The different impact of attention, movement, and sensory information on body metric representation.

A growing body of research investigating the relationship between body representation and tool-use has shown that body representation is highly malleable. The nature of the body representation does not consist only of sensory attributes but also of motor action-oriented qualities, which may modulate the subjective experience of our own body. However, how these multisensory factors and integrations may specifically guide and constrain body reorientation's plasticity has been under-investigated. In this study, we used a forearm bisection task to selectively investigate the contribution of motor, sensory, and attentional aspects in guiding body representation malleability. Results show that the perceived forearm midpoint deviates from the real one. This shift is further modulated by a motor task but not by a sensory task, whereas the attentional task generates more uncertain results. Our findings provide novel insight into the individual role of movement, somatosensation, and attention in modulating body metric representation.

Objects with motor valence affect the visual processing of human body parts: Evidence from behavioural and ERP studies.

Recent findings indicate that the mental representation of an object contains crucial information about the motor interactions relevant for its intended functional use, suggesting a possible action-specific link with body effectors. For example, in the visual system, the extrastriate body area (EBA) responds to full body and body part images according to a functional/semantic organizational principle. However, the pliancy of the relationship between objects and body parts remains under-investigated. The present study aims to i) investigate this relationship more directly by assessing whether recognition of specific body parts can be facilitated by a brief exposure to functionally-related objects (Experiment 1) and ii) whether the functional relationship between objects and body parts modulates a posterior body-sensitive ERP waveform, peaking around 200 msec, and the more centro-parietal P300, linked to item categorization processes and visual awareness (Experiment 2). Participants were asked to quickly recognize targets (pictures of hands or feet) preceded by a functionally related (e.g., drum for hand target), unrelated (e.g., drum for foot target), or neutral (e.g., unknown object for both targets) prime. Findings showed that participants' performance was significantly more accurate with related than unrelated primes and that ERP amplitudes were modulated by the relationship between the prime and the target. These findings confirm the existence of action-specific links between objects and body parts and expand on recent findings on categorical organization of neural responses to human effectors in the visual system.

Same action in different spatial locations induces selective modulation of body metric representation.

Recent studies have hypothesized that the stereotypical representation of the body may reflect some functional aspects of routine actions that are performed in specific peripersonal domains. For example, the lower and upper limbs tend to 'act' in different peripersonal spaces and perform different functions. The present study aims to directly investigate the relationship between body representation and the spatial context where actions are performed. By means of a modified version of the body image task, we investigated body representation before and after a sorting task training in two groups of participants who were asked to carry out the same task/actions in two different spaces: on a table or on the floor, while sitting on a chair. Findings showed that a significant recalibration of the perceived upper arms' length occurred when participants were asked to perform a motor task on the floor. These results seem to suggest that the modulation of the body representation reflects an increase action capabilities driven by the contribution of motor training, and importantly, the location in which the action occurs. Furthermore, the modulation was not limited to the body part actively involved in the action (the arms), it extended to other upper body parts (the torso) to maintain, we propose, a functionally coherent representation of the upper body.

The downsized hand in personal neglect.

Introduction: Personal neglect (PN) refers to a form of hemi-inattention toward the contralesional body space and it usually occurs following a right brain lesion. Recent studies suggest that PN indicates a disorder of body representation. Specifically, patients with PN show difficulties in identifying differences between left and right hands and have an altered visuospatial body map, which is associated with disrupted mental body representations. However, the metric representation of the body, and in particular the hands, has not been systematically addressed in patients showing this form of neglect. Method: In the present study, we have investigated this representation by testing the perceived hands' width of 11 hemiplegic patients with right hemisphere cerebral lesions (5 with PN) and 12 healthy controls on a judgment of passability task. Patients and controls were asked to imagine inserting their hand (left and right) through a series of vertical apertures of different sizes and to judge whether their hand could fit through. Due to the heterogeneity of the data, both parametric and non-parametric approaches were used. Furthermore, additional single-case analyses were conducted. Results: Study findings showed that patients with PN showed a significant underestimation of the left hand compared with their right hand. In contrast, whilst the right hand was equally distorted in both patients' groups, the hemiplegic patients with no evidence of PN tended to perceive the affected hand as larger than their ipsilesional one. Conclusions: In line with the literature, our findings confirm an underlying distorted body representation following right brain damage. However, for the first time, we report both a quantitative and qualitative difference in impact of hemiplegia and PN on body representation of the contralesional body space.

The functional body: does body representation reflect functional properties?

There is a growing interest in the distortions of body representation in healthy population and most studies have focused their attention on specific parts of the body, such as the hands. Only three studies have considered the representation of the body as a whole. Findings, acquired by different means of assessment methods, are partially contrasting, leading to different interpretations. The present study aims to investigate which aspects of body representation can be preserved regardless of the method adopted and whether current and previous findings can be explained by a unique theoretical model. In Experiments 1a and 1b, we adopted a modified version of the Body Image Task to investigate body representations in real scale and the relationship of its parts. Participants judged the location of body landmarks by pointing on their own silhouette imagined on a wall in front of them. In Experiment 2, we investigated (i) whether the pattern of distortions observed in the first experiment are maintained across different methods by asking participants to estimate the veracity and proportionality of the length of their own body parts; and (ii) whether similar distortions can be generalized to stereotypical representations. Overall, we observed a consistent pattern of distortions, whereby upper body limbs are underestimated and lower parts of the body are overestimated across all experiments and conditions. These findings are then interpreted as the result of a functional relationship between body parts and daily actions, which underlie a close modulation of body schema and body image. This interpretation offers a reconciliation of seemingly contradictory findings in the literature and supports to the co-construction model (Pitron et al. in Conscious Cognit 65:352-358, 2018).

Different tool training induces specific effects on body metric representation.

Morphology and functional aspects of the tool have been proposed to be critical factors modulating tool use-induced plasticity. However, how these aspects contribute to changing body representation has been underinvestigated. In the arm bisection task, participants have to estimate the length of their own arm by indicating its midpoint, a paradigm used to investigate the representation of the metric properties of the body. We employed this paradigm to investigate the impact of different actions onto tool embodiment. Our findings suggest that a training requiring actions mostly with proximal (shoulder) or distal (wrist) parts induces a different shift in the perceived arm midpoint. This effect is independent of, but enhanced by, the use of the tool during the training and in part influenced by specific demands of the task. These results suggest that specific motor patterns required by the training can induce different changes of body representation, calling for rethinking the concept of tool embodiment, which would be characterized not simply by the morphology of the tools, but also by the actions required for their specific use.

The 'Neglected' Personal Neglect.

A review of patients with brain injury showing personal neglect is presented. The aim is to shed light on this aspect of neglect often unresearched or only indirectly investigated, and to discuss recent findings concerning the methods used to assess personal neglect, its neural correlates and its association with the more often explored aspect of extrapersonal neglect. The review was performed using PubMed and PsychInfo databases to search for papers published in the last 123 years (until January 2018). We reviewed 81 papers describing either single or group studies for a total of 2247 patients. The results of this review showed that various aspects of personal neglect are still controversial and outcomes potentially contradictory. Despite the data reported in the present review suggest that personal neglect is more frequently associated with lesions of the right hemisphere, the left hemisphere may also play an important role. Not surprisingly, personal neglect and extrapersonal neglect seem to co-occur. However double dissociations of these two forms of neglect have been reported, and they seem to dissociate both from a functional and an anatomical perspective. More recent interpretations of personal neglect suggest that it may result from a disrupted body representation. The development of reliable psychometric tools with shared diagnostic criteria is essential to identify different degrees of personal neglect for different body parts and to better refine personal neglect in comparison to extrapersonal neglect and disorders related to distortions of personal domain.