Biomedical subjects

E Zaidel

Publications and source records attributed to E Zaidel.

At least 37 records · Page 2Linked to original sources

PubMed1996

The effects of procedural variations on lateralized Stroop effects.

Several issues in the classic Stroop effect remain open, including (i) the stage of processing which gives rise to the effect, (ii) the effect of some procedural manipulations, (iii) the effect of hemispheric specialization and of interhemispheric interactions, and (iv) the existence of individual differences. In this paper, we investigate these issues using a series of experiments with central, lateral, and bilateral presentations of the Stroop stimuli. A total of 146 right-handed subjects took part in a multiexperiment study with relatively equal numbers of the two sexes participating in each experiment. We found that manual responses diluted but did not abolish the Stroop interference relative to vocal responses, arguing for a late processing stage account of the effect. However, separating the color patch from the color word either unilaterally or bilaterally did not significantly change the magnitude of the Stroop interference, arguing against a cost of interhemispheric transfer in the Stroop effect in normal subjects. We did, however, find evidence for hemispheric specialization in Stroop interference, greater in the left hemisphere than in the right hemisphere. Color words in the RVF produced the greatest Stroop effects regardless of the location of the color patch. In most cases, this laterality effect interacted with the sex of the subject, such that only males and a subgroup of females (i.e., those tested during a low estrogen phase in the menstrual cycle) showed evidence for greater Stroop effects when a color word projected to the left hemisphere than when it projected to the right hemisphere, regardless of the placement of the color patch.

Adult↗

PubMed1996

Hemispheric independence in word recognition: evidence from unilateral and bilateral presentations.

We compared behavioral laterality effects in a lexical decision task using cued unilateral or bilateral presentations of different stimuli to normal subjects. The goals were to determine the effects of lexical variables on word recognition in each hemisphere under conditions of maximal independence of information processing in the two hemispheres and to assess the degree of residual interhemispheric effects that can still exist then. Bilateral presentations increased hemispheric independence in word recognition, indexed by a significant interaction of response hand with target visual field. Bilateral presentations also selectively impaired word decisions, suggesting that word processing benefits from interhemispheric interactions, whereas nonword processing is done independently in each hemisphere. Indeed, there was a significant congruity effect for word targets only, whereby the wordness of the unattended stimulus affected the speed of processing of attended word targets. Word frequency and regularity affected both hemispheres equally, arguing against the hemispheric interpretation on the dual route model of word recognition. Length affected the processing of nonwords more than words and in the left visual field more than in the right visual field. Taken together, the data support the conclusion that each normal hemisphere can control word recognition independently of the other.

Brain↗

PubMed1996

Differences in hemispheric asymmetry between dyslexic and normal children on a lateralised lexical decision task.

The present experiment was conducted in order to further investigate the relationship between deficits in left hemisphere processing and phonetic decoding in dyslexic children. We administered a lateralised lexical decision task that manipulated wordness, length, and word regularity of grapheme-phoneme conversion. Right-handed male dyslexic children and normal control children were presented with words and pronounceable nonwords. Although there were no overall differences in hemispheric asymmetry between the groups, they did differ in laterality effects in accuracy when responding to nonwords and to phonetically regular words, with the normal children showing the right visual field advantage/ sensitivity (left hemisphere dominance/sensitivity), while the dyslexics failed to show any visual field advantage or sensitivity for these stimuli. Further, group differences were observed in left but not right hemisphere functioning. The results suggest that deficits in left hemisphere processing are apparent only when the dyslexics are attempting to utilise the rules of phonics. Support for the use of this paradigm for use with dyslexic children is also discussed.

Journal Article↗

PubMed1996

The role of the right hemisphere in the physiological and cognitive components of emotional processing.

Right hemisphere specialization for emotional processing was investigated using behavioral and psychophysiological methods. Fifty undergraduates were shown slides depicting negative emotional and neutral scenes briefly lateralized to the right or left cerebral hemispheres and asked to categorize each as emotional or neutral. Pulse volume and heart rate (HR) measured physiological processing and reaction time measured cognitive processing. The largest vasoconstriction responses and HR deceleration were obtained for emotional items in the right hemisphere. However, reaction time failed to show right hemisphere superiority in perceptual/cognitive processing, demonstrating instead slowest responses to emotional stimuli presented to the right hemisphere together with evidence for left hemisphere competence. Selective right hemispheric activation in autonomic responses, combined with the lack of right hemisphere specialization in the cognitive task, suggests that the physiological response system rather than the perceptual/cognitive system is the locus of the right hemisphere superiority for emotion.

Adult↗

PubMed1995

The interpretation of sentence ambiguity in patients with unilateral focal brain surgery.

Interpretations of ambiguous sentences were studied in patients with unilateral anterior temporal lobectomy or selective amygdalo-hippocampectomy. The sentences represented lexical and syntactic ambiguities. In both left- and right-sided groups, regardless of type of surgery, total mean score on the test was below normal. Left-sided cases, regardless of type of surgery, provided significantly fewer alternative interpretations than right-sided cases. The results suggest greater left than right hemisphere specialization in both lexical and syntactic processing, but also suggest right hemisphere involvement in resolution of lexical ambiguity.

Adult↗

PubMed1995

Channels of the corpus callosum. Evidence from simple reaction times to lateralized flashes in the normal and the split brain.

We studied 75 normal subjects and three commissurotomized patients using unimanual simple reaction times to lateralized flashes as a behavioural estimate of interhemispheric transmission time. Three different versions of the paradigm were performed: (i) the basic task; (ii) a motor task, with an increased complexity of the motor response; and (iii) a visual task, with an increased complexity of the visual stimulus presentation. We tested two hypotheses. First, that the new versions of the simple reaction time task result in shifts in hemispheric specialization for processing motor output (indicated by a main effect of response hand) or visual input (indicated by a main effect of visual field) alone, without affecting callosal transmission. In that case normals and split brain patients would show no significant task by response hand by visual field interaction and no significant task by crossed-uncrossed difference interaction. Secondly, that the new versions of the task affect callosal transfer. In that case, normals, but not split brain patients, would show a significant task by response hand by visual field interaction and a significant task by crossed-uncrossed difference interaction. Results are consistent with the latter hypothesis, showing that the motor task significantly changed the response hand by visual field interaction and the crossed-uncrossed difference, but only in normal subjects, perhaps producing a switch in the callosal channel subserving the interhemispheric transfer.

Adult↗

PubMed1995

Alien hand syndrome: interhemispheric motor disconnection due to a lesion in the midbody of the corpus callosum.

The neuroanatomic substrate of the alien hand syndrome has remained controversial due to the noncircumscribed nature of cerebral injuries present in most cases. There have been few cases studied in which damage was restricted to portions of the body of the callosum, and most of those involved surgical callosotomy for tumors or epilepsy. We report the case of a woman with a transient alien hand syndrome caused by a stroke limited to the middle and posterior portions of the body of the corpus callosum. This case provides supportive evidence for damage to the midbody of the corpus callosum as the anatomic basis of nondominant alien hand syndrome and conforms to a model of interhemispheric motor disconnection as the essential component of this unusual behavioral syndrome. This disconnection can occur with injuries involving interhemispheric premotor and motor fibers traveling in the midportion of the callosum in individuals with left hemisphere dominance for motor activities.

Aged↗

PubMed1995

Sexual dimorphism in interhemispheric relations: anatomical-behavioral convergence.

An embryogenetic hypothesis states that hemispheric specialization is inversely related to callosal connectivity (Geschwind and Galaburda, 1985). We tested this hypothesis (i) anatomically by relating postmortem planum temporale asymmetry to regional callosal morphology and (ii) behaviorally by relating the right visual field advantage in a lateralized lexical decision task with associative primes to regional callosal morphometry using magnetic resonance imaging (MRI). The postmortem study showed a significant negative correlation between planum temporale asymmetry and the number of small diameter fibers in the isthmus of the corpus callosum, but only for males. The MRI study showed a significant negative correlation between the right visual hemifield advantage for associated words and the cross section size of the isthmus of the corpus callosum, but again only in males. There was no sex difference in either the anatomical asymmetry, the behavioral asymmetry, or the callosal morphology. These convergent results suggest that there is a sexual dimorphism in interhemispheric relations in humans.

Adult↗

PubMed1995

The anatomical substrates for language and hemispheric specialization.

Three main lines of investigation are discussed in this paper: (1) the comparison between the anatomical arrangement of the language areas and the large-scale neurocognitive cortical networks partly involved in active or working memory; (2) the relations between hemispheric specialization and the development of interhemispheric communication; and (3) the analysis of individual differences in brain organization for language. The hypothesis and evidence presented stem from work being performed in our laboratories.

Cerebral Cortex↗

PubMed1994

Callosal transmission time before and after partial commissurotomy.

Interhemispheric transmission time was measured in a patient, before and after partial commissurotomy sparing the splenium of the corpus callosum, using a simple reaction time paradigm with unimanual responses to lateralized flashes at 4 degrees and 8 degrees of eccentricity. Post-operative transfer time was longer than pre-operative transfer time at 8 degrees but not at 4 degrees of eccentricity. These data do not support the notion that the callosal transfer time is always faster through motor rather than visual fibers. They rather suggest that the callosal transfer time through visual fibers is longer than the callosal transfer time through motor fibers only for flashes at large eccentricities.

Adult↗

PubMed1994

Interhemispheric cooperation during lexical processing is mediated by the corpus callosum: evidence from the split-brain.

If two copies of a meaningful word are tachistoscopically presented simultaneously in both visual half-fields of normal subjects the word will be processed more rapidly and more accurately compared to unilateral presentation (bilateral gain). The word-specific bilateral gain may be due to excitatory transcallosal connections within interhemispheric cell assemblies corresponding to words. In this case, the bilateral gain should be absent in split-brain patients. L.B., a split-brain patient, performed a lexical decision task with words and non-words presented in the left visual field, the right visual field, or in both visual fields simultaneously. As predicted, bilateral presentations did not improve performance compared to unilateral presentation in the right visual field. This result suggests that transcallosal connections play a significant role in lexical processing.

Adult↗

PubMed1994

Anatomical-behavioral relationships: corpus callosum morphometry and hemispheric specialization.

We obtained midsagittal measures of the corpus callosum in 60 healthy young adults (right-handed and left-handed males and females), and examined whether individual differences in anatomical measures of callosal connectivity are related to behavioral laterality measures in the same subjects. In an attempt to tap functionally-distinct callosal "channels", four behavioral laterality tasks were used that differed in sensory modality (visual, auditory, tactile) and/or level of cognitive processing (sensory versus semantic). In addition, the tasks had both intrahemispheric and interhemispheric conditions. Sex differences were found for measures of the posterior body (i.e. isthmus) of the corpus callosum, which, in turn, interacted with handedness. In contrast, only handedness effects were found for the behavioral laterality measures. Anatomical-behavioral correlations did not disclose relationships between callosal size and performance on task conditions requiring sensory interhemispheric integration or transfer. Instead, the correlational findings are consistent with the view that the corpus callosum participates in such higher order "control" functions as the support of bilateral representation of language, functional interhemispheric inhibition, and the maintenance of hemispheric differences in arousal. This is consistent with the finding that regional callosal size is related to the number of small diameter fibers, which are presumed to interconnect homologous association cortices in the two hemispheres.

Adult↗

PubMed1994

Letter matching within and between the disconnected hemispheres.

Three patients with complete cerebral commissurotomy from the California series were given two letter-matching tasks, one requiring physical identity and the other requiring nominal identity. The pairs of letters were presented unilaterally to each disconnected hemisphere or bilaterally, with each hemisphere receiving one of the letters to be compared. The disconnected hemispheres of all three patients showed good performance in the unilateral conditions, even when visual field and response hand were crossed. The crossed visual field-hand conditions resulted in both slower and less accurate responses. Only N.G. was able to cross-compare letters in the bilateral condition and only for physical identity. The results qualify previous reports that higher-level information can transfer subcallosally while visual information cannot.

Cerebral Cortex↗

PubMed1994

Lexical decision after left, right and bilateral presentation of function words, content words and non-words: evidence for interhemispheric interaction.

Function words, content words and pronounceable non-words (pseudowords) were presented tachistoscopically either in the left or the right visual field or with identical copies flashed simultaneously to both visual half-fields. Consistent with earlier studies [10], function words were found to show a right visual field advantage, whereas for content words the right visual field advantage was absent. Compared to either of the unilateral modes of presentation, bilateral presentation of identical word stimuli improved accuracy and latency significantly. The bilateral (Bi) advantage was largest for content words, and was also highly significant for function words in both latency and accuracy. The Bi gain was absent for non-words (significant interaction of Wordness x Visual Field). These results indicate that the lexicons of the left and right hemisphere can "collaborate" rather than inhibit each other or act independently when processing the same linguistic stimuli. Our findings are consistent with the view that the neuronal counterparts of words are Hebbian cell assemblies consisting of strongly connected excitatory neurons of both hemispheres. Since function words show a right visual field advantage in addition to their Bi gain, their assemblies are likely to have most of their neurons located in the left hemisphere. Neuronal assemblies corresponding to content words may be less strongly lateralized.

Adolescent↗

PubMed1994

The Benton-Van Allen faces: a lateralized tachistoscopic study.

The Benton-Van Allen Facial Recognition Test (FRT) was adapted to a lateralized same-different task. The lateralized same targets were either physically identical to the central upright faces or had the same face identity but were transformed (3/4-views or shadowed faces). Faces were also modified to include or exclude external features. There was a left hemifield (right hemisphere) advantage only for the most difficult, shadowed faces. The absence of a left hemifield advantage for the matching of upright faces to identical or 3/4-view faces shows bilateral competence for face processing, both by physical and by face identity, and confirms previous observations that the FRT does not discriminate left from right hemisphere-damaged patients. Removal of external features affected performance in the right but not the left visual field, suggesting that the left hemisphere uses a less feature-dependent mechanism than the right hemisphere. This effect was only present in females, who were more lateralized than males.

Dominance, Cerebral↗

PubMed1994

Nominal and physical decision criteria in same-different judgments.

We propose a model in which the physical and nominal dimensions of letter pairs are compared independently of whether subjects use physical (shape task) or nominal (name task) identity as the decision criterion. We attempt to explain the fast-same effect, the preponderance of false-different errors, and the nominal-physical disparity as results of congruent and incongruent outputs of physical and nominal comparison devices that function in both tasks. Subjects performed both tasks with and without response deadlines. The stimuli were presented foveally or unilaterally to one or the other hemisphere. With foveal presentations, the nominal-physical disparity disappeared when congruent and incongruent cells were compared, the fast-same effect occurred only in the shape task, and there was a preponderance of false-different errors only in the name task. Response times and error patterns from centrally presented trials conformed to the predictions of the model. Performance patterns from the lateralized trials conformed only partially. The implications of the data are discussed in the context of several theoretical models of same/different judgments.

Adult↗

PubMed1993

Language and task effects on lateralized word recognition.

Behavioral laterality effects in naming and lexical decision in Farsi and English were used to evaluate three theories of cross-linguistic differences. First, the Scanning hypothesis predicts a smaller right visual hemifield advantage (RVFA) in Farsi in both tasks. Second, the Cerebral Dominance hypothesis predicts a consistent RVFA in both languages. Third, the Right Hemisphere hypothesis predicts a selective decrease in RVFA in Farsi for those components of the task that involve lexical semantic access. Results supported the Right Hemisphere hypothesis, showing greater right hemisphere contribution to orthographic addressing in Farsi than in English.

Adolescent↗

PubMed1993

Corpus callosum morphometry and dichotic listening performance: individual differences in functional interhemispheric inhibition?

We examined the relationship between midsagittal corpus callosum area, as seen by magnetic resonance imaging, and behavioral laterality effects from a dichotic listening task requiring cross-callosal relay of an auditory signal, in 60 healthy young adults. Four patients with complete forebrain commissurotomy were also given the dichotic listening task, confirming that in this task, the report of left ear items is dependent on callosal pathways. Contrary to our predictions, callosum measures were unrelated to either a laterality measure or to inferior (typically left) ear performance. Surprisingly, superior (typically right) ear accuracies, which do not depend on cross-callosal sensory transfer, were significantly and negatively correlated with callosum size. These findings show that normal variations in callosum size do not appear to contribute significantly to individual differences in hemispheric specialization. Callosum size may, instead, be associated with degree of functional interhemispheric inhibition.

Acoustic Stimulation↗