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Biomedical subjects

Elisabetta Làdavas

Publications and source records attributed to Elisabetta Làdavas.

At least 19 recordsLinked to original sources
PubMed2006

Can vision of the body ameliorate impaired somatosensory function?

Viewing the body is reported to improve tactile acuity [Kennett, S., Taylor-Clarke, M., & Haggard, P. (2001). Non-informative vision improves the spatial resolution of touch in humans. Current Biology, 11, 1188-1191]. The aim of the present study was to investigate whether this effect might be useful in improving somatosensory deficits of brain damaged patients. To support this proposal, we firstly tested the hypothesis that vision might modulate tactile performance when tactile information is limited. Thirty-two healthy subjects performed a two points discrimination task (2PDT) in three conditions: looking at their stimulated forearm, at a neutral object or at a rubber foot. The results showed that the effectiveness of visual enhancement of touch varies as a function of subjects' tactile acuity. Moreover, the accuracy in 2PDT was higher when viewing their arm only in subjects with lower tactile sensitivity. To directly demonstrate that viewing the body might ameliorate tactile deficits, the same experiment was conducted on 10 brain damaged patients suffering a reduced somatosensory sensitivity. An amelioration of the performance was found in viewing arm condition. These findings suggest that the interaction between different sensory modalities might be effective in ameliorating deficits in single modalities.

Adult↗
PubMed2006

When true memory availability promotes false memory: evidence from confabulating patients.

We explored the extent to which confabulators are susceptible to false recall and false recognition, and whether false recognition is reduced when memory for studied items is experimentally enhanced. Five confabulating patients, nine non-confabulating amnesics--including patients with (F amnesics) and without frontal-lobe dysfunction (NF amnesics)--and 14 control subjects underwent the DRM paradigm [Roediger, H. L., & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory and Cognition, 21, 803-814.] in two experimental conditions. In both conditions participants studied eight lists of semantic associates, and free recall was tested after the presentation of each list. In the Standard condition recognition was tested after the presentation of all the lists, whereas in the Proximal condition patients were administered a six-item recognition task after the presentation of each list. Participants also provided remember or know judgements, and described the content of their recollections. All groups of patients recalled a lower proportion of targets and critical lures than did control subjects, but confabulators recalled more words unrelated to the studied lists than did NF amnesics and controls. All groups of participants improved true recognition across conditions. However, whereas normal controls suppressed false recognition to critical lures in the Proximal compared to the Standard condition, and non-confabulating amnesics showed comparable gist-based false recognition, confabulators showed increased levels of false recognition to critical lures across conditions. Furthermore, NF amnesics significantly reduced false recognition to unrelated lures in the Proximal compared to the Standard condition, whereas confabulators were unable to suppress false recognition to unrelated lures across conditions. Analysis of the phenomenological experience showed that, unlike non-confabulating amnesics, confabulators characterized true and false memories with irrelevant information related to test items. Results are interpreted in light of confabulators' monitoring deficits.

Adult↗
PubMed2006

Central executive system impairment in traumatic brain injury.

PRIMARY OBJECTIVE: This study investigated whether cognitive impairment after traumatic brain injury (TBI) can be considered a consequence of (1) a speed processing deficit or (2) an impairment of the Central Executive System (CES) of working memory. METHODS AND PROCEDURES: Thirty-seven TBI patients underwent a standardized battery of neuropsychological tests evaluating speed processing, sustained attention, short-term memory, working memory, divided attention, executive functions and long-term memory. MAIN OUTCOMES AND RESULTS: Patients showed severe deficits in working memory, divided attention, executive functions and long-term memory. Divided attention, long-term memory and executive functions deficits significantly correlated with working memory, but not with speed processing deficits. Moreover, multiple regression analyses showed that a CES impairment and not a speed processing deficit predicted divided attention, executive functions and long-term memory deficits. The severity and the site of brain lesions did not predict the level of CES or speed processing impairment. CONCLUSIONS: The cognitive impairment following TBI seem to be caused by an impairment of the Central Executive System, rather than a speed processing deficit.

Adolescent↗
PubMed2005

Neuropsychological evidence of modular organization of the near peripersonal space.

BACKGROUND: The space closely surrounding the body, near peripersonal space, is represented through multisensory coding, as witnessed by the spatial distribution of visual-tactile extinction in brain-damaged patients. Typically, tactile stimuli delivered on the contralesional hand are more severely extinguished by visual stimuli presented near to than far from the ipsilesional hand. OBJECTIVE: To investigate whether the near peripersonal space is a unitary multisensory representation of the peribody space or is organized in a modular fashion, separately representing different body parts. METHODS: Cross-modal extinction was used to assess right brain-damaged patients with left tactile extinction by presenting a combination of ipsilesional visual and contralesional tactile stimuli, both between homologous body parts (i.e., the two hands and sides of the face) and between nonhomologous body parts (i.e., right hand + left face and right face + left hand). RESULTS: Visual-tactile extinction observed in the near peripersonal space of homologous body parts was more severe than that obtained between nonhomologous body parts. In contrast, cross-modal extinction observed in the far peripersonal space was overall weak and comparable when stimulating homologous or nonhomologous body sectors. In addition, a clear near-far modulation of visual-tactile extinction was obtained only when stimulating homologous, but not nonhomologous, body parts. These findings were observed irrespective of the severity of unisensory tactile extinction. CONCLUSIONS: Near peripersonal space is not unitary but is functionally organized in modules and consists of at least two different spatial representations, one around the hand and another around the face, which might be selectively affected in patients with extinction.

Aged↗
PubMed2005

Mechanisms underlying neglect recovery after prism adaptation.

Prism adaptation (PA) has been demonstrated to be effective in improving hemispatial neglect. However not all patients seem to benefit from this procedure. Thus, the objective of the present work is to provide behavioural and neuroanatomical predictors of recovery by exploring the reorganization of low-order visuo-motor behaviour and high-order visuo-spatial representation induced by PA. To this end, 16 neglect patients (experimental group) were submitted to a PA treatment for 10 daily sessions. Neglect and oculo-motor responses were assessed before the treatment, 1 week, 1 and 3 months after the treatment. Eight control patients, who received general cognitive stimulation, were submitted to the same tests at the same time interval. The results showed that experimental patients obtained, as a consequence of PA, a long lasting neglect recovery, a reorganization of low-order visuo-motor behaviour during and after prism exposure (error reduction and after-effect, respectively) and a leftward deviation of oculo-motor responses. Importantly, the level of error reduction obtained in the first week of treatment was predictive of neglect recovery and the amelioration of oculo-motor responses, and the degree of eye movement deviation was positively related to neglect amelioration. Finally, the study of patients' neuroanatomical data showed that severe occipital lesions were associated with a lack of error reduction, poor neglect recovery and reduced oculo-motor system amelioration. In conclusion, the present results suggest that low-order visuo-motor reorganization induced by PA promotes a resetting of the oculo-motor system leading to an improvement in high-order visuo-spatial representation able to ameliorate neglect.

Aged↗
PubMed2005

Visual search improvement in hemianopic patients after audio-visual stimulation.

One of the most effective techniques in the rehabilitation of visual field defects is based on implementation of oculomotor strategies to compensate for visual field loss. In the present study we develop a new rehabilitation approach based on the audio-visual stimulation of the visual field. Since it has been demonstrated that audio-visual interaction in multisensory neurons can improve temporally visual perception in patients with hemianopia, the aim of the present study was to verify whether a systematic audio-visual stimulation might induce a long-lasting amelioration of visual field disorders. Eight patients with chronic visual field defects were trained to detect the presence of visual targets. During the training, the visual stimulus could be presented alone, i.e. unimodal condition, or together with an acoustic stimulus, i.e. crossmodal conditions. In the crossmodal conditions, the spatial disparity between the visual and the acoustic stimuli were systematically varied (0, 16 and 32 degrees of disparity). Furthermore, the temporal interval between the acoustic stimulus and the visual target in the crossmodal conditions was gradually reduced from 500 to 0 ms. Patients underwent the treatment for 4 h daily, over a period of nearly 2 weeks. The results showed a progressive improvement of visual detections during the training and an improvement of visual oculomotor exploration that allowed patients to efficiently compensate for the loss of vision. More interesting, there was a transfer of treatment gains to functional measures assessing visual field exploration and to daily-life activities, which was found stable at the 1 month follow-up control session. These findings are very promising with respect to the possibility of taking advantage of human multisensory capabilities to recover from unimodal sensory impairments.

Acoustic Stimulation↗
PubMed2005

Poor hand-pointing to sounds in right brain-damaged patients: not just a problem of spatial-hearing.

We asked 22 right brain-damaged (RBD) patients and 11 elderly healthy controls to perform hand-pointing movements to free-field unseen sounds, while modulating two non-auditory variables: the initial position of the responding hand (left, centre or right) and the presence or absence of task-irrelevant ambient vision. RBD patients suffering from visual neglect, unlike RBD patients without neglect and healthy controls, showed a systematic rightward error in sound localisation, which was modulated by the non-auditory variables. Localisation errors were exacerbated by initial hand-position to the right of the body-midline, and reduced by the leftwards initial hand-position. Moreover, for the visual neglect patients, mere presence of ambient vision worsened localisation errors. These results demonstrate that although hand-pointing to sounds has often been considered a straightforward approach to investigate sound-localisation abilities in brain-damaged patients, in some patients it may actually reveal localisation deficits that reflect a combination of impaired spatial-hearing and spatial biases from other sensory modalities (i.e., vision and proprioception).

Aged↗
PubMed2005

Visual localization of sounds.

Circumscribed hemispheric lesions in the right hemisphere have been shown to impair auditory spatial functions. Due to a strong crossmodal links that exist between vision and audition, in the present study, we have hypothesized that multisensory integration can play a specific role in recovery from spatial representational deficits. To this aim, a patient with severe auditory localization defect was asked to indicate verbally the spatial position where the sound was presented. The auditory targets were presented at different spatial locations, at 8 degrees, 24 degrees, 40 degrees, 56 degrees to either sides of the central fixation point. The task was performed either in a unimodal condition (i.e., only sounds were presented) or in crossmodal conditions (i.e., a visual stimulus was presented simultaneously to the auditory target). In the crossmodal conditions, the visual cue was presented either at the same spatial position as the sound or at 16 degrees or 32 degrees, nasal or temporal, of spatial disparity from the auditory target. The results showed that a visual stimulus strongly improves the patient's ability to localize the sounds, but only when it was presented in the same spatial position of the auditory target.

Acoustic Stimulation↗
PubMed2005

Shaping multisensory action-space with tools: evidence from patients with cross-modal extinction.

Recent findings from neurophysiology, neuropsychology and psychology have shown that peri-personal space is represented through an integrated multisensory processing. In humans, the interaction between peri-personal space representation and action execution can be revealed through the use of tools that, by extending the reachable space, modify the strength of visual-tactile extinction. We have previously shown that the peri-hand space whereby vision and touch are integrated can be expanded, and contracted, depending upon tool-use. Here, we show that these dynamic changes critically depend upon active tool-use, as they are not found after an equally long, but passive exposure to an elongated (hand+tool) body configuration. We also show that the extent of the peri-hand space elongation, as assessed at fixed far location (60 cm from the hand), varies according to the tool length such that a 30 cm long tool produced less elongation than a 60 cm long tool. This reveals for the first time that the distal border of elongated area is not sharply limited to the tool length, but extends beyond its physical size to include a peri-tool space whereby the strength of visual-tactile integration seems to fade. Remarkably, a similar amount of peri-hand space elongation was found when the effects of using a 30 cm long tool were compared with those produced by using a tool that was physically 60 cm long, but operationally 30 cm long. By dissociating with this 'hybrid' tool, the amount of space that is globally added to the hand (60 cm) from the one that is actually reachable (30 cm), we provide here the first evidence that the extent of peri-hand space elongation after tool use is tightly related to the functionally effective length of the tool, and not merely to its absolute length.

Adult↗
PubMed2005

Gaze direction modulates auditory spatial deficits in stroke patients with neglect.

We investigated the effects of eye position on auditory spatial deficits in four patients with left neglect and right-hemisphere damage, using three blocked gaze directions (35 degrees to the right, central, or 35 degrees to the left), while preventing any head-movement to ensure that initial auditory inputs remained constant regardless of eye-in-orbit position. The auditory task required speeded discrimination of sound elevation, with patients moving a central lever up or down according to the vertical position of a peripheral target sound, regardless of its side (left or right). Replicating previous auditory research, the patients' vertical discrimination performance was worse for auditory targets on the contralesional (left) versus the ipsilesional side, indicating neglect-related auditory deficits on this task. Critically, while this worse performance for left than right auditory targets was present (for both reaction times and errors) when gaze was directed centrally or rightwards, it was considerably reduced when gaze was directed leftwards. These results demonstrate that lateral gaze-direction can modulate neglect-related auditory spatial deficits, even though eye-position did not alter the initial auditory inputs. This outcome may relate to audio-visual links in spatial orienting and potentially some retinocentric influences on perceived sound location, although the latter alone could not explain all our results. Such findings might involve multisensory brain structures in which responses to sounds are modulated by eye-in-orbit position.

Attention↗
PubMed2005

Audiovisual integration in patients with visual deficit.

In the present study, we investigated the possibility that bimodal audiovisual stimulation of the affected hemifield can improve perception of the visual events in the blind hemifield of hemianopic patients, as it was previously demonstrated in neglect patients. Moreover, it has been shown that "hetero-modal" and "sensory-specific" cortices are involved in cross-modal integration. Thus, the second aim of the present study was to examine whether audiovisual integration influences visual detection in patients with different cortical lesions responsible of different kinds of visual disorders. More specifically, we investigated cross-modal, audiovisual integration in patients with visual impairment due to a visual field deficit (e.g., hemianopia) or visuospatial attentional deficit (e.g., neglect) and patients with both hemianopia and neglect. Patients were asked to detect visual stimuli presented alone or in combination with auditory stimuli that could be spatially aligned or not with the visual ones. The results showed an enhancement of visual detection in cross-modal condition (spatially aligned condition) comparing to unimodal visual condition only in patients with hemianopia or neglect; by contrast, the multisensory integration did not occur when patients presented both deficits. These data suggest that patients with visual disorders can enormously benefit the multisensory integration. Moreover, they showed a different influence of cortical lesion on multisensory integration. Thus, the present results show the important adaptive meaning of multisensory integration and are very promising with respect to the possibility of recovery from visual and spatial impairments.

Acoustic Stimulation↗
PubMed2004

"Acoustical vision" of below threshold stimuli: interaction among spatially converging audiovisual inputs.

Crossmodal spatial integration between auditory and visual stimuli is a common phenomenon in space perception. The principles underlying such integration have been outlined by neurophysiological and behavioral studies in animals; this study investigated whether the integrative effects observed in animals also apply to humans. In this experiment we systematically varied the spatial disparity (0 degrees, 16 degrees, and 32 degrees) and the temporal interval (0, 100, 200, 300, 400, and 500 ms) between the visual and the auditory stimuli. Normal subjects were required to detect visual stimuli presented below threshold either in unimodal visual conditions or in crossmodal audiovisual conditions. Signal detection measures were used. An enhancement of the perceptual sensitivity (d') for luminance detection was found when the audiovisual stimuli followed a simple spatial and temporal rule, governing multisensory integration at the neuronal level.

Acoustic Stimulation↗
PubMed2004

Recovery of oculo-motor bias in neglect patients after prism adaptation.

Patients with "neglect dyslexia" usually make errors in reading the left part of words and non-words. It has been shown that "neglect dyslexia" can improve following a short period of adaptation to wedge prisms [Neuropsychologia 40 (2002) 718], however the mechanisms underlying this amelioration are still unknown. The present study evaluated the effect of prism adaptation (PA) on ocular scanning behaviour of neglect dyslexia patients by investigating: (a) the first saccade landing position during reading a letter string and (b) the distribution of fixation time as a function of the side of oculo-motor exploration of words and non-words. This in order to assess whether possible changes (in reading performance) after the adaptation might be attributed to a resetting of the oculo-motor system. Eye movements' performances were recorded before and after a single prismatic exposure on right brain-damaged patients with left hemispatial neglect and "neglect dyslexia". The results obtained in Experimental neglect patients before and after PA were then compared to that of control neglect patients, who were wearing goggles with neutral lenses. Moreover, in order to provide normative data on ocular scanning behaviour during letter string reading, neurologically healthy subjects were also studied. Following a single session of prism adaptation, the results showed, in the Experimental neglect patients, an improvement of neglect dyslexia, an increased left-sided exploration of the letter string and an increased amplitude of the first left-sided saccade. In contrast, in the Control neglect patients, neglect dyslexia as well as the oculo-motor system behaviour, remained the same after the use of goggles with neutral lenses. These findings demonstrate that the beneficial effect induced by a single prismatic adaptation may be conceived as a complex interaction between sensory stimulation and a resetting of oculo-motor system.

Adaptation, Physiological↗
PubMed2003

Task-dependent visual coding of sound position in visuospatial neglect patients.

Recent neurophysiological evidence has shown that sound position can be coded in multiple frames of reference in the animal brain (i.e. head-centred, eye-centred, or intermediate head/eye centred). Here, we provide evidence for multiple coding of sound positions in humans, by studying pointing to sounds in 14 right brain-damaged (RBD) patients with or without visual neglect (a visuospatial neurological disturbance typically affecting contralesional space). Patients were asked to indicate the position of free-field sounds, either with a hand-pointing or with a head-turning response. Pointing movements were performed either blindfolded or with eyes open, but no visual feedback was available about sound position or the motor response. All RBD patients showed some impairment in sound localisation, particularly for sounds towards the contralesional side. In addition, task-irrelevant vision was more detrimental for hand-pointing than head-turning responses, only for neglect patients. We propose that this finding reflects visual coding of sound position when the eyes are open, which extends the pathological visuospatial bias of neglect patients to sound localisation. Moreover, the absence of any modulatory effects of ambient vision when head-turning responses were adopted suggests task-dependent visual coding of sound position, in agreement with multiple frames of reference for sound localisation.

Aged↗
PubMed2003

Beyond the window: multisensory representation of peripersonal space across a transparent barrier.

A large body of neuropsychological evidence has been recently provided showing that humans can code visual objects in nearby space through multisensory visuo-tactile integrative processes, which share several similarities with the functional properties of bimodal neurons documented in neurophysiological studies. In particular, the phenomenon of visuo-tactile extinction reveals that crossmodal integration may take place in a privileged manner within a limited sector of space closely surrounding the body surface, i.e. in the near peripersonal space. Here we report that visuo-tactile extinction can seemingly be obtained when a physical, transparent barrier is interposed between the patients' hand and a proximal visual stimulus. These findings show that visuo-tactile representation of peripersonal space can be formed despite the subject's explicit awareness concerning the physical impossibility for the hand to be touched. This phenomenon indicates that multisensory integrative processing can occur in a bottom-up fashion without necessarily being modulated by more 'cognitive' processes. Such integration may be functionally important for automatic reactions such as head turning or hand withdrawal.

Aged↗
PubMed2002

Enhancement of visual perception by crossmodal visuo-auditory interaction.

Neurophysiological studies have shown in animals that a sudden sound enhanced perceptual processing of subsequent visual stimuli. In the present study, we explored the possibility that such enhancement also exists in humans and can be explained through crossmodal integration effects, whereby the interaction occurs at the level of bimodal neurons. Subjects were required to detect visual stimuli in a unimodal visual condition or in crossmodal audio-visual conditions. The spatial and the temporal proximity of multisensory stimuli were systematically varied. An enhancement of the perceptual sensitivity (d') for luminance detection was found when the audiovisual stimuli followed a rather clear spatial and temporal rule, governing multisensory integration at the neuronal level.

Adult↗
PubMed2002

Auditory peripersonal space in humans.

In the present study we report neuropsychological evidence of the existence of an auditory peripersonal space representation around the head in humans and its characteristics. In a group of right brain-damaged patients with tactile extinction, we found that a sound delivered near the ipsilesional side of the head (20 cm) strongly extinguished a tactile stimulus delivered to the contralesional side of the head (cross-modal auditory-tactile extinction). By contrast, when an auditory stimulus was presented far from the head (70 cm), cross-modal extinction was dramatically reduced. This spatially specific cross-modal extinction was most consistently found (i.e., both in the front and back spaces) when a complex sound was presented, like a white noise burst. Pure tones produced spatially specific cross-modal extinction when presented in the back space, but not in the front space. In addition, the most severe cross-modal extinction emerged when sounds came from behind the head, thus showing that the back space is more sensitive than the front space to the sensory interaction of auditory-tactile inputs. Finally, when cross-modal effects were investigated by reversing the spatial arrangement of cross-modal stimuli (i.e., touch on the right and sound on the left), we found that an ipsilesional tactile stimulus, although inducing a small amount of cross-modal tactile-auditory extinction, did not produce any spatial-specific effect. Therefore, the selective aspects of cross-modal interaction found near the head cannot be explained by a competition between a damaged left spatial representation and an intact right spatial representation. Thus, consistent with neurophysiological evidence from monkeys, our findings strongly support the existence, in humans, of an integrated cross-modal system coding auditory and tactile stimuli near the body, that is, in the peripersonal space.

Aged↗