Right-handed Group Research Articles

Apraxia during Wada testing

Apraxia is the loss of the ability to perform learned skilled movements correctly. In right-handers, apraxia and aphasia are most frequently associated with left-hemisphere lesions. When they are dissociated, however, aphasia is more common in the absence of apraxia than vice versa. There are two hypotheses that can account for this discrepancy: (1) in right-handers, praxis is more likely than language to be mediated by the right hemisphere, or (2) the left-hemisphere network that mediates language is either more widely distributed than the network that mediates praxis or is more likely to be in the middle cerebral artery distribution. We studied apraxia in a group of right-handers undergoing selective hemispheric anesthesia, or Wada testing. All nine subjects had language lateralized to the left hemisphere, and seven of the nine had praxis lateralized to the left hemisphere. Two of the subjects had praxis bilaterally represented. Although our data suggest that speech and praxis functions tend to be lateralized to the left hemisphere in most right-handers, praxis appears to be more distributed between the hemispheres than speech-language functions. Furthermore, an analysis of the types of errors made during praxis testing suggests differential roles of the hemispheres in praxis functions.

A Note on Trichotomous Classification of Handedness and Fine-Motor Performance in Children

Abstract The fine-motor performance (finger-tapping speed) of a trichotomous hand-preference grouping (right, left, mixed) of 4- to 6-year-olds matched on age and sex was examined. Results indicated no significant differences in overall performance between groups, nor could any variations be attributed to sex. Regarding within-group performance, only the right-handed group exhibited limb differentiation by tapping significantly faster with the preferred (right) hand. Thus, contrary to some reports, left- and mixed-handers do not seem to be inferior to consistent right-handers in the performance of a fine-motor task. These findings are discussed in light of developmental theory and are parallel with previous studies of adults and dichotomous investigations of children.

Brain mapping and evoked potentials in sleep, hypnosis and waking state

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory `musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and `musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.

Sexual dimorphism in body and brain weight and its association with paw preference in cats.

Sexual dimorphism in body and brain weight was studied in cats. Paw preference was assessed by food reaching test. Sexual dimorphism in body weight related to paw preference. Males weighted more than females in total sample and non-right-handed (NRH) cats (no significant difference in right-handed group). NRH males weighted more than right-handed (RH) males (no difference in females). Absolute total-brain weight did not show sexual dimorphism. Relative total-brain weight was sexually dimorphic only in NRH cats (females more than males). RH males weighted more than NRH males (no significant difference in females). Only absolute right-brain weighted more in males than females (total sample). Otherwise, no significant difference was found between absolute right- and left-brain weights of male and female cats. The relative right- and left-brain weighted more in females than males only in NRH cats (no sexual dimorphism in RH cats); more in RH males than NRH males; no difference in RH and NRH females. The overall results indicated that sexual dimorphism in body and brain weight is associated with cerebral lateralization in cats.

Skill at image generation: Handedness interacts with strategy preference for individuals majoring in spatial fields

Abstract Study 1 was was designed to identify a subgroup of non-right-handers in spatial fields who excel over right-handers in spatial ability. The study investigated image generation skill in individuals majoring in spatial fields (art, math/science) in college. In order to identify this subgroup, the role of three factors was examined: handedness (non-right-handers vs. right-handers with first-degree relatives who are all right-handed vs. right-handers with at least one non-right-handed first-degree relative), preferred strategy for processing spatial information (visualised spatial metrics vs. verbalised spatial relations), and sex. We found that strategy preference interacted with handedness. The non-right-handers who excelled relative to a right-handed group were those who preferred a visualised spatial metric strategy for processing spatial information. Among visualisers, non-right-handers performed at the highest level, significantly above right-handers with all right-handed relatives. In contrast, among verbalisers, right-handers with right-handed relatives performed at the highest level, significantly above right-handers with non-right-handed relatives. The latter effect for right-handers was replicated in Study 2, for a sample of mathematically precocious youth. We concluded that determination of strategy preference is critical in identifying the handedness group that excels at image generation. Effective use of a strategy may depend on a compatibility between preferred processing style and brain organisation.

Neuropsychological Sequelae of Stroke as a Function of Handedness

The preservation of visuospatial ability relative to verbal ability following right middle cerebral artery stroke was assessed in 19 left- and 19 right-handed male patients who were group-matched on the basis of age, education, and time elapsed since stroke. Analysis of covariance (covarying education) indicated that the left- and right-handed groups were significantly different with regard to the discrepancy between Verbal IQ and Performance IQ, with the left-handed patients showing a smaller difference than the right-handers. These results provide further evidence that sinistrality may be associated with less hemispheric specialization.

A Simple Dual-Task Study of Laterality, Sex-Differences and Handedness

Nine-hundred and eight-one right-handed and 55 left-handed subjects were required to tap with a pen for 10 secs between targets 6 cm apart whilst either saying nothing, reciting a tongue-twister or saying la-la. The numbers of dots produced in 10 secs in each condition were analysed. The right-handed group demonstrated the usually found degradation in their right-hand performance whilst reciting the meaningful words, but showed a lesser effect when saying la-la. Their left-handed performance was essentially unaffected. Absolutely no evidence for the presence of a sex difference in lateralization of language was found. The much smaller sample of left-handed subjects presented a complex picture of no significant effects, whether they were the sole left-handers in their family, or had other left-handed close relations.

COSET CONSTRUCTION OF SUPERSTRINGS VIA THE COADJOINT ORBIT METHOD

The previously proposed general construction of geometric actions on infinite-dimensional group coadjoint orbits in terms of fundamental group one-cocycles is applied to provide an alternative formulation of the Green-Schwarz superstring. It is shown that the latter model can be consistently constructed as geometric action on a certain infinite-dimensional coset space of the semi-direct product of left- and right-handed Virasoro groups with a Kac-Moody group based on an appropriate modification of the super-Heisenberg-Weyl group.

Visual attention in left sylvian strokes

This report is comprised of four sections. Part of the literature on right visual field neglect is summarized in the first one. Entitled “Guggenheim data”, the second section concerns sentence-picture matching behaviors within a group of unilingual adult right-handers — 100 of them healthy and 169 seen after a unilateral stroke — who were administered a test including 6 sentence-picture matching stimuli (syntactically “simple” or “complex” utterances of the examiner were to be matched to one of four line drawings of proportional levels of iconographic complexity that were presented as a single left-right dimidiated display). Contralateral neglect was found to be present in both the left and the right brain-damaged subgroups. This behavior was shown to be independent (a) of concomitant hemianopsia and (b) of educational level. However, while right brain-damaged subjects neglected to the left for both simple and complex stimuli, left brain-damaged ones presented significant neglect to the right for complex stimuli only. Entitled “MRC data”, the third section concerns sentence-picture matching behaviors within a group of 170 adult right-handers — 113 of them healthy and 57 with unilateral brain damage — who were administered a test including 46 sentence-picture matching stimuli. This further set of data confirms the existence of unilateral neglect in left as well as in right brain-damaged subjects. In the fourth section, (a) an hypothesis is formulated suggesting that unilateral visual field neglect is linked to nature of stimuli and tasks as much as if not more than to laterality of lesions; (b) various ways of testing this hypothesis are discussed together with ensuing predictions; and (c) anomalies in sentence-picture matching behavior among left brain damaged subjects are interpreted as potentially indicative of an interaction between dysfunction in auditory comprehension and right visual field neglect.

Left and right-handed dyslexic boys: An empirical test of some assumptions of the Geschwind-Behan hypothesis

Twenty-six dyslexic boys (13 left-handers and 13 right-handers) were tested for hemispheric asymmetry with dichotic listening (DL) and a visual half-field test (VHF). The purpose of the study was an empirical test of the Geschwind-Behan [ Proc. natn. Acad. Sci. USA 79, 5097–5100, 1982] hypothesis of a difference in hemispheric asymmetry between left- and right-handed dyslexic boys. Following Geschwind and Behan, left-handedness and dyslexia are caused by a common factor affecting the development of the left hemisphere in utero which results in a right hemisphere dominance. As a consequence, handedness but not language is shifted to the right hemisphere. We therefore predicted that left-handed dyslexics should be superior to right-handed dyslexics on visuospatial tasks, but perform similar to right-handers on verbal tasks. The results revealed a significant right ear advantage (REA) in both groups during a dichotic listening test to verbal stimuli. The left-handed group was however superior to the right-handed group in recognition of visuospatial stimuli presented in the left half-field in a visual half-field test. It is concluded that the results provide some, although weak, support for the Geschwind-Behan hypothesis.

Relationship between Manual Midline Crossing and Hand Preference

The relationship between manual midline crossing and hand preference was studied in 200 2- to 6-year-old children. Performance patterns of right-, left-, and mixed-handed children were compared. Right- and left-handed children exhibited significantly greater frequency of preferred than nonpreferred hand use for total hand use and for contralateral hand responses. The right-handed group showed a developmental trend for contralateral hand responses, with age-related changes due to a progressive increase in frequency of contralateral right (preferred) hand responses. The mixed-handed group displayed a weak preference toward use of the right hand for total hand use and for contralateral hand responses. A general reduction in frequency of midline crossing cited within the mixed-handed group was due to reduced frequency of contralateral right-hand responses. The theoretical significance of the research findings and their implications for sensory integration test interpretation are discussed.

The “Forced-Attention Paradigm” in Dichotic Listening to CV-Syllables: A Comparison Between Adults and Children

The present study was concerned with the effects of directional attention on the right-ear-advantage (REA) in dichotic listening. It was suggested that if selective attention contributes to the REA during a non-forced, free recall condition, then comparing the unattended left and right ear scores when attention is forced to the right and the left ear, respectively, would yield an “attention-free” estimate of the REA. Each subject participated in a non-forced, free recall, condition; in a forced-right condition; and in a forced-left condition. During the two forced conditions, subjects were instructed to only attend to and report the right and left ear inputs, respectively. The stimuli were the six stop-consonants paired with the vowel a. Four right-handed groups participated (N = 18): Adult males, adult females, boys (8-9 years), girls (8-9 years). The results showed a significant REA in all groups during the non-forced condition. During the forced-right condition, significantly more correct recalls were obtained from the right compared to the left ear in all groups. During the forced-left condition, significantly more correct recalls from the left compared to the right ear was obtained only in the two adult groups, but not in the children groups. Finally, comparing correct recals from the unattended right ear (during the forced-left condition) with the unattended left ear (during the forced-right condition) revealed a significant REA in all groups except for the adult females.

A superstring inspired low-energy electro-weak model

The phenomenological implications are studied of the assumption that low-energy electro-weak symmetry beyond the standard model is SU(3) c × SU(2) L × SU(2) R × U(1)× U(1) as implied by certain superstring E 6-models. SU(2) R is different from the right-handed group of left-right symmetric models. Among the results are (i) a lower bound on the SU(2) R scale of 2.5×10 5 GeV; (ii) pattern of singlet quark masses m g 1 : m g 2 : m g 3 = m u: m c: m t, and (iii) vanishing of neutrino mass due to the presence of a global U(1) symmetry in the model.

Lateral saccadic latencies and handedness

Lateral saccadic latencies were determined in 18 right-handers and 18 left-handers. Within the right-handed group the mean latency was significantly shorter when looking from the left to the right (242.7 msec) than from right to left (265.0 msec), whereas no significant directional difference was found in the left-handed group. An age effect was also found with longer latencies being associated with increased age. These findings agree with those of Pirozzolo and Rayner ( Neuropsychologia 18, 225–229, 1980) and provide further evidence of the pervasiveness of functional asymmetry in the human brain. The present findings suggest that motoric or central integrative mechanisms may contribute more to saccadic directional asymmetries than do perceptual differences.

Immediate Free Recall of Unilateral Spoken Word Lists

Neither a group of pure right-handers nor a complementary group excluding pure right-handers showed much sign of a significant monaural REa for free recall performance, in contrast to the effect found by Turvey, Pisoni and Croog (1972) for probed recall performance by a group of unknown handedness. However other evidence was found of an influence of laterality in this relatively high-level task, deriving from the observation of a significant Ear ×. Speed × Serial Position interaction. In non-sinistrals application of dual-process memory theory to the results showed that the right ear retrieved a greater proportion of recall than did the left ear from the long-term store, while conversely and possibly as a compensation for this the left ear relied more heavily than the right ear did on the short-term store. This effect was replicated in the sinistral group, though in an attenuated form, as would be expected if it is a consequence of hemispheric asymmetry for language.

Lateral dominance and aesthetic preference

Left and right handers were found to differ in their preferences for mirror versions of vacation slides. Preferences of one group of right handers were predictive of preferences for another group of right handers, but not of left handers. In a second study, it was found that slides strongly prefered by dextrals were those with the more important content, or the greater heaviness on the right, and that slide asymmetry was highly correlated with dextral, but not sinistral preferences. Results were interpreted as reflecting a left field perceptual bias induced by selective right hemisphere activation in right handers.

Handedness, speech lateralization and ability

Data on verbal and performance tasks are presented from a large sample of the normal population and from a group of men with chronic unilateral cerebral lesions due to missile injury. It is suggested that: 1. ( a)|unselected groups of left-handers in the normal population perform as well as right-handers on standard cognitive tasks; 2. ( b)|non-right-handed men with unilateral cerebral lesions are not less impaired in verbal and performance tasks than a comparable right-handed group; 3. ( c)|unusual patterns of cerebral organisation may be associated with non-familial sinistrality and pure left-handedness.

Hemispheric differences in a letter classification task

The experiment examined hemispheric differences in same-different judgments for unilaterally presented letter pairs which could be classified as “same” on the basis of name identity (NI, e.g., Aa) or physical identity (PI, e.g., AA). Two groups of Ss were tested, a right-handed group and a predominantly left-handed group. The experiment employed a reaction time measure, and fixed the duration of brief exposures to yield an overall performance level of 90% correct. Analysis of the results focused on the difference between RTs for the NI matches and for the PI matches in each hemisphere. The method allowed differences in cognitive processing to be assessed while sensory and response factors were minimized. The right-handed group all showed a smaller mean NI-PI difference in the left hemisphere (84 msec) than in the right hemisphere (181 msec). The left-handed group showed smaller and less consistent differences, but the group as a whole had a reversed asymmetry, with a mean NI-PI difference of 128 msee in the left hemisphere and 90 msec in the right hemisphere.

A Comparison of Left-Handed and Right-Handed Subjects on Verbal and Non-Verbal Dichotic Listening Tasks

Twenty-five left-handed and 25 right-handed subjects performed three dichotic listening tasks, two verbal and one non-verbal. Comparisons were made between mean scores obtained at the right and left ears, as well as between the handedness groups. The following results were obtained: The mean right ear score was higher than the mean left ear score for both handedness groups on both of the verbal dichotic tasks. This was significant for the right-handed group on both verbal tasks, but for the left-handed group it was significant on only one verbal task. The mean left ear score was higher than the mean right ear score for both handedness groups on the non-verbal dichotic task. This betweenears difference was statistically significant for the right-handed group only. Comparison of the two handedness groups on each of the three dichotic tests revealed that more left-handed subjects had ear leads which were the reverse of that found for the groups as a whole. This difference between the handedness groups, however, was statistically significant on only one of the dichotic tests. The mean left ear score was higher than the mean right ear score for both handedness groups on the non-verbal dichotic task. This betweenears difference was statistically significant for the right-handed group only. These data were re-analyzed comparing the size of the absolute between-ears difference scores of those individuals whose ear leads consistently were the reverse of the group as a whole, with subjects who showed no reversals. It was found that the reversal group had smaller mean scores on all three tests, and that this was significant on the two verbal tests. Although more left-handed subjects were found among the reversal group, the data tentatively indicate that the above finding holds true regardless of the handedness of the subjects in the reversal group. The above findings were interpreted as reflecting the different roles of the two cerebral hemispheres, as well as the degree of hemispheric equipotentiality.

Further data on the handedness of sleep.

Among the subjects were found 161 who were dominatingly right-handed and 31 who were dominatingly left-handed. With the righthand group, 52% went to sleep on their right side and 24% on their left. In the cases of the left-hand group, 54% went to sleep on their right and 39% on their left. Questions about the position during sleep gave figures which might be interpreted to show better sleep in the habitual position, but the differences were very small and some instances tended to suggest other implications. (PsycINFO Database Record (c) 2006 APA, all rights reserved)