Biomedical subjects

J Liederman

Publications and source records attributed to J Liederman.

15 recordsLinked to original sources

PubMed1991

Right hemisphere participation in reading.

This study examined whether the right hemisphere's contribution to lexical semantic processing is greatest when it is "disinhibited." Skilled reading may require the controlled modulation of interhemispheric interaction: the left hemisphere (or some other control mechanism) may regulate the subprocesses of reading by selectively "inhibiting" and "disinhibiting" right hemisphere function. Right-handed undergraduates concurrently performed two tasks: a lateralized semantic or rhyme task and a verbal memory task. It was hypothesized that right hemisphere reading processes would be disinhibited when the left hemisphere was "occupied" with the memory task. This hypothesis was supported for a subgroup of subjects who showed evidence of inhibition of right hemisphere function (i.e., left hemisphere dominance for lexical processing) when the lateralized semantic task was performed alone. Across subjects, there was a strong correlation between the degree of left hemisphere dominance in the single-task semantic conditions and the degree of disinhibition of right hemisphere function in the dual-task semantic condition.

Adult↗

PubMed1990

The effect of task difficulty upon the extent to which performance benefits from between-hemisphere division of inputs.

The means by which the two hemispheres coordinate processing of information are not well understood. By means of a tachistoscopic paradigm, we have shown repeatedly that performance is better when two conflicting tasks are presented to separate hemispheres than when both tasks are presented to a single hemisphere. The present study examines whether this effect is restricted to a specific range of task difficulty. Adult right-handers viewed two conflicting naming tasks by means of a tachistoscope. Task difficulty was lowered by reducing processing load (Experiment I: N = 32). Task difficulty was raised by projecting a visual mask 40 ms after offset of the visual displays (Experiment II: N = 10). At lower levels of processing load, dividing conflicting tasks between the hemispheres was beneficial, but not significantly so. At higher levels of load, and at either higher or lower loads with a visual mask, there were significant benefits associated with dividing conflicting tasks between the hemispheres. Three alternative explanations are discussed for the absence of an advantage associated with between-hemisphere division of inputs when task difficulty is reduced.

Brain↗

PubMed1988

The brainstem auditory evoked potential asymmetry is replicable and reliable.

Lateralization of neural function is generally thought to occur only at the level of the cerebral cortex and perhaps the thalamus. Levine and McGaffigan [EEG Clin. Neurophysiol. 55, 532-537, 1983] challenged this view by identifying a neural asymmetry at the level of the brainstem. They analyzed brainstem auditory evoked potentials (BAEPs) and found that peak III(+) amplitude (baseline-to-peak) was significantly larger in response to right than to left ear stimulation. The current paper demonstrates that this BAEP asymmetry is (a) reliable within and between subjects, (b) present for 33/sec and 10/sec click rates, and (c) more reliable when amplitude is measured peak-to-peak. This brainstem asymmetry may reflect the general tendency of humans to orient rightward and/or may be a precursor of higher level asymmetries.

Adult↗

PubMed1987

A modified finger lift test reveals an asymmetry of motor overflow in adults.

A method of eliciting motor overflow in neurologically intact adults is reported. A weight was placed on either the middle or ring finger of the left or right hand, and the subject was instructed to lift that finger. Involuntary finger lifts of the contralateral hand were recorded. There were 32 right-handers per experiment. In Experiments I and II, the amount of weight placed on the subject's finger was in proportion to body weight, whereas in Experiment III, it was in proportion to each finger's strength. Across experiments, motor overflow was more prevalent when the left, rather than the right, hand was weighted. This shows that the asymmetry in motor overflow previously reported in children and brain-damaged adults also occurs in healthy adults, and that this movement asymmetry is not an artifact of the relative weakness of the left hand in right-handed individuals.

Body Weight↗

PubMed1987

Developmental versus individual differences in the ability of the hemispheres to operate independently.

We have claimed that the ability to use the two cerebral hemispheres independently improves during early adolescence: Adults benefited from division of conflicting tasks between the hemispheres (Liederman & Meehan, in press; Merola & Liederman, 1987), whereas 10-year-old children did not (Merola & Liederman, 1985). The current research was undertaken to rule out the possibility that differences in the degree of hemispheric independence between adults and children were due to: (a) differences in overall performance or (b) differences in cognitive ability. The performance of ten adults was reduced to that of the 10-year-olds (by inserting a visual mask between trials). Nonetheless, 90% of the adults showed hemispheric independence, whereas only 50% of the children did. In addition, when high scholastic aptitude children were compared to adults, the difference in hemispheric independence remained. A causal model indicated that age and scholastic aptitude have unique effects upon hemispheric independence. Thus, there are both developmental and individual differences in the degree of hemispheric independence.

Adolescent↗

PubMed1987

An analysis of the naming deficit of left-handers.

Left-handers have been found to have a naming deficit when confronted with briefly flashed words. Three alternative explanations of this deficit were tested: whether it was due to deviant interhemispheric cooperation, relatively diffuse neural organization, or left hemispheric dysfunction. In Experiment I, four words were presented for 190 ms, unilaterally (to a single hemisphere), or bilaterally (between the hemispheres). Although left-handers (N = 48) named significantly less than right-handers (N = 30), performance was parallel across hemispheric conditions. Experiment II required semantic categorization, but not naming. The performance of the left-handers (N = 27) was indistinguishable from that of right-handers (N = 27) both in terms of overall performance and interhemispheric collaboration. It is concluded that the linguistic deficit of left-handers is specific to oral naming and that it is not caused by deviant interhemispheric cooperation.

Brain↗

PubMed1987

Reconciling stable asymmetry with recovery of function: an adaptive systems perspective on functional plasticity.

This article examines alternative ways of resolving an apparent paradox that has emerged from neuropsychological studies of language development: How can the developmentally stable functional asymmetry ("hemispheric specialization") observed in neurologically intact children be reconciled with the dramatic recovery of function often displayed following unilateral brain damage? The alternative resolutions we consider differ most critically in the roles they assign to lesion-induced neural reorganizations versus lesion-related release of preexisting functional potentials. Though arguments are given in favor of the latter as the primary factor in functional recovery, the primary goal of the article is to clarify the conceptual issues raised by recent empirical research.

Brain↗

PubMed1986

When is between-hemisphere division of labor advantageous?

Division of labor between the hemispheres is sometimes advantageous. Merola and Liederman (1985) have shown that adolescents' naming performance is superior when two different kinds of letter input are divided between the hemispheres than when both kinds of letter input are projected to a single hemisphere. We now investigated whether the advantage of between-hemisphere division of inputs increases from adolescence to adulthood; occurs when a secondary, concurrent verbal memory task is added; and corresponds with superior performance on the secondary task. Results indicated that use of the hemispheres as insulated work stations increased from adolescence to adulthood, and did not diminish when memory was stressed. However, between-hemisphere division of labor for the primary task did not facilitate secondary task performance.

Adolescent↗

PubMed1986

Determinants of the enhancement of the right visual field advantage by bilateral vs. unilateral stimuli.

Bilateral presentation of two different verbal inputs usually produces a stronger left hemispheric/right visual field (RVF) processing advantage than unilateral presentation. Previous reports of this effect confounded stimulus load with display configuration. Two experiments are presented in which the number of items during unilateral and bilateral trials was equated. The RVF advantage was enhanced during a free recall paradigm (Experiment I) but not during a partial report paradigm in which subjects were cued in advance to report only the top or the bottom of the display (Experiment II). This demonstrates that the effect does not depend upon the number of inputs per display and can not invariably be produced by bilateral/bihemispheric stimulation. It is suggested that subjects may be strongly biased to give priority to items delivered to the RVF/left hemisphere during bilateral trials. However, when this bias is constrained by rendering half of the RVF inputs irrelevant, subjects may be forced to pay equal attention to LVF inputs. Thus, eliminating the attentional bias eliminates the enhancement of the RVF advantage during bilateral trials.

Adolescent↗

PubMed1986

Handedness is not a unidimensional trait.

Most theories about the inheritance of hand preference assume that handedness is a unidimensional trait which forms a continuous distribution. This paper demonstrates that sampling a wide range of manual activities reveals dimensions of hand preference that are independent. 180 right handed and 110 left handed adults indicated their hand preference for 55 activities according to a five point scale. A Varimax Factor Analysis revealed four factors which accounted for 80 percent of the variance. Factor 3 was of special interest because it represented behaviors which rely upon the axial musculature and involve strength more than dexterity. Hand preference for items on this factor were less laterally biased than on factors which included such fine motor behaviors as writing or drawing. These results suggest that manual preference is governed by more than one neural system and that these systems may be independently lateralized.

Adolescent↗

PubMed1986

Words created by children versus aphasic adults: an analysis of their form and communicative effectiveness.

The creation of words through the novel combination of English morphemes (e.g., "map ball" to refer to a globe) was studied in 40 preschool children, 40 grade school children, and 40 adults. These lexical innovations were collected while subjects named pictured objects, and were evaluated in terms of incidence, communicative effectiveness, novelty, semantic accuracy, and certain linguistic characteristics. Preschool children's innovations were as communicatively effective as those of grade school children and adults and contained the highest proportion of innovations with redundant elements. Grade school children produced the highest proportion with semantic inaccuracies. This suggests that preschoolers invent words from a limited set of highly familiar terms, whereas grade schoolers rely more on partially known terms. In addition, the children's innovations differed significantly from those previously collected from aphasic adults. This demonstrates that aphasia does not cause a regression to an early level of linguistic sophistication.

Anomia↗

PubMed1986

Subtraction in addition to addition: dual task performance improves when tasks are presented to separate hemispheres.

This research links neuro- and cognitive psychology by asking whether performance of two concurrent cognitive tasks is facilitated by presentation of each task to a different cerebral hemisphere. Subjects were required to perform two arithmetic problems which were presented simultaneously. One problem required addition; the other subtraction. In Experiment I, briefly exposed numbers were exposed for 100 ms and were arranged so that a digit at fixation had to be added to a top number and subtracted from a bottom number. In Experiment II, the numbers were reversed so that the addition task was below the subtraction task. During Bilateral/bihemispheric trials, the addition problem was presented to one visual field and the subtraction problem to the other visual field. During Unilateral/single hemisphere trials, the addition and subtraction problems were projected to only one visual field. Results indicated that a higher proportion of problems were correctly solved during the Bilateral/bihemispheric trials than during the Unilateral/single hemisphere trials. These data suggest that dividing simultaneous inputs so that each hemisphere is confronted with a task requiring only one kind of cognitive operation facilitates performance, perhaps by minimizing intertask interference. This study illustrates one kind of hemispheric cooperation which facilitates dual task performance.

Cerebral Cortex↗

PubMed1986

Interhemispheric interference during word naming.

The hypothesis that the use of two hemispheres as receiving stations for information, rather than just one hemisphere, decreases interference between items, and improves performance, was tested by requiring subjects to identify four words simultaneously projected to one visual field (Unilateral-single hemisphere presentation) or divided between two visual fields (Bilateral-bihemispheric presentation.) In Experiment I, words projected to different hemispheres were incorrectly "blended" into a single response as frequently as words projected to a single hemisphere. In Experiment II, subjects were told that half of the display was irrelevant. Irrelevant words which were projected to a different hemisphere than the relevant words were incorrectly named as often as when all four words were projected to the same hemisphere. In addition, overall performance during Bilateral-bihemispheric presentations did not exceed that during the better of the two Unilateral-single hemisphere presentations, not only when naming was required (Experiments I and II), but even when only recognition was required (Experiment III). This demonstrates that division of inputs between the hemispheres does not always improve performance.

Eye Movements↗

PubMed1985

Interhemispheric collaboration in response to simultaneous bilateral input.

Two experiments tested whether processing is speeded when inputs are divided between the hemispheres rather than projected to a single hemisphere. Bilateral (bihemispheric) vs unilateral (single hemisphere) word pairs were tachistoscopically presented. Subjects responded when the words semantically matched. Irrespective of distance, visual angle and compatibility with reading biases, bilateral/bihemispheric performance was as fast as the better of the two individual unilateral/single hemisphere conditions and faster than their average. This pattern occurred only at the beginning of each experiment. With practice, performance significantly improved in the single but not the bihemispheric conditions. The excellent initial performance during the bihemispheric condition and its lack of improvement with practice are discussed with reference to models of interhemispheric collaboration.

Adolescent↗

PubMed1985

Developmental changes in hemispheric independence.

In this research, we questioned whether children's relative inability to use the 2 cerebral hemispheres independently contributes toward their difficulty with the simultaneous execution of conflicting tasks. 2 naming tasks were simultaneously presented to either 1 visual field/hemisphere combination (unilateral) or were divided between visual fields/hemispheres (bilateral). We predicted that bilateral presentation would improve performance by insulating these conflicting tasks from mutual interference and that there would be a developmental shift in the size of the advantage for bilateral presentation. This hypothesis was confirmed in a sample of 120 children (N = 40 per group). Older children (12- and 14-year-olds) named more items when they were presented bilaterally, rather than unilaterally, when conflicting inputs were directed to different hemispheres. Younger children (10-year-olds) displayed no advantage for bilateral presentation regardless of whether conflicting tasks were projected to the same hemisphere or different hemispheres. The fact that 10-year-olds did not benefit from division of conflicting inputs between the hemispheres was interpreted as a symptom of their relative inability to use the hemispheres independently.

Adolescent↗