Biomedical subjects
Publications and source records attributed to E Bisiach.
The effects of vestibular stimulation on somatoparaphrenic delusion were investigated in a patient suffering from a fronto-temporo-parietal infarction located in the right hemisphere. Transitory remission of the patient's delusional belief was consistently observed during unilateral vestibular activation obtained by means of cold-water irrigation of the left (contralesional) ear.
Four neglect patients are reported who where unable to detect left-side differences in pairs of drawings though being sometimes influenced by such differences in making preference judgements. In most instances, tracing the silhouette of the drawings did not help patients to find the difference despite the fact that tracing implied crossing the altered detail or following its contour with the fingertip. This finding cannot easily be accommodated by current theories of unilateral neglect.
Right-brain-damaged patients showing unilateral neglect underwent a specifically devised line-bisection task that allowed uncoupling of the direction of visual attention from that of hand movement. This made it possible to isolate and separately assess perceptual and premotor factors of the disorder. Comparison of experimental and radiologic data suggested that premotor factors were more pronounced in patients with lesions involving the frontal lobes than in patients with lesions confined to postrolandic areas. The technique employed is compatible with bedside examination and provides data useful for standard assessment of neglect symptomatology for both clinical and experimental purposes.
Visual extinction on double simultaneous stimulation was investigated in left and right brain-damaged patients in two response conditions: verbal and motor. In right brain-damaged patients contralesional detection was significantly worse when monitored by motor rather than by verbal responses in condition of single as well as of double stimulation. Previous research in normal subjects had shown that the left hemisphere is selectively involved in choice reactions such as those occurring in the motor condition of the present experiment in brain-damaged patients. The results of the latter are interpreted using as a basis the findings of that research and Kinsbourne's hemisphere activation hypothesis concerning unilateral neglect of space.
The performance of unilateral brain-damaged patients on recognition of random shapes was investigated by means of two different experiments. In experiment I interitem similarity and number of response-choice alternatives were varied to evaluate their possible influence on the subjects' performance. In experiment II stimulus exposure time was varied, In both experiments left brain-damaged patients with visual field defect obtained lower scores than control subjects. Right brain-damaged patients with visual field defect obtained scores significantly lower than controls only in the brief exposure condition.
Right brain-damaged patients with unilateral neglect were asked to detect differences within pairs of patterns moving left- or rightward behind a narrow vertical slit. It was seen that differences occurring on the left side of the mentally reconstructed images were less easily detected; therefore it is suggested that a representational disorder plays a primary role in unilateral neglect. In the light of these findings, it is possible to take into consideration some implications of unilateral neglect for theories of conscious brain activity.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Fifty-eight subjects were shown tachistoscopically grey rectangles, at the centre of the field of vision. The rectangles extended equally to the left and right of the visual fixation point, and were presented under four background conditions: all white, all black, white in the left half of the field and black in the right half, black in the left and white in the right half. "Chimerical" backgrounds were assumed to create an interhemispheric ambiguity in the perception of the greyness of the stimuli as a consequence of opposed brightness contrasts. The reported birghtness was therefore expected to reflect a hemispheric dominance or an interhemispheric averaging of information. The results of the experiment supported the second hypothesis.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Visual similarity judgements among rectangles varying in form and area were investigated in control subjects and in patients with lesions confined to either cerebral hemisphere. While an overweighing of form with respect to area was found in both control subjects and right brain-damaged, left brain-damaged patients equally weighted the two relevant dimensions. Beyond revealing differential processing rules related to the side of the injury in the brain, the findings lend themselves to some speculation about cerebral dominance.
The aim of this study was to point out a hemisphere asymmetry in focal brain-damaged patients and a hand asymmetry in normals on halving binocularly a horizontal line. 50 left hemisphere and 53 right hemisphere patients (both subdivided by presence/absence of visual field defect) and 50 controls (divided by the hand they used to carry out the task) were employed. 4 differently long segments made up the test material and the error scores with respect to the geometric midpoint were worked out by means of parametric statistical procedures. It turned out that: (i) healthy subjects committed a mean leftward displacement, regardless of the hand they used. All the same, only the halving error committed by the right hand is significant keeping as reference the geometric midpoint of the segment; (ii) left and right hemisphere-damaged patients committed halving errors, that are opposite in direction, leftward for the former and rightward for the latter; (iii) the behaviour of right patients with visual field defects is the only to be significantly different from that of the corresponding controls. Our findings point to prevailing importance of the right hemisphere mainly of its posterior areas, in the halving task.
Visuoperceptual categorization was investigated in patients with unilateral brain damage by a task in which meaningless shapes had to be classified with reference to a number of prototype patterns. Right brain-damaged subjects with visual field defect turned out to have a narrower categorization span. As this outcome seems to be scarcely consonant with a lower level disorder of visual processing, a major competence of the right hemisphere is suggested for visuoperceptual categorization.