricted their vision to a small portion of the scene. Experiment 1 demonstrated that SL showed unusually low proportions of fixations to the eyes in social scenes, which contrasted with all other participants who demonstrated the standard preferential bias toward eyes. Experiments 2 and 3 revealed that when healthy participants viewed scenes through a window that was contingent on where they looked (Experiment 2) or where they moved a computer mouse (Experiment 3), their behavior closely mirrored that of patient SL. These findings suggest that a constricted window of visual processing has important consequences for how simultanagnosic patients explore their world. Our paradigm's capacity to mimic simultanagnosic behaviors while viewing complex scenes implies that it may be a valid way of modeling Simultanagnosia in healthy individuals, providing a useful tool for future research. More broadly, our results support the thesis that people fixate the eyes in social scenes because they are informative to the meaning of the scene.
Kirsten A. Dalrymple - One of the best experts on this subject based on the ideXlab platform.
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A world unglued: Simultanagnosia as a spatial restriction of attention
Frontiers in human neuroscience, 2013Co-Authors: Kirsten A. Dalrymple, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention that leaves a patient’s world unglued: scenes and objects are perceived in a piecemeal manner. It is generally agreed that Simultanagnosia is related to an impairment of attention, but it is unclear whether this impairment is object- or space-based in nature. We first consider the findings that support a concept of Simultanagnosia as deficit of object-based attention. We then examine the evidence suggesting that Simultanagnosia results from damage to a space-based attentional system, and in particular a model of Simultanagnosia as a narrowed spatial window of attention. We ask whether seemingly object-based deficits can be explained by space-based mechanisms, and consider the evidence that object processing influences spatial deficits in this condition. Finally, we discuss limitations of a space-based attentional explanation.
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Eyeing the eyes in social scenes: Evidence for top-down control of stimulus selection in Simultanagnosia
Cognitive neuropsychology, 2013Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alexander K. Gray, Brielle L. Perler, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention resulting from bilateral parieto-occipital lesions. Healthy individuals look at eyes to infer people's attentional states, but simultanagnosics allocate abnormally few fixations to eyes in scenes. It is unclear why simultanagnosics fail to fixate eyes, but it might reflect that they are (a) unable to locate and fixate them, or (b) do not prioritize attentional states. We compared eye movements of simultanagnosic G.B. to those of healthy subjects viewing scenes normally or through a restricted window of vision. They described scenes and explicitly inferred attentional states of people in scenes. G.B. and subjects viewing scenes through a restricted window made few fixations on eyes when describing scenes, yet increased fixations on eyes when inferring attention. Thus G.B. understands that eyes are important for inferring attentional states and can exert top-down control to seek out and process the gaze of others when attentional states are of interest.
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Reviewed by:
2013Co-Authors: Alan Kingstone, Jason J.s. Barton, Pascal Molenberghs, Kirsten A. DalrympleAbstract:doi: 10.3389/fnhum.2013.00145 A world unglued: Simultanagnosia as a spatial restriction of attentio
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Experiencing Simultanagnosia through windowed viewing of complex social scenes.
Brain research, 2010Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention, defined as an inability to see more than one object at once. It has been conceived as being due to a constriction of the visual "window" of attention, a metaphor that we examine in the present article. A simultanagnosic patient (SL) and two non-simultanagnosic control patients (KC and ES) described social scenes while their eye movements were monitored. These data were compared to a group of healthy subjects who described the same scenes under the same conditions as the patients, or through an aperture that restricted their vision to a small portion of the scene. Experiment 1 demonstrated that SL showed unusually low proportions of fixations to the eyes in social scenes, which contrasted with all other participants who demonstrated the standard preferential bias toward eyes. Experiments 2 and 3 revealed that when healthy participants viewed scenes through a window that was contingent on where they looked (Experiment 2) or where they moved a computer mouse (Experiment 3), their behavior closely mirrored that of patient SL. These findings suggest that a constricted window of visual processing has important consequences for how simultanagnosic patients explore their world. Our paradigm's capacity to mimic simultanagnosic behaviors while viewing complex scenes implies that it may be a valid way of modeling Simultanagnosia in healthy individuals, providing a useful tool for future research. More broadly, our results support the thesis that people fixate the eyes in social scenes because they are informative to the meaning of the scene.
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Opening a window on attention: documenting and simulating recovery from Simultanagnosia.
Cortex; a journal devoted to the study of the nervous system and behavior, 2010Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention: the inability to see more than one object at one time. Some hypothesize that this is due to a constriction of the visual "window" of attention. Little is known about how simultanagnosics explore complex stimuli and how their behaviour changes with recovery. We monitored the eye movements of simulta- nagnosic patient SL to see how she scans social scenes shortly after onset of simulta- nagnosia (Time 1) and after some recovery (Time 2). At Time 1 SL had an abnormally low proportion of fixations to the eyes of the people in the scenes. She made a significantly larger proportion of fixations to the eyes at Time 2. We hypothesized that this change was related to an expansion of her restricted window of attention. Previously we simulated SL's behaviour in healthy subjects by having them view stimuli through a restricted viewing window. We used this simulation paradigm here to test our expanding window hypothesis. Subjects viewing social scenes through a larger window allocated more fixations to the eyes of people in the scenes than subjects viewing scenes through a smaller window, supporting our hypothesis. Recovery in Simultanagnosia may be related to the expansion of the restricted attentional window that characterizes the disorder.
Jason J.s. Barton - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Simulating Simultanagnosia: spatially constricted vision mimics local capture and the global processing deficit
2016Co-Authors: David Cameron, Jason J.s. Barton, Alan KingstoneAbstract:Abstract Patients with Simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time. As a result, these patients see the world in a piecemeal fashion, seeing the local components of objects or scenes at the expense of the global picture. To directly test the relationship between the restriction of the attentional window in Simultanagnosia and patients ’ diffi-culty with global-level processing, we used a gaze-con-tingent display to create a literal restriction of vision for healthy participants while they performed a global/local identification task. Participants in this viewing condition were instructed to identify the global and local aspects of hierarchical letter stimuli of different sizes and densities. They performed well at the local identification task, and their patterns of inaccuracies for the global level task were highly similar to the pattern of inaccuracies typically seen with simultanagnosic patients. This suggests that a restricted spatial area of visual processing, combined with normal limits to visual processing, can lead to difficulties with global-level perception
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A world unglued: Simultanagnosia as a spatial restriction of attention
Frontiers in human neuroscience, 2013Co-Authors: Kirsten A. Dalrymple, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention that leaves a patient’s world unglued: scenes and objects are perceived in a piecemeal manner. It is generally agreed that Simultanagnosia is related to an impairment of attention, but it is unclear whether this impairment is object- or space-based in nature. We first consider the findings that support a concept of Simultanagnosia as deficit of object-based attention. We then examine the evidence suggesting that Simultanagnosia results from damage to a space-based attentional system, and in particular a model of Simultanagnosia as a narrowed spatial window of attention. We ask whether seemingly object-based deficits can be explained by space-based mechanisms, and consider the evidence that object processing influences spatial deficits in this condition. Finally, we discuss limitations of a space-based attentional explanation.
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Eyeing the eyes in social scenes: Evidence for top-down control of stimulus selection in Simultanagnosia
Cognitive neuropsychology, 2013Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alexander K. Gray, Brielle L. Perler, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention resulting from bilateral parieto-occipital lesions. Healthy individuals look at eyes to infer people's attentional states, but simultanagnosics allocate abnormally few fixations to eyes in scenes. It is unclear why simultanagnosics fail to fixate eyes, but it might reflect that they are (a) unable to locate and fixate them, or (b) do not prioritize attentional states. We compared eye movements of simultanagnosic G.B. to those of healthy subjects viewing scenes normally or through a restricted window of vision. They described scenes and explicitly inferred attentional states of people in scenes. G.B. and subjects viewing scenes through a restricted window made few fixations on eyes when describing scenes, yet increased fixations on eyes when inferring attention. Thus G.B. understands that eyes are important for inferring attentional states and can exert top-down control to seek out and process the gaze of others when attentional states are of interest.
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Reviewed by:
2013Co-Authors: Alan Kingstone, Jason J.s. Barton, Pascal Molenberghs, Kirsten A. DalrympleAbstract:doi: 10.3389/fnhum.2013.00145 A world unglued: Simultanagnosia as a spatial restriction of attentio
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Experiencing Simultanagnosia through windowed viewing of complex social scenes.
Brain research, 2010Co-Authors: Kirsten A. Dalrymple, Elina Birmingham, Walter F. Bischof, Jason J.s. Barton, Alan KingstoneAbstract:Simultanagnosia is a disorder of visual attention, defined as an inability to see more than one object at once. It has been conceived as being due to a constriction of the visual "window" of attention, a metaphor that we examine in the present article. A simultanagnosic patient (SL) and two non-simultanagnosic control patients (KC and ES) described social scenes while their eye movements were monitored. These data were compared to a group of healthy subjects who described the same scenes under the same conditions as the patients, or through an aperture that restricted their vision to a small portion of the scene. Experiment 1 demonstrated that SL showed unusually low proportions of fixations to the eyes in social scenes, which contrasted with all other participants who demonstrated the standard preferential bias toward eyes. Experiments 2 and 3 revealed that when healthy participants viewed scenes through a window that was contingent on where they looked (Experiment 2) or where they moved a computer mouse (Experiment 3), their behavior closely mirrored that of patient SL. These findings suggest that a constricted window of visual processing has important consequences for how simultanagnosic patients explore their world. Our paradigm's capacity to mimic simultanagnosic behaviors while viewing complex scenes implies that it may be a valid way of modeling Simultanagnosia in healthy individuals, providing a useful tool for future research. More broadly, our results support the thesis that people fixate the eyes in social scenes because they are informative to the meaning of the scene.
Elisabeth Huberle - One of the best experts on this subject based on the ideXlab platform.
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A JOURNAL OF NEUROLOGY Enabling global processing in Simultanagnosia by psychophysical biasing of visual pathways
2015Co-Authors: Cibu Thomas, Hans-otto Karnath, Elisabeth Huberle, Kestutis Kveraga, Moshe BarAbstract:A fundamental aspect of visual cognition is our disposition to see the ‘forest before the trees’. However, damage to the posterior parietal cortex, a critical brain region along the dorsal visual pathway, can produce a neurological disorder called simultanag-nosia, characterized by a debilitating inability to perceive the ‘forest ’ but not the ‘trees ’ (i.e. impaired global processing despite intact local processing). This impairment in perceiving the global shape persists even though the ventral visual pathway, the primary recognition pathway, is intact in these patients. Here, we enabled global processing in patients with Simultanagnosia using a psychophysical technique, which allowed us to bias stimuli such that they are processed predominantly by the intact ventral visual pathway. Our findings reveal that the impairment in global processing that characterizes Simultanagnosia stems from a disruption in the processing of low-spatial frequencies through the dorsal pathway. These findings advance our under-standing of the relationship between visuospatial attention and perception and reveal the neural mechanism mediating the disposition to see the ‘forest before the trees’
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Involvement of the tpj area in processing of novel global forms
Journal of cognitive neuroscience, 2015Co-Authors: Johannes Rennig, Elisabeth Huberle, Marc Himmelbach, Hans-otto KarnathAbstract:The neuropsychological syndrome "Simultanagnosia" is characterized by the inability to integrate local elements into a global entity. This deficit in Gestalt perception is mainly apparent for novel global structures administered in clinical tests or unfamiliar visual scenes. Recognition of familiar complex objects or well-known visual scenes is often unaffected. Recent neuroimaging studies and reports from Simultanagnosia patients suggest a crucial involvement of temporoparietal brain areas in processing of hierarchically organized visual material. In this study, we investigated the specific role of the TPJ in Gestalt perception. On the basis of perceptual characteristics known from Simultanagnosia, we hypothesized that TPJ is dominantly involved in processing of novel object arrangements. To answer this question, we performed a learning study with hierarchical stimuli and tested behavioral and neuronal characteristics of Gestalt perception pre-and posttraining. The study included 16 psychophysical training sessions and two neuroimaging sessions. Participants improved their behavioral performance for trained global stimuli and showed limited transfer to untrained global material. We found significant training dependent neuronal signal modulations in anterior right hemispheric TPJ regions. These activation changes were specific to trained global stimuli, whereas no systematic neuronal response changes were observed for recognition of untrained global stimuli, local elements and regular objects that served as control stimuli. In line with perceptual characteristics in Simultanagnosia, the results argue for an involvement of TPJ in processing of novel global structures. We discuss the signal modulations in the context of a more efficient or different neuronal strategy to process familiar global stimuli.
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COGNITIVE NEUROSCIENCE Perception of global gestalt by temporal integration in Simultanagnosia
2015Co-Authors: Elisabeth Huberle, Paul Rupek, Hans-otto KarnathAbstract:Patients with bilateral parieto-occipital brain damage may show intact processing of individual objects, while their perception of multiple objects is disturbed at the same time. The deficit is termed ‘Simultanagnosia ’ and has been discussed in the context of restricted visual working memory and impaired visuo-spatial attention. Recent observations indicated that the recognition of global shapes can be modulated by the spatial distance between individual objects in patients with Simultanagnosia and thus is not an all-or-nothing phenomenon depending on spatial continuity. However, grouping mechanisms not only require the spatial integration of visual information, but also involve integration processes over time. The present study investigated motion-defined integration mechanisms in two patients with Simultanagnosia. We applied hierarchical organized stimuli of global objects that consisted of coherently moving dots (‘shape-from-motion’). In addition, we tested the patients ’ ability to recognize biological motion by presenting characteristic human movements (‘point-light-walker’). The data revealed largely preserved perception of biological motion, while the perception of motion-defined shapes was impaired. Our findings suggest separate mechanisms underlying the recognition of biological motion and shapes defined by coherently moving dots. They thus argue against a restriction in the overall capacity of visual working memory over time as a general explanation for the impaired global shape recognition in patients with Simultanagnosia
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Bilateral Theta-Burst TMS to Influence Global Gestalt Perception
PloS one, 2012Co-Authors: Bernd Ritzinger, Elisabeth Huberle, Hans-otto KarnathAbstract:While early and higher visual areas along the ventral visual pathway in the inferotemporal cortex are critical for the recognition of individual objects, the neural representation of human perception of complex global visual scenes remains under debate. Stroke patients with a selective deficit in the perception of a complex global Gestalt with intact recognition of individual objects – a deficit termed Simultanagnosia – greatly helped to study this question. Interestingly, Simultanagnosia typically results from bilateral lesions of the temporo-parietal junction (TPJ). The present study aimed to verify the relevance of this area for human global Gestalt perception. We applied continuous theta-burst TMS either unilaterally (left or right) or bilateral simultaneously over TPJ. Healthy subjects were presented with hierarchically organized visual stimuli that allowed parametrical degrading of the object at the global level. Identification of the global Gestalt was significantly modulated only for the bilateral TPJ stimulation condition. Our results strengthen the view that global Gestalt perception in the human brain involves TPJ and is co-dependent on both hemispheres.
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Enabling global processing in Simultanagnosia by psychophysical biasing of visual pathways.
Brain : a journal of neurology, 2012Co-Authors: Cibu Thomas, Hans-otto Karnath, Elisabeth Huberle, Kestutis Kveraga, Moshe BarAbstract:A fundamental aspect of visual cognition is our disposition to see the 'forest before the trees'. However, damage to the posterior parietal cortex, a critical brain region along the dorsal visual pathway, can produce a neurological disorder called Simultanagnosia, characterized by a debilitating inability to perceive the 'forest' but not the 'trees' (i.e. impaired global processing despite intact local processing). This impairment in perceiving the global shape persists even though the ventral visual pathway, the primary recognition pathway, is intact in these patients. Here, we enabled global processing in patients with Simultanagnosia using a psychophysical technique, which allowed us to bias stimuli such that they are processed predominantly by the intact ventral visual pathway. Our findings reveal that the impairment in global processing that characterizes Simultanagnosia stems from a disruption in the processing of low-spatial frequencies through the dorsal pathway. These findings advance our understanding of the relationship between visuospatial attention and perception and reveal the neural mechanism mediating the disposition to see the 'forest before the trees'.