Elisabeth Huberle

Perception of biological motion in visual agnosia

Over the past 25 years, visual processing has been discussed in the context of the dual stream hypothesis consisting of a ventral (“what”) and a dorsal (“where”) visual information processing pathway. Patients with brain damage of the ventral pathway typically present with signs of visual agnosia, the inability to identify and discriminate objects by visual exploration, but show normal perception of motion perception. A dissociation between the perception of biological motion and non-biological motion has been suggested: perception of biological motion might be impaired when “non-biological” motion perception is intact and vice versa. The impact of object recognition on the perception of biological motion remains unclear. We thus investigated this question in a patient with severe visual agnosia, who showed normal perception of non-biological motion. The data suggested that the patients perception of biological motion remained largely intact. However, when tested with objects constructed of coherently moving dots (“Shape-from-Motion”), recognition was severely impaired. The results are discussed in the context of possible mechanisms of biological motion perception.

Global shape recognition is modulated by the spatial distance of local elements: Evidence from simultanagnosia

Simultanagnosia is a rare deficit that impairs individuals in perceiving several objects at the same time. It is usually observed following bilateral parieto-occipital brain damage. Despite the restrictions in perceiving the global aspect of a scene, processing of individual objects remains unaffected. The mechanisms underlying simultanagnosia are not well understood. Previous findings indicated that the integration of multiple objects into a holistic representation of the environment is not impossible per se, but might depend on the spatial relationship between individual objects. The present study examined the influence of inter-element distances between individual objects on the recognition of global shapes in two patients with simultanagnosia. We presented Navon hierarchical letter stimuli with different inter-element distances between letters at the Local Scale. Improved recognition at the Global Scale was observed in both patients by reducing the inter-element distance. Global shape recognition in simultanagnosia thus seems to be modulated by the spatial distance of local elements and does not appear to be an all-or-nothing phenomenon depending on spatial continuity. The findings seem to argue against a deficit in visual working memory capacity as the primary deficit in simultanagnosia. However, further research is necessary to investigate alternative interpretations.

Association of trait emotional intelligence and individual fMRI-activation patterns during the perception of social signals from voice and face

Multimodal integration of nonverbal social signals is essential for successful social interaction. Previous studies have implicated the posterior superior temporal sulcus (pSTS) in the perception of social signals such as nonverbal emotional signals as well as in social cognitive functions like mentalizing/theory of mind. In the present study, we evaluated the relationships between trait emotional intelligence (EI) and fMRI activation patterns in individual subjects during the multimodal perception of nonverbal emotional signals from voice and face. Trait EI was linked to hemodynamic responses in the right pSTS, an area which also exhibits a distinct sensitivity to human voices and faces. Within all other regions known to subserve the perceptual audiovisual integration of human social signals (i.e., amygdala, fusiform gyrus, thalamus), no such linked responses were observed. This functional difference in the network for the audiovisual perception of human social signals indicates a specific contribution of the pSTS as a possible interface between the perception of social information and social cognition. Hum Brain Mapp, 2010.

The role of temporo-parietal junction (TPJ) in global Gestalt perception

Grouping processes enable the coherent perception of our environment. A number of brain areas has been suggested to be involved in the integration of elements into objects including early and higher visual areas along the ventral visual pathway as well as motion-processing areas of the dorsal visual pathway. However, integration not only is required for the cortical representation of individual objects, but is also essential for the perception of more complex visual scenes consisting of several different objects and/or shapes. The present fMRI experiments aimed to address such integration processes. We investigated the neural correlates underlying the global Gestalt perception of hierarchically organized stimuli that allowed parametrical degrading of the object at the global level. The comparison of intact versus disturbed perception of the global Gestalt revealed a network of cortical areas including the temporo-parietal junction (TPJ), anterior cingulate cortex and the precuneus. The TPJ location corresponds well with the areas known to be typically lesioned in stroke patients with simultanagnosia following bilateral brain damage. These patients typically show a deficit in identifying the global Gestalt of a visual scene. Further, we found the closest relation between behavioral performance and fMRI activation for the TPJ. Our data thus argue for a significant role of the TPJ in human global Gestalt perception.

The temporo-parietal junction contributes to global gestalt perception—evidence from studies in chess experts

In a recent neuroimaging study the comparison of intact vs. disturbed perception of global gestalt indicated a significant role of the temporo-parietal junction (TPJ) in the intact perception of global gestalt (Huberle and Karnath, 2012). This location corresponded well with the areas known to be damaged or impaired in patients with simultanagnosia after stroke or due to neurodegenerative diseases. It was concluded that the TPJ plays an important role in the integration of individual items to a holistic percept. Thus, increased BOLD signals should be found in this region whenever a task calls for the integration of multiple visual items. Behavioral experiments in chess experts suggested that their superior skills in comparison to chess novices are partly based on fast holistic processing of chess positions with multiple pieces. We thus analyzed BOLD data from four fMRI studies that compared chess experts with chess novices during the presentation of complex chess-related visual stimuli (Bilalić et al., 2010, 2011a,b, 2012). Three regions of interests were defined by significant TPJ clusters in the abovementioned study of global gestalt perception (Huberle and Karnath, 2012) and BOLD signal amplitudes in these regions were compared between chess experts and novices. These cross-paradigm ROI analyses revealed higher signals at the TPJ in chess experts in comparison to novices during presentations of complex chess positions. This difference was consistent across the different tasks in five independent experiments. Our results confirm the assumption that the TPJ region identified in previous work on global gestalt perception plays an important role in the processing of complex visual stimulus configurations.

Retinal versus physical stimulus size as determinants of visual perception in simultanagnosia

Patients with simultanagnosia following bilateral parieto-temporo-occipital brain damage show a characteristic impairment of global gestalt perception, while their perception of individual objects or elements remains intact. For instance, when shown ‘hierarchical’ stimuli comprising a larger global object (e.g. a large letter) made up from smaller components (e.g. multiple small letters), they typically report seeing one of the smaller components but not the global figure. Recent work on simultanagnosia revealed that global perception can be improved if local element spacing is reduced. However, it is still unclear whether the retinal separation or the physical (post-size-constancy) spatial separation is critical. Here, we presented various hierarchical global/local letter stimuli at different viewing distances and sizes to separate the impacts of retinal versus physical size. Our findings indicate a key role for visual angle in determining simultanagnosic perception. We observed that not only retinal spacing (in terms of visual angle) between local elements had a major impact on global perception in simultanagnosia, but also the physical size of the separation between local elements, provided that binocular cues to viewing distance were available. The results indicate both pre-size-constancy retinal influences and binocular-post-constancy influences upon conscious perception in simultanagnosia.

Saliency modulates global perception in simultanagnosia.

Patients with parieto-occipital brain damage may show simultanagnosia, a selective impairment in the simultaneous perception and integration of multiple objects (global perception) with normal recognition of individual objects. Recent findings in patients with simultanagnosia indicate improved global perception at smaller spatial distances between local elements of hierarchical organized complex visual arrays. Global perception thus does not appear to be an all-or-nothing phenomenon but can be modified by the spatial relationship between local elements. The present study aimed to define characteristics of a general principle that accounts for improved global perception of hierarchically organized complex visual arrays in patients with simultanagnosia with respect to the spatial properties of local elements. In detail, we investigated the role of the number and size of the local elements as well as their relationship with each other for the global perception. The findings indicate that global perception increases independently of the size of the global object and depends on the spatial relationship between the local elements and the global object. The results further argue against the possibility of a restriction in the attended or perceived area in simultanagnosia, in the sense that the integration of local elements into a global scene is impaired if a certain spatial “field of view” is exceeded. A possible explanation for these observations might be a shift from global to local saliency in simultanagnosia.

Perception of global gestalt by temporal integration in simultanagnosia.

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.

Involvement of the tpj area in processing of novel global forms

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.

Bilateral theta-burst TMS to influence global gestalt perception

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.