Mind, brain, and functional neuroimaging.
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Brain Mapping↗
Biomedical subjects
Giuseppe Vallar
Publications and source records attributed to Giuseppe Vallar.
Productive and defective impairments in the neglect syndrome: graphic perseveration, drawing productions and optic prism exposure.
The effects of adaptation to prisms displacing rightwards the field of vision on omission errors, and on perseveration and other graphic productions in a line cancellation task, were assessed in nine right-brain-damaged patients with left unilateral spatial neglect. Prism adaptation improved both neglect, as indexed by omission errors, and perseveration behaviour, up to a delay of 60 min. No correlation was found between omission and perseveration errors in all assessments. The suggestion is made that perseveration and other complex graphic productions made by right brain-damaged-patients with left spatial unilateral neglect is due to a defective monitoring of complex motor behaviour, frequently associated to cerebral damage involving the right frontal lobe. Interpretations of perseveration behaviour in terms of allochiria and directional hypokinesia are considered, and their limits discussed.
Adaptation, Physiological↗
Anosognosia for motor and sensory deficits after unilateral brain damage: a review.
PURPOSE: The syndrome of unawareness (anosognosia) for sensory and motor neurological deficits (hemiplegia, hemianaesthesia, and hemianopia), contralateral to the side of a hemispheric lesion, is reviewed. CONTENT: Main topics include: basic historical facts; the types of patient's interview and specific questions used to reveal the deficits; the clinical patterns of presentation; the associations and dissociations of the different anosognosic manifestations, and their relationships with associated disorders of sensory, memory, and executive-intellectual functions; the hemispheric asymmetry of anosognosia, that, as the syndrome of unilateral spatial neglect, is more frequent and severe after damage to the right cerebral hemisphere; the relationships between spatial neglect and the anosognosias, and their neural correlates; the effects of lateralized sensory stimulations on defective awareness of neurological impairments. CONCLUSIONS: The argument is made that anosognosia for sensory and motor neurological deficits should be considered as a multi-component syndrome, including a number of specific disorders that are due to the impairment of discrete monitoring systems, specific for the different supervised functions. The putative causal role of associated deficits of other parts of the sensory-motor or cognitive (e.g., memory, general intelligence) system is critically discussed. These specific control processes may be physically implemented in brain areas anatomically (and functionally) close to those subserving the monitored function.
Behavior↗
Left neglect dyslexia and the effect of stimulus duration.
The present study investigated the effects of the duration of the stimulus on the reading performance of right-brain-damaged patients with left neglect dyslexia. Three Italian patients read aloud words and nonwords, under conditions of unlimited time of stimulus exposure and of timed presentation. In the untimed condition, the majority of the patients' errors involved the left side of the letter string (i.e., neglect dyslexia errors). Conversely, in the timed condition, although the overall level of performance decreased, errors were more evenly distributed across the whole letter string (i.e., visual - nonlateralized - errors). This reduction of neglect errors with a reduced time of presentation of the stimulus may reflect the read out of elements of the letter string from a preserved visual storage component, such as iconic memory. Conversely, a time-unlimited presentation of the stimulus may bring about the rightward bias that characterizes the performance of neglect patients, possibly by a capture of the patients' attention by the final (rightward) letters of the string.
Adult↗
Numbers and space: a cognitive illusion?
This study investigated the relationships between numerical and spatial representations by means of a bisection task, exploring the view that the core representation of number meaning is spatially organized as a mental number line. In Experiment nos. 1 (bisection of digit strings) and 2 (bisection of flanked lines) spatial biases towards the larger digit were found to be related only to processing of relative magnitude. Experiment nos. 3 (bisection of an unfilled space) and 4 (bisection of flanked lines/unfilled spaces) aimed at disclosing perceptual, attentional, and numerical constraints on the bias induced by the position of the larger digit. This effect is interpreted in terms of a cognitive illusion of length, whereby a spatial bias compensates for the numerical disparity. This seems to operate in a categorical fashion ("small/large"), and to be congruent with the assumption that relatively large numbers are associated with the right side of a mental representational space.
Adult↗
The neuropsychology of human memory.
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Amnesia, Retrograde↗
Hermann Zingerle's "Impaired perception of the own body due to organic brain disorders". 1913. 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.
Body Image↗
Neuroanatomy of cognition, neuroanatomy and cognition.
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Animals↗
Reading aloud and lexical decision in neglect dyslexia patients: a dissociation.
This study investigated the dissociation between reading aloud and lexical decision in six Italian right-brain-damaged patients with left neglect dyslexia. Patients were requested to perform two tasks: (a) reading aloud and lexical decision on monomorphemic words of different frequencies and non-words with different degrees of similarity to real words (Experiment 1); (b) reading aloud and lexical decision on morphologically complex (suffixed) derived words and morphologically complex (suffixed) non-words (Experiment 2). The patients' performance on lexical decision was compared to that of a group of matched control subjects. Patients showed left neglect dyslexia in the reading aloud task, but had a normal level of performance in the lexical decision task. Furthermore, patients were affected by the same morpho-lexical variables that influence lexical decision in normal subjects, suggesting a largely preserved morpho-lexical processing of written letter strings, as assessed by the task of lexical decision. The mechanisms underlying the preservation of lexical decision in patients with left neglect dyslexia are discussed in the light of dual route models of reading.
Aged↗
Anosognosia for left-sided motor and sensory deficits, motor neglect, and sensory hemiinattention: is there a relationship?
In recent years, research on unilateral spatial neglect has focused on dissociations between different aspects of the clinical syndrome, which is now considered by many students as a multi-componential disorder. Notwithstanding this leading view, there is at least one empirical argument which supports a unitary interpretation of the disorder. This is based on the observation, now replicated many times, that a variety of sensory stimulations (vestibular, optokinetic, transcutaneous mechanical vibration and nervous electrical, visual prism adaptation) involving a lateral change (left-right asymmetry) in the input pattern, affect in a very similar fashion virtually all manifestations of the syndrome, including: visuo-spatial neglect; hemianaesthesia (somatosensory hemi-inattention); extinction, hemiparesis, hemiplegia, and anosognosia for these motor disorders; somatoparaphrenia. These effects may be accounted for with reference to a spatial medium, articulated in a number of specific components, which is modulated by sensory input in a fundamentally similar fashion. Recent investigations concerning the neural bases of some of these stimulations support this view. In this chapter the case of the co-variation of the effects of vestibular stimulation on motor deficits and on anosognosia for hemiplegia is considered. The suggestion is made that one mechanism underlying anosognosia for hemiplegia is unawareness of a deficit of intention, or movement planning component, rather than, or in addition to, unawareness of a primary motor deficit. Temporary remission of anosognosia after vestibular stimulation may represent recovery from this neglect-related component, of which, as of other manifestations of the syndrome, patients are typically unaware. The recovered intention to move may allow the detection by the patient of the presence of a residual primary motor deficit, through a feedback mechanism.
Agnosia↗
Spatial cognition: evidence from visual neglect.
Recent work on human attention and representational systems has benefited from a growing interplay between research on normal attention and neuropsychological disorders such as visual neglect. Research over the past 30 years has convincingly shown that, far from being a unitary condition, neglect is a protean disorder whose symptoms can selectively affect different sensory modalities, cognitive processes, spatial domains and coordinate systems. These clinical findings, together with those of functional neuroimaging, have increased knowledge about the anatomical and functional architecture of normal subsystems involved in spatial cognition. We provide a selective overview of how recent investigations of visual neglect are beginning to elucidate the underlying structure of spatial processes and mental representations.
Journal Article↗
Neglect syndromes: the role of the parietal cortex.
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Attention↗
Exploring the syndrome of spatial unilateral neglect through an illusion of length.
Both a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients' bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects.
Adult↗
Feeling touches in someone else's hand.
Cerebral damage may induce a delusional belief so that patients claim that their limbs contralateral to the side of the lesion belong to someone else (somatoparaphrenia). This disorder, which is not due to a general delirium, is frequently accompanied by the inability to feel tactile sensations in the 'non-belonging' part of the body. We report the unique case of a patient with somatoparaphrenia in whom dense tactile imperception in the left hand dramatically recovered when she was instructed to report touches delivered to her niece's hand, rather than to her own hand. We suggest that, through this verbal instruction, the mismatch between the patient's belief about the ownership of her left hand and her ability to perceive touch on it was transiently recomposed. This is evidence that apparently elementary deficits, such as hemianesthesia, and selective delusional behavior, such as somatoparaphrenia, may both originate from an impairment of the body image.
Aged↗
Spatial awareness: a function of the posterior parietal lobe?
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Animals↗
Is the intact side really intact? Perseverative responses in patients with unilateral neglect: a productive manifestation.
The main defective manifestations of extra-personal unilateral spatial neglect concern the side of space contralateral to the hemispheric lesion (contralesional). Since the disorder is more frequent and severe after damage to the right hemisphere, patients typically fail to explore the left side and ignore stimuli located in that sector of space. The patients' behaviour in the side of space ipsilateral to the side of the lesion (ipsilesional) is not intact, however. In cancellation tasks, it can be observed that patients with unilateral neglect, in addition to failing to respond to contralesional stimuli, may show perseverative behaviour, crossing out many times the same stimulus in the ipsilesional side of the sheet. We analyzed the occurrence of this phenomenon during the execution of a cancellation task in a large series of brain-damaged patients with left- and right-sided hemispheric lesions, with and without evidence of unilateral spatial neglect, and in a group of patients suffering from senile dementia of the Alzheimer-type. Perseverative responses were found to be much more frequent in patients with spatial neglect and when the frontal lobe or subcortical structures were damaged. The results are interpreted in the context of a multi-componential view of the neglect syndrome, with reference to a distinction originally put forward by Derek Denny-Brown (1958) between 'frontal or magnetic' and 'parietal or repellent' apraxia. In patients with spatial neglect, frontal damage releases drawing perseverative behaviour in the ipsilesional sector of space. Perseveration in exploratory tasks constitutes a main instance of the productive manifestations of spatial neglect.
Aged↗