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The ability of seeing with the mind's eye, the visual mental imagery, is peculiarly compromised in patients with representational neglect. Representational neglect affects the processing of the left side of a mental image and may selectively concern the ability to imagine places and/or objects. Right-brain damaged patients with representational neglect for places (RN+) lose the ability to imagine themselves within a familiar place and fail in transforming an egocentric representation of the environment into an allocentric one and vice-versa. A peak region located at the posterior junction between the parietal and temporal lobes has emerged as pivotal in determining representational neglect for places. Here we aimed at verifying whether white matter disconnections affecting parietal lobe, by preventing the integration of egocentric information with the allocentric one, play a role in representational neglect for places. A track-wise statistical analysis on 58 right brain damaged patients, with and without extrapersonal perceptual neglect and/or representational neglect for places, suggests that the disconnection of the superior longitudinal fasciculus and that of the posterior arcuate segment, together with the disconnection of a fronto-parietal u-shaped tract, may be crucial in determining the representational neglect for places. These results suggest that representational neglect for places emerges from a complex pattern of lesion location and disconnection that involves parietal, temporal and frontal lobes.

The ability to imagine the world from a different viewpoint is a fundamental competence for spatial reorientation and for imagining what another individual sees in the environment. Here, we investigated the neural bases of such an ability using functional magnetic resonance imaging. Healthy participants detected target displacements across consecutive views of a familiar virtual room, either from the perspective of an avatar (primed condition) or in the absence of such a prime (unprimed condition). In the primed condition, the perspective at test always corresponded to the avatar's perspective, while in the unprimed condition it was randomly chosen as 0, 45 or 135deg of viewpoint rotation. We observed a behavioral advantage in performing a perspective transformation during the primed condition as compared to an equivalent amount of unprimed perspective change. Although many cortical regions (dorsal parietal, parieto-temporo-occipital junction, precuneus and retrosplenial cortex/parieto-occipital sulcus or RSC/POS) were involved in encoding and retrieving target location from different perspectives and were modulated by the amount of viewpoint rotation, the RSC/POS was the only area showing decreased activity in the primed as compared to the unprimed condition, suggesting that this region anticipates the upcoming perspective change. The retrosplenial cortex/parieto-occipital sulcus appears to play a special role in the allocentric coding of heading directions., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Humans have an advanced ability to recall places and scenes from memory, which they scan with their "mind's eye" in order to cope with daily demands such as navigating and learning new environments. In the striking neurological syndrome called representational or imaginal neglect, patients with right brain damage fail to report contralesional, left-sided elements of familiar places relative to their imaginary vantage point. Notwithstanding descriptions of single cases of representational neglect dissociated from perceptual or visual neglect, it is still unknown whether this disorder is due to specific brain lesions. Here we show that the ability to properly recall and inspect places from memory is supported by a neural network dissociated from that necessary to properly scan single objects from memory or the external visual world. Lesion-symptoms mapping of 40 right-damaged patients with and without imaginal neglect identified a peak region located at the posterior junction between the parietal and temporal lobes (pTPJ), where the angular and supramarginal gyri abut on the posterior temporal cortex. This region is known to support first-person perspective transformations and is connected with systems relevant for navigation and retrieval from autobiographical memory. Our results provide new insights on human spatial memory and imagery and their relationship with visuospatial attention, directly affecting recent neural and computational models., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In the visuospatial domain, perspective taking is the ability to imagine how a visual scene appears from an external observer's viewpoint, and can be studied by asking subjects to encode object locations in a visual scene where another individual is present and then detecting their displacement when seeing the scene from the other's viewpoint. In the current study, we explored the relationship between visuospatial perspective taking and self-report measures of the cognitive and emotional components of empathy in young adults. To this aim, we employed a priming paradigm, in which the presence of an avatar allowed to anticipate the next perceived perspective on the visual scene. We found that the emotional dimension of empathy was positively correlated with the behavioral advantage provided by the presence of the avatar, relative to unprimed perspective changes. These data suggest a link between the tendency to vicariously experience the others' emotions and the ability to perform self-other spatial transformations.

Background: As social animals we share the space with other people. It is known that perceived extension of the peripersonal space (the reaching space) is affected by the implicit representation of our own and other's action potentialities. Our issue concerns whether the co-presence of a body in the scene influences our extrapersonal space (beyond reaching distance) categorization., Methodology/principal Findings: We investigated, through 3D virtual scenes of a realistic environment, whether egocentric spatial categorization can be influenced by the presence of another human body (Exp. 1) and whether the effect is due to her action potentialities or simply to her human-like morphology (Exp. 2). Subjects were asked to judge the location ("Near" or "Far") of a target object located at different distances from their egocentric perspective. In Exp. 1, the judgment was given either in presence of a virtual avatar (Self-with-Other), or a non-corporeal object (Self-with-Object) or nothing (Self). In Exp. 2, the Self condition was replaced by a Self-with-Dummy condition, in which an inanimate body (a wooden dummy) was present. Mean Judgment Transition Thresholds (JTTs) were calculated for each subject in each experimental condition. Self-with-Other condition induced a significant extension of the space judged as "Near" as compared to both the Self-with-Object condition and the Self condition. Such extension was observed also in Exp. 2 in the Self-with-Dummy condition. Results suggest that the presence of others impacts on our perception of extrapersonal space. This effect holds also when the other is a human-like wooden dummy, suggesting that structural and morphological shapes resembling human bodies are sufficient conditions for the effect to occur., Conclusions: The observed extension of the portion of space judged as near could represent a wider portion of "accessible" space, thus an advantage in the struggle to survive in presence of other potential competing individuals.

Posterior parahippocampal gyrus (PPHG) is strongly involved during scene recognition and spatial cognition. How PPHG electrophysiological activity could underlie these functions, and whether they share similar timing mechanisms is unknown. We addressed this question in two intracerebral experiments which revealed that PPHG neural activity dissociated an early stimulus-driven effect (>200 and <500 ms) and a late task-related effect (>600 and <800 ms). Strongest PPHG gamma band (50-150 Hz) activities were found early when subjects passively viewed scenes (scene selectivity effect) and lately when they had to estimate the position of an object relative to the environment (allocentric effect). Based on single trial analyses, we were able to predict when patients viewed scenes (compared to other visual categories) and when they performed allocentric judgments (compared to other spatial judgments). The anatomical location corresponding to the strongest effects was in the depth of the collateral sulcus. Our findings directly affect current theories of visual scene processing and spatial orientation by providing new timing constraints and by demonstrating the existence of separable information processing stages in the functionally defined parahippocampal place area., (Copyright © 2012 Wiley Periodicals, Inc.)

Remembering object locations across different views is a fundamental competence for keeping oriented in large-scale space. Here we investigated such ability by comparing encoding and retrieval of locations across viewpoint changes relative to different spatial frames of reference. We acquired functional magnetic resonance images while subjects detected target displacements across consecutive views of a familiar virtual room, reporting changes in the target absolute position in the room (stable environmental frame), changes in its position relative to a set of movable objects (unstable object-based frame), and changes relative to their point of view (control viewer-centered frame). Behavioral costs were higher for the stable environmental frame, and a cortical network including the lingual/parahippocampal gyrus (LPHG) and the retrosplenial complex (RSC) selectively encoded spatial locations relative to this frame. Several regions, including the dorsal fronto-parietal cortex and the LPHG, were modulated by the amount of experienced viewpoint change, but only the RSC was selectively modulated by the amount of viewpoint change relative to the environmental frame, thus showing a special role in coding one's own position and heading in familiar environments., (Copyright © 2012 Elsevier B.V. All rights reserved.)

We benefited from the flexibility provided by virtual reality to enhance a classical paradigm on array and self mental rotations and related questions on a set of items. We used this paradigm to investigate how the Level of Schizotypy in nonclinical subjects might influence their behavior in egocentric and allocentric mental transformations. Three elements of novelty were introduced: (i) we separated the phases of mental transformation (Imagined Rotation Phase) and task performance (Task Phase), (ii) we measured the time required for Imagined Rotation Phase and Task Phase separately, and (iii) we cued self-rotations with a virtual human being (self-avatar) or an inanimate object (self-chair). Twenty-four nonclinical participants were categorized in low- and high-schizotypal subjects (Low-S, High-S). A mixed-design analysis of variance showed that High-S were significantly faster than Low-S during the Imagined Rotation Phase (array and self-chair rotations) and during the Task Phase (self-chair). High-S were also faster in the self-chair than in the self-avatar rotation, supporting the existence of a dissociation between perspective changing and perspective taking in High-S. In line with the literature, we found that participant performances decreased with increasing angular difference between the initial and the imagined perspective.

To date, mutual interaction between action and perception has been investigated mainly by focusing on single individuals. However, we perceive affording objects and acts upon them in a surrounding world inhabited by other perceiving and acting bodies. Thus, the issue arises as to whether our action-oriented object perception might be modulated by the presence of another potential actor. To tackle this issue we used the spatial alignment effect paradigm and systematically examined this effect when a visually presented handled object was located close either to the perceiver or to another individual (a virtual avatar). We found that the spatial alignment effect occurred whenever the object was presented within the reaching space of a potential actor, regardless of whether it was the participant's own or the other's reaching space. These findings show that objects may afford a suitable motor act when they are ready not only to our own hand but also, and most importantly, to the other's hand. Our proposal is that this effect is likely to be due to a mapping of our own and the other's reaching space and we posit that such mapping could play a critical role in joining our own and the other's action.

A series of experiments provide evidence that affordances rely not only on the mutual appropriateness of the features of an object and the abilities of an individual, but also on the fact that those features fall within her own reachable space, thus being really ready-to-her-own-hand. We used a spatial alignment effect paradigm and systematically examined this effect when the visually presented object was located either within or outside the peripersonal space of the participants, both from a metric (Experiment 1) and from a functional point of view (Experiment 2). We found that objectual features evoke actions only when the object is presented within the portion of the peripersonal space that is effectively reachable by the participants. Experiments 3 and 4 ruled out that our results could be merely accounted for by differences in the visual salience of the presented objects. Our data suggest that the power of an object to automatically trigger an action is strictly linked to the effective possibility that an individual has to interact with it.

We review human functional neuroimaging studies that have explicitly investigated the reference frames used in different cortical regions for representing spatial locations of objects. Beyond the general distinction between "egocentric" and "allocentric" reference frames, we provide evidence for the selective involvement of the posterior parietal cortex and associated frontal regions in the specific process of egocentric localization of visual and somatosensory stimuli with respect to relevant body parts ("body referencing"). Similarly, parahippocampal and retrosplenial regions, together with specific parietal subregions such as the precuneus, are selectively involved in a specific form of allocentric representation in which object locations are encoded relative to enduring spatial features of a familiar environment ("environmental referencing"). We also present a novel functional magnetic resonance imaging study showing that these regions are selectively activated, whenever a purely perceptual spatial task involves an object which maintains a stable location in space during the whole experiment, irrespective of its perceptual features and its orienting value as a landmark. This effect can be dissociated from the consequences of an explicit memory recall of landmark locations, a process that further engages the retrosplenial cortex.

Psychotic symptoms in schizophrenia patients encompass the difficulty to distinguish between the respective points of view of self and others. The capacity to adopt and switch between different perspectives is, however, fundamental for ego- and allocentric spatial referencing. We tested whether schizophrenia patients are able to adopt and maintain a non-egocentric point of view in a complex visual environment. Twenty-four chronic schizophrenic outpatients (11 females) and 25 controls matched for age, gender, years of education and handedness were recruited from a population-based sample. In a virtual environment, participants had to make a decision as to which of two trash cans was closest to themselves (viewer-centered, egocentric), to a ball (object-centered, unstable allocentric), or to a palace (landmark-centered, stable allocentric). Main outcome measures were reaction time, error rate, learning rate and local task switch cost. While egocentric reaction time was preserved, patients showed an increased reaction time in both allocentric referencing conditions (stable and unstable) and an overall increased error rate. Switch cost was diminished in patients when changing from the egocentric to the landmark-centered condition and elevated when changing from the landmark-centered to the egocentric condition. The results imply that schizophrenia patients' adoption of an egocentric perspective is preserved. However, adopting an allocentric point of view and switching between egocentric and landmark-centered perspectives are impaired. Perturbations in non-egocentric referencing and transferring efficiently between different referential systems might contribute to altered personal and social world comprehension in schizophrenia., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Human awareness of left space may be disrupted by cerebral lesions to the right hemisphere (hemispatial neglect). Current knowledge on the anatomical bases of this complex syndrome is based on the results of group studies that investigated primarily the best known aspect of the syndrome, which is visual neglect for near extrapersonal (or peripersonal) space. However, another component-neglect for personal space-is more often associated with, than double-dissociated from, extrapersonal neglect, especially, in chronic patients. The present investigation aimed at exploring the anatomical substrate of both extrapersonal and personal neglect by using different advanced methodological approaches to lesion-function correlation. Fifty-two right ischaemic patients were submitted to neuropsychological assessment and in-depth MRI evaluation. The borders of each patient's lesion were delimited onto its own high-resolution anatomical image and then submitted to an automated spatial normalization algorithm. Besides conventional lesion density plots and subtraction analysis, region-based statistical analyses were performed on percentage values of the lesioned tissue also using a new parcellation of the white matter (WM). Data were finally submitted to voxelwise statistical analysis using a recently proposed method (voxel-based lesion-symptom mapping). Results converged in showing that awareness of extrapersonal space is based on the integrity of a circuit of right frontal (ventral premotor cortex and middle frontal gyrus) and superior temporal regions, whereas awareness of personal space is rooted in right inferior parietal regions (supramarginal gyrus, post-central gyrus and especially the WM medial to them). Common but less crucial regions for both neglect sub-types were located in the temporo-peri-Sylvian cortex. We suggest that extrapersonal space awareness critically involves a ventral circuit recently described for the exogenous allocation and reorienting of attention in space. Disruption of personal space awareness, instead, seems to be due to a functional disconnection between regions important for coding proprioceptive and somatosensory inputs, and regions coding more abstract egocentric representations of the body in space. In conclusion, present data strongly support a segregation of personal and extrapersonal spatial awareness in humans, both from a functional and an anatomical point of view.

Functional magnetic resonance imaging was used to compare the neural correlates of three different types of spatial coding, which are implicated in crucial cognitive functions of our everyday life, such as visuomotor coordination and orientation in topographical space. By manipulating the requested spatial reference during a task of relative distance estimation, we directly compared viewer-centered, object-centered, and landmark-centered spatial coding of the same realistic 3-D information. Common activation was found in bilateral parietal, occipital, and right frontal premotor regions. The retrosplenial and ventromedial occipital-temporal cortex (and parts of the parietal and occipital cortex) were significantly more activated during the landmark-centered condition. The ventrolateral occipital-temporal cortex was particularly involved in object-centered coding. Results strongly demonstrate that viewer-centered (egocentric) coding is restricted to the dorsal stream and connected frontal regions, whereas a coding centered on external references requires both dorsal and ventral regions, depending on the reference being a movable object or a landmark.

According to the action-specific theory of perception, a person's dynamic ability to act in the environment affects her/his spatial perception. Empirical evidence shows that the elderly perceive distances as farther compared with younger adults and that the harder the ground surface to walk, the farther the perceived distance. Such results suggest a general perceptual readaptation promoted by the aging process that is fine-tuned with the decline of the motor resources. However, it is still unknown whether the elderly space perception is affected by interindividual differences in their functional autonomy (FA) and whether the decline of motor resources affects spatial categorization only when distances are judged with reference to the observer's own body or also when they are judged with reference to the body of another agent present in the scene. To this aim, a sample of elderly adults with preserved cognitive functions but different levels of FA, measured through the Instrumental Activity of Daily Living (IADL) scale, were enrolled and tested on the extrapersonal space categorization task. This task requires judging the position of a target as "Near" or "Far" with respect to different reference frames (RFs): centered on the observer's body (Self RF) or centered on external elements, like another body (Other RF) or an object (Object RF). Results indicated that the higher the level of FA, the wider the space categorized as "Near" when adopting as reference frame our own body or the body of another agent in the scene, but not a static object. In conclusion, the individual functional autonomy of elderly individuals, which is strongly influenced by motor resources and efficiency, modulates how the surrounding space is represented, but only when the distance judgment implies an agent body, thus providing new relevant data for recent embodied cognition models of aging. [ABSTRACT FROM AUTHOR]

Recent results have shown that the way we categorize space varies as a function of the frame of reference. If the reference frame (RF) is another person vs. an object, the distance is judged as reduced. It has been suggested that such an effect is due to the spontaneous processing of the other's motor potentialities. To investigate the impact of movement representation on space perception, we used biological motion displays as a prime for a spatial categorization task. In Exp. 1, participants were presented with a point-light walker or a scrambled motion, and then judged the location (“Near” or “Far”) of a target with a human body or an inanimate object as RF. In Exp. 2, participants were primed with point-light walkers of different speeds: a runner, a normal walker and a slow walker. In Exp. 3 they were primed with a point-light display depicting a human body sitting down on or standing up from a chair, with a human body RF either oriented or not oriented towards the target. Results showed a reduced judged distance when the human body RF was primed with a point-light walker (Exp. 1). Furthermore, we found an additional reduction of the judged distance when priming with a runner (Exp. 2). Finally, Exp. 3 showed that the human body RF has to be target oriented as a precondition for priming effects of the point-light walker. [ABSTRACT FROM AUTHOR]