Hand preference, performance abilities, and hand selection in children

How Might the Relation of the Development of Hand Preferences to the Development of Cognitive Functions be Examined During Infancy: A Sketch?

Investigations of the relation of the development of hand preferences to the development of other sensorimotor and cognitive abilities are plagued by confusing and contradictory results. In part, the confusion derives from the failure to create accurate, appropriate, and reliable descriptions of the development of hand preferences and the cognitive or sensorimotor ability of interest. This paper sketches an ideal longitudinal study (from birth through 5 years) with a large sample size that should provide reliable evidence for the understanding of the relation of hand preferences to cognitive development. Since hand preference differences would affect the way infants engage in manual actions with objects and these differences would likely affect how they come to comprehend object relations, differences in the development of cognition across handedness groups would be a good test of certain forms of embodiment theory.

The parietal lobe and the vestibular system

The vestibular cortex differs in various ways from other sensory cortices. It consists of a network of several distinct and separate temporoparietal areas. Its core region, the parietoinsular vestibular cortex (PIVC), is located in the posterior insula and retroinsular region and includes the parietal operculum. The entire network is multisensory (in particular, vestibular, visual, and somatosensory). The peripheral and central vestibular systems are bilaterally organized; there are various pontomesencephalic brainstem crossings and at least two transcallosal connections of both hemispheres, between the PIVC and the motion-sensitive visual cortex areas, which also mediate vestibular input. Structural and functional vestibular dominance characterizes the right hemisphere in right-handers and the left hemisphere in left-handers. This explains why right-hemispheric lesions in right-handers more often generally cause hemispatial neglect and the pusher syndrome, both of which involve vestibular function. Vestibular input also contributes to cognition and may determine individual lateralization of brain functions such as handedness. Bilateral organization is a major key to understanding cortical functions and disorders, for example, the visual-vestibular interaction that occurs in spatial orientation. Although the vestibular cortex is represented in both hemispheres, there is only one global percept of body position and motion. The chiefly vestibular aspects of the multiple functions and disorders of the parietal lobe dealt with in this chapter cannot be strictly separated from various multisensory vestibular functions within the entire brain.

The development of neuromotor skills and hand preference during infancy

Assessing infant handedness has been controversial. Different assessment techniques and theoretical approaches produce different results. Evidence from a dynamic systems perspective showed that the development of postural control during infancy affects the expression of an infant's handedness. However, others found that developmental changes in postural control influenced the amount of symmetrical (bimanual) reaching during infancy, but not hand preference. Since most studies of infant handedness use age to assess development, perhaps measures of an infant's developing neuromotor control, irrespective of age, would better predict changes in an infant's hand preference. To assess neuromotor development, items from [Touwen's (1976) Neurological development in infancy. Lavenham, Suffolk: The Lavenham Press, LTD]. "Group III" indices were used. These items assess developmental changes in neuromotor abilities throughout the 6-14-month age period. Hand preference for acquiring objects was measured during these same months. Group Based Trajectory Models (GBTM) of 380 infants identified four different groups of infants according to the trajectory of the development of their hand preferences (32% Early Right, 12% Early Left, 25% Late Right, 30% No Preference). A multilevel model was used to compare these four developmental trajectories according to age and neuromotor development. Age, not neuromotor development, is a better predictor of differences in developmental trajectories of the four hand preference groups. However, Late Right infants are significantly less developed at 6 months than No Preference, Early Right and Left infants and both Early Right and Left infants are most advanced at 6 months. All groups exhibit similar rates of neuromotor development indicating no "catch-up" by the Late Right infants. Thus, any assessment of infant handedness will incorporate necessarily four groups of infants with differently developing hand preferences and neuromotor abilities.

Is Hand Selection Modulated by Cognitive-perceptual Load?

Previous studies proposed that selecting which hand to use for a reaching task appears to be modulated by a factor described as "task difficulty". However, what features of a task might contribute to greater or lesser "difficulty" in the context of hand selection decisions has yet to be determined. There has been evidence that biomechanical and kinematic factors such as movement smoothness and work can predict patterns of selection across the workspace, suggesting a role of predictive cost analysis in hand-selection. We hypothesize that this type of prediction for hand-selection should recruit substantial cognitive resources and thus should be influenced by cognitive-perceptual loading. We test this hypothesis by assessing the role of cognitive-perceptual loading on hand selection decisions, using a visual search task that presents different levels of difficulty (cognitive-perceptual load), as established in previous studies on overall response time and efficiency of visual search. Although the data are necessarily preliminary due to small sample size, our data suggested an influence of cognitive-perceptual load on hand selection, such that the dominant hand was selected more frequently as cognitive load increased. Interestingly, cognitive-perceptual loading also increased cross-midline reaches with both hands. Because crossing midline is more costly in terms of kinematic and kinetic factors, our findings suggest that cognitive processes are normally engaged to avoid costly actions, and that the choice not-to-cross midline requires cognitive resources.

Infant motor activity during sleep: Simultaneous use of two actigraphs comparing right and left legs

Motor asymmetry during the first hours of sleep documented in adults found higher activity in the non-dominant limb. The stage of development at which such asymmetries first appear is unknown. Twenty healthy infants were followed from 7 to 12months of age, at 3-week intervals, comparing motor activity of the right and left legs during sleep using twin actigraphs (AMI). Hour-by-hour analysis of the first seven hours of nocturnal sleep found no consistent difference in activity levels between the right and left legs. Using the standard algorithm for infants, which provides an overall estimate of sleep quality, revealed discrepancies in night waking episodes (Right versus Left) in 33% of the nights. Results pertaining to leg movement suggest that motor asymmetry is not yet present during the first year of life. However, given the large discrepancies in the detection of night waking, further investigation of the developmental course of circadian motor asymmetry is warranted.

Prefrontal Hemodynamics in Toddlers at Rest: A Pilot Study of Developmental Variability

Functional near infrared spectroscopy (fNIRS) is a non-invasive functional neuroimaging modality. Although, it is amenable to use in infants and young children, there is a lack of fNIRS research within the toddler age range. In this study, we used fNIRS to measure cerebral hemodynamics in the prefrontal cortex (PFC) in 18-36 months old toddlers (n = 29) as part of a longitudinal study that enrolled typically-developing toddlers as well as those "at risk" for language and other delays based on presence of early language delays. In these toddlers, we explored two hemodynamic response indices during periods of rest during which time audiovisual children's programming was presented. First, we investigate Lateralization Index, based on differences in oxy-hemoglobin saturation from left and right prefrontal cortex. Then, we measure oxygenation variability (OV) index, based on variability in oxygen saturation at frequencies attributed to cerebral autoregulation. Preliminary findings show that lower cognitive (including language) abilities are associated with fNIRS measures of both lower OV index and more extreme Lateralization index values. These preliminary findings show the feasibility of using fNIRS in toddlers, including those at risk for developmental delay, and lay the groundwork for future studies.

Lateralization of ERPs to speech and handedness in the early development of Autism Spectrum Disorder

BACKGROUND

Language is a highly lateralized function, with typically developing individuals showing left hemispheric specialization. Individuals with autism spectrum disorder (ASD) often show reduced or reversed hemispheric lateralization in response to language. However, it is unclear when this difference emerges and whether or not it can serve as an early ASD biomarker. Additionally, atypical language lateralization is not specific to ASD as it is also seen more frequently in individuals with mixed- and left-handedness. Here, we examined early asymmetry patterns measured through neural responses to speech sounds at 12 months and behavioral observations of handedness at 36 months in children with and without ASD.

METHODS

Three different groups of children participated in the study: low-risk controls (LRC), high risk for ASD (HRA; infants with older sibling with ASD) without ASD, and HRA infants who later receive a diagnosis of ASD (ASD). Event-related potentials (ERPs) to speech sounds were recorded at 12 months. Utilizing a novel observational approach, handedness was measured by hand preference on a variety of behaviors at 36 months.

RESULTS

At 12 months, lateralization patterns of ERPs to speech stimuli differed across the groups with the ASD group showing reversed lateralization compared to the LRC group. At 36 months, factor analysis of behavioral observations of hand preferences indicated a one-factor model with medium to high factor loadings. A composite handedness score was derived; no group differences were observed. There was no association between lateralization to speech at 12 months and handedness at 36 months in the LRC and HRA groups. However, children with ASD did show an association such that infants with lateralization patterns more similar to the LRC group at 12 months were stronger right-handers at 36 months.

CONCLUSIONS

These results highlight early developmental patterns that might be specific to ASD, including a potential early biomarker of reversed lateralization to speech stimuli at 12 months, and a relation between behavioral and neural asymmetries. Future investigations of early asymmetry patterns, especially atypical hemispheric specialization, may be informative in the early identification of ASD.

Motor-Enriched Learning Activities Can Improve Mathematical Performance in Preadolescent Children

Objective: An emerging field of research indicates that physical activity can benefit cognitive functions and academic achievements in children. However, less is known about how academic achievements can benefit from specific types of motor activities (e.g., fine and gross) integrated into learning activities. Thus, the aim of this study was to investigate whether fine or gross motor activity integrated into math lessons (i.e., motor-enrichment) could improve children's mathematical performance. Methods: A 6-week within school cluster-randomized intervention study investigated the effects of motor-enriched mathematical teaching in Danish preadolescent children (n = 165, age = 7.5 ± 0.02 years). Three groups were included: a control group (CON), which received non-motor enriched conventional mathematical teaching, a fine motor math group (FMM) and a gross motor math group (GMM), which received mathematical teaching enriched with fine and gross motor activity, respectively. The children were tested before (T0), immediately after (T1) and 8 weeks after the intervention (T2). A standardized mathematical test (50 tasks) was used to evaluate mathematical performance. Furthermore, it was investigated whether motor-enriched math was accompanied by different effects in low and normal math performers. Additionally, the study investigated the potential contribution of cognitive functions and motor skills on mathematical performance. Results: All groups improved their mathematical performance from T0 to T1. However, from T0 to T1, the improvement was significantly greater in GMM compared to FMM (1.87 ± 0.71 correct answers) (p = 0.02). At T2 no significant differences in mathematical performance were observed. A subgroup analysis revealed that normal math-performers benefitted from GMM compared to both CON 1.78 ± 0.73 correct answers (p = 0.04) and FMM 2.14 ± 0.72 correct answers (p = 0.008). These effects were not observed in low math-performers. The effects were partly accounted for by visuo-spatial short-term memory and gross motor skills. Conclusion: The study demonstrates that motor enriched learning activities can improve mathematical performance. In normal math performers GMM led to larger improvements than FMM and CON. This was not the case for the low math performers. Future studies should further elucidate the neurophysiological mechanisms underlying the observed behavioral effects.

Using Bishop's Card Reaching Task to Assess Hand Preference in 8- to 10-Year-Old Czech Children

Hand preference is one of the most apparent functional asymmetry in humans. Under contralateral control, performance is more proficient with the preferred hand; however, the difference between the two hands is greater in right handers, considering left handers generally display less cerebral lateralization. One method of evaluating hand preference is Bishop's card reaching task; however, information regarding validity and sensitivity with children in limited. This study assessed the relationship between Bishop's card reaching task and five hand preference tasks in 8- to 10-year-old typically-developing children from the Czech Republic (N = 376). Structural equation modelling identified a one factor model as the most suitable, including Bishop's card reaching task and three hand preference tasks (ringing, throwing, and rolling with dice). The factor validity (.89) and sensitivity of Bishop's card reaching task (90% to 97%) provided a very good identification of hand preference. These results support the suitability of Bishop's card reaching task as a separate test for determining hand preference in children. Accordingly, we suggest that the assessment of handedness, particularly in neurodevelopmental disorders where the proportion of right-handers and left-handers is disrupted (e.g., children with DCD or ADHD), should make use of Bishop's card reaching task alongside other unimanual tasks.

Hemispheric speech lateralisation in the developing brain is related to motor praxis ability

Commonly displayed functional asymmetries such as hand dominance and hemispheric speech lateralisation are well researched in adults. However there is debate about when such functions become lateralised in the typically developing brain. This study examined whether patterns of speech laterality and hand dominance were related and whether they varied with age in typically developing children. 148 children aged 3-10 years performed an electronic pegboard task to determine hand dominance; a subset of 38 of these children also underwent functional Transcranial Doppler (fTCD) imaging to derive a lateralisation index (LI) for hemispheric activation during speech production using an animation description paradigm. There was no main effect of age in the speech laterality scores, however, younger children showed a greater difference in performance between their hands on the motor task. Furthermore, this between-hand performance difference significantly interacted with direction of speech laterality, with a smaller between-hand difference relating to increased left hemisphere activation. This data shows that both handedness and speech lateralisation appear relatively determined by age 3, but that atypical cerebral lateralisation is linked to greater performance differences in hand skill, irrespective of age. Results are discussed in terms of the common neural systems underpinning handedness and speech lateralisation.

Handedness in Children With Autism Spectrum Disorder

The left hemisphere is usually predominant in manual skills and language, suggesting a link between hand dominance and language. Studies of autism spectrum disorder show atypical handedness; however, few have examined language-handedness associations. Handedness, assessed by task performance, and standardized receptive and expressive language tests were completed in 110 autism spectrum disorder children (96 boys; M age = 8.3 years, SD = 3.8) and 45 typically developing children (37 boys; M age = 8.6 years, SD = 4.3), 3 to 17 years of age. The autism spectrum disorder group had a lower handedness score (was less strongly lateralized) than the control group. In the autism spectrum disorder group, there was a small effect of handedness on language; right-handers had better language than non-right-handers. Results suggest poorer language prognosis may be associated with left- or mixed-handedness in autism spectrum disorder.

Lateral asymmetry as a function of motor practice type of complex upper- and lower-limb movement in young children

The influence of different motor practice types on lateral asymmetry of performance was investigated in 40 preschool children. Lateral preference was measured prior the experiment. For the purpose of present study dribbling a ball with a hand and foot was used to assess lateral asymmetry of performance before and after three different motor practice types. Motor practice with the non-dominant, dominant, and both (contralateral) limbs took place in the indoor facility 4 times/week for 6 weeks. Each session lasted 30-40 min. Our results showed that unilateral practice of dribbling is more beneficial for diminishing lateral asymmetry of performance in comparison to bilateral practice. Moreover, participants who practiced with their dominant limb diminished lateral asymmetry of performance the most and made the largest overall improvement. We did not find important differences between acquisitions of dribbling with upper- and lower-extremity. In this sense, the results support the notion of lateral asymmetry of performance to be task-specific.

The Influence of Hand Preference on Grip Strength in Children and Adolescents; A Cross-Sectional Study of 2284 Children and Adolescents

Introduction

In adults the preferred hand is often considered to be around 10% stronger than the non-preferred hand. Whether the same is true for children and adolescents remains unclear. The objective of this study is therefore to determine whether there is a difference in grip strength between the preferred and non-preferred hand in developing children, to establish whether this difference is similar for children of a different gender or hand preference, and whether there is a difference in grip strength of the preferred hand of left-preferent (LP) and right-preferent (RP) children.

Design

Cross-sectional study.

Participants

Participants were recruited from schools in the northern provinces of the Netherlands. The study included healthy children and adolescents in the age range of 4–17 years.

Outcome Measures

Each child was allowed a total of four attempts using the JAMAR hand dynamometer, two attempts with each hand. All individual attempts were scored. Hand preference was determined by asking which hand was used to write, or in the case of 4- and 5-year-olds, which hand was used to draw a shape.

Results

The study population comprised 2284 children and adolescents. RP boys and girls scored significantly higher with their preferred hand, the difference amounting to 9.5 and 10.1% respectively. LP girls scored significantly higher with their preferred hand, but this difference was only 3.0%. For LP boys no significant difference was found in favor of either hand. LP children score higher with the non-preferred hand and tie scores on both hands more often than RP children.

Conclusion

The 10% rule of hand preference is applicable to RP children ranging in age between 4 and 17 years, but not to LP children. In contrast to LP boys, LP girls are generally significantly stronger with their preferred hand.

Left-Right Axis Differentiation and Functional Lateralization: a Haplotype in the Methyltransferase Encoding Gene SETDB2 Might Mediate Handedness in Healthy Adults

Handedness is a multifactorial trait, and genes contributing to the differentiation of the left-right axis during embryogenesis have been identified as a major gene group associated with this trait. The methyltransferase SETDB2 (SET domain, bifurcated 2) has been shown to regulate structural left-right asymmetry in the vertebrate central nervous system by suppressing fgf8 expression. Here, we investigated the relation of genetic variation in SETDB2-and its paralogue SETDB1-with different handedness phenotypes in 950 healthy adult participants. We identified a haplotype on SETDB2 for which homozygous individuals showed a significantly lower lateralization quotient for handedness than the rest of the cohort after correction for multiple comparisons. Moreover, direction of handedness was significantly associated with genetic variation in this haplotype. This effect was mainly, but not exclusively, driven by the sequence variation rs4942830, as individuals homozygous for the A allele of this single nucleotide polymorphism had a significantly lower lateralization quotient than individuals with at least one T allele. These findings further confirm a role of genetic pathways relevant for structural left-right axis differentiation for functional lateralization. Moreover, as the protein encoded by SETDB2 regulates gene expression epigenetically by histone H3 methylation, our findings highlight the importance of investigating the role of epigenetic modulations of gene expression in relation to handedness.

The influence of M. P. Bryden's work on lateralization of motor skill: Is the preferred hand selected for and better at tasks requiring a high degree of skill?

One question of interest to Dr M. P. Bryden was how skilled motor behaviour, task complexity, and the degree of handedness are linked. His research suggested that there would be dissociation between hand preference and performance for skilled versus unskilled actions. The thought was that "simple" or unskilled tasks such reaching or grasping could be performed equally well by either hand, and thus either could be selected. Skilled tasks such as fine manipulation would be performed best by the preferred hand and thus it would be selected more frequently. Over the past two decades, researchers have attempted to determine whether such a definition of skilled action best encapsulates the specialization of the preferred hand. The current paper will review M. P. Bryden's research on skilled motor behaviour, as well as more recent work, and explore the question of whether the preferred hand is actually superior and preferred for actions requiring manipulation.

Asymmetrical motor behaviour as a window to early leg preference: a longitudinal study in infants 7-12 months of age

This longitudinal study explored leg preference in infancy during half-kneel pulling-to-stand (PTS) and asymmetrical four-point kneeling, which is part of the typical motor repertoire of infants. The special characteristics of the half-kneel PTS as a discrete task, performed in a bilateral context provide the opportunity to explore leg preference during an asymmetrical behaviour. Twenty-seven infants were observed in their homes, every 3 weeks between the ages of 7-12 months. Leg preference was determined by the "lead-out" limb used as the infants pulled to stand from the half-kneeling position (half-kneel PTS). As a complementary measure, the leading leg during asymmetrical four-point kneeling and crawling ("asymmetrical four-point patterns") was used in the 10 infants who developed these patterns. The infants studied showed a general preference for using a leading leg during half-kneel PTS, which was mostly consistent over the study period. A strong correlation was found between leg preferences during half-kneel PTS and asymmetrical four-point patterns. The findings documented functional asymmetry in infant lower limbs during half-kneel PTS and asymmetrical four-point patterns, highlighting the importance of the tasks used to define leg preference.

Neurodevelopmental Outcomes and Neural Mechanisms Associated with Non-right Handedness in Children Born Very Preterm

Non-right handedness (NRH) is reportedly more common in very preterm (VPT; <32 weeks' gestation) children compared with term-born peers, but it is unclear whether neonatal brain injury or altered brain morphology and microstructure underpins NRH in this population. Given that NRH has been inconsistently reported to be associated with cognitive and motor difficulties, this study aimed to examine associations between handedness and neurodevelopmental outcomes in VPT 7-year-olds. Furthermore, the relationship between neonatal brain injury and integrity of motor tracts (corpus callosum and corticospinal tract) with handedness at age 7 years in VPT children was explored. One hundred seventy-five VPT and 69 term-born children completed neuropsychological and motor assessments and a measure of handedness at 7 years' corrected age. At term-equivalent age, brain injury on MRI was assessed and diffusion tensor measures were obtained for the corpus callosum and posterior limb of the internal capsule. There was little evidence of stronger NRH in the VPT group compared with term controls (regression coefficient [b] -1.95, 95% confidence interval [-5.67, 1.77]). Poorer academic and working memory outcomes were associated with stronger NRH in the VPT group. While there was little evidence that neonatal unilateral brain injury was associated with stronger NRH, increased area and fractional anisotropy of the corpus callosum splenium were predictive of stronger NRH in the VPT group. VPT birth may alter the relationship between handedness and academic outcomes, and neonatal corpus callosum integrity predicts hand preference in VPT children at school age. (JINS, 2015, 21, 610-621).

Is strength of handedness reliable over repeated testing? An examination of typical development and autism spectrum disorder

Despite a lack of agreement concerning the age at which adult-like patterns of handedness emerge, it is generally understood that hand preference presents early in life and development is variable. Young children (ages 3-5 years) are described as having weak hand preference; however, older children (ages 7-10 years) display stronger patterns. Here, strength of hand preference refers to reliable use of the preferred hand. In comparison to their typically developing (TD) peers, individuals with autism spectrum disorder (ASD) are described as having a weak hand preference. This study aimed to extend the literature to assess three measures of handedness (Waterloo Handedness Questionnaire - WHQ, Annett pegboard - AP, and WatHand Cabinet Test - WHCT) in two repeated sessions. The first research question aimed to delineate if the strength of hand use changes across testing sessions as a function of age in typical development. Right-handed children reported a reliable preference for the right hand on the WHQ, similar to adults. A marginally significant difference was revealed between 3- to 4- and 5- to 6-year-olds on the AP. This was attributed to weak lateralization in 3- to 4-year-olds, where the establishment of hand preference by age 6 leads to superior performance with the preferred hand in 5- to 6-year-olds. Finally, for the WHCT, 3- to 4-year-olds had the highest bimanual score, indicating use of the same hand to lift the cabinet door and retrieve an object. It is likely that the task was not motorically complex enough to drive preferred hand selection for older participants. The second research question sought to determine if there is difference between (TD) children and children with ASD. No differences were revealed; however, children with ASD did display variable AP performance, providing partial support for previous literature. Findings will be discussed in light of relevant literature.

Skilled performance tests and their use in diagnosing handedness and footedness at children of lower school age 8-10

Previous research has shown that hand and foot preferences do not develop in parallel in children and it has been discovered that in children foot preference stabilizes later. Therefore, the aim of this study is to verify whether the differences in stabilization will also be manifested through less consistent results of selected skilled foot performance tests in a comparison with selected skilled hand performance tests. A total of 210 8-10 year old children from elementary schools were recruited for this study. Hand and foot preferences were first tested using hand and foot preference observable measure tasks; consequently, all participants performed four skilled hand performance tests and three foot performance tests. Unlike in complex skilled hand performance tests, which showed a significant convergent validity 0.56-0.89 with hand preference tasks, in complex skilled foot performance tests a very low convergent validity 0.25-0.46 with foot preference tasks was detected. The only skilled foot performance indicator which showed an acceptable convergent validity with foot preference tasks was the "foot tapping" test 0.65-0.85, which represents rather a gross motor activity. Moreover, further results of the tests suggest that complex or fine motor performance tests used for diagnosing laterality of the lower limb that have a manipulative character probably do not represent suitable indicators for children in the given age category. The same trend was revealed in both females and males. This indicates that the level of laterality assessed as difference in skilfulness between the preferred and the non-preferred limb in children in the given age group probably develops in the same way in both genders.

Hand preference across the lifespan: effects of end-goal, task nature, and object location

In the present study we investigate age-related changes in hand preference for grasping and the influence of task demands on such preference. Children (2–11), young-adults (17–28) and older-adults (57–90) were examined in a grasp-to-eat and a grasp-to-construct task. The end-goal of these tasks was different (eat vs. construct) as was the nature of the task (unimanual vs. bimanual). In both tasks, ipsilateral and contralateral grasps were analyzed. Results showed a right-hand preference that did not change with age. Across the three age groups, a more robust right-hand preference was observed for the unimanual, grasp-to-eat task. To disentangle if the nature (unimanual) or the end-goal (grasp-to-eat) was the driver of the robust right-hand preference, a follow up experiment was conducted. Young-adult participants completed a unimanual grasp-to-place task. This was contrasted with the unimanual grasp-to-eat task and the bimanual grasp-to-construct task. Rates of hand preference for the grasp-to-eat task remained the highest when compared to the other two grasping tasks. Together, the results demonstrate that hand preference remains stable from childhood to older adulthood, and they suggest that a left hemisphere specialization exists for grasping, particularly when bringing food to the mouth.

One hand or the other? Effector selection biases in right and left handers

Much debate in the handedness literature has centred on the relative merits of questionnaire-based measures assessing hand preference versus simple movement tasks such as peg moving or finger tapping, assessing hand performance. A third paradigm has grown in popularity, which assesses choices by participants when either hand could be used to execute movements. These newer measures may be useful in predicting possible "reversed" asymmetries in proportions of non-right handed ("adextral") people. In the current studies we examine hand choice in large samples of dextral (right handed) and adextral participants. Unlike in some previous experiments on choice, we found that left handers were as biased towards their dominant hand as were right handers, for grasping during a puzzle-making task (study 1). In a second study, participants had to point to either of two suddenly appearing targets with one hand or the other. In study 2, left handers were not significantly less one handed than their right-handed counterparts as in study 1. In a final study, we used random effects meta analysis to summarise the possible differences in hand choice between left handers and right handers across all hand choice studies published to date. The meta analysis suggests that right handers use their dominant hand 12.5% more than left handers favour their dominant hand (with 95% confidence that the real difference lies between 7% and 18%). These last results suggest that our two experiments reported here may represent statistical Type 2 errors. This mean difference may be related to greater left hemispheric language and praxic laterality in right handers. Nevertheless, more data are needed regarding the precise proportions of left and right handers who favour their preferred hands for different tasks.

Evidence for right-hand feeding biases in a left-handed population

We have recently shown that actions with similar kinematic requirements, but different end-state goals may be supported by distinct neural networks. Specifically, we demonstrated that when right-handed individuals reach-to-grasp food items with intent to eat, they produce smaller maximum grip apertures (MGAs) than when they grasp the same item with intent to place it in a location near the mouth. This effect was restricted to right-handed movements; left-handed movements showed no difference between tasks. The current study investigates whether (and to which side) the effect may be lateralized in left-handed individuals. Twenty-one self-identified left-handed participants grasped food items of three different sizes while grasp kinematics were captured via an Optotrak Certus motion capture array. A main effect of task was identified wherein the grasp-to-eat action generated significantly smaller MGAs than did the grasp-to-place action. Further analysis revealed that similar to the findings in right-handed individuals, this effect was significant only during right-handed movements. Upon further inspection however, we found individual differences in the magnitude and direction of the observed lateralization. These results underscore the evolutionary significance of the grasp-to-eat movement in producing population-level right-handedness in humans as well as highlighting the heterogeneity of the left-handed population.

Hand preference of individuals with blindness in everyday activities: The effects of age of sight loss, age, and gender

The research aims of the present study were: (a) to assess the hand preference of blind persons in everyday activities on the basis of gender, type of blindness, and age; and (b) to conduct the above analysis at both the item level and the latent trait level, after concluding the optimum factor structure of the instrument. Participants were 82 individuals with visual impairments and blindness. Their mean age was 29.99 years. Handedness was evaluated using a modified version of the Edinburgh Handedness Inventory (Oldfield, 1971). When comparing handedness preferences across age of sight loss, gender, and age groups results indicated that there were significant differences in preference for several everyday tasks across age of sight loss and age groups but not gender. These results were also confirmed at the latent-trait mean level. The present findings add to the extant literature that highlighted hand preferences for individuals with visual impairments and blindness.