Use Of Left Hand Research Articles

Lateralization of Feeding Behaviour in White-Fronted Lemur (Eulemur albifrons) and Ring-Tailed Lemur (Lemur catta) in Captivity

Introduction: Functional cerebral asymmetry is reflected in the lateralization of some behavioural patterns in many vertebrate species. In primates, behavioural lateralization has been related to both life style and age and sex, and it affects behaviours such as feeding and other tasks that require precision movements. Methods: We have studied feeding lateralization concerning the use of right and left hand to take the food in two species of lemurs in captivity, the mainly arboreal white-fronted lemur and the more terrestrial ring-tailed lemur, taking also account the age and the sex of the individuals. We calculated for each individual the hand preference (if it was the case) by means of z scores, and the strength of such preference using the handedness index (HI). Finally, we determined for each species the existence of right/left bias at the group level with the t Student test. Results: Half of the white-fronted lemurs (7 of 14) showed lateralization in feeding, while only a few ring-tailed lemurs (3 of 19) showed it. In the first species, a light bias seems to emerge (5 individuals used mostly the right hand for taking the food, while only 2 used mainly the left hand), while in the second species no bias could really be appreciated. Conclusion: Feeding lateralization was more accentuated in white-fronted lemur, in which a light bias towards the use of the right hand seems to be evidenced. No clear effect of age and sex on the presence and direction of lateralization could be evidenced. The results somehow contrast with what the postural theory of lateralization postulates about the preferential use of the right hand in terrestrial species.

A Dynamic Model of Human Limb Selection

Two experiments and a dynamic model forhuman limb selection are reported. In Experiment 1, left-handed and right-handed participants (N = 36) repeatedly used one hand for grasping a small cube. After a clear switch in the cube’s location, perseverative limb selection was revealed in both handedness groups. In Experiment 2, the cubes were presented in a clockwise and counter-clockwise sequence to right-handed participants (N = 15). A spatial shift in the switch point between right-hand use and left-hand use was observed. The model simulates the experiments by implementing the nonlinear multiple-timescale dynamics of the action-selection process underlying limb selection. It integrates two mechanisms that were earlier proposed to underlie this selection aspect of manual activity: limb dominance and attentional information. Finally, the model is used to simulate an influential earlier experiment, by establishing a conceptual link between cross-lateral inhibition asymmetry and the direction and strength of handedness.

Production of co-speech gestures in the right hemisphere: Evidence from individuals with complete or anterior callosotomy

IntroductionA right-hand preference for co-speech gestures in right-handed neurotypical individuals as well as the co-occurrence of speech and gesture has induced neuropsychological research to primarily target the left hemisphere when investigating co-speech gesture production. However, the substantial number of spontaneous left-hand gestures in right-handed individuals has, thus far, been unexplained. Recent studies in individuals with complete callosotomy and exclusive left hemisphere speech production show a reliable left-hand preference for co-speech gestures, indicating a right hemispheric generation. However, the findings raise the issue if the separate right hemisphere is able to also generate representational gestures. The present study challenges the proposition of a specific right hemispheric contribution to gesture production by differentiating gesture types including representational ones in individuals with complete callosotomy and by including individuals with anterior callosotomy in whom neural reorganization is less extensive. MethodsThree right-handed individuals with complete commissurotomy (A.A., N.G., G.C.) and three right-handed individuals with anterior callosotomy (C.E., S.R., L. D), all with left hemisphere language dominance, and a matched right-handed neurotypical control group (n = 10) were examined in an experimental setting, including re-narration of a nonverbal animated cartoon and responding to intelligence questions. The participants’ video-taped hand movement behavior was analyzed by two independent certified raters with the NEUROGES-ELAN system for nonverbal behavior and gesture. Unimanual right-hand and left-hand gestures were classified into eight gesture types. ResultsThe individuals with complete and anterior callosotomy performed unimanual co-speech gestures with the left as well as the right hand, with no significant preference of one hand for gestures overall. Concerning the specific gesture types, the group with complete callosotomy showed a significant right-hand preference for pantomime gestures, which also applied to the callosotomy total group. The group with anterior callosotomy displayed a significant left-hand preference for form presentation gestures. As a trend, the callosotomy total group differed from the neurotypical group as they performed more left-hand egocentric deictic and left-hand form presentation gestures. DiscussionThe present study replicates the finding of a substantial left-hand use for unimanual co-speech gestures in individuals with complete callosotomy. The proposition of a right hemispheric contribution to gesture production independent from left hemispheric language production is corroborated by the finding that individuals with anterior callosotomy show a similar pattern of hand use for gestures. Representational gestures were displayed with either hand, suggesting that in particular right hemispheric spatial cognition can be directly expressed in gesture. The significant right-hand preference for pantomime gesture was outstanding and compatible with the established left hemispheric specialization for tool use praxis. The findings shed a new light on the left-hand gestures in neurotypical individuals, suggesting that these can be generated in the right hemisphere.

The Successful Use of a Virtual Application to Enhance Formative Feedback- and Competency-Based Assessments in Surgical Training

INTRODUCTION: This study aimed to use a customized phone and computer application to improve formative feedback in surgery and assess competency over time. METHODS: General surgery residents at a single institution were enrolled in a prospective cohort study from August 2021 to February 2022. A survey was conducted at the beginning and conclusion of the study period to assess perceptions on feedback regarding technical skills. Afterwards, a customized phone application was used to assess competency using the Zwisch scale and a dictation feature. Salient features of the app included 15 core operations (appendectomy, cholecystectomy, hernia repair, laparotomy, etc) broken into 7-10 key steps, objective structured assessment of technical skills (OSATS), components that went well, and areas for improvement. RESULTS: Twenty-two surgery residents submitted 260 virtual feedback-forms over a six-month period. After the study, residents’ perception that they were receiving valuable, weekly feedback regarding technical skills increased from 27.2% to 100.0% (p < 0.001). The application also allowed the program to track competency over time and provide insight into critical areas for improvement (Fig. 1). Two of the most commonly dictated phrases by faculty included “make better use of your left hand,” and “remain aware of providing adequate counter-tension.” 90.9% of residents stated that the use of the virtual application enhanced their operative experience and would recommend its continued use for feedback and competency-based assessments.CONCLUSION: Phone applications greatly enhance formative, technical feedback for residents. These virtual applications can also be effectively used to assess improving competency over core operations in general surgery training.

Cultural Underpinnings on the Use of Left-Hand in Gbanjong Community of the Tolon District of Ghana

It is a common belief in Ghana’s Tolon District’s Gbanjong community in the Northern region that left-handed people are less effective in society. The research looked into the cultural influences or underpinnings on the use of the left-hand in the Gbanjong community. The study employs a qualitative research methodology. Data was gathered through interviews, observation, and focus groups. There was a review of both primary and secondary literature. For people who use left-hand in the community, a purposive sampling strategy was applied. The study also used a random sample of chiefs, sub-chiefs, and opinion leaders. In all, 47 community members were sampled and interviewed. The study revealed some cultural underpinnings on the use of left-hand in the community, such as bad luck, can only marry chiefs and princes, cannot make quality traditional cultural local meals, myths, Evil and devilish occurrences. There were also some psychosocial and theological biases discovered during the research. The research revealed that left-hand users want changes that take into account their functionally diverse attributes and demonstrate a greater level of cultural tolerance towards them. Individual differences must be recognized and accounted for in all cultural customs and traditional issues, in accordance with Article 3 (1 p.2) of the Convention on the Rights of the Child. The study concludes that the people of the Gbanjong community in Ghana’s Tolon District should not have their choice of hand as a cultural grounding. The study has established that there are somecultural underpinnings or obstacles that exist in the world for left-hand use and contributes to the existing data on social acceptance of persons who are created differently. Keywords: Left-handed, Taboos, Right-hand, Culture, Physical Activity, Customs, Underpinnings

Does hand modulate the reshaping of the attentional system during rightward prism adaptation? An fMRI study.

Adaptation to right-deviating prisms (R-PA), that is, learning to point with the right hand to targets perceived through prisms, has been shown to change spatial topography within the inferior parietal lobule (IPL) by increasing responses to left, central, and right targets on the left hemisphere and decreasing responses to right and central targets on the right hemisphere. As pointed out previously, this corresponds to a switch of the dominance of the ventral attentional network from the right to the left hemisphere. Since the encoding of hand movements in pointing paradigms is side-dependent, the choice of right vs. left hand for pointing during R-PA may influence the visuomotor adaptation process and hence the reshaping of the attentional system. We have tested this hypothesis in normal subjects by comparing activation patterns to visual targets in left, central, and right fields elicited before and after adaptation to rightward-deviating prisms using the right hand (RWRH) with those in two control groups. The first control group underwent adaptation to rightward-deviating prisms using the left hand, whereas the second control group underwent adaptation to leftward-deviating prisms using the right hand. The present study confirmed the previously described enhancement of left and central visual field representation within left IPL following R-PA. It further showed that the use of right vs. left hand during adaptation modulates this enhancement in some but not all parts of the left IPL. Interestingly, in some clusters identified in this study, L-PA with right hand mimics partially the effect of R-PA by enhancing activation elicited by left stimuli in the left IPL and by decreasing activation elicited by right stimuli in the right IPL. Thus, the use of right vs. left hand modulates the R-PA-induced reshaping of the ventral attentional system. Whether the choice of hand during R-PA affects also the reshaping of the dorsal attentional system remains to be determined as well as possible clinical applications of this approach. Depending on the patients' conditions, using the right or the left hand during PA might potentiate the beneficial effects of this intervention.

Human handedness: A meta-analysis.

Across time and place, right hand preference has been the norm, but what is the precise prevalence of left- and right-handedness? Frequency of left-handedness has shaped and underpinned different fields of research, from cognitive neuroscience to human evolution, but reliable distributional estimates are still lacking. While hundreds of empirical studies have assessed handedness, a large-scale, comprehensive review of the prevalence of handedness and the factors that moderate it, is currently missing. Here, we report 5 meta-analyses on hand preference for different manual tasks and show that left-handedness prevalence lies between 9.3% (using the most stringent criterion of left-handedness) to 18.1% (using the most lenient criterion of nonright-handedness), with the best overall estimate being 10.6% (10.4% when excluding studies assessing elite athletes' handedness). Handedness variability depends on (a) study characteristics, namely year of publication and ways to measure and classify handedness, and (b) participant characteristics, namely sex and ancestry. Our analysis identifies the role of moderators that require taking into account in future studies on handedness and hemispheric asymmetries. We argue that the same evolutionary mechanisms should apply across geographical regions to maintain the roughly 1:10 ratio, while cultural factors, such as pressure against left-hand use, moderate the magnitude of the prevalence of left-handedness. Although handedness appears as a straightforward trait, there is no universal agreement on how to assess it. Therefore, we urge researchers to fully report study and participant characteristics as well as the detailed procedure by which handedness was assessed and make raw data publicly available. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Preschool language ability is predicted by toddler hand preference trajectories.

Prior work has found links between consistency in toddler handedness for the fine motor skill role-differentiated bimanual manipulation (RDBM), and language development at 2 and 3 years of age. The current study investigated whether consistency in handedness from 18 to 24 months (N = 90) for RDBM predicts receptive and expressive language abilities assessed using the Preschool Language Scales 5th edition (PLS-5) at 5 years old. Latent class growth analyses identified 3 stable RDBM hand preference trajectories: a left hand preference with moderate right hand use (left-moderate right), a right hand preference with moderate left hand use (right-moderate left), and a right hand preference with only mild left hand use (right-mild left). At 5 years of age, children with a right-mild left handedness trajectory as toddlers scored significantly higher on receptive and expressive language abilities compared to children with a left-moderate right hand preference. Children with a right-mild left hand preference for RDBM also scored significantly higher on receptive language abilities compared to children with a right-moderate left RDBM hand preference. Children with left-moderate right and children with a right-moderate left hand preference for RDBM as toddlers did not differ in receptive or expressive language abilities at 5 years. Results indicate that individual differences in hand preference consistency for fine motor skill in toddlerhood have cascading effects on language outcomes into the preschool years. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Instructor Opinions on the Use of Turkish Folk Music of Syncopated Style in Cello Training

The ability of the music teacher to provide a more qualified education in the professional life and to express himself musically is directly proportional to the quality of the previous instrument training. Studies revealed that the Turkish music products are not used sufficiently in the instrument training given by the institutions of music education and the inadequacy of the customized Turkish music products for use in education.&#x0D; &#x0D; From this point of view, the aim of this study is to determine the usage status of works and studies of Turkish folk music of syncopated style arranged for cello training and the effects of theoretical knowledge, technical and musical readiness on performing works with syncopated method and to determine the effects of their level and to reveal the problems experienced by the students and to offer solutions for these problems in the direction of the opinions of the instructors who give cello training to music teacher education undergraduates. &#x0D; &#x0D; The data were collected through a semi-structured interview form developed by the researcher. In the analysis of the collected data, descriptive analysis method was used from qualitative research methods.&#x0D; &#x0D; When the data were analyzed, it can be concluded that Turkish folk music works and studies of syncopated style used in cello education are numerically inadequate, that the limited available resources are higher than the levels of the students, and that the students have a good theoretical knowledge level about the subject but the levels of readiness in terms of cello techniques in practice are insufficient to perform these tunes. The most important problems experienced by students in performing these melodies are level difficulty, sight-reading, left hand position shifts and use of bows.

On the Other Hand: Left Hand, Right Brain, Mental Disorder, and History by Howard I. Kushner

Reviewed by: On the Other Hand: Left Hand, Right Brain, Mental Disorder, and History by Howard I. Kushner Lauren Julius Harris Howard I. Kushner. On the Other Hand: Left Hand, Right Brain, Mental Disorder, and History. Baltimore: Johns Hopkins University Press, 2017. xiii + 216 pp. Ill. $26.95 (978-1-4214-2333-3). How to explain handedness, and why do most people prefer their right? The question goes back at least as far as Ancient Greece, when Plato linked handedness to culture, and Aristotle called it natural and inherited. Howard Kushner, author of On the Other Hand, and himself left-handed—among the 10 to 12 percent—calls his interest “as psychiatrists used to say, . . . overdetermined, a combination of personal experience overlaid with clinical observations” (p. 11). It began with the lack of left-handed desks in school, which he’s sure contributed to his inability to master cursive writing. In twelve chapters and just 154 pages, Kushner tells how laterality researchers address key questions about handedness: how to measure it, whether only humans show it, its proposed cultural, genetic, and evolutionary origins, and whether left-handedness is associated with such characteristics and conditions as criminality, accident-proneness, and physical and mental disorders ranging from stuttering and reading disability to autism and schizophrenia, along with a dramatically shorter lifespan—but also whether left-handers excel in certain cognitive domains, including art and mathematics, and in sports like fencing and boxing. Anyone seeking an introduction to the enormous, often abstruse literature on handedness, current and past, can learn much from this book. Here are examples from some of the chapters: “By the Numbers” examines measurement issues, provides a questionnaire for self-assessment, and shows how in decades past and still today in certain parts of the world, practices against left-hand use, especially for writing and utensil use, reduced left-handers’ numbers well below the current figure, at least based on these measures. Their lifespans, however, won’t be reduced: such claims are “overwhelmingly rejected” (p. 36) by laterality researchers. “Genes and Kangaroos” notes that certain gene variants may be linked to “hand skill” and that other species show limb preference (kangaroos and chimpanzees, for example), although not to the same degree as humans. It also corrects certain pop-psychology ideas about handedness and lateralization of function, among them that the hemispheres have “completely different tasks” (p. 10) and that left-handers are the only ones “in their right minds.” “Disability, Ability, and the Left Hand” reports a “lack of robust connections” between left-handedness and learning disorders (p. 147) and, similarly, for autism and schizophrenia. “Criminals or Victims” describes the historical roots of the “tension” between characterizations of left-handers as abnormal and disabled and the idea that they’re “talented victims of discrimination” (p. 15). “Changing Hands, Tying Tongues” scrutinizes historical and current evidence linking left-handedness and stuttering and asks whether King George VI’s struggles with stuttering (dramatized in the film The King’s Speech) came from having [End Page 568] been, like many left-handed children in the early 1900s, forced to write with the right hand. “Genetic Models and Selective Advantage” goes deeper into genetic models and describes the “fighting hypothesis” designed to explain not only why left-handers have always been a minority but why they exist at all. It supposes that in potentially deadly encounters between left- and right-handers, left-handers, being a minority, were likelier to prevail from having more opportunities to face right-handers than right-handers had against them, and that the same advantage can explain their success in close-interactive contests like fencing and boxing. On so large a canvas, lapses are understandable. For example, laterality researcher M. Philip Bryden’s first name was Mark, not “Michael” (p. 102); Behavioral Neurology isn’t the title of Norman Geschwind’s “1965 landmark study” (p. 92); it’s the name of the discipline he helped create; there’s no evidence that Julius Caesar was “left-handed” (p. 50); and while it’s correct that for the “vast majority of left-handers, like right-handers,” the left hemisphere leads for speech and language based on evidence of speech loss and impaired...

CULTURAL COMMUNICATION:AN ANTHROPOLOGICALVIEWS ON THE USE OF LEFT HAND BY THE SOCIETY AROUND KAMPUS PERAK, SOUTHEAST SULAWESI

The phenomenon of left hand use (which is culturally unusual) by the community around the Campus Perak urges the authors explore its background from the cultural approach in an ethnographic study. There had been some community practices around Campus Perak in Southeast Sulawesi that are considered as anomalies by outsiders' perspectives. Among those anomalies is the use of the left hand in giving something to others, such as serving food, writing, and signing letters. This paper explores the use of the left hand amidst the society around the Perak Campus. In general, several ethnic groups inhabit the area around campus, thus no particular ethnic dominates the use of everyday language. Tribal languages are commonly used among people from the similar ethnicity. In the context offormal ceremonies involving community outside Campus Perak, the use of left hand was seen as a culture shock. Meanwhile, the use of left hand was (intra)culturally acceptable since children were taught using left hands by their parents. &#x0D; KEY WORDS: Left Hand, Cultural Communication, Campus Perak, Society

Toddler hand preference trajectories predict 3-year language outcome.

A growing body of work suggests that early motor experience affects development in unexpected domains. In the current study, children's hand preference for role-differentiated bimanual manipulation (RDBM) was measured at monthly intervals from 18 to 24 months of age (N = 90). At 3 years of age, children's language ability was assessed using the Preschool Language Scales 5th edition (PLS™-5). Three distinct RDBM hand preference trajectories were identified using latent class growth analysis: (1) children with a left hand preference but a moderate amount of right hand use; (2) children with a right hand preference but a moderate amount of left hand use; and (3) children with a right hand preference and only a mild amount of left hand use. Stability over time within all three trajectories indicated that children did not change hand use patterns from 18 to 24 months. Children with the greatest amount of preferred (i.e., right) hand use demonstrated higher expressive language scores compared to children in both trajectories with moderate levels of non-preferred hand use. Children with the greatest amount of right hand use also had higher scores for receptive language compared to children with a right hand preference but moderate left hand use. Results support that consistency in handedness as measured by the amount of preferred hand use is related to distal language outcomes in development.

Modulating Children's Manual Preference Through Spontaneous Nondominant Hand Use.

We evaluated the effect of repeated use of the nonpreferred hand on young children's manual preference by positioning toys in the left hemifield in egocentric coordinates to induce right-handed 4-5-year-olds to use their left hands spontaneously. We induced motor activities in the laterally biased workspace by presenting tasks in a ludic context over different days, similar to their daily kindergarten experience. Preceding and following these lateralized experiences, the children were tested on a task requiring reaching, grasping, and inserting cards into a slot. In the 1-day retention assessment, we found that repeated use of the nonpreferred left hand in the previous phase led to increased use of the left hand to perform the probing task. Following 14 days of rest, the children with induced left-hand experiences used exclusively their left hands to manipulate the leftmost card positions. We propose that repeated use of the nonpreferred left hand leads to increased confidence to plan left-handed movements for subsequent tasks.

Effect of target animacy on hand preference in Sichuan snub-nosed monkeys (Rhinopithecus roxellana).

Twenty-eight captive Sichuan snub-nosed monkeys (Rhinopithecus roxellana) were involved in the current study. Many individuals showed handedness, with a modest tendency toward left-hand use especially for animate targets, although no group-level handedness was found. There was no significant gender difference in the direction and strength of hand preference for both targets. Females showed a significantly higher overall rate of actions toward animate targets than inanimate targets for both hands, whereas males displayed almost the reversed pattern. There were no significant interactions between lateral hand use and target animacy for either males or females. Most individuals showed rightward or leftward laterality shift trends between inanimate and animate targets. These findings to some extent support the existence of a potential trend concerning a categorical neural distinction between targets demanding functional manipulation (inanimate objects) and those demanding social manipulation (animate objects), even though specialized hand preference based on target animacy has not been fully established in this arboreal Old World monkey species.

Increased functional connectivity between cortical hand areas and praxis network associated with training-related improvements in non-dominant hand precision drawing

Chronic forced use of the non-dominant left hand yields substantial improvements in the precision and quality of writing and drawing. These changes may arise from increased access by the non-dominant (right) hemisphere to dominant (left) hemisphere mechanisms specialized for end-point precision control. To evaluate this prediction, 22 healthy right-handed adults underwent resting state functional connectivity (FC) MRI scans before and after 10 days of training on a left hand precision drawing task. 89% of participants significantly improved left hand speed, accuracy, and smoothness. Smoothness gains were specific to the trained left hand and persistent: 6 months after training, 71% of participants exhibited above-baseline movement smoothness. Contrary to expectations, we found no evidence of increased FC between right and left hemisphere hand areas. Instead, training-related improvements in left hand movement smoothness were associated with increased FC between both sensorimotor hand areas and a left-lateralized parieto-prefrontal network implicated in manual praxis. By contrast, skill retention at 6 months was predicted by changes including decreased FC between the representation of the trained left hand and bilateral sensorimotor, parietal, and premotor cortices, possibly reflecting consolidation and a disengagement of early learning processes. These data indicate that modest amounts of training (<200min total) can induce substantial, persistent improvements the precision and quality of non-dominant hand control in healthy adults, supported by strengthened connectivity between bilateral sensorimotor hand areas and a left-lateralized parieto-prefrontal praxis network.

Handedness for Unimanual Grasping in 564 Great Apes: The Effect on Grip Morphology and a Comparison with Hand Use for a Bimanual Coordinated Task.

A number of factors have been proposed to influence within and between species variation in handedness in non-human primates. In the initial study, we assessed the influence of grip morphology on hand use for simple reaching in a sample of 564 great apes including 49 orangutans Pongo pygmaeus, 66 gorillas Gorilla gorilla, 354 chimpanzees Pan troglodytes and 95 bonobos Pan paniscus. Overall, we found a significant right hand bias for reaching. We also found a significant effect of the grip morphology of hand use. Grasping with the thumb and index finger was more prevalent in the right compared to left hand in all four species. There was no significant sex effect on the patterns of handedness. In a subsample of apes, we also compared consistency in hand use for simple reaching with previously published data on a task that measures handedness for bimanual actions. We found that the ratio of subjects with consistent right compared to left hand use was more prevalent in bonobos, chimpanzees and gorillas but not orangutans. However, for all species, the proportion of subjects with inconsistent hand preferences between the tasks was relatively high suggesting some measures may be more sensitive in assessing handedness than others.

Does target animacy influence manual laterality of monkeys? First answer from northern pig-tailed macaques (Macaca leonina).

The evolutionary origin of human right-handedness remains unclear. Many factors such as emotion and tool use have been implicated in primate handedness evolution. With regard to emotional lateralization, most related research focuses on facial asymmetry and behavioral laterality under the non-social context, whereas few studies investigate social laterality. This study, for the first time, investigates the effect of target animacy on hand preference in Old World monkeys, compares our findings with previous related studies in great apes and humans, and aids in filling the knowledge gap on primate handedness evolution. Nine captive northern pig-tailed macaques (Macaca leonina) were chosen as focal subjects in this study. There was no group-level handedness for both animate and inanimate targets. No significant interaction was found between lateral hand use and target animacy. Left-hand use was more frequent than right-hand use for animate targets, whereas right-hand use was more frequent than left-hand use for inanimate targets, both of which demonstrate no significant level. On the whole, northern pig-tailed macaques showed a similar tendency as that in great apes and humans. Regarding handedness linked with emotive stimuli, it is likely that Old World monkeys, great apes and humans evolved from a common ancestor.

Abstract W P138: Hand Asymmetries in the Control of Grasp Force Post-Stroke

Background and Purpose: Stroke survivors have difficulty overcoming deficits associated with grasping ability that differ for their right and left hand. However, grasp force deficits unique to each hand are not clearly characterized. The purpose of this study was to determine right and left hand differences in control of grasp force for individuals who were right handed pre-stroke. Methods: Twenty-one participants (13 with left hemispheric &amp; 8 with right hemispheric stroke) completed clinical assessments and performed hand-grasp tasks using Instrumented Strain Gauges embedded with force sensors. Pre / post stroke hand preference scores were obtained using the self-reported Edinburgh Handedness Inventory (EHI). A right and left hand Reference Force (RF) was based on 20% of the right and left maximum grasp force. The Matching Force (MF) was performed by the opposite hand. Visual feedback represented by a horizontal line on a computer monitor displayed the 20% RF. MF, performed without visual feedback, indicated whether the participant overshot or undershot the RF and was quantified as the Constant Error. Results: EHI scores for right hemispheric stroke patients were 0.86 / 1.00 pre, and 0.92 / 1.00 post stroke, indicating greater right hand use post stroke. EHI scores for left hemispheric stroke patients were 0.91 / 1.00 pre, and 0.59 / 1.00 post stroke, indicating less right hand use and greater left hand use post stroke. The ANOVA showed a significant three-way interaction for matching hand *reference hand* affected side F(2, 38) =4.42, p &lt; 0.05) for constant error. Right hemispheric stroke patients showed left hand MF undershoots for right hand RF (p &lt; 0.05). Left hemispheric stroke patients showed right hand MF undershoots for left hand RF (p &lt; 0.05). Conclusions: Shifts in handedness scores and asymmetries in force matching performance were dependent on lesion location. From a clinical perspective, stroke survivors may not be aware of how hand differences in the control of grasp force influence their ability to perform everyday tasks despite knowing that one hand may be weaker than the other. This suggests using a lesion-side specific treatment technique to improve awareness and function when performing unimanual and bimanual hand-grasp tasks.

Modulation of manual preference induced by lateralized practice diffuses over distinct motor tasks: age-related effects.

In this study we investigated the effect of use of the non-preferred left hand to practice different motor tasks on manual preference in children and adults. Manual preference was evaluated before, immediately after and 20 days following practice. Evaluation was made with tasks of distinct levels of complexity requiring reaching and manipulation of cards at different eccentricities in the workspace. Results showed that left hand use in adults induced increased preference of that hand at the central position when performing the simple task, while left hand use by the children induced increased preference of the left hand at the rightmost positions in the performance of the complex task. These effects were retained over the rest period following practice. Kinematic analysis showed that left hand use during practice did not lead to modification of intermanual performance asymmetry. These results indicate that modulation of manual preference was a consequence of higher frequency of use of the left hand during practice rather than of change in motor performance. Findings presented here support the conceptualization that confidence on successful performance when using a particular limb generates a bias in hand selection, which diffuses over distinct motor tasks.

Biased hand use in captive emperor tamarins (Saguinus imperator).

Comparing forelimb use across primates can improve the understanding of the mechanisms and functions of brain asymmetry. We broadened the comparative framework by investigating hand use biases across spontaneous behaviors in 11 captive emperor tamarins of 2 family groups. We found a right preference across 58% of pooled unimanual bouts and 60% of all tasks. The maximum biases for a single task were 88% right-hand use and 78% left-hand use. On an individual basis, for most tasks, 6 tamarins preferred their right hand, 2 tamarins the left, and 2 animals were ambidextrous. Only a single tamarin did not switch between left and right hand bias according to task, but displayed a consistent right-hand bias. Our accompanying review of the 2 dozen previous callitrichid hand use studies confirms this picture. Across the board, these report hand preferences for single tasks. Task specialization is found in less than half of the studies, hand specialization in less than a third, whereas population level handedness is almost never reported. Importantly, right-hand use is preponderant, but very rarely consistent across tasks or subjects. This might be attributable to the fact that often-employed simple (food-reaching) tasks may not be coupled to a specialized hemisphere and therefore not constrain forelimb use. A better understanding of what causes directional forelimb use in callitrichids and other animals is currently hampered by a lack of standardized methods including measurement criteria, task difficulty, and social setting as well as a dearth of taxonomic diversity and field studies.