1,721,014 research outputs found
Social scaling of extrapersonal space: target objects are judged as closer when the reference frame is a human agent with available movement potentialities
Full text linkSpace perception depends on our motion potentialities and our intended actions are affected by space perception. Research on peripersonal space (the space in reaching distance) shows that we perceive an object as being closer when we (Witt, Proffitt, & Epstein, 2005; Witt & Proffitt, 2008) or another actor (Costantini, Ambrosini, Sinigaglia, & Gallese, 2011; Bloesch, Davoli, Roth, Brockmole, & Abrams, 2012) can interact with it. Similarly, an object only triggers specific movements when it is placed in our peripersonal space (Costantini, Ambrosini, Tieri, Sinigaglia, & Committeri, 2010) or in the other's peripersonal space (Costantini, Committeri, & Sinigaglia, 2011; Cardellicchio, Sinigaglia, & Costantini, 2013). Moreover, also the extrapersonal space (the space outside reaching distance) seems to be perceived in relation to our movement capabilities: the more effort it takes to cover a distance, the greater we perceive the distance to be (Proffitt, Stefanucci, Banton, & Epstein, 2003; Sugovic & Witt, 2013). However, not much is known about the influence of the other's movement potentialities on our extrapersonal space perception. Three experiments were carried out investigating the categorization of distance in extrapersonal space using human or non-human allocentric reference frames (RF). Subjects were asked to judge the distance ("Near" or "Far") of a target object (a beach umbrella) placed at progressively increasing or decreasing distances until a change from near to far or vice versa was reported. In the first experiment we found a significant "Near space extension" when the allocentric RF was a human virtual agent instead of a static, inanimate object. In the second experiment we tested whether the "Near space extension" depended on the anatomical structure of the RF or its movement potentialities by adding a wooden dummy. The "Near space extension" was only observed for the human agent but not for the dummy. Finally, to rule out the possibility that the effect was simply due to a line-of-sight mechanism (visual perspective taking) we compared the human agent free to move with the same agent tied to a pole with a rope, thus reducing movement potentialities while maintaining equal visual accessibility. The "Near space extension" disappeared when this manipulation was introduced, showing that movement potentialities are the relevant factor for such an effect. Our results demonstrate for the first time that during allocentric distance judgments within extrapersonal space, we implicitly process the movement potentialities of the RF. A target object is perceived as being closer when the allocentric RF is a human with available movement potentialities, suggesting a mechanism of social scaling of extrapersonal space processing
Causal topography of visual cortex in perceptual learning
No full textIndividuals are able to improve their visual skill with practice, a phenomenon called Visual Perceptual Learning (VPL). We previously observed that after training on a difficult shape identification task, the dorsal visual regions (i.e. right V2d/V3 and right lateral occipital, LO) corresponding to the trained visual quadrant, and their homologous in the opposite hemisphere, exhibited a selective activation at the end of the learning. By contrast, such modulation was not observed in the ventral visual regions, corresponding to the untrained quadrants. The causal role of the trained visual cortex was previously showed in a TMS study as its inactivation impaired behavioral performance to learned stimuli. Here, using the same experimental design, we employed TMS over the homologous of the trained area (i.e. left V2d/V3) as well as over the untrained region (i.e. right V4) to causally map the visual network during the perceptual learning. We report a decrease of accuracy after TMS over left V2d/V3 as compared to both right V4 and Sham (inactive stimulation) conditions. Importantly, TMS effect was correlated with the degree of learning, such that subjects with lower accuracy at the end of the training exhibited stronger TMS impairment. These results provide evidence that segregated regions within the visual network are causally involved in visual perceptual learning
Spatial coding of visual and somatic sensory information in body-centered coordinates.
No full textBecause sensory systems use different spatial coordinate frames, cross-modal sensory integration and sensory-motor coordinate transformations must occur to build integrated spatial representations. Multimodal neurons using non-retinal body-centred reference frames are found in the posterior parietal and frontal cortices of monkeys. We used functional magnetic resonance imaging to reveal regions of the human brain using body-centred coordinates to code the spatial position of both visual and somatic sensory stimuli. Participants determined whether a visible vertical bar (visual modality) or a location touched by the right index finger (somatic sensory modality) lay to the left or to the right of their body mid-sagittal plane. This task was compared to a spatial control task having the same stimuli and motor responses and comparable difficulty, but not requiring body-centred coding of stimulus position. In both sensory modalities, the body-centred coding task activated a bilateral fronto-parietal network, though more extensively in the right hemisphere, to include posterior parietal regions around the intraparietal sulcus and frontal regions around the precentral and superior frontal sulci, the inferior frontal gyrus and the superior frontal gyrus on the medial wall. The occipito-temporal junction and other extrastriate regions exhibited bilateral activation enhancement related to body-centred coding when driven by visual stimuli. We conclude that posterior parietal and frontal regions of humans, as in monkeys, appear to provide multimodal integrated spatial representations in body-centred coordinates, and these data furnish the first indication of such processing networks in the human brain
Psychophisical properties of line bisection and body midline perception in unilateral neglect.
No full textPast research associated unilateral neglect with a systematic ipsilesional shift of the perceived position of the body midline; however, this was not confirmed by recent experiments. We used the constant stimuli method to control for potential artifacts intrinsic to the techniques used in previous studies. Body midline perception was measured in the visual and proprioceptive modalities in ten patients with left unilateral neglect, ten control patients and ten normal subjects and compared with a visual line bisection task, also using the constant stimuli method. Neglect patients showed a significant rightward bias in the line bisection task, but no consistent directional bias either in the proprioceptive or in the visual body midline task. These results clearly counter the association between neglect and an ipsilesional shift of the body midline. However, in the body midline tasks neglect patients made more errors in judgement on both sides of their subjective midline, both with respect to the control groups and with respect to the line bisection task. This may imply that a specific impairment of body-centered representations is indeed present and manifests as a non directional increase in response variability, rather than as a systematic shift. It is suggested that body- and object-related tasks (such as line bisection) may be processed by independent cognitive computations. This interpretation is discussed with reference to a recent neuroimaging study investigating the same kinds of tasks
Selective effects of a brain tumor on the metric representation of the hand: a pre- versus post-surgery comparison
Full text linkBody representation disorders are complex, varied, striking, and very disabling in most cases. Deficits of body representation have been described after lesions to multimodal and sensorimotor cortical areas. A few studies have reported the effects of tumors on the representation of the body, but little is known about the changes after tumor resection. Moreover, the impact of brain lesions on the hand size representation has been investigated in few clinical cases. Hands are of special importance, as no other body part has the ability for movement and interaction with the environment that the hands have, and we use them for a multitude of daily activities. Studies with clinical population can add further knowledge into the way hands are represented. Here, we report a single case study of a patient (AM) who was an expert bodybuilder and underwent a surgery to remove a glioblastoma in the left posterior prefrontal and precentral cortex at the level of the hand’s motor region. Pre- (20 days) and post- (4 months) surgery assessment did not show any motor or cognitive impairments. A hand localization task was used, before and after surgery (12 months), to measure possible changes of the metric representation of his right hand. Results showed a post-surgery modulation of the typically distorted hand representation, with an overall accuracy improvement, especially on width dimension. These findings support the direct involvement of sensorimotor areas in the implicit representation of the body size and its relevance on defining specific size representation dimensions
Effects of individual discount rate and uncertainty perception on compliance with containment measures during the COVID-19 pandemic
Full text linkAnti-contagion measures restricting individual freedom, such as social distancing and wearing a mask, are crucial to contain the COVID-19 pandemic. Decision-making patterns and attitudes about uncertainty can highly influence the adherence to these restrictive measures. Here we investigated the relationship between risky behavior and individual preferences for immediate vs. delayed reward, as indexed by temporal discounting (TD), as well as the association between these measures and confidence in the future, perceived risk and confidence in the containment measures. These measures were collected through an online survey administered on 353 participants at the end of the more restrictive phase of the first Italian lockdown. The results showed an unexpected inverse relationship between the individual pattern of choice preferences and risky behavior, with an overall greater adherence to containment measures in more discounter participants. These findings were interpreted in terms of a reframing process in which behaviors aimed at protecting oneself from contagion turn into immediate gains rather than losses. Interestingly, an excessive confidence in a better future was correlated with a higher tendency to assume risky behavior, thereby high-lighting the downside of an overly and blindly optimistic view
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