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Biomedical subjects

N Soroker

Publications and source records attributed to N Soroker.

At least 19 recordsLinked to original sources
PubMed2000

Electrophysiological evidence for an early(pre-attentive) information processing deficit in patients with right hemisphere damage and unilateral neglect.

Patients with right hemisphere damage and contralesional neglect are often unaware of visual, auditory or tactile stimuli occurring on their left side. In an effort to understand the contribution of pre-attentive processes to this phenomenon, we examined the processing of the pitch, duration and spatial location of auditory stimuli using an electrophysiological probe, the mismatch negativity (MMN). This event-related brain potential indexes the integrity of cerebral processes that respond automatically to deviations from regularity in the acoustic environment. We compared the MMN elicited by right- and left-sided deviant stimuli in 10 patients with left unilateral neglect and 10 age-matched healthy volunteers, exploring an anticipated dissociation between the processing of spatial localization of sounds and the processing of the other auditory dimensions. Across dimensions, the MMN elicited by deviance occurring to the left of the patients was reduced relative to that elicited by deviance occurring to the right. This effect was robust for spatial location, and less so for pitch, whereas the processing of stimulus duration was not significantly affected by the side of stimulation. In healthy subjects, deviance in either side elicited similar MMN. We suggest that an early deficit in detecting changes in the environment hampers the involuntary triggering of attention in those patients and discuss the specific role of encoding spatial location in the establishment of conscious awareness.

Adult↗
PubMed1999

Selective visual streaming in face recognition: evidence from developmental prosopagnosia.

Computational considerations suggest that efficient face identification requires the categorization and exclusive streaming of previously encoded face visual primitives into a dedicated face recognition system. Unique evidence supporting this claim is provided by a rare case of developmental pure prosopagnosia with otherwise normal visual and cognitive functions. Despite his normal visual memory and ability to describe faces, he is extremely impaired in face recognition. An early event related brain potential (N170) that is normally elicited exclusively by human faces, showed no specificity in this person. MRI revealed a smaller then normal right temporal lobe. These data emphasize the indispensability of the early streaming process for face recognition.

Adult↗
PubMed1999

Effects of right- and left-hemisphere damage on understanding conversational implicatures.

Processing of implicatures was examined in 27 right-brain-damaged (RBD) and 31 left-brain-damaged (LBD) stroke patients with focal lesions using a new implicatures battery (IB) as part of an exploration of the neural basis and modularity of natural language pragmatics. Following Grice, we sampled implicatures of Quantity, Quality, Relation, and Manner. Verbal implicatures consisted of two-sentence conversational vignettes which are literally problematic. Nonverbal implicatures consisted mostly of famous paintings that are literally problematic (e.g., Magritte's "Le Domain d'Arnheim"). The patient has to identify and solve the problem. To compare with performance on the IB, patients also received a Hebrew adaptation of Gardner and Brownell's Right Hemisphere Communication Battery, a new test of basic speech acts (verbal and nonverbal assertions, questions, requests, and commands), a Hebrew version of the Western Aphasia Battery, and standardized neuropsychological tests. Both LBD and RBD patients were significantly impaired in implicature processing relative to age-matched normal controls. In general, both patient groups showed weak correlations of implicatures with extents of lesions in left perisylvian language area or its right-hemisphere (RH) homolog. However, performance of LBD and RBD patients on the IB revealed different patterns of correlations with other pragmatic, language, and nonlanguage tests. In LBD patients, there was a greater association between performance on verbal and nonverbal implicatures and between performance on implicatures and basic speech acts than in RBD patients. Given the different modes in which right-and left-hemisphere (LH) damage affect the processing of conversational implicatures, it remains to be discovered how the two hemispheres interact to process natural language pragmatics in the normal brain in real time.

Adult↗
PubMed1999

Functional disability and rehabilitation outcome in right hemisphere damaged patients with and without unilateral spatial neglect.

OBJECTIVE: To evaluate the impact of unilateral spatial neglect (USN) on the rehabilitation outcome and long-term functioning in activities of daily living (ADL) and instrumental ADL (IADL) of right hemisphere damaged (RHD) stroke patients. DESIGN: Assessments of sensory-motor and cognitive impairment and of functional disability were conducted upon admission to rehabilitation, upon discharge from the rehabilitation hospital, and 6 months after discharge, up to a year postonset. SETTING: The Loewenstein Rehabilitation Hospital, which receives patients from all general hospitals in Israel. PATIENTS: Forty consecutive admissions of adult right-handed patients with a first, single, right hemispheric stroke proven by computed tomography. Based on their total score in the Behavioral Inattention Test for neglect, patients were divided into two groups: 19 with neglect (USN+) and 21 without neglect (USN-). OUTCOME MEASURES: Functional Independence Measure, for ADL; The Rabideau Kitchen Evaluation, for IADL. RESULTS: Impairment and disability levels of RHD patients with and without USN were clearly differentiated. Neglect is associated with lower performance on measures of impairment (sensory-motor and cognitive), as well as on measures of disability in ADL and IADL. Differences were significant in all testing periods. The recovery pattern of USN+ patients is slower and more attenuated. In both groups, most improvement occurs in the first 5 months after onset. USN is the major predictor of rehabilitation outcome from admission to follow-up. CONCLUSIONS: The significance of neglect as a major source of stroke-related long-term disability justifies further research efforts to develop appropriate therapeutic modalities for this complex, multifactorial syndrome.

Activities of Daily Living↗
PubMed1998

Gesture and the processing of speech: neuropsychological evidence.

Patterns of speech-related ('coverbal') gestures were investigated in three groups of right-handed, brain-damaged patients and in matched controls. One group had anomic aphasia with a primarily semantic impairment ('semantic'); one group had a primarily phonological impairment, reflected in both repetition and naming ('phonologic'); a third group had a primarily conceptual impairment, with relatively good naming ('conceptual'). Coverbal gestures were video recorded during the description of complex pictures and analyzed for physical properties, timing in relation to speech and ideational content. The semantic and phonologic subjects produced a large number of ideational gestures relative to their lexical production, while the related production of the conceptual subjects was similar to that of the unimpaired controls. The composition of ideational gestures in the semantic and phonologic groups was similar to that of the control groups, while conceptual subjects produced fewer iconic gestures (i.e., gestures that show in their form the content of a word or phrase). The iconic gestures of the conceptual patients tended to start further from their lexical affiliates than those of all other subjects. We conclude that ideational gestures probably facilitate word retrieval, as well as reflect the transfer of information between propositional and non-propositional (visual and motoric) representations during message construction. We suggest that conceptual and lexical processes differ in the way they constrain ideational gestures.

Adult↗
PubMed1997

Learning spatial sequences in unilateral neglect.

Brain-damaged patients with unilateral spatial neglect ignore aspects of the world located on the side opposite their lesion. In the present study we examined the performance of unilateral neglect patients (UN) on an SRT task in which a hybrid repeating sequence (21313) was used. We analyzed the patients' performance for each location separately as a function of the target's location in the trial preceding the response. The UN patients were severely limited in their learning of the sequence when compared to normal controls. In particular, they appeared to learn unique associations (21 and 13) but not ambiguous ones (31 and 32). We discuss two possible explanations for this phenomenon. The first is that UN patients show a deficit similar to that of normal subjects in dual task situations. The second is that the learning deficit is unique to spatial processing impairments of UN patients and is not directly related to research with normal population. We outline future research that may distinguish between these two explanations.

Attention↗
PubMed1997

Auditory inattention in right-hemisphere-damaged patients with and without visual neglect.

Fifteen right-hemisphere-damaged patients, eight with- and seven without visual neglect (N+ and N-, respectively), were assessed for the presence of auditory neglect using free-field bilateral simultaneous stimulation (BSS) and pseudorandom unilateral stimulation. Eight healthy subjects served as controls. Both N+ and N- groups extinguished left-sided sound stimuli in the BSS condition. N+ (but not N-) patients showed a right-side advantage in sound localization and were inferior, compared to normal individuals, in their ability to localize unilaterally administered sounds on the left side. Blindfolding significantly improved the localization performance. In a task demanding stimulus identification, both N+ and N- groups performed abnormally when auditory stimuli came from the left. Free-field stimulation is thus an adequate technique for the detection of auditory neglect. The results are consistent with the notion that left-sided neglect reflects a pathologically exaggerated attentional bias towards the right in normal individuals.

Adult↗
PubMed1997

Visual extinction and cortical connectivity in human vision.

Visual extinction is a common, poorly understood, consequence of unilateral cerebral damage, where a patient fails to detect one of two simultaneously presented stimuli (the one more contralateral to the lesion), despite the fact that each stimulus is correctly detected when presented in isolation. The phenomenon implies a failure of shifting attention from an attended object to an unattended one. We show here that pair detection is improved in conditions where the two stimuli presented to the two halves of the visual field are proximal, co-oriented and co-axial. It is further shown that stimulus properties producing reduced extinction correlate with the selectivity pattern of spatial lateral interactions observed in the primary visual cortex. We suggest that neuronal activity in early stages of cortical visual processing encodes, using long-range lateral interactions, an image description in which visual objects are already segmented and marked. Segmentation seems to function properly even in the presence of significant destruction of the parietal cortex leading to extinction.

Cerebral Cortex↗
PubMed1995

Effects of hemi-thalamic damage on K-complexes evoked by monaural stimuli during midafternoon sleep.

Polygraphic recording of midafternoon sleep were made in two patients with unilateral hemorrhagic infarction in the thalamus. One patient had massive signs of reduced attention in the contralesional space following right lateral thalamic lesion. The other patient had infarction centered in the left posterior ventrolateral thalamus with no signs of hemineglect. In both cases, waking and sleep records showed symmetric background EEG at C3 and C4. In contrast, monaural sounds (clicks) elicited bilaterally symmetrical K-complexes only in the second patient. In the other patient with right thalamic lesion, both left- and right-ear clicks failed to elicit K-complexes in the right cerebral hemisphere, whereas normal K-complexes continued to appear at C3 as well as at Fz. In neither patient did the frequency of evoked K-complexes depend on the side of the stimulated ear. Unlike K-complexes, sleep spindles were bilaterally absent in patient 1. The right hemisphere does not seem to have a special role in control of circuits generating K-complexes.

Acoustic Stimulation↗
PubMed1995

"McGurk illusion" to bilateral administration of sensory stimuli in patients with hemispatial neglect.

The illusion of McGurk (Nature 264, 746-748, 1976) refers to the blending of conflicting audio-visual messages. By taking advantage of this phenomenon the study explored whether visual cues (i.e. manner of articulation) in ipsilesional (right) space would help a patient with auditory neglect to mentally reconstruct syllabic sounds voiced in contralesional (left) space. We examined seven patients with clinically detectable visual neglect following right hemisphere damage. All had signs of auditory neglect as documented by the inferior identification of syllables delivered through a loudspeaker on the left side. In contrast, syllabic sounds delivered contralesionally together with visual stimuli in the ipsilesional space significantly increased identification of "neglected" syllabic sounds. Of the increased responses, 23% were classified as illusory blends, thereby suggesting that manner of articulation provides a valuable clue as to the possible "best fit" for a consonant. The susceptibility to the blend illusion was identical in patients and controls. Results indicate that neglected auditory stimuli are retrieved in patients with right hemisphere lesion by the mechanism of the ventriloquist illusion in the presence of a carefully timed sequence of comparisons of auditory signals in the neglected space with visual signals in the attended space. The possibility that neuronal mechanisms that serve audio-visual merger in spatial localization are also utilized for processing speech distinctions is discussed.

Acoustic Stimulation↗
PubMed1995

Ventriloquist effect reinstates responsiveness to auditory stimuli in the 'ignored' space in patients with hemispatial neglect.

We examined 6 patients with robust visual neglect following right hemisphere damage. All of them had signs of auditory neglect as documented by the inferior identification of syllables delivered through a loudspeaker on the left side. When the same stimuli on the left were administered in the presence of a fictitious source of sound (a dummy loudspeaker) visible in the homolesional space, a significant increase in the identification score of sounds was obtained (the "ventriloquist" effect). The result is in keeping with a notion of a strong coupling between auditory and visual systems. The effect is attributed to the activation by the fictitious source of sound of the audio-visual map in the left hemisphere. We draw attention to the possibility that loss of awareness of auditory input may arise due to the disconnection of the visual input from the audio-visual template.

Adult↗
PubMed1994

Mesh-glove. 2. Modulation of residual upper limb motor control after stroke with whole-hand electric stimulation.

The effects of whole-hand electrical stimulation via a wired mesh-glove upon the residual motor control of the upper extremity are described. Clinical observations were made in 2 patients with nonfunctional upper limbs, 4 and 2 years after stroke, who had been enrolled in the home mesh-glove program for 6 and 4 months, respectively. The stimulation paradigm is novel and the target of stimulation is the hand. Preliminary results indicate beneficial effects such as reduction in muscle hypertonia and facilitation of isolated hand movements.

Aged↗
PubMed1992

Differential effect of right and left hemispheric lesions on two memory tasks: free recall of items and recall of spatial location.

The effect of lateralized cerebral damage on free recall of items and recall of spatial location, under intentional and incidental learning conditions, was investigated. Eleven right brain-damaged (RBD) patients, 10 left brain-damaged (LBD) patients, 14 young and 11 elderly normal controls, participated in this study. The overall performance of the control groups was better than that of the patient groups. For all groups, free recall was better under intentional than under incidental learning condition. On recall of spatial location the learning condition had a differential effect on the groups. The RBD group performed better than the LBD group under intentional learning condition, while the reverse was found under incidental learning condition. The young-control group showed an advantage over the elderly-control group under intentional but not under incidental learning condition. The results are discussed in regard to different approaches to the distinction between automatic and effortful memory processes and their lateralization in the cerebral hemispheres.

Adult↗
PubMed1991

Polysomnography in locked-in syndrome.

Sleep patterns were evaluated in a case of 'locked-in' syndrome. This patient had an ischemic infarction involving the ventral portion of the upper half of the pons bilaterally, with a posteromedial extension into the tegmentum. Reticular structures, notably the median raphe nuclei, supposed to play a major regulatory role in sleep, were most probably involved. Unexpectedly, repeated polysomnographic studies revealed sleep patterns with only minor abnormalities.

Electroencephalography↗
PubMed1991

Differential effect of right and left hemispheric lesions on two memory tasks: free recall and frequency judgement.

We investigated the relationship between lateralized cerebral damage and two memory tasks; free recall and frequency judgement. Free recall is considered to be processed effortfully while frequency judgement is considered to be processed automatically (Hasher and Zacks). Nine right brain-damaged patients (RBD), nine left brain-damaged patients (LBD) and nine control subjects participated in this study. It was hypothesized that RBD would show an advantage over LBD on the free-recall task, whereas LBD would show an advantage over RBD on the frequency-judgement task. In accordance with our hypothesis, free-recall was more impaired in LBD than in RBD. In the frequency-judgement task, an effect of laterality of lesion was found in high (4-6) and low (0-1) frequencies, but not in the medium (2-3) frequencies. The anticipated LBD advantage was shown in judgement of the high frequencies, but unexpectedly RBD performed better than LBD in low frequencies. The results are discussed in terms of the relationship between effortful and automatic memory processes and cerebral lateralization.

Aged↗
PubMed1991

Covariance analysis of laboratory variance in steady-state serum phenytoin concentrations.

Inpatients (n = 57) on long term prophylaxis with 2 oral phenytoin preparations were followed up via monthly checks of serum drug concentrations. Duplicate serum aliquots were submitted to 2 laboratories, and covariance analysis was used to estimate laboratory error. The laboratory-associated variance of examinations using the 'EMIT' or 'TDX' systems was 7.1 to 10 (mg/L)2, while that of chromatographic assays was 37.1 (mg/L)2. Laboratory errors were distributed in a non-normal fashion. The ratio of the maximum rate of metabolism (Vmax) and the Michaelis-Menten constant (Km) tended to remain constant between individuals. A linear analytical model showed little more residual variance than one based on Michaelis-Menten pharmacokinetics.

Administration, Oral↗
PubMed1990

Stuttering as a manifestation of right-hemispheric subcortical stroke.

A right-handed man developed stuttering, without aphasia, as a result of a circumscribed subcortical infarction in the right hemisphere. He never stuttered before and has no family history of stuttering. Damage to callosal pathways coordinating the activity of both hemispheres during speech is proposed as a possible explanation for the stuttering.

Aged↗