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Nachum Soroker

Publications and source records attributed to Nachum Soroker.

11 recordsLinked to original sources
PubMed2005

Task alternation cost without task alternation: measuring intentionality.

A behavioral dissociation between intention and action was demonstrated by patient AF who sustained damage to the left-hemisphere including the basal ganglia. The patient was tested in a task switching paradigm involving two choice reaction-time tasks: SIZE (small/large) and SHAPE (circle/square). The last block in each of the two sessions involved only one task. AF switched tasks reasonably well in the first 40 trials, but unlike her matched control group, in all the remaining trials when two tasks were involved, she performed only the SIZE task. Interestingly, although no task switching took place, AF continued to demonstrate behaviorally her intention to switch tasks. First, she exhibited "task alternation cost", poorer performance relative to instructed single-task trials. Second, shifting to an instructed single-task condition was accompanied by an initial response slowing, indicating a change in goal-state. Finally, when instructed to switch tasks, AF demonstrated the "task-congruency effect", indicating interference from the instructed but competing stimulus-response mapping. Two groups of university students were instructed to perform only the SIZE task, after initial switching, either while ignoring the SHAPE cues ("Ignore") or while being prepared for the SHAPE task only when the cue appeared in red, which never happened ("Attend color"). AF's performance resembled the one of the "Attend color" group and not the "Ignore" group. The results indicate that AF had a partially activated intention to switch tasks. The implications to intentionality and task switching theory are discussed.

Attention↗
PubMed2005

Processing of basic speech acts following localized brain damage: a new light on the neuroanatomy of language.

We examined the effect of localized brain lesions on processing of the basic speech acts (BSAs) of question, assertion, request, and command. Both left and right cerebral damage produced significant deficits relative to normal controls, and left brain damaged patients performed worse than patients with right-sided lesions. This finding argues against the common conjecture that the right hemisphere of most right-handers plays a dominant role in natural language pragmatics. In right-hemisphere damaged patients, there was no correlation between location and extent of lesion in perisylvian cortex and performance on BSAs. By contrast, processing of the different BSAs by left hemisphere-damaged patients was strongly affected by perisylvian lesion location, with each BSA showing a distinct pattern of localization. This finding raises the possibility that the classical left perisylvian localization of language functions, as measured by clinical aphasia batteries, partly reflects the localization of the BSAs required to perform these functions.

Adult↗
PubMed2005

Assessment of spatial attention after brain damage with a dynamic reaction time test.

Lateralized spatial biases after brain damage are commonly assessed using batteries of paper-and-pencil tests. These tests hardly allow quantification of performance in different locations in space, and they tend to lose sensitivity along the course of recovery. We tested the dynamic Starry Night Test (SNT), a novel computerized test measuring reaction time and detection accuracy for visual target stimuli in a dynamic background, in 32 inpatients with right hemisphere stroke (RHS), 16 patients with left hemisphere stroke (LHS), and 9 healthy controls. As a group, only the RHS patients were significantly slower to respond to contralesional targets. Individually, 21 (66%) RHS patients and 5 (31%) LHS patients showed statistically significant contralateral deficits. In a number of RHS patients the SNT was more sensitive to the ipsilesional bias of spatial attention than the Behavioral Inattention Test (BIT), a standardized paper-and-pencil test battery of unilateral spatial neglect. Two illustrative case reports show that the dynamic SNT, but not the BIT, was sensitive to the spatial deficit in recovered patients, one of whom was involved in repeated car accidents. The SNT overcomes serious shortcomings of paper-and-pencil tests of unilateral neglect. It provides a simple quantitative tool for monitoring the natural and treatment-induced recovery of patients.

Adult↗
PubMed2004

Differential processing of word and color in unilateral spatial neglect.

The aim of the present study was to investigate mechanisms underlying processing of contralesional visual stimuli in brain-damaged patients with unilateral spatial neglect (USN). Nine right-hemisphere-damaged stroke patients with left-sided neglect and nine controls performed a reaction-time task involving manual response to a central color patch (target stimulus) flanked to the left or right by a Stroop stimulus they had to ignore. While the word dimension of the flanker affected patients' responses considerably and equally when presented to either side, the color dimension of the flanker had no effect when presented to the left, but had a large effect when presented to the right. Four of the patients performed a control task requiring same/different judgments between either of the two flanker dimensions (color and word) and the central target. Their performance indicated that they were able to process color information from the contralesional field, despite their results in the first experiment. These findings demonstrate a dissociation between how the patients processed different dimensions of the same stimuli and imply that the extent of processing in the contralesional hemifield depends both on task requirements and on the exact features of the stimuli. The implications of these results on normal attentional mechanisms is also discussed.

Adult↗
PubMed2004

Role of disengagement failure and attentional gradient in unilateral spatial neglect - a longitudinal study.

PURPOSE: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilateral spatial neglect (USN) and in recovery from neglect. METHOD: Eight right-hemisphere-damaged stroke patients performed the standardized Behavioural-Inattention-Test battery for visual neglect, line-bisection tests, and two computerized reaction-time (RT) tasks: a variant of Posner's 'Spatial-Cueing' paradigm (with special emphasis on the magnitude of leftward disengagement time) and a signal-detection task (marking the spatial gradient of attention by the distribution of RTs to target stimuli in different spatial locations). The correlation between the different measures was assessed at two points in time, before and after a period of rehabilitation treatment. RESULTS: A recovery pattern could be identified in both RT paradigms. However, the correlation between standard measures of neglect and performance on both, spatial-cueing and signal-detection tasks, was weak. CONCLUSION: Neither difficulty disengaging attention from an ipsilesional stimulus nor changes in the attentional gradient can fully explain the processes underlying USN and its recovery. A large interpersonal variance exists among USN patients in the expression of disengagement and other spatial-attention deficits. Hence, individual patients should be tested by measuring different factors known to play a role in USN. This information is crucial for assigning the appropriate treatment for each patient in accord with the specific deficit revealed.

Adult↗
PubMed2004

Abnormal binocular rivalry in unilateral neglect: evidence for a non-spatial mechanism of extinction.

Unilateral spatial neglect (USN) is considered to be an attention deficit, which is primarily related to space. Recent evidence points to the relevance of non-spatially lateralized mechanisms, with impairments found in rapid stimulus presentation conditions. Here we used the phenomenon of binocular rivalry (BR) to explore a non-spatial deficit over long temporal intervals. Six right-hemisphere damaged (RHD) patients with contralesional neglect (USN+), five RHD patients without neglect (USN-) and six normal controls were tested on the basic properties of BR induced by dichoptic presentation of orthogonal gratings at fixation. USN+ patients had much slower perceptual alternations compared to the USN- and normal groups (factors 2.5 and 4, respectively), and were much more sensitive to inter-ocular changes in relative stimulus contrast, which, unlike normals, altered both the suppression and dominance phases. Most notably, a small advantage of one monocular stimulus caused a long-term extinction of the other stimulus in the USN+ group alone. We explain the results in terms of impaired habituation to dominant and attended stimuli, which normally prevents a winner-takes-all behavior and extinction of the weak. This impaired habituation may in turn contribute to inappropriate environmental monitoring and attenuated novelty-seeking behavior.

Adult↗
PubMed2004

Differential effect of right and left basal ganglionic infarctions on procedural learning.

OBJECTIVE: To assess the effect of ischemic infarctions affecting the basal ganglia (BG) region on a series of procedural learning tasks. BACKGROUND: The basal ganglia hypothesis of procedural learning is a matter of debate. As most of the relevant research so far is based on examination of patients suffering from Parkinson disease, this inconsistency might reflect either lesion heterogeneity existing in this pathologic group or the heterogeneity of the procedural learning tasks. METHOD: Twelve patients with lesions confined to the right (BGr), 10 to the left (BGI) BG region, and 15 matched controls participated in the study. Three procedural learning tasks were used: Tower of Hanoi Puzzle, Mirror Reading, and Porteus Mazes. Declarative memory and general intelligence were also tested. RESULTS: Verbal declarative memory was impaired in the BG1 group. For each procedural learning task, baseline performance and learning rate were analyzed. Tower of Hanoi Puzzle: Baseline performance of the BG1 group was impaired compared with the other groups. The BGr group was the only group that did not improve over learning trials. MR: Baseline performance of the BGr group was impaired compared with the other groups. The groups' learning rate did not differ significantly. Porteus Mazes: Baseline performance of both patient groups was impaired compared with that of the control group. Learning rate over repetitive trials of the same maze was impaired in the BGr group. However, the transfer of procedural learning to a newly exposed maze was impaired in the BG1 group. CONCLUSIONS: First, right and left basal ganglia play different roles in different procedural learning tasks. Second, procedural learning is not a unitary capacity subserved by any single neural mechanism.

Aged↗
PubMed2003

Blood homocysteine levels in stroke patients undergoing rehabilitation.

BACKGROUND: One of the major concerns of a stroke victim is the threatening possibility of loosing all the functional achievements attained through prolonged rehabilitation effort, in case of a recurrent cerebrovascular event. Recently, elevated serum homocysteine (Hcy) level was found to be associated with an increased risk for atherosclerotic vascular disease. The aim of the present study was to assess the yield of screening stroke patients for hyperhomocysteinemia, as part of the measures taken to reduce the risk of stroke recurrence. MATERIAL/METHODS: Blood Hcy levels of stroke patients undergoing rehabilitation were compared to the Hcy levels of patients admitted for rehabilitation following brain damage of non-vascular etiologies. RESULTS: The mean Hcy level was found to be significantly higher in the former group (10.21+/-7.81 micromol/L and 6.16+/-4.28 micromol/L in the stroke group and in the non-vascular group, respectively [p<0.003]). However, when analysis of variance was applied and the correlation with age was accounted for, the difference between the groups became insignificant. CONCLUSIONS: Considering the current high cost of blood Hcy tests, the above findings do not support adoption of an overall, non-selective screening policy for hyperhomocysteinemia in stroke patients. However, it may be justified to measure Hcy levels, as well as folic acid, vitamin B6 and vitamin B12 levels, in selected stroke cases. Further study is needed in order to set clear guidelines for the search after this possible risk factor of stroke, one of the major causes of morbidity and mortality in modern society.

Biomarkers↗
PubMed2002

Awareness of deficits in stroke rehabilitation.

The aim of this study was to evaluate the awareness of deficit profiles of stroke patients undergoing rehabilitation, and examine the impact of unawareness on rehabilitation functional outcomes. Sixty first-event stroke patients, 36 after right hemisphere damage and 24 after left hemispheric damage were included. The Awareness Interview was administered at admission to rehabilitation, and patients' responses were compared with standardized cognitive and neurological evaluations. The FIM motor scale and a safety rating were used to measure functional outcomes at discharge from rehabilitation and at 1-year follow up. The frequency of unawareness for motor and sensory deficits was low, whereas unawareness of cognitive deficits was much higher. Unawareness was not associated with a specific lesion site, however a significant association was found with cortical involvement, and with lesion size. In the right hemispheric damage group a significant negative correlation was found between total unawareness scores and discharge functional outcomes. Multiple regression revealed that unawareness at admission was a significant predictor of discharge FIM motor scores in the right hemispheric damage group, beyond the contribution of cognitive and demographic variables. Findings delineate the multifaceted nature of unawareness phenomenon, and highlight the significance of unawareness in post-stroke rehabilitation.

Analysis of Variance↗
PubMed2002

Cheyne-Stokes respiration during sleep: a possible effect of body position.

BACKGROUND: Cheyne-Stokes Respiration (CSR) is a common finding in Chronic Heart Failure and Stroke patients. The body position effect during sleep on obstructive breathing abnormalities is well known. However, the effect of body position during sleep on breathing abnormalities of central type like CSR has not been well documented. MATERIAL/METHODS: Six sleep studies (two complete Polysomnographic (PSG) evaluations and four Pulse Oximetry recordings (PO)), were carried out in a 57-year-old female patient with a recent Cerebro Vascular Accident (CVA who had both Obstructive Sleep Apnea (OSA) and CSR. RESULTS: The first PSG was carried out two months post-stroke and revealed a severe, continuous CSR pattern during Non Rapid Eye Movements (NREM) sleep (mainly with central apneas), and Obstructive Sleep Apnea (OSA) during Rapid Eye Movements (REM) sleep, independent of body position: Supine Respiratory Disturbance Index (SRDI) = 85.2 and Lateral RDI (LRDI) = 95.4. A second PSG was performed three months later after an overall clinical improvement and showed a complete disappearance of CSR during NREM sleep and OSA during REM sleep in her lateral posture (LRDI = 0), while the RDI in the supine posture was only slightly improved (SRDI = 73.2). The CSR pattern was less severe and was characterized mainly by central hypopneas. Two PO recordings between the PSG studies showed similar improvement trends. Two additional PO recordings, two and three weeks after the last PSG (the first one with the patient lying supine and the second one with the patient lying on her side throughout the night), revealed a further significant improvement in the supine posture (SRDI = 37.5). CONCLUSIONS: The results of this study suggest that body posture may play a role not only in the prevalence and severity of obstructive breathing disorders, but also in CSR, a central type of breathing abnormalities during sleep.

Cheyne-Stokes Respiration↗