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E Làdavas

Publications and source records attributed to E Làdavas.

30 records · Page 2Linked to original sources
PubMed1993

Implicit associative priming in a patient with left visual neglect.

Recent studies have suggested that patients with visual neglect may process, even if without awareness, perceptual features of the neglected stimuli. The aim of the current study was to further investigate whether the ignored stimuli are processed at a deeper level. Findings from a patient with damage to the right hemisphere and with left visual neglect (no hemianopia) are reported. He showed an associative priming in the neglected space: response to a word in the right visual field was faster when the word was preceded by the brief presentation of an associated word in the neglected field. When obliged to orient attention to the left side of a computer screen, he was not able to detect the presence of, to read aloud, or to judge the lexical status and semantic content of left-sided stimuli. This patient was able to perform a covert post-perceptual processing of the neglected stimuli, but could not do so when explicitly requested.

Attention↗
PubMed1993

The role of right side objects in left side neglect: a dissociation between perceptual and directional motor neglect.

Based on a test introduced by Tegnér and Levander, Brain 114, 1943-1951, 1991, right brain-damaged patients were assigned to a group with unilateral perceptual neglect and a group with directional motor neglect. Brain scans showed that all directional motor neglect patients had frontal lesions, whereas in perceptual neglect patients the frontal lobes were always spared. All patients were asked to execute two tasks, which were also administered to a control group. One task consisted in pointing to tokens symmetrically distributed on a display. The other task consisted in picking up the same tokens. The tasks were first executed with the aid of vision and then in a blindfolded condition. In the case of patients with perceptual neglect, performance on the left side was better in the pick-up task than in the pointing task and improved in the blindfolded condition. Neither patients with directional motor neglect nor control patients showed these effects. The results were explained in terms of the hyperattentional hypothesis of perceptual neglect, according to which, in this form of neglect, attention is captured by the objects that lie on the right side of space.

Aged↗
PubMed1990

The deployment of visual attention in the intact field of hemineglect patients.

Patients with left hemispatial neglect after right hemisphere lesions and control patients with right hemisphere lesions were presented in the ipsilesional (i.e., intact) visual field with stimuli that could occupy left-right relative positions. The patients were required to discriminate between target stimuli and distractors by emitting go/no-go responses. Reaction times (RTs) and measures of sensitivity (d') and response bias (beta) were obtained. The within-subjects comparisons showed that neglect patients were faster in the right than the left relative position, whereas control patients were faster in the left than the right relative position. The between-subjects comparisons showed that neglect patients were faster than control patients in the right relative position but slower in the left relative position. These effects were due to changes in processing efficiency, as attested by the fact that the differences in response speed were accompanied by congruent differences in sensitivity, whereas no differences in response bias were found. The results were interpreted by assuming that neglect patients focus attention on the right relative position and, therefore, have a small attentional focus concentrated on that position. By contrast, control patients, like normal subjects, would distribute attention between the two possible stimulus positions and, therefore, allocate attention to a larger portion of the visual field.

Analysis of Variance↗
PubMed1990

Selective spatial attention in patients with visual extinction.

The present study was designed to verify the attentional performance of patients with parietal lesions in the experimental condition in which they had to pay attention to 3 spatial positions located on the left, on the right and directly above the fixation stimulus (Experiment 1) and to only 1 of the 3 spatial positions at a time (Experiment 2). Twelve patients (6 subjects with right parietal lesions and 6 subjects without neurological deficits) participated in the experiment. The results of Experiment 1 showed that in patients with right parietal lesions the speed and accuracy of response to horizontally aligned stimuli increased gradually from right to left, whereas the control group showed only the effect due to the different retinal eccentricities of the 3 stimuli, that is, responses to central stimuli were faster and more accurate than responses to left and right stimuli. The results of Experiment 2 showed that both the neurological and control groups were faster to respond to central than to left and right stimuli, and that the neurological group was faster to respond to right than left stimuli, whereas no difference in RTs between two visual fields was obtained in the control group. Furthermore, when the patients had to respond to 3 spatial locations aligned horizontally (Experiment 1), the speed and accuracy of response to the right stimulus were the same as when they had to focus attention on it (Experiment 2). These results showed that the focus of attention in patients with visual extinction is on the rightmost stimulus and that the increased attention to the right is accompanied by a decreased attention to the left.

Analysis of Variance↗
PubMed1989

Unilateral attention deficits and hemispheric asymmetries in the control of visual attention.

The present study sought to determine the roles of the two hemispheres in arousal and the selective components of attention. Ten patients with left and right parietal lesions and ten with left and right temporal lesions participated in the experiment. The hypothesis that posterior parietal lesions, whether left or right, cause two selective attentional deficits, namely, a reduced reactivity to stimuli in the visual field contralateral to the lesion, and a reduced reactivity to any stimulus which occupies a relative contralateral spatial position, was tested by asking the patient to tilt their head either to the left or to the right by 90 degrees and to respond to two stimuli displayed above and on either side of fixation mark. The arousal component of attention was studied by analysing the overall RT to visual stimuli independent of their spatial positions. The results showed that (1) patients with either left or right parietal damage are impaired in shifting attention from the ipsilateral to the contralateral visual field, and, within each visual field, in a direction contraversive to the lesion and (2) these two attentional deficits are more severe after right than after left parietal damage. Furthermore, the results show that the difficulty in maintaining a high level of alertness is a specific deficit of patients with right hemispheric lesion and not of patients with an extinction syndrome, insofar as there is no significant difference in overall RT between patients with parietal and temporal lesions.

Adult↗
PubMed1983

[Spatial compatibility and position of the effectors].

Mean reaction times obtained with crossed hands (right had on the left and left hand on the right) are slower than reaction times obtained with uncrossed hands (right hand on the right and left hand on the left). These results have been explained as a compatibility effect between the responding hand and its spatial position. The goal of the present experiment was to establish whether the position of the hand is encoded by the subjects relative to their body (absolute position) or relative to the other hand (relative position). The subjects performed a discrimination task on two visual stimuli. Stimuli and hands were either on the same side of the body (both on the left or both on the right) or had different absolute position. In all conditions the subjects responded with crossed and uncrossed hands. The results support the hypothesis that relative position is encoded.

Functional Laterality↗
PubMed1983

Do laterality measures relate to speed of response in central vision?

This study was aimed at determining whether an efficiency index (speed of response in central vision) related to a laterality index (difference in speed of response between right and left field presentations). In Experiment 1 female subjects were required to discriminate facial emotional expressions shown in either central vision or the periphery. In Experiment 2 male and female subjects had to classify as same or different pairs of letters printed in different typefaces. It was found that the efficiency index related (negatively) to the laterality index only in Experiment 1 so that slower responses indicate larger visual field differences. The results are discussed in terms of current models of hemispheric specialization.

Discrimination Learning↗
PubMed1982

The development of facedness.

Thirty-two children of both sexes, ranging in age from 6 to 13 years, were photographed while posing or imitating happiness, sadness or surprise. Full-face photographs which were considered by independent judges to express the intended emotions were submitted to a split-face recombination procedure that created two composites from each face, one from the left side and the other from the right. Independent observers found the left composites to be more expressive than the right in the older group (age 12-13), but not in the younger groups, who evinced no left-right asymmetries. This finding applied similarly to the three emotions, and did not depend on an age-related change in the capacity for emotional expression. Further, left-right asymmetries in facial expression, where present, did not correlate with difference in size between the two halves of the face, and were found for both the upper and lower parts of the face. It is concluded that the advantage of the left hemiface for emotional expression, which is typical of adults, is the result of growth and development. While this facial asymmetry is likely to depend on an hemispheric asymmetry favoring the right side of the brain for the volitional control of the facial musculature, the neural mechanisms of the phenomenon of facedness are still largely obscure.

Age Factors↗
PubMed1979

Hemisphere-dependent cognitive performances in epileptic patients.

Short-term memory (STM), long-term memory (LTM), and recency judgment were investigated in 75 right-handed nonaphasic patients without visual deficits who had epileptic foci localized in one of four different regions of the brain: right temporal lobe, left temporal lobe, right frontal lobe, and left frontal lobe. The results led to the following conclusions: (1) left temporal lesions yielded comparatively greater impairment for the verbal LTM task, whereas right temporal lesions were more disruptive for the spatial LTM task; (2) no significant differences between left- and right-brain-damaged patients in STM tasks were obtained; (3) left frontal lesions yielded deficits in a recency task in accordance with hemispheric specialization; (4) only prolonged epileptic syndromes impaired neuropsychological performance in those tests; (5) comparisons between male and female patients and between those with and without clear evidence of a structural lesion did not reach statistical significance.

Adolescent↗
PubMedDate not supplied

Dissociation of ophthalmokinetic and melokinetic attention in unilateral neglect.

A line cancellation task was performed by 36 right brain-damaged patients with unilateral neglect under four different conditions: normal and mirror-reversed view, with and without cueing. Two types of unilateral neglect were distinguished by directing ophthalmo- and melokinetic components of visuomanual scanning to opposite sides of the stimulus array. In ophthalmokinetic neglect, contralesional visual scanning of the stimulus array was defective, while manual scanning was unimpaired. The converse was true of melokinetic neglect. Ophthalmokinetic neglect was predominantly associated with posterior brain damage, while melokinetic neglect was predominantly associated with frontal or subcortical brain damage. In a few instances, cueing visuomanual scanning toward the neglected side of the stimulus array converted ophthalmokinetic into melokinetic neglect, and vice versa. The results are held to be indicative of two components of space representation and to provide further evidence of response-driven modulation of perceptual awareness.

Adult↗
PubMedDate not supplied

Lexical processes and eye movements in neglect dyslexia.

Neglect dyslexia is a disturbance in the allocation of spatial attention over a letter string following unilateral brain damage. Patients with this condition may fail to read letters on the contralesional side of an orthographic string. In some of these cases, reading is better with words than with non-words. This word superiority effect has received a variety of explanations that differ, among other things, with regard to the spatial distribution of attention across the letter string during reading. The primary goal of the present study was to explore the interaction between attention and lexical processes by recording eye movements in a patient (F.C.) with severe left neglect dyslexia who was required to read isolated word and non-word stimuli of various length. F.C.'s ocular exploration of orthographic stimuli was highly sensitive to the lexical status of the letter string. We found that: (1) the location to which F.C. directed his initial saccade (obtained approximately 230 ms post-stimulus onset) differed between word and non-word stimuli; (2) the patient spent a greater amount of time fixating the contralesional side of word than non-word strings. Moreover, we also found that F.C. failed to identify the left letters of a string despite having fixated them, thus showing a clear dissociation between eye movement responses and conscious access to orthographic stimuli. Our data suggest the existence of multiple interactions between lexical, attentional and eye movement systems that occur from very initial stages of visual word recognition.

Attention↗