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When patients with left hemineglect are shown the centre of a memorised line and are asked to mark both the endpoints, they place the left one significantly farther. This contralesional bias appears to be incoherent with respect to most... more
When patients with left hemineglect are shown the centre of a memorised line and are asked to mark both the endpoints, they place the left one significantly farther. This contralesional bias appears to be incoherent with respect to most current interpretations of neglect [7].In the present study, ten patients with left hemineglect and two control groups were presented the centre of a line and one of its endpoints and had to mark the missing one at the correct distance. With this modification, subjects had not to rely on stored information about the line, but simply to reproduce a distance either to the left or to the right separately. The task was performed in three different spatial locations with respect to subjects’ body midline.Similarly to the original endpoints’ task, neglect patients showed a leftward bias, placing the left endpoint significantly farther than the right one. However, this was not associated with a paradoxical contralesional over-extension with respect to the distance to reproduce. Indeed, when marking the left endpoint, patients were accurate (when performing in the right hemispace) or even underestimated the distance to reproduce (when performing centrally and in the left hemispace). Instead, the leftward bias was due to severe underestimation errors when marking the right endpoint, which were independent of the stimulus location.These results demonstrate that the leftward bias in the endpoints’ task is relative rather than absolute and does not reflect a paradoxical overestimation in length reproduction towards the left side. © 1999 Elsevier Science Ltd. All rights reserved.
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Unilateral neglect following damage to the right hemisphere of the brain can be characterized by failure of the global attentional mechanisms of the right hemisphere to direct the local detail processors of the left hemisphere towards the... more
Unilateral neglect following damage to the right hemisphere of the brain can be characterized by failure of the global attentional mechanisms of the right hemisphere to direct the local detail processors of the left hemisphere towards the contralesional left hemispace. This is suggested by patients who recognize the global form of the left side of shapes (the forest) but fail to cancel out its local details (the trees). Here we report the opposite behavioural dissociation in a patient (Q.M.) with damage to the right hemisphere of the brain. Q.M. detected local details (such as the tail of a dog) on the left or right side of visual shapes, regardless of whether these details belonged to predefined target shapes (a dog in this case) or to distractor shapes differing on the opposite side (a dog with a swan's neck and head, for example). Psychological testing showed an abnormal tendency of this patient to respond to local features, but perfect accuracy in interpreting global features when the local features could not interfere in global processing. The results indicate that the left hemisphere can integrate multiple local features simultaneously but loses global awareness as soon as local features individually compete for response selection. However, awareness of the whole is not necessary for the sequential processing of the parts.
Research Interests: Pharmacology, Biochemistry, Bioinformatics, Evolutionary Biology, Genetics, and 58 moreMarine Biology, Neuroscience, Environmental Science, Geophysics, Physics, Materials Science, Quantum Physics, Developmental Biology, Immunology, Climate Change, Molecular Biology, Structural Biology, Genomics, RNA, Computational Biology, Transcriptomics, Visual perception, Biotechnology, Systems Biology, Cancer, Biology, Attention, Metabolomics, Cell Cycle, Proteomics, Ecology, Drug Discovery, Evolution, Nanotechnology, Magnetic Resonance Spectroscopy, Astrophysics, Neurobiology, Medicine, Multidisciplinary, Palaeobiology, Functional Genomics, Nature, Information Processing, Signal Transduction, Astronomy, DNA, Right Hemisphere Functions, Vision, Brain, Humans, Female, Cell Signalling, Medical Research, Brain Ischemia, Awareness, Response-Selection, Middle Aged, Psychological Tests, Unilateral Neglect, Hemianopsia, Left Hemisphere, Local Features, and Earth Science
The present study quantitatively investigated the slow and quick phases of optokinetic nystagmus (OKN) in four groups of patients: right unilateral brain-damaged patients with neglect, left and right patients without neglect or hemianopia... more
The present study quantitatively investigated the slow and quick phases of optokinetic nystagmus (OKN) in four groups of patients: right unilateral brain-damaged patients with neglect, left and right patients without neglect or hemianopia and patients with left or right retrogeniculate lesions and lateral homonymous hemianopia. Our results indicate that only neglect patients show a perturbation of both components of OKN. A comparison among MRI images of different patients shows that a region involving area 37 and adjacent areas 39 and 19, was impaired in all patients with neglect, but not in any other patient with either right or left lesions.