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Biomedical subjects

M A Jeeves

Publications and source records attributed to M A Jeeves.

At least 19 recordsLinked to original sources
PubMed1999

Bilateral field advantage and evoked potential interhemispheric transmission in commissurotomy and callosal agenesis.

The role of the corpus callosum versus other cerebral commissures in the interhemispheric integration of visual information was studied in four individuals with complete agenesis of the corpus callosum, two individuals with partial agenesis, one total commissurotomy patient, and normal individuals. Evoked potential (EP) indices of interhemispheric transmission of visual sensory responses were observed during matching of unilateral and bilateral visual field letters and patterns. Neither the commissurotomy nor any of the acallosal patients had ipsilateral hemisphere visual EPs (P1 and N1), demonstrating that the posterior callosum is necessary for interhemispheric transmission of these components of visual evoked potentials. While the commissurotomy patient could not compare bilaterally presented letters, the anterior commissure of the acallosal patients appeared to be sufficient for interhemispheric comparison of single letters. However, bilateral comparison of more complex visual patterns resulted in considerable difficulty for complete agenesis patients, while comparison of patterns was more nearly normal when anterior callosal fibers were present (partial agenesis).

Adolescent↗
PubMed1996

Interhemispheric transfer time differences related to aging and gender.

The difference in simple reaction times to unstructured stimuli contralateral to the hand used for response ('crossed' responses) and those stimuli ipsilateral to the hand used for response ('uncrossed' responses)--or crossed-uncrossed difference (CUD) is assumed to be a reliable index of interhemispheric transfer time (IHTT). Studies using the CUD paradigm with acallosal patients as well as a variety of populations with known variations in callosal size or functioning have demonstrated that such callosal differences are reflected in differences in recorded CUD times. Recent studies have suggested that elderly individuals show a reduction in size of the corpus callosum, particularly in the anterior region. In order to assess any potential change in callosal transfer efficiency with aging. CUDs were obtained from elderly (60+ years) and younger subjects (18 30 years). The elderly subjects showed a significantly elongated CUD compared to younger subjects, with elderly females contributing the greatest increase. No significant gender differences were found for younger subjects. In addition, an unexpected trend for an overall right field reaction time advantage was found for all subgroups, accompanied by a larger calculated CUD for right hand responses than for left hand responses.

Adolescent↗
PubMed1996

Maximizing the bilateral field advantage on verbal and nonverbal matching tasks.

Research has established that response latencies are generally shorter on visual matching tasks when one target is projected to each hemifield (bilateral presentation) than when both targets are projected to the same hemifield (unilateral presentation). This effect, called the bilateral field advantage (BFA), has recently shown promise as a predictor of callosal dysfunction. As a step toward developing a reliable BFA index, the present study examined two factors that appear to influence the extent of BFA in normal subjects. Twenty-seven right-handed college students performed a verbal matching task (using letter pairs drawn from the set AaBb) and a nonverbal matching task (using dot pattern pairs constructed with 4 dots in a 3 x 3 matrix). Order of task varied across subjects (dots followed by letters, or letters followed by dots, or letter trials and dot trials interleaved at random). The targets were presented either unilaterally or bilaterally. Results revealed a robust BFA for the letter-matching task in all three task order conditions, suggesting that the letter task may be suitable for inclusion in a battery of tasks for clinical assessment. The dot-matching task did not yield a significant BFA when administered as the first task. The dot task BFA increased when the letter task preceded it, and became comparable to the letter task BFA in the interleaved condition.

Adult↗
PubMed1996

The role of attention in visual bilateral matching tasks.

The consistent finding of studies employing visual matching tasks has been a reaction time and accuracy advantage for judgements about stimuli presented bilaterally when compared to the average performance of the two unilateral field presentations. As with recent studies showing the influence of attention on reaction times to unilateral presentations, we hypothesized that attentional mechanisms may also play a role in the speed advantage seen with bilateral letter presentations. The present study employed random dot-patterns ("dot-primes"), presented in the upper half of the LVF, RVF, Bilateral VF, or absent, as abrupt onset peripheral cues to attract attention automatically. Letter pairs followed immediately (14 msecs) after the dot-primes in the lower half of the LVF, RVF, or Bilateral VF. The results for unilateral dot-primes, followed by unilateral letter pairs, were consistent with previous studies showing that the field advantage for a particular task can be altered using abrupt onset attentional cues, with the advantage going to the field where the attentional prime is presented. Bilateral dot-primes did reduce latencies to subsequent bilateral letter pairs, but bilateral primes also reduced latencies to both LVF and RVF letter pairs, in nearly the same proportion as for bilateral letter pairs. Latencies for RVF-primes/Bilateral-letters were as fast as for Bilateral-primes/Bilateral-letters, and both of these conditions were significantly faster than LVF-primes/Bilateral-letters. The results suggest that attention plays a relatively minor role in the bilateral field advantage, and that non-attentional factors (i.e. interhemispheric dynamics) account for most of the asymmetric unilateral-prime influence on bilateral performance. Possible interhemispheric factors which may contribute to these results are discussed.

Adult↗
PubMed1994

Directional asymmetries in interhemispheric transmission time: evidence from visual evoked potentials.

The hypothesis was tested that interhemispheric transfer time (IHTT), as measured in the latency of bilaterally recorded visual evoked potentials, is directionally asymmetric, i.e. that an IHTT is faster for transmission from right-to-left hemisphere, than from left-to-right. A meta-analysis of 18 experiments within the published literature reporting visual evoked potential IHTTs indicates a significant experiment-wise predominance of faster right-to-left IHTTs. A new experiment is also reported in which significantly faster right-to-left IHTT was found in visual evoked potentials recorded from parietal electrodes to lateral visual field presentations while subjects performed a task requiring complex stimulus recognition and analysis, and a choice response.

Choice Behavior↗
PubMed1993

Bilateral visual field processing and evoked potential interhemispheric transmission time.

The relationship between the efficiency of interhemispheric interactions via the corpus callosum and the speed and accuracy in making comparisons of information simultaneously presented to the right and left visual fields was studied by comparing bilateral (vs unilateral) advantages in matching letters, with evoked potential measures of interhemispheric transmission time (EP-IHTT). The primary finding was a strong correlation suggesting that larger bilateral field advantages in reaction time are associated with faster EP-IHTT. However, the association between EP-IHTT and bilateral advantage was strong only for transmission speed from left hemisphere to right hemisphere, but not for speed of transmission in the opposite direction. The data are consistent with a hypothesis of asymmetric homologue enhancement, i.e. a directionally asymmetric callosal influence which facilitates processing of letter stimuli in the right hemisphere allowing for increased response speed and accuracy of bilateral visual field comparisons.

Adolescent↗
PubMed1993

The bilateral field advantage on a letter-matching task.

A series of studies have reported that responding is faster when letter pairs to be matched are projected to two hemispheres rather than one. Four experiments described here tested this bilateral field advantage and identified factors that influence its extent. Subjects were shown letter pairs drawn from the ensemble "AaBb", and classified the letter pairs as "Match" if the letters had the same name (regardless of case) and "No Match" if they did not. In the first two experiments the letter pairs were presented unilaterally (both letters in one visual field), bilaterally (one letter in each visual field), or centrally (both letters on the vertical midline, above and below fixation), in order to investigate how the bilateral field advantage is influenced by screen location. The third experiment added a bilateral-diagonal position (to check for artefacts related to horizontal scanning strategies), and the fourth experiment added distractor digits (to equate initial processing demands in the bilateral and unilateral conditions). Results indicate that the bilateral field advantage is a robust phenomenon, although several manipulations reduced its magnitude. Implications of these findings for models of hemispheric collaboration and interhemispheric processing are discussed.

Adolescent↗
PubMed1992

Hemispheric interactions: the bilateral advantage and task difficulty.

Twenty-five normal subjects made "same-different" responses to dot patterns presented in the LVF, RVF or bilaterally. Task difficulty was manipulated in each condition by varying the number of dots in the two patterns presented from two to four to six. The pairs of patterns always had the same number of dots on a given trial. Response latency and accuracy worsened as the number of dots increased for all three presentation conditions and for both "same" and "different" judgements. Overall, responding was faster and the number of errors lower on Bilateral presentations. For response latencies to identical patterns of dots, the size of the bilateral advantage increased relative to RVF responding as task difficulty increased but did not change significantly relative to LVF responding. When the two patterns were not identical the size of the advantage did not change as task difficulty increased. "Same" judgements were faster but less accurate than "different" judgements. A model of hemispheric interactions is proposed to account for the findings.

Adult↗
PubMed1991

Stereo perception in callosal agenesis and partial callosotomy.

Stereoperception in two acallosal patients and two partial callosotomy patients was compared with that of three normal subjects. All three patients with the splenium missing, whether due to agenesis or surgical intervention, showed midline deficits and broadly similar profiles; namely, they made few uncrossed midline responses. The patient with partial callosal section but with the splenium almost totally spared performed better at the midline than in the periphery. All degrees of disconnection produced some overall loss of performance, confirming the results of Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987). The results are discussed in the context of earlier reports of human and animal studies of stereoperception. Bearing in mind reports of structural alterations in layer III of the striate cortex in acallosals (Shoumjra, K. et al. Brain Res. 93, 241-252, 1975. Also, Akert, K. et al. Trans. Am. Neurol. Assoc. 79, 151-153, 1954), it is speculated that the specific difficulties encountered by them in handling uncrossed disparities may be due to a marked reduction or absence of far neurones in acallosal brains (Poggio, G. F. and Poggio, T. Ann. Rev. Neurosci. 7, 379-412, 1984). The likely importance of the anterior commissure in the efficient integration of crossed disparity (near neurones) (Cowey, A. In Brain Mechanisms and Spatial Vision, D. Ingle (Editor), NATO Advanced Study Institute Series, Martinus Nijhoff, The Hague, 1985) is seen as a possible explanation of the acallosals relative success in making crossed disparity judgements. The variability of performance in normals documented by Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987) is, not surprisingly, even more marked amongst acallosals.

Adult↗
PubMed1990

Reading in callosal agenesis.

It has been suggested that deficits in explicit phonological processing are causal in developmental dyslexia. Deficits in such skills have been reported in developmental phonological dyslexia, though not in developmental surface dyslexia. The reading performance of two children with callosal agenesis, who have been previously shown to have impairments on rhyming tasks, are reported. Neither child is dyslexic in the traditional sense, since word reading levels are appropriate for age. However, both children have impaired development of the phonological reading route despite normal lexical skills. The pattern of their reading is therefore comparable to developmental phonological dyslexia. Problems in explicit phonological processing may be causal in the failure to establish an efficient phonological reading route but this is insufficient to create difficulty with word recognition itself. The corpus callosum may be essential for the normal development of a phonological reading route.

Agenesis of Corpus Callosum↗
PubMed1989

Ten pen men: rhyming skills in two children with callosal agenesis.

Cases of callosal agenesis provide unique opportunities to investigate the normal role of the corpus callosum in the development of cognitive functions, including language. The only language impairment which has been consistently observed in three acallosal patients is on the retrieval of words from rhyming cues. Two new cases of callosal agenesis in children of normal intelligence are presented. Their performance on a variety of rhyming tasks involving both production and recognition of rhyme is reported. Both children display deficits and possible explanations are discussed.

Adolescent↗
PubMed1988

The formation of finger grip during prehension in an acallosal patient.

The grasping behaviour of an acallosal patient is compared with that of a group of normals. Video records of the hands of the patient and the normals allowed frame by frame analysis of the prehensile movements involved. The normals behaved according to the earlier reports by Jeannerod [Behav. Brain Res. 19, 99-116, 1986; and in Two Hemispheres--One Brain, F. Leporé, M. Ptito and H. H. Jasper (Editors), pp. 369-383, Alan R. Liss, Inc., New York, 1986] with the thumb and forefinger closing upon the object to be grasped by the time it was reached. By contrast the acallosal did not begin to close the finger and thumb until after contact was made with the object. The results are seen as further evidence for (a) the enhanced development of uncrossed ipsilateral pathways in acallosals and (b) absence in acallosals of the normal inhibitory action of the callosum in suppressing such enhanced ipsilateral output which consequently competes with the contralateral output controlling the fingers.

Adult↗
PubMed1988

Bimanual co-ordination in callosal agenesis and partial commissurotomy.

Studies [Preilowski, B.F.B. in Cerebral Localization, pp. 116-131, Springer, Berlin, 1975; Reynolds, D.M. and Jeeves, M.A. Neuropsychologia 12, 287-290, 1974] of bilateral motor coordination in commissurotomy patients pointed to the importance of direct interhemispheric integration for the fine regulation of the lower motor system within each hemisphere. When external visual feedback was withdrawn in the performance of a bimanual tracking task, partial commissurotomy patients, in whom the anterior portions of the callosum were cut, deviated significantly when drawing lines which required asymmetrical input from the two hands. The task devised by Preilowski was given to two adult acallosals, an 11 yr old acallosal boy, and an 11 yr old girl in whom the centre one-third of the corpus callosum had been sectioned. The acallosals performed in a manner similar to Preilowski's partial commissurotomy patients. The results were interpreted as confirming the interhemispheric integrative function of the corpus callosum. It is argued that they constitute further evidence for the existence of hemispheric dominance for motor control in acallosals. The partial commissurotomy patient did not differ in performance from normals. Her results were consistent with the view that it is the anterior parts of the callosum which are crucial for the interhemispheric integration of the lower motor system in each hemisphere.

Adult↗
PubMed1988

Cerebral asymmetries and interhemispheric processes.

Those who attempt to characterize the functions of the cerebral hemispheres tend, broadly speaking, to do so either in terms of structural specializations or of different information-processing modes. Often little attention is paid to the possible importance, in determining the outcome of experiments in this field, of interhemispheric processes. An experiment is described which concurrently studies hemispheric response differences and interhemispheric processes. Sets of dot patterns are learned, each made up of an original and three distortions of the original. The degree of distortion is systematically changed and is quantified in terms of information theory. Subjects then examine pairs of patterns and decide whether they belong to the 'same' family, i.e. an original and one of its distortions, or 'different', i.e. a pattern previously learned and a completely new one. Manual response times are recorded for 'same' and 'different' responses and functions plotted of response latencies against degree of pattern distortion. The pairs of patterns are presented under three different conditions. Either both patterns in one visual field (unilateral condition), one pattern in each visual field (bilateral condition) or the patterns one above the other straddling the vertical meridian (central condition). Response latencies are shortest for the bilateral condition, next shortest for the unilateral condition and slowest for the central condition. Models which may account for these results are examined and one crucially involving changed information transmission rates with increasing distortion of patterns to be compared is found to provide the most parsimonious explanation of the results from all three experimental conditions.

Adolescent↗
PubMed1988

Interhemispheric transfer of spatial tactile information in callosal agenesis and partial commissurotomy.

The De Renzi Rod Test was used to investigate the transfer of spatial tactile information between hands in acallosals and partial commissurotomy patients. The right-handed performance of young acallosals was impaired, confirming the results of an earlier study by Meerwaldt (1983). The adult acallosals, with one exception, showed no difference between right and left hand performances. Two partial callosotomy patients with sparing of the most caudal parts of the body of the callosum showed no difference between the hands. A third callosotomy patient with little, if any, sparing of the most caudal part of the body of the callosum showed a marked impairment when performing the tactile task with the right hand. The unimpaired performances of the adult acallosals are attributed to the use of ipsilateral pathways and the development of behavioural strategies. The callosotomy patients' results are consistent with the mapping by Pandya and Seltzer (1986) of the interhemispheric callosal pathways between the cortical parietal areas in non-human primates.

Adult↗
PubMed1987

A further study of language function in callosal agenesis.

A subset of the tests of language ability administered by M. Dennis (1981, Brain and Language, 12, 33-53) was given to two adult acallosal patients. One of the patients studied showed widespread language deficits not restricted to the syntactic-pragmatic core as in Dennis' patient. The other showed a very specific deficit which does not encompass syntactic-pragmatic skills. The data does not support the view that the corpus callosum is necessary for the normal development of specific language functions.

Adolescent↗