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E Zaidel

Publications and source records attributed to E Zaidel.

16 recordsLinked to original sources
PubMed1992

Fiber composition of the human corpus callosum.

The densities of fibers of different sizes were calculated in ten regions of the corpus callosum of twenty human brains (ten females, ten males). Light microscopic examination revealed a consistent pattern of regional differentiation of fiber types in the corpus callosum. Thin fibers are most dense in the anterior corpus callosum (genu), and decrease in density posteriorly towards the posterior midbody, where they reach a minimum. Towards the posterior corpus callosum (splenium), the density of thin fibers increases again, but in the posterior pole of the callosum the density decreases locally. Large-diameter fibers show a pattern complementary to that of thin fibers, having a peak of density in the posterior midbody and a local increase of density in the posterior pole of the corpus callosum. Across subjects, the overall density of callosal fibers had no significant correlation with callosal area and an increased callosal area indicated an increased total number of fibers crossing through. Considering different fiber sizes, this was only true for small diameter fibers, whose large majority is believed to interconnect association cortex. No sex differences in fiber composition of the corpus callosum were found.

Adult↗
PubMed1992

Individual differences in brain asymmetries and fiber composition in the human corpus callosum.

There have been several recent reports concerning individual differences in the gross morphometry of the human corpus callosum. However, no studies exist on individual differences in the fiber composition of the corpus callosum. Here we report for the first time the relation of fiber composition in specific callosal segments (as seen in light microscopy) to anatomical asymmetries in language-gifted cortex, as a function of sex. We found a significant negative correlation between Sylvian fissure asymmetries and the total numbers of fibers in the isthmus of males, and in the anterior splenium of females. In addition, a population of relatively large fibers (between 1 micron and 3 microns in diameter) in the isthmus showed a strong negative correlation with perisylvian asymmetries only in males. These findings suggest a sex-dependent, pathway-specific decrease in interhemispheric connectivity with increasing lateralization.

Adult↗
PubMed1992

Letter matching in the hemispheres: speed-accuracy trade-offs.

Eight subjects performed physical and nominal letter-matching tasks for pairs of letters presented in the left, right, or central visual fields, using a unimanual two-choice response-time paradigm. Latencies were manipulated by using a cued response procedure, and speed-sensitivity and speed-bias functions were calculated separately for each of the peripheral visual field by response hand conditions. Hemispheric contributions to these tasks were investigated by looking for evidence of exclusive specialization and callosal transfer. The results suggest that both hemispheres are able to perform the tasks and that they do so using similar processing strategies, but they differ in the response-choice stage of the nominal identity task.

Adult↗
PubMed1992

Morphometry of the Sylvian fissure and the corpus callosum, with emphasis on sex differences.

The relationship between anatomical asymmetries in the perisylvian region and the sizes of different regions of the corpus callosum was investigated post-mortem in 40 brains of right-handed hospital admissions (20 males, 20 females) with no cortical involvement. There were no sex differences either in anatomical asymmetries or in regional size of the callosum. There was a negative correlation between the absolute value of Sylvian fissure (planum temporale) asymmetries and the size of the isthmus in males but not in females. Further, there was a significant negative correlation between the size of the Sylvian fissure (or planum temporale) and the size of the callosal mid-body in males but not in females. There was no correlation between the asymmetry of the planum temporale magnitude of left-right and total size of the planum (left+right). These findings constrain theories about the ontogenesis of hemispheric specialization through changes in callosal connectivity and about sex differences in interhemispheric organization.

Adult↗
PubMed1991

The effects of word length and emotionality on hemispheric contribution to lexical decision.

The effects of emotionality and length on lateralized lexical decision of abstract nouns were investigated in 41 normal and three commissurotomized subjects. Emotionality had the same effect in both visual fields: Emotional words were responded to more accurately than neutral words. Length had different effects in the two visual fields: The accuracy of lexical decisions in the left visual field was selectively higher for four-letter words and in the right visual field it was selectively lower for six-letter words. The latency of lexical decisions revealed equivalent length effects in both visual fields. Of the commissurotomy patients, only L.B.'s left hemisphere performed above chance and revealed a length effect. Length effects are interpreted to reflect a change from a parallel graphic analysis to a sequential parsing strategy when resources are limited. Such a change can occur for words or nonwords in either visual hemifield.

Brain↗
PubMed1991

Rhyming and the right hemisphere.

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.

Adult↗
PubMed1990

Effect of response programming on hemispheric differences in lexical decision.

A lateralized tachistoscopic lexical decision task with concrete nouns and orthographically regular nonwords was administered to normal subjects in three conditions using unimanual responses: Yes-No, Go-NoGo with nonword targets, and Go-NoGo with word targets. There was an overall right visual field advantage in accuracy and sensitivity, an interaction between visual hemifield and wordness in latency, and an overall "word" bias. No effect interacted with experimental conditions, showing that response programming did not affect hemispheric asymmetries. The data suggest independent lexical access and similar response programming in each hemisphere. These results are examined in light of three psycholinguistic models of lexical access and are interpreted to support instead a fourth one which posits separate and parallel computations for word decisions and for nonword decisions in each hemisphere.

Adolescent↗
PubMed1990

Concreteness: nouns, verbs, and hemispheres.

The preferential processing of concrete versus abstract nouns, and of active versus static or "quiet" verbs, was investigated using a lateralized lexical decision task in 32 normal and 4 commissurotomized subjects. Both groups of subjects showed the concreteness effect for nouns in both visual fields. The disconnected right hemisphere of two commissurotomized subjects responded with above chance performance only to concrete nouns. Neither group showed an activeness effect for verbs in either visual field. This supports an imageability rather than a multisensory representation interpretation of the concreteness effect. A comparison of responses to words and to nonwords revealed that males had a "no" bias to stimuli in the left visual field, and both males and females showed a slight "yes" bias for stimuli in the right visual field. These data suggest that the lexical decision task is complex and that word and nonword decisions constitute partly independent functional components. We interpret the sex differences as an indication of strategic rather than functional differences in lateralization patterns between males and females.

Adult↗
PubMed1990

Visual field differences in the magnitude of the Oppel-Kundt illusion vary with processing time.

Three experiments were performed to investigate hemispheric differences in susceptibility to the Oppel-Kundt illusion presented tachistoscopically to the two visual hemifields. Experiment 1 used a successive comparison mode, in which 16 undergraduate students indicated whether the second of two successive extents looked shorter or longer than the first. Experiment 2 (20 under-graduates) and Experiment 3 (1 commissurotomy patient) required judgments of two extents presented simultaneously. The first experiment found no significant visual field differences, although females were more susceptible than males. In the second experiment, the illusion magnitude was greater in the left visual field, and in the third experiment, it was greater in the right visual field. Post hoc analyses resolve the conflicting results and show that in all three experiments, the susceptibility of the right hemisphere declined more than that of the left hemisphere during illusion processing. An interpretation is offered in terms of two parallel processes, one that is fast, uses feature extraction, and is performed more effectively in the left hemisphere, and one that is slow, uses visuospatial analysis to compute distances between parts of the illusion figure, and is performed more effectively in the right hemisphere.

Adolescent↗
PubMed1989

Right hemisphere contribution to lexical access in an aphasic with deep dyslexia.

Three hemifield tachistoscopic studies of a right-handed patient with acquired Broca's aphasia and deep dyslexia, but with intact visual fields, are presented to support the hypothesis of right hemisphere (RH) participation in deep dyslexic reading. A systematic comparison of this deep dyslexic with the disconnected RHs of two patients with complete cerebral commissurotomy disclosed a similar, but not identical, pattern of abilities. The results demonstrate partial reliance on the RH for accessing the meaning of single words, but not for phonological encoding in this patient.

Adult↗
PubMed1989

Simple reaction times to lateralized light flashes. Varieties of interhemispheric communication routes.

Simple unimanual reaction times to lateralized light flashes were measured in 40 normal subjects, 4 commissurotomized patients, and a boy with callosal agenesis. In all subjects, reaction times tended to be shorter when the stimuli were presented on the same side as the response hand (uncrossed condition) than on the opposite side (crossed condition). In 2 experiments, the magnitude of the crossed-uncrossed difference (CUD) was greatest in the commissurotimized patients (ranging from 35 to 96 ms), the acallosal boy showed an intermediate CUD (20 and 12 ms for the first and second experiment, respectively), and normal subjects exhibited the smallest CUD (an insignificant 1 ms difference and a significant 3 ms difference in the first and second experiment, respectively). For all subjects, reaction times increased when the stimulus light intensity was decreased (Experiment 1) or when stimulus eccentricity was increased (Experiment 2). However, the effects of these visual parameters on the CUD revealed group and individual differences. Neither stimulus light intensity nor eccentricity affected the CUD in the normals, in 1 of the commissurotomized patients, and in the acallosal boy. The CUDs in these subjects are attributed to the transfer of nonsensory information via the corpus callosum, via ipsilateral corticospinal tracts, and via the anterior commissure or ipsilateral motor pathways, respectively. The CUDs of 2 commissurotomized patients varied with stimulus eccentricity but not intensity. Subcallosal interhemispheric visual transfer is thus apparently more sensitive to stimulus eccentricity than to intensity. The final commissurotomized patient, R.Y., had slower and less accurate responses to stimuli presented in the right visual hemifield during left, but not right, hand responses. An asymmetry in subcortical visual interhemispheric communication is suspected in this patient. The disparate results amongst these subjects are discussed and contrasted with previous findings. Finally, an information processing model of cortical and subcortical interhemispheric communication is presented.

Agenesis of Corpus Callosum↗
PubMed1976

Auditory vocabulary of the right hemisphere following brain bisection or hemidecortication.

Unilateral scores of two commissurotomy and three (one left and two right) hemispherectomy patients were obtained on standardized auditory language comprehension tests which use pointing responses to a pictorial array. Unilateral performance by the commissurotomy patients was achieved by restricting the pictorial array to one visual half field, using a novel contact lens system which permits ocular scanning of the lateralized stimulus and self-monitoring of task performance. Using the Peabody and Ammons Picture Vocabulary Tests, the auditory vocabulary in the disconnected or isolated right hemispheres was found to be equivalent to that of normal subjects of ages 8:1 to 16:3 with a mean of 11:7 (eleven years and 7 months old). At the same time, standardized aphasia tests showed that the picture vocabulary in the right hemispheres is similar to that of a heterogeneous population of aphasics, even though the right hemispheres did not behave quite like any classical aphasic diagnostic group. No significant differences were found between right hemisphere comprehension of object vs. action names. Results indicated that vocabulary as a function of word frequency followed the same pattern in the right and left hemisphere although the right hemisphere was consistently lower. This parallel between the two hemispheres was conjectured to reflect some similar or even shared lexical structures in the two hemispheres. Together with other data on the performance of the right hemisphere on the Token Test (Zaidel, 1976), the results suggest a complex model of the development of language laterality in the brain, in which some, but not all, auditory language functions continue to develop in the right hemisphere past what is generally regarded as the critical period for language acquistion. In general, auditory language comprehension is better characterized as that of an "average aphasic" than that of a child of a specific age.

Aphasia↗