[show abstract][hide abstract] ABSTRACT: In the present study we explored the effect of prismatic adaptation (PA) applied to the upper right limb on the walking trajectory of a neglect patient with more severe neglect in far than in near space. The patient was asked to bisect a line fixed to the floor by walking across it before and after four sessions of PA distributed over a time frame of 67 days. Gait path was analyzed by means of an optoelectronic motion analysis system. The walking tra-jectory improved following PA and the result was maintained at follow-up, 15 months after treatment. The improvement was greater for the predicted bisection error (estimated on the basis of the trajectory extrapolated from the first walking step) than for the observed bisection error (measured at line bisection). These results show that PA may act on high level spatial representation of gait trajectory rather than on lower level sensory-motor gait components and suggest that PA may have a long-lasting rehabilitative effect on neglect patients showing a deviated walking trajectory.
Frontiers in Human Neuroscience 07/2013; · 2.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: What is the relationship between numerical and visual space? Here we tried to shed new light on this debated issue investigating whether and how the two forms of representation are associated or dissociated when co-activated. We carried out a series of visual-numerical bisection experiments on a large group of right brain-damaged patients (N=32) with and without left neglect. We examined (a) the degree of association between the pathological rightward error in the bisection of numerical intervals and left neglect (Experiment 1); (b) if the size of the numerical interval modulates spatial errors in bisection tasks in which numerical and visual space representations are co-activated (Experiment 2). The results showed that (a) numerical bisection error and left spatial neglect are doubly dissociated and that, when both are present, they are not correlated; (b) the size of the numerical interval did not affect the spatial bisection error but influenced the numerical bisection error. These data suggest that attentional processes involved in the navigation along visual space and numerical internal representations are independent neurocognitive operations. We must emphasize that our findings should be taken with caution because they are based mainly on negative results.
[show abstract][hide abstract] ABSTRACT: On the one hand, it is often assumed that the Rubber Hand Illusion (RHI) is constrained by a structural body model so that one cannot implement supernumerary limbs. On the other hand, several recent studies reported illusory duplication of the right hand in subjects exposed to two adjacent rubber hands. The present study tested whether spatial constraints may affect the possibility of inducing the sense of ownership to two rubber hands located side by side to the left of the subject's hand. We found that only the closest rubber hand appeared both objectively (proprioceptive drift) and subjectively (ownership rating) embodied. Crucially, synchronous touch of a second, but farther, rubber hand disrupted the objective measure of the RHI, but not the subjective one. We concluded that, in order to elicit a genuine RHI for multiple rubber hands, the two rubber hands must be at the same distance from the subject's hand/body.
Consciousness and Cognition 03/2012; 21(2):799-812. · 2.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rightward spatial bias shown by left neglect patients and the small leftward bias displayed by healthy subjects (pseudoneglect) have been interpreted as phenomena sharing a common attentional imbalance mechanism. Here we investigated whether pseudoneglect, similarly as neglect, can occur in an object-centred frame of reference. Thirty healthy participants repeatedly bisected the elongated caricature of a basset hound with the head on the left and the tail on the right or viceversa. In the last critical trials, the figure appeared horizontally mirrored. The bisection error reversed from the left to the right space in the critical trials. This result shows that it is possible to induce object-centred pseudoneglect on newly established knowledge about the canonical orientation of non-verbal visual stimuli.
Experimental Brain Research 08/2009; 200(1):61-6. · 2.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: While the sense of bodily ownership has now been widely investigated through the rubber hand illusion (RHI), very little is known about the sense of disownership. It has been hypothesized that the RHI also affects the ownership feelings towards the participant's own hand, as if the rubber hand replaced the participant's actual hand. Somatosensory changes observed in the participants' hand while experiencing the RHI have been taken as evidence for disownership of their real hand. Here we propose a theoretical framework to disambiguate whether such somatosensory changes are to be ascribed to the disownership of the real hand or rather to the anomalous visuo-proprioceptive conflict experienced by the participant during the RHI.
In experiment 1, reaction times (RTs) to tactile stimuli delivered to the participants' hand slowed down following the establishment of the RHI. In experiment 2, the misalignment of visual and proprioceptive inputs was obtained via prismatic displacement, a situation in which ownership of the seen hand was doubtless. This condition slowed down the participants' tactile RTs. Thus, similar effects on touch perception emerged following RHI and prismatic displacement. Both manipulations also induced a proprioceptive drift, toward the fake hand in the first experiment and toward the visual position of the participants' hand in the second experiment.
These findings reveal that somatosensory alterations in the experimental hand resulting from the RHI result from cross-modal mismatch between the seen and felt position of the hand. As such, they are not necessarily a signature of disownership.
PLoS ONE 02/2009; 4(9):e6920. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Unilateral neglect patients typically omit to cancel contralesional targets. Moreover, they can repeatedly cancel ipsilesional stimuli exhibiting what is termed 'perseverative behavior'. Two alternative accounts of this behavior have been proposed. According to one of them, it is considered as integral to neglect and due either to a perceptual (allochiria), or a premotor (directional hypokinesia) pathological mechanism leading to the ipsilesional displacement of contralesional responses. According to the other one, perseverations are interpreted as the consequence of motor-control-disinhibition co-occurring with, although independent of, spatial neglect. We compared some crucial predictions of these two hypotheses on a group of 10 right-brain-damaged patients, eight with neglect and two without neglect, showing a perseverative behavior in both conventional and experimental cancellation tasks. In our experiment, the spatial location and the numerosity of targets were manipulated to obtain different degrees of horizontal alignment between targets on the left and on the right of the central vertical axis of the sheet. We found that ipsilesional perseverations were not influenced by left neglected targets and were not correlated to neglect severity. Additionally, perseverative errors were associated with right basal ganglia lesions rather than with presence of neglect. These findings support the view that two different pathological mechanisms might be involved in left spatial neglect and ipsilesional perseverative behavior.
[show abstract][hide abstract] ABSTRACT: A right-neglect patient with focal left-hemisphere damage to the posterior superior parietal lobe was assessed for numerical knowledge and tested on the bisection of numerical intervals and visual lines. The semantic and verbal knowledge of numbers was preserved, whereas the performance in numerical tasks that strongly emphasize the visuo-spatial layout of numbers (e.g. number bisection) was impaired. The behavioral pattern of error in the two bisection tasks mirrored the one previously described in left-neglect patients. In other words, our patient misplaced the subjective midpoint (numerical or visual) to the left as function of the interval size. These data, paired with the patient's lesion site are strictly consistent with the tripartite organization of number-related processes in the parietal lobes as proposed by Dehaene and colleagues. According to these authors, the posterior superior parietal lobe on both hemispheres underpins the attentional orientation on the putative mental number line, the horizontal segment of the intraparietal sulcus is bilaterally related to the semantic of the numerical domain, whereas the left angular gyrus subserves the verbal knowledge of numbers. In summary, our results suggest that the processes involved in the navigation along the mental number line, which are related to the parietal mechanisms for spatial attention, and the processes involved in the semantic and verbal knowledge of numbers, are dissociable.
Brain and Cognition 08/2008; 69(1):81-8. · 2.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the present paper, we shall review clinical evidence and theoretical models related to anosognosia for sensorimotor impairments that may help in understanding the normal processing underlying conscious self-awareness. The dissociations between anosognosia for hemiplegia and anosognosia for hemianaesthesia are considered to give important clinical evidence supporting the hypothesis that awareness of sensory and motor deficits depends on the functioning of discrete self-monitoring processes. We shall also present clinical and anatomical data on four single case reports of patients selectively affected by anosognosia for hemianaesthesia. The differences in the anatomical localization of lesions causing anosognosia for hemiplegia and anosognosia for hemianaesthesia are taken as evidence that cerebral circuits subserving these monitoring processes are located in separate brain areas, which may be involved both in the execution of primary functions and the emergence of awareness related to the monitoring of the same functions. The implications of these findings for the structure of conscious processes shall be also discussed.
[show abstract][hide abstract] ABSTRACT: In a first experiment we studied, through a line bisection task, (a) the frequency of the selective disruption of far or near space representations in a group of 28 right brain-damaged patients and (b) the effect of tool use on line bisection error in far and near space in order to clarify whether the kind of action performed by the subject influences the extension of space representation, as suggested by previous studies. In a second experiment, carried out on two neglect patients, we asked whether the representation of "near" and "far" space depends on the sensory feedback during the execution of the action or whether it is independent on sensory feedback and more related to the action programmed as a consequence of the kind of tool used. Our data show (a) that dissociations between far and near space neglect are a frequent observation in right brain damaged patients and that most of these patients are able to recode space representations when tools change the spatial relation between the agent's body and the target object; (b) that spatial remapping can be elicited by the kind of action associated to the tool used and by the sensory feedback (either visual or proprioceptive) available during the execution of the task. In particular, presence of tactile proprioceptive feedback elicited remapping of far space into near space, whereas absence of visual feedback induced remapping of near space into far space.
[show abstract][hide abstract] ABSTRACT: The authors review the drawing disorders that can be observed in patients with brain damage (in particular, those with constructional apraxia and unilateral spatial neglect), the impact of brain damage on the output of professional artists, and the distortions of body image that characterise the work of many great artists, from Rubens to Lucien Freud. These different perspectives share the basic assumption that the graphic and artistic output of patients, normal subjects, and exceptionally gifted individuals may represent a window onto the neural organisation of body image.