Posner has suggested that unilateral spatial neglect could be due to a difficulty in disengaging attention from its current focus to orient it toward the neglected half space. Clinical and experimental data suggest, however, that this disengaging difficulty could be only one aspect of a more complex disturbance also characterised by an early automatic orienting of attention toward the half space ipsilateral to the lesion. To test this hypothesis, two different investigations in unselected groups of patients with right and left brain-damage were carried out. The first investigation, to evaluate forms of lateral orienting of attention severe enough to provoke an overt gaze deviation, consisted of the systematic assessment of the phenomenon of "magnetic gaze attraction". The second investigation, to detect milder forms of automatic orienting of attention, analysed the temporal sequence followed in identifying the pictures represented in an "Overlapping Figures task", to see if patients tended to identify first figures lying in the half space ipsilateral to the lesion. In both investigations results consistently showed: a) that patients with right brain damage tend to orient attention automatically toward the ipsilateral half space more than patients with left brain damage; b) that this tendency is tightly linked to the presence of behavioural manifestations of hemi-neglect. These results are therefore consistent with the hypothesis that hemi-neglect is a multi-component syndrome with an early orienting of attention toward the half space ipsilateral to the lesion as the first of these components.

Using a quantitative measure, we analyzed the relationship between visuospatial and representational neglect in right- and left-brain-damaged patients and found signs of representational neglect only in right-brain-damaged patients. Although representational neglect was always associated with visuospatial neglect, suggesting that the two forms share a common underlying mechanism, the most frequent finding in right-brain--damaged patients was that of visuospatial neglect in isolation. A strong influence of the phenomenon of attentional attraction toward space ipsilateral to the lesion in visuospatial, as opposed to imaginal, tasks can account for this finding.

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An Overlapping Figures test, considered as appropriate to study focusing of attention on small but complex stimuli falling in the central parts of visual field and a Searching for Animals test, designed to study the exploration of large parts of extrapersonal space, were administered to 38 controls, and 90 right and 82 left brain-damaged patients. The investigation was designed to test the hypothesis that the extent of space to be explored may have a different influence on unilateral spatial neglect of right and left brain-damaged patients. Both right and left brain-damaged patients showed an asymmetric exploration of space on the Searching for Animals test, making more omissions on the side contralateral to the damaged hemisphere than on the ipsilateral one. On the Overlapping Figures test, however, only right brain-damaged patients showed a clear tendency to omit figures lying on the left side of the composite pattern. This finding suggests that inability to extract visual information from one side of the stimuli during single eye fixations may be the most characteristic feature of unilateral spatial neglect resulting from right hemisphere lesions.

Contrasting results have been obtained in previous investigations, which have used the standard version of Raven's Colored Progressive Matrices for studying the effects of localized brain lesion on visual-spatial intelligence. Some of these discrepancies might be due to the fact that specific factors, such as unilateral spatial neglect, could contribute to decreased performance obtained on Raven's test by patients with focal brain lesions. A new set of Colored Matrices, devised to minimize the influence of unilateral spatial neglect without changing the essential features of the original task, was therefore constructed. The test was administered to 76 normal controls, 74 right brain-damaged patients, 87 aphasics, and 61 nonaphasic left brain-damaged patients, in order to study the effect of laterality of lesions and of language impairment on Raven's scores. The results show that, if the influence of unilateral spatial neglect is minimized and Raven's scores are corrected in reference to age, educational level, and lesion size, then: no significant differences are observed between right and left brain-damaged patients; aphasics score worse than nonaphasic left brain-damaged patients; impairment is greater in patients with Wernicke's and Global aphasia (i.e., in patients with severe language comprehension disorders) than in patients classified as Broca's, Anomic, or Conduction aphasia; impairment is greater in patients with semantic-lexical discrimination errors than in patients free from semantic-lexical comprehension disorders.