Perceptual and premotor factors 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.

rTMS of the unaffected hemisphere transiently reduces contralesional visuospatial hemineglect.

To verify the role of interhemispheric influences on manifestations of neglect, the authors investigated the effects of a transient repetitive transcranial magnetic stimulation (rTMS)-induced disruption of the unaffected hemisphere on contralesional visuospatial neglect in two left- and five right-brain-damaged patients. Parietal rTMS of the unaffected hemisphere during the execution of a computerized task of bisected line's length judgment transiently decreased the magnitude of neglect as expressed in the number of errors.

Remission of somatoparaphrenic delusion through vestibular stimulation.

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.

Unilateral neglect: personal and extra-personal.

Ninety-seven right brain-damaged patients were given two tasks aimed at assessing unilateral neglect in personal and in extra-personal space. The frequency of the two aspects of neglect, as well as their patterns of association with each other and with more elementary neurological disorders are reported and discussed. The results suggest a non-unitary frame of spatial reference for unilateral neglect, which may tentatively be interpreted in terms of a personal vs extra-personal dichotomy.

Remission of hemineglect and anosognosia during vestibular stimulation.

The effects of vestibular stimulation on extrapersonal and personal neglect and on awareness of disease were investigated in four patients with severe neglect and anosognosia. Neglect phenomena improved in all patients, while an effect on anosognosia was found in two cases. These preliminary findings indicate a possible role of vestibular stimulation on hemispheric activation.

Unilateral neglect in route description.

Route description was investigated in two patients suffering from left unilateral neglect. Both had evident difficulty with left turns. This finding suggests that the topological correspondence between represented environment and representational mechanisms in the brain is not confined to frozen (picture-like) perspectives.

Unawareness of disease following lesions of the right hemisphere: anosognosia for hemiplegia and anosognosia for hemianopia.

Unawareness of motor and visual-field defects was investigated in 97 right brain-damaged subjects. Both kinds of anosognosia were found to be double-dissociated from more elementary neurological disorders and from personal and extra-personal neglect. The relationships between anosognosia and unilateral neglect are discussed and allusion is made to the implications concerning the neurological organization of higher control functions.

Analogical representation and language structure.

Severe impairment of the analogue of mental representation is not compensated for by putative language-based cognitive processes in non-dysphasic brain-damaged patients. This undermines the hypothesis of an independent role for language in the generation of thought. Against this view it may be contended that there seems to be no obvious way in which analogical mental representation can decide between alternative syntactical structures available for the expression of thought. We performed a visual imagery experiment in which we asked 40 subjects to imagine visual scenes representing the meanings of simple utterances presented to them. The subjects then had to indicate the relative position, in each visual image, of two objects mentioned in each utterance. Series of utterances were presented differing syntactically (active or passive phrase) and semantically (specifying in different ways the spatial and temporal relations between the objects mentioned). The results of this mental imagery experiment indirectly support the hypothesis that syntactical structures can be represented in a nonlinguistic analogue medium.

Challenging current accounts of unilateral neglect.

Two left-neglect patients were asked (i) to bisect a 15 cm line, (ii) to bisect the empty space between the endpoints of a 15 cm virtual line, and (iii) to set the endpoints of a 15 cm virtual line, given its midpoint. With one patient, the subjective midpoint of the virtual line was found to be displaced leftwards with respect to the subjective midpoint of the real line, whereas with the other it was found to be displaced rightwards. However, in condition (iii) both patients significantly underestimated the distance from the centre of the rightmost point of the virtual line while relatively overestimating that from the centre to the left endpoint. This latter result challenges current accounts of unilateral neglect.

Two-dimensional distortion of space representation in unilateral neglect: perceptual and response-related factors.

The paper reports the results of an experiment in which left-neglect patients were required to point at the location they judged vertically to correspond (within the frame of the visual stimulus display they were given) with a cue that was variably located along a left-right axis lying proximally or distally with respect to the left-right axis over which they had to give their response. Patients were found to make rightward errors as in a similar, single-case study. The significant positive correlation between those errors and the degree of response bias on a manual-response version of the Milner Landmark Task suggests that rightward pointing errors made by left-neglect patients in conditions such as those set in the present experiment are due to a dysfunction selectively affecting an output-related component of space representation.

Timing of right parietal and frontal cortex activity in visuo-spatial perception: a TMS study in normal individuals.

In a recent study we showed that repetitive transcranial magnetic stimulation (rTMS) with train duration of 400 ms over right frontal and right posterior parietal cortices gives rise to transitory contralateral visuo-spatial neglect in normal subjects. In the present experiment we investigated whether using single-pulse TMS it is possible to obtain information about the timing of cortical activity related to spatial cognition. Nine healthy subjects performed in baseline condition and during TMS a tachistoscopic task, requiring a forced-choice estimation of the length of the two segments of prebisected horizontal lines. Single-pulse TMS was triggered at various time intervals (150 ms, 225 ms, 300 ms) after visual stimulus onset with a focal coil over P6 and F4 (according to 10/20 EEG system). Relative transitory rightward bias was observed only when parietal TMS was delivered 150 ms after visual stimulus presentation. Frontal stimulation induced no effect on visuo-spatial perception with the time intervals explored.

Contralateral neglect induced by right posterior parietal rTMS in healthy subjects.

We applied repetitive transcranial magnetic stimulation (rTMS) in order to induce interference on visuo-spatial perception in 11 healthy subjects. Subjects performed a visuo-spatial task requiring judgements about the symmetry of prebisected lines. Visual stimuli consisted of symmetrically or asymmetrically transected lines, tachystoscopically presented for 50 ms on a computer-monitor. Performance was examined in basal condition and during rTMS trains of 10 stimuli at 25 Hz, delivered through a focal coil over right or left posterior parietal cortex (P5 and P6 sites) and triggered synchronously with visual stimulus. Randomly intermixed sham rTMS trains were employed to control for non-specific effects. Right parietal rTMS induced a significant rightward bias in symmetry judgements as compared with basal and sham rTMS conditions. No differences emerged between other conditions.

1 Hz repetitive transcranial magnetic stimulation of the unaffected hemisphere ameliorates contralesional visuospatial neglect in humans.

The aim of the study was to investigate whether low-frequency repetitive transcranial magnetic stimulation (rTMS) over the unaffected hemisphere can ameliorate visuospatial neglect. We treated three right brain damaged patients with left neglect. 900 pulses (1 Hz frequency) were given over left posterior parietal cortex every other day for 2 weeks. Patients performed a computerized task requiring length judgement of prebisected lines, tachistoscopically presented for 150 ms. With respect to rTMS the task was given 15 days before, at the beginning, at the end and 15 days after. At these times patients performed also line bisection and clock drawing tasks. rTMS induced a significant improvement of visuo-spatial performance that remained quite unchanged 15 days after. Patients performance at Time 3 and 4 improved also as concerns line bisection and clock drawing tasks.

Unilateral neglect of representational space.

Two patients showing left unilateral neglect were asked to describe imagined perspectives of familiar surroundings. Left-sided details were largely omitted in the descriptions. Some theoretical implications of the occurrence of unilateral neglect in representational space are briefly considered.

Cerebral dominance and visual similarity judgements.

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.

Break-down of perceptual awareness in unilateral neglect.

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.

Recognition of random shapes in unilateral brain damaged patients: a reappraisal.

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.

Decision in ambiguity: hemispheric dominance or interaction?

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.

Hemispheric lateralization of the decisional stage in choice reaction times to visual unstructured stimuli.

Simple manual RTs to lateral visual stimuli were found to be faster in uncrossed than in crossed anatomical conditions. Neither hand nor hemifield effects were found. By contrast significant asymmetries were found in Choice RTs involving both hemispheres, even in uncrossed condition. The field effect was marked when the responding hand was the right but insignificant when the responding hand was the left. The data seem consistent with a model which assumes the location of the decisional structures in the left hemisphere.

Verbal-response and manual-response versions of the Milner Landmark task: normative data.

The paper reports normative data relative to a shortened form of two versions of the Milner Landmark task, involving verbal and manual response, respectively, which have been found to provide crucial information to discriminate perceptual from response bias in unilateral neglect. Normative data based on a large group of subjects were believed to be necessary because the Landmark task is held to be worth further investigation: (a) in comparison with other tasks devised for similar purposes, (b) in elucidating clinico-anatomical correlations, and (c) in planning selective remediation programmes. The results of the investigation provide criteria on the basis of which a patient's bias can be classified as being normal, borderline, or pathological.