Representation Of Extrapersonal Space Research Articles

Embodying their own wheelchair modifies extrapersonal space perception in people with spinal cord injury.

Despite the many links between body representation, acting and perceiving the environment, no research has to date explored whether specific tool embodiment in conditions of sensorimotor deprivation influences extrapersonal space perception. We tested 20 spinal cord injured (SCI) individuals to investigate whether specific wheelchair embodiment interacts with extrapersonal space representation. As a measure of wheelchair embodiment, we used a Body View Enhancement Task in which participants (either sitting in their own wheelchair or in one which they had never used before) were asked to respond promptly to flashing lights presented on their above- and below-lesion body parts. Similar or slower reaction times (RT) to stimuli on the body and wheelchair indicate, respectively, the presence or absence of tool embodiment. The RTs showed that the participants embodied their own wheelchair but not the other one. Moreover, they coded their deprived lower limbs as external objects and, when not in their own wheelchair, also showed disownership of their intact upper limbs. To measure extrapersonal space perception, we used a novel, ad hoc designed paradigm in which the participants were asked to observe a 3D scenario by means of immersive virtual reality and estimate the distance of a flag positioned on a ramp. In healthy subjects, errors in estimation increased as the distance increased, suggesting that they mentally represent the physical distance. The same occurred with the SCI participants, but only when they were in their own wheelchair. The results demonstrate for the first time that tool embodiment modifies extrapersonal space estimations.

Walking-related locomotion is facilitated by the perception of distant targets in the extrapersonal space

The Gibsonian notion of affordance has been massively employed in cognitive sciences to characterize the tight interdependence between hand-related actions, manipulable objects and peripersonal space. A behavioural facilitation effect, indeed, is observed for grasping actions directed to objects located in the ‘reachable’ peripersonal space. Relevantly, this relationship is supported by dedicated neural systems in the brain. The original notion of affordance, however, was directly inspired by real-time interactions between animals and their extended natural environment. Consistently, also the extrapersonal space representation can be significantly modulated by action-related factors, and the brain contains dedicated systems for the representation of topographical space and navigation. Here we examined whether a facilitation effect could be also described for a walking-related action in the far extrapersonal space. To this aim, we employed a go/no-go paradigm requiring subjects to execute a footstep ahead in response to pictures of a virtual reality environment containing objects located at different distances (near, far) and eccentricities (central, peripheral). A walking-related, facilitation effect for distant extrapersonal locations was found, suggesting an automatic trigger of walking by positions that preferentially guide spatial exploration. Based on the parallelism with the literature on micro-affordances, we propose that this effect can be described in terms of “macro-affordances”.

Hyperschematia after right brain damage: a meaningful entity?

In recent years we reported three right-brain-damaged patients, who exhibited a left-sided disprortionate expansion of drawings, both by copying and from memory, contralateral to the side of the hemispheric lesion (Neurology, 67: 1801, 2006, Neurocase 14: 369, 2008). We proposed the term “hyperschematia” for such an expansion, with reference to an interpretation in terms of a lateral leftward distortion of the representation of extra-personal space, with a leftward anisometric expansion (relaxation) of the spatial medium. The symptom-complex shown by right-brain-damaged patients with “hyperschematia” includes: (1) a disproportionate leftward expansion of drawings (with possible addition of details), by copy and from memory (also in clay modeling, in one patient); (2) an overestimation of left lateral extent, when a leftward movement is required, associated in some patients with a perceptual underestimation; (3) unawareness of the disorder; (4) no unilateral spatial neglect. In most right-brain-damaged patients, left “hyperschematia” involves extra-personal space. In one patient the deficit was confined to a body part (left half-face: personal “hyperschematia”). The neural underpinnings of the disorder include damage to the fronto-temporo-parietal cortices, and subcortical structures in the right cerebral hemisphere, in the vascular territory of the middle cerebral artery. Here, four novel additional patients are reported. Finally, “hypeschematia” is reconsidered, in its clinical components, the underlying pathological mechanisms, as well as its neural underpinnings.

Personal neglect—A disorder of body representation?

The cognitive mechanisms underlying personal neglect are not well known. One theory postulates that personal neglect is due to a disorder of contralesional body representation. In the present study, we have investigated whether personal neglect is best explained by impairments in the representation of the contralesional side of the body, in particular, or a dysfunction of the mental representation of the contralesional space in general. For this, 22 patients with right hemisphere cerebral lesions (7 with personal neglect, 15 without personal neglect) and 13 healthy controls have been studied using two experimental tasks measuring representation of the body and extrapersonal space. In the tasks, photographs of left and right hands as well as left and right rear-view mirrors presented from the front and the back had to be judged as left or right. Our results show that patients with personal neglect made more errors when asked to judge stimuli of left hands and left rear-view mirrors than either patients without personal neglect or healthy controls. Furthermore, regression analyses indicated that errors in interpreting left hands were the best predictor of personal neglect, while other variables such as extrapersonal neglect, somatosensory or motor impairments, or deficits in left extrapersonal space representation had no predictive value of personal neglect. These findings suggest that deficient body representation is the major mechanism underlying personal neglect.

Vestibular syndrome: A change in internal spatial representation

The vestibular system contributes to a wide range of functions from reflexes to spatial representation. This paper reviews behavioral, perceptive, and cognitive data that highlight the role of changes in internal spatial representation on the vestibular syndrome. Firstly, we review how visual vertical perception and postural orientation depend on multiple reference frames and multisensory integration and how reference frames are selected according to the status of the peripheral vestibular system (i.e., unilateral or bilateral hyporeflexia), the environmental constraints (i.e., sensory cues), and the postural constraints (i.e., balance control). We show how changes in reference frames are able to modify vestibular lesion-induced postural and locomotor deficits and propose that fast changes in reference frame may be considered as fast-adaptive processes after vestibular loss. Secondly, we review data dealing with the influence of vestibular loss on higher levels of internal representation sustaining spatial orientation and navigation. Particular emphasis is placed on spatial performance according to task complexity (i.e., the required level of spatial knowledge) and to the sensory cues available to define the position and orientation within the environment (i.e., real navigation in darkness or visual virtual navigation without any actual self-motion). We suggest that vestibular signals are necessary for other sensory cues to be properly integrated and that vestibular cues are involved in extrapersonal space representation. In this respect, vestibular-induced changes would be based on a dynamic mental representation of space that is continuously updated and that supports fast-adaptive processes.

3D left hyperschematia after right brain damage

A quantitative assessment of a distortion involving the left side of space, both in two-dimensional (drawing), and three-dimensional (modeling), visuo-constructional tasks is reported in a patient with a right temporoparieto-occipital lesion, and left hemianopia, without visuospatial neglect. In drawing and clay modeling of objects the patient exhibited a disproportionate enlargement of the left-hand side of objects. Matching perceptually two rectangles, the patient underestimated the left side of the stimulus. In a visuomotor task requiring the reproduction of horizontal extent, the patient exhibited a leftward overextension. Observations in two right-brain-damaged patients by Rode, Michel, Rossetti, Boisson, and Vallar (2006, Neurology, 67, 1801) are confirmed and extended. The patient's impairment may involve a disordered representation of extrapersonal space, with a leftward disproportionate expansion of the spatial medium (‘hyperschematia’). Accordingly, symmetrical productions are compensatorily expanded leftwards, and the left sides of objects are perceived as smaller in horizontal extent. The disorder is largely independent of left spatial neglect.

Fundamental Requirements for Primary Visual Perception

A novel perspective for the necessary and sufficient conditions for primary visual perception is proposed based upon relating recent discoveries from the visual sciences to relevant foundational neurological observations. This analysis suggests that a fundamental requirement for the emergence of normal primary visual perception is the coupling between the early visual cortices in the occipital lobe subserving image content with specific areas in the parietal lobe subserving selective attention, representations of extrapersonal space, the body schema, and the initiation of perceptual ownership. Fully intact primary visual perception, which includes the normal placement of image content within extrapersonal space, seems to require at each instant a mutually consistent completeness and corresponding removal of ambiguities in each of the linked neural representations subserving image, space and self. Experimental approaches that could either invalidate or strengthen the proposed framework are suggested as well as opportunities to differentiate some aspects of normal primary visual perception from the severely compromised visual experience that survives bilateral parieto-occipital lesions (Balint's syndrome) when visual experience may persist for single but unlocalizable objects.

Female Advantage for Object Location Memory in Peripersonal but not Extrapersonal Space

The neural representation of peripersonal space may be distinct from the representation of extrapersonal space. Sex differences in the performance of motor tasks might relate to proximity to the body. In the spatial domain, females excel at tasks performed in peripersonal space, like the Object Location Memory Task (OLMT), whereas males excel at tasks performed in extrapersonal space, such as navigation. We compared performance on the OLMT in peripersonal space with performance on the same task in extrapersonal space (using a between-subjects design). As predicted, the typical female advantage was observed for the peripersonal OLMT. However, for the extrapersonal OLMT, the female advantage disappeared and males actually outperformed females. These results suggest that the sex differences observed in the OLMT, and potentially other tasks that exhibit sex differences in performance, may be related to sex differences to spatial-motor systems that are preferentially tuned to proximity.

Left size distortion (hyperschematia) after right brain damage

To quantitate a size distortion involving the side of space contralateral to the lesion (contralesional) in two right-brain-damaged patients. We studied two right-brain-damaged patients with lesions sparing the occipital lobe and a mild left neglect on target cancellation or line bisection. The lesions involved the temporoparietal region (Patient 1) and the basal ganglia and the insula (Patients 1 and 2). Patients were given drawing tasks and tasks requiring perceptual and visuomotor judgments of horizontal extent. In drawing objects such as a daisy both from memory and by copying, patients exhibited a disproportionate enlargement of the left-hand side of objects and added more left-sided petals to the drawn daisy. This pathologic behavior persisted when the patients were blindfolded and was likely to reflect a perceptual, rather than premotor, size distortion. In a task requiring the perceptual matching of two rectangles, patients underestimated the left-sided stimulus. In a visuomotor task requiring the reproduction of the horizontal extent of a segment, patients exhibited a hyperextension, when a leftward movement was required. We showed a disordered representation of extrapersonal space, possibly involving a contralesional relaxation of the spatial medium. The deficit does not arise at the level of retinotopic coordinate frames and is independent of unilateral spatial neglect.

Responses of neurons in the lateral intraparietal area to central visual cues

Goal-directed behavior is characterized by flexible stimulus-action mappings. The lateral intraparietal area (area LIP) contains a representation of extra-personal space that is used to guide goal-directed behavior. To examine further how area LIP contributes to these flexible stimulus-action mappings, we recorded LIP activity while rhesus monkeys participated in two different cueing tasks. In the first task, the color of a central light indicated the location of a monkey's saccadic endpoint in the absence of any other visual stimuli. In the second task, the color of a central light indicated which of two visual targets was the saccadic goal. In both tasks, LIP activity was modulated by these non-spatial cues. These observations further suggest a role for area LIP in mediating endogenous associations that link stimuli with actions.

Functional Architecture of Retinotopy in Visual Association Cortex of Behaving Monkey

While the receptive field properties of single neurons in the inferior parietal cortex have been quantitatively described from numerous electrical measurements, the visual topography of area 7a and the adjacent dorsal prelunate area (DP) remains unknown. This lacuna may be a technical byproduct of the difficulty of reconstructing tens to hundreds of penetrations, or may be the result of varying functional retinotopic architectures. Intrinsic optical imaging, performed in behaving monkey for extended periods of time, was used to evaluate retinotopy simultaneously at multiple positions across the cortical surface. As electrical recordings through an implanted artificial dura are difficult, the measurement and quantification of retinotopy with long-term recordings was validated by imaging early visual cortex (areas V1 and V2). Retinotopic topography was found in each of the three other areas studied within a single day's experiment. However, the ventral portion of DP (DPv) had a retinotopic topography that varied from day to day, while the more dorsal aspects (DPd) exhibited consistent retinotopy. This suggests that the dorsal prelunate gyrus may consist of more than one visual area. The retinotopy of area 7a also varied from day to day. Possible mechanisms for this variability across days are discussed as well as its impact upon our understanding of the representation of extrapersonal space in the inferior parietal cortex.

Hermann Zingerle's “Impaired Perception of the own Body Due to Organic Brain Disorders”: An Introductory Comment, and an Abridged Translation

In the late 1970's Edoardo Bisiach and his coworkers provided definitive evidence that spatial unilateral neglect involves a disorder of the internal representation of extra-personal space. A few years later Bisiach and Berti (1987) revived the so far neglected contribution of an Austrian neurologist, Hermann Zingerle (1913). Ninety years ago Zingerle had described the symptom-complex of two right-brain-damaged patients, who showed left hemisomatoagnosia, unawareness of left hemiplegia, and left motor neglect. In addition to the detailed case reports, Zingerle had put forward a unitary interpretation of these deficits in terms of a disordered representation of one side of the body (dyschiria). A unitary representational account of these unilateral impairments was conspicuously absent in the contemporary neurological literature (Anton, Pick, Babinski), and attracted Bisiach's interest. An abridged translation of Zingerle's paper is provided. The clinical case reports and Zingerle's conclusions are discussed, with reference both to Bisiach's views, and to present knowledge of unilateral spatial neglect.

Analysis of optic flow in the monkey parietal area 7a.

Environmentally relevant stimuli were used to examine the selectivity of area 7a neurons to optic flow using moving, flickering dots. Monkeys performed a psychophysical task requiring them to detect changes in translation, rotational and radially structured optic flow fields consisting of collections of moving dots which are free of form cues. The neurons in area 7a were selectively responsive to all the different types of moving stimuli. Two types of tuning for motion selectivity were found. Some neurons were tuned to distinguish a particular direction of optic flow (e.g. radial expansion versus radial compression), while others were tuned to distinguish between different classes of optic flow (e.g. radial motion versus planar rotation). The latter tuning was unlike that reported for area MST by others and may represent a novel representation of optic flow. The response of these neurons to translating bars was compared to that of optic flow fields. There appeared to be no similarity in the tuning to the two types of motion. Furthermore, there does not appear to be an identity between the neurons that could be classified as opponent vector and those selective for radial optic flow. Area 7a is involved in the further analysis of optic flow beyond the cortical areas MT and MST and provides a novel representation of motion. These results are consistent with the neurons in area 7a utilizing motion for the construction of a spatial representation of extra-personal space.

Inputs from motor and premotor cortex to the superior colliculus of the macaque monkey

In retrograde studies of corticotectal projections in the monkey using horseradish peroxidase (HRP), projections of the frontal lobes were found to originate not only from the frontal eye fields and prefrontal association cortex but also from both motor and premotor cortex. Even small HRP injections into the superficial layers of the superior colliculus yielded labelled cells in the agranular cortex (area 6) of the anterior bank of the arcuate sulcus. After large collicular injections affecting all layers, labelled cells were found in both motor and premotor cortex. This projection appeared to be topographically organized. Injections into the anterolateral parts of the superior colliculus labelled cells that were distributed within the presumed finger-hand—arm-shoulder representation, whereas after more caudal injections labelled cells occurred more in the presumed arm-trunk representation. The supplementary motor cortex was not found to contain labelled cells. The corticotectal cells in the motor cortex differed from those in the premotor cortex in their size distribution; the former being small, the latter both small and large. The functional significance of the motor and premotor input into the superior colliculus for sensory, and particularly visual, guidance of movements is discussed in view of a collicular role in the extrapersonal space representation and of its possible participation in steering arm and hand movements.

Right Hemispheric Mediation of Dream Visualization: A Case Study

Our paper addresses, as did a recent study by Greenwood et al. (1977), the question of differential right vs. left hemispheric involvement in REM-sleep dreaming. A male subject with extensive lesioning of the right hemisphere and consequent contralateral homonymous hemianopia was studied for 2 nights in a sleep laboratory where a dream report was collected following each of 6 awakenings from REM sleep. The subject's dream reports were typically sequential and narrative in form, but were lacking specifically in continuous visual imagery. The occasional visual images that appeared in the subject's dreams were described as fragmentary and static in nature. The subject also was unable to perform waking tasks requiring the kinematic representation of extrapersonal space. These observations support the hypotheses that dream narratives may derive from different neurocognitive sources than do the specifically visual realizations of those narratives, and that the visual mediation of dream experience may depend on right-hemispheric processing. Differences between our findings and those of Greenwood et al. may be attributable to differences in dream interview technique.

A cortical network for directed attention and unilateral neglect.

Unilateral neglect reflects a disturbance in the spatial distribution of directed attention. A review of unilateral neglect syndromes in monkeys and humans suggests that four cerebral regions provide an integrated network for the modulation of directed attention within extrapersonal space. Each component region has a unique functional role that reflects its profile of anatomical connectivity, and each gives rise to a different clinical type of unilateral neglect when damaged. A posterior parietal component provides an internal sensory map and perhaps also a mechanism for modifying the extent of synaptic space devoted to specific portions of the external world; a limbic component in the cingulate gyrus regulates the spatial distribution of motivational valence; a frontal component coordinates the motor programs for exploration, scanning, reaching, and fixating; and a reticular component provides the underlying level of arousal and vigilance. This hypothetical network requires at least three complementary and interacting representations of extrapersonal space: a sensory representation in posterior parietal cortex, a schema for distributing exploratory movements in frontal cortex, and a motivational map in the cingulate cortex. Lesions in only one component of this network yield partial unilateral neglect syndromes, while those that encompass all the components result in profound deficits that transcend the mass effect of the larger lesion. This network approach to the localization of complex functions offers an alternative to more extreme approaches, some of which stress an exclusive concentration of function within individual centers in the brain and others which advocate a more uniform (equipotential or holistic) distribution. In human beings, unilateral neglect syndromes are more frequent and severe after lesions in the right hemisphere. Also, right hemisphere mechanisms appear more effective in the execution of attentional tasks. Furthermore, the attentional functions of the right hemisphere span both hemispaces, while the left hemisphere seems to contain the neural apparatus mostly for contralateral attention. This evidence indicates that the right hemisphere of dextrals has a functional specialization for the distribution of directed attention within extrapersonal space.