Handedness measured by finger tapping: a continuous variable

Handedness in twins reared apart: A review of the literature and new data

Reared-apart twin studies are a powerful means for identifying the relative contributions of heredity and environment to variation in human physical and behavioural traits. One such characteristic is handedness, for which it has long been noted that approximately 20% of twin pairs are comprised of one right-handed cotwin and one left-handed cotwin. Reared-together twin studies suggest a slightly greater concordance in monozygotic (MZT) than dizygotic (DZT) twins, implying that genetics influences hand preference. We report here two studies of handedness in reared-apart twins. Study 1 synthesizes the available data and estimates that at least N = 560 same-sex reared-apart twin pairs (for which zygosity is known with reasonable confidence) have been identified. Of these, handedness data are available for both members of n = 415 pairs. We observed similar levels of concordance/discordance for reared-apart monozygotic (MZA) and dizygotic (DZA) twins. However, although direction of handedness (right or left) has frequently been examined, strength of handedness (strong or weak) has not. Study 2 examined strength of hand preference and relative hand skill, as well as right- and left-hand speed, information available for participants in the Minnesota Study of Twins Reared Apart (MISTRA). We provide evidence of heritability for right-hand and left-hand speed. We also found hand preference strength was more alike than chance in DZA, but not MZA, twins. Findings are discussed in relation to genetic and environmental influences on human handedness.

Lateralized behaviors in living humans: Application in the context of hominin brain evolution

The left and right hemispheres of our brains differ subtly in structure, and each is dominant in processing specific cognitive tasks. Our species has a unique system of distributing behavior and cognition between each cerebral hemisphere, with a preponderance of pronounced side biases and lateralized functions. This hemisphere-dependent relationship between cognitive, sensory or motor function and a set of brain structures is called hemispheric specialization. Hemispheric specialization has led to the emergence of model systems to link anatomical asymmetries to brain function and behavior. Scientific research on hemispheric specialization and lateralized functions in living humans focuses on three major domains: (1) hand preferences, (2) language, and (3) visuospatial skills and attention. In this chapter we present an overview of this research with a specific focus on living humans and the applications of this research in the context of hominin brain evolution. Our objective is to put into perspective what we know about brain-behavior relationships in living humans and how we can apply the same methods to investigate this relationship in fossil hominin species, and thus improve our understanding of the emergence and development of complex cognitive abilities.

A longitudinal examination of perinatal testosterone, estradiol and vitamin D as predictors of handedness outcomes in childhood and adolescence

The developmental origins of handedness remain elusive, though very early emergence suggests individual differences manifesting in utero could play an important role. Prenatal testosterone and Vitamin D exposure are considered, yet findings and interpretations remain equivocal. We examined n = 767 offspring from a population-based pregnancy cohort (The Raine Study) for whom early biological data and childhood/adolescent handedness data were available. We tested whether 18-week maternal circulatory Vitamin D (25[OH]D), and testosterone and estradiol from umbilical cord blood sampled at birth predicted variance in direction of hand preference (right/left), along with right- and left-hand speed, and the strength and direction of relative hand skill as measured by a finger-tapping task completed at 10 (Y10) and/or 16 (Y16) years. Although higher concentrations of Vitamin D predicted more leftward and less lateralized (regardless of direction) relative hand skill profiles, taken as a whole, statistically significant findings typically did not replicate across time-point (Y10/Y16) or sex (male/female) and were rarely detected across different (bivariate/multivariate) levels of analysis. Considering the number of statistical tests and generally inconsistent findings, our results suggest that perinatal testosterone and estradiol contribute minimally, if at all, to subsequent variance in handedness. Vitamin D, however, may be of interest in future studies.

Lateralization of Impedance Control in Dynamic Versus Static Bimanual Tasks

In activities of daily living that require bimanual coordination, humans often assign a role to each hand. How do task requirements affect this role assignment? To address this question, we investigated how healthy right-handed participants bimanually manipulated a static or dynamic virtual object using wrist flexion/extension while receiving haptic feedback through the interacting object's torque. On selected trials, the object shook strongly to destabilize the bimanual grip. Our results show that participants reacted to the shaking by increasing their wrist co-contraction. Unlike in previous work, handedness was not the determining factor in choosing which wrist to co-contract to stabilize the object. However, each participant preferred to co-contract one hand over the other, a choice that was consistent for both the static and dynamic objects. While role allocation did not seem to be affected by task requirements, it may have resulted in different motor behaviours as indicated by the changes in the object torque. Further investigation is needed to elucidate the factors that determine the preference in stabilizing with either the dominant or non-dominant hand.

Tapping Performance of Professional and Amateur Darbuka Players

Motor skills of professional musicians can be regarded as a model to investigate human skill acquisition after prolonged practice. Although rhythmic tapping skills of musicians such as drummers and pianists were investigated previously, the tapping performance of hand percussionists is still largely unknown. In this study, we investigated the tapping performance of professional and amateur darbuka players. Three tapping tasks were performed: single-, double-, and triple-finger tapping tasks. The participants were asked to tap as fast as possible for 12 s in the single-finger tapping task while they tapped as fast and alternate/even as possible in the double- and triple-finger tapping tasks. The tapping speed and variability of inter-tap interval (ITI) and tapping amplitude were assessed for each task. In the single-finger and triple-finger tapping tasks, there was no significant difference in the tapping speed between the professional and amateur darbuka players. In the double-finger tapping task, the tapping speed was significantly faster in the professional players than the amateur players. Interestingly, the professional players showed faster tapping speed in both familiar and unfamiliar patterns of finger coordination. The tapping speed of the double-finger tapping task was significantly correlated with the duration and the age of commencement of darbuka training. The professional players also showed less variability of ITI and tapping amplitude compared to the amateur players. These results suggest that prolonged practice of the hand percussion increases the performance stability and coordination speed of both familiar and unfamiliar patterns.

The Handedness Index Practical Task (HI20): An economic behavioural measure for assessing manual preference

ABSTRACTBecause self-report hand preference measures are limited to investigating cognitive aspects of manual laterality, valid, easy-to-administer and economic behavioural methods are needed for capturing the motoric component of handedness. Therefore, this study introduces the Handedness Index Practical Task (HI₂₀) and tests it in a sample of 206 students (M_age = 23.79 years, SD_age = 3.01 years), half of whom were self-specified left-handers. After confirming good reliabilities at the subscale and total scale levels, k-means cluster analysis allowed an empirically based partitioning of test subjects into left- (n = 72), mixed- (n = 23) and right-handers (n = 111). To validate this categorization and the HI₂₀ index, data were compared with the Edinburgh Handedness Inventory (EHI), EHI-short, HI₂₂ and hand grip strength. The congruency between the HI₂₀ clusters and alternative categorizations ranged from 95.6% to 84.0%, while the clusters explained large portions of variance in grip strength differences. The HI₂₀ sub- and total scores showed strong correlations with other measures of lateral preference. Altogether, the freely available HI₂₀ emerges as a reliable and valid alternative for behavioural handedness assessment, whose power lies in explaining differential hand use patterns and enabling fine-grained examinations of handedness.

Digit ratio (2D:4D) and handedness: A meta-analysis of the available literature

The Geschwind-Behan-Galaburda and sexual differentiation models predict an association between elevated foetal androgen exposure and left-handedness whereas the callosal hypothesis predicts the opposite. We present a meta-analysis of correlations between handedness and digit ratio (2D:4D), a putative marker of prenatal testosterone. Left-handedness predicted low (male-typical) right-hand digit ratio (R2D:4D), high (female-typical) left-hand digit ratio (L2D:4D), and low R2D:4D-L2D:4D directional asymmetry (D_[R-L]). Effect sizes were extremely small and not moderated by sex or method of measuring handedness or 2D:4D. The same general pattern was observed after excluding the very large study (110,329 males, 90,412 females) of Manning and Peters ([2009]. Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study. Laterality: Asymmetries of Body, Brain and Cognition, 14(5), 528-540. doi:10.1080/13576500802637872); however, no significant effects for R2D:4D were observed once these samples were removed. The results do not confirm any theory linking prenatal androgens with handedness, so we speculate they instead reflect the mechanical action of writing causing subtle changes in the musculature and/or fat pads of the fingers. Gripping a pen/pencil might cause an increase in 2D relative to 4D (and/or decrease in 4D relative to 2D) resulting in higher ratios on the writing-hand; furthermore, this could differ between left- and right-handers due to writing in the left-to-right direction (as in English) having asymmetrical effects depending on which hand is used.

Motor control characteristics of upper limbs in response to assistive forces during bilateral tasks

Most research on power assist suits (PASs) that concerned PAS-human interactions has used human physical reactions as criteria to evaluate the mechanical function, however, with minimal emphasis on human reactions in response to PASs. In this study, we focused on the physiological responses of the upper limbs including muscle activity of the biceps brachii and the triceps brachii, co-activation, force steadiness (CV) and rated perceived exertion (RPE) to various patterns of bilateral assistive force, such as unilateral assistance (L0% & R67% [% = percentage of workload force, L = left arm, R = right arm], L67% & R0%, L0% & R33%, L33% & R0%), symmetrical (L0% & R0%, L33% & R33%, L67% & R67%) and asymmetrical bilateral assistance (L33% & R67%, L67% & R33%), during bilateral isometric force-matching tasks. The results showed a similar muscular response of the two arms to bilateral assistive conditions, and the muscle activity of the arm that was being observed decreased only when the assistive force that applied on itself increased, indicating that both arms may have adopted similar but independent motor control mechanisms to acclimate to the bilateral assistive forces. Comparison between the two unilateral assistances (L0% & R33% and L33% & R0%) and the two asymmetrical bilateral assistances (L33% & R67%, L67% & R33%) showed no significant differences in muscular responses, CV and RPE, indicating that bilateral assistances with bilateral interchanged assistive levels may be equally effective regardless of which arm the higher assistive force is applied to. Comparison between unilateral and symmetrical assistive conditions that have similar overall workloads (L67% & R0%, L33% & R33%, L0% & R67%) showed a lower CV and RPE score at symmetrical assistance compared with unilateral assistance, suggesting that assisting both arms with the same level simultaneously improves task performances compared with applying the assistive force to only one arm.

Neural support of manual preference revealed by BOLD variations during right and left finger-tapping in a sample of 287 healthy adults balanced for handedness

We have identified the brain areas involved in Manual Preference (MP) in 143 left-handers (LH) and 144 right-handers (RH). First, we selected the pairs of homotopic regions of interest (hROIs) of the AICHA atlas with significant contralateral activation and asymmetry during the right hand and the left hand Finger-Tapping (FT) both in RH and LH. Thirteen hROIs were selected, including the primary and secondary sensorimotor and premotor cortices, thalamus, dorsal putamen, and cerebellar lobule IV. In both groups, contralateral activations and ipsilateral deactivations were seen, with stronger asymmetries when the preferred hand was used. Comparing with different models for the prediction of MP, we found that the differences in activity during preferred hand minus non-preferred hand movement in 11 contralateral and/or ipsilateral hROIS were best at explaining handedness distribution. Two different mechanisms were identified: 1. Stronger contralateral activity of cortical and cerebellar motor areas during right hand movement, seen in both groups but modulated by handedness; 2. Stronger deactivation in ipsilateral areas during dominant hand movement in both groups, LH here mirroring RH. The present study thus demonstrates that handedness neural support is complex and not simply based on a mirrored organization of hand motor areas.

Handedness and White Matter Networks

The development and persistence of laterality is a key feature of human motor behavior, with the asymmetry of hand use being the most prominent. The idea that asymmetrical functions of the hands reflect asymmetries in terms of structural and functional brain organization has been tested many times. However, despite advances in laterality research and increased understanding of this population-level bias, the neural basis of handedness remains elusive. Recent developments in diffusion magnetic resonance imaging enabled the exploration of lateralized motor behavior also in terms of white matter and connectional neuroanatomy. Despite incomplete and partly inconsistent evidence, structural connectivity of both intrahemispheric and interhemispheric white matter seems to differ between left and right-handers. Handedness was related to asymmetry of intrahemispheric pathways important for visuomotor and visuospatial processing (superior longitudinal fasciculus), but not to projection tracts supporting motor execution (corticospinal tract). Moreover, the interindividual variability of the main commissural pathway corpus callosum seems to be associated with handedness. The review highlights the importance of exploring new avenues for the study of handedness and presents the latest state of knowledge that can be used to guide future neuroscientific and genetic research.

Quantitative assessment of fine motor skills in children using magnetic sensors

AIM

We aimed to establish objective and quantitative data on fine motor development in typically developing children using magnetic sensors.

METHODS

The study included 110 Japanese elementary school children volunteers (57 boys, 53 girls). The participants were instructed to tap their thumbs and index fingers together repetitively for 10 s. After attaching coils to the participants' right and left thumbs and index fingers, participants executed "in-phase" and "anti-phase" tapping. We used two-way analysis of variance to analyze the influences of age and sex on fine motor development.

RESULTS

The "number of taps" significantly increased with age, while the "standard deviation (SD) of tapping interval" significantly decreased. More than half of the "acceleration" parameters significantly increased with age. Boys performed significantly faster than girls in some parameters of "velocity" and "acceleration," while girls had significantly lower "SD of local maximum velocity in opening motion" and "SD of local minimum velocity in closing motion."

DISCUSSION

We established both objective and quantitative reference data on fine motor development in typically developing Japanese children aged between 7 and 12 years using magnetic sensors. We revealed that this system can monitor real-time details of the parameters involved in the finger-tapping movement in children without complications. This device could be useful for obtaining objective and quantitative data on fine motor skills in the clinical assessment of developmental coordination disorder, assessments of educational intervention, or rehabilitation and discovery of new therapeutic agents.

Prevalence and heritability of handedness in a Hong Kong Chinese twin and singleton sample

BACKGROUND

Left-handedness prevalence has been consistently reported at around 10% with heritability estimates at around 25%. Higher left-handedness prevalence has been reported in males and in twins. Lower prevalence has been reported in Asia, but it remains unclear whether this is due to biological or cultural factors. Most studies are based on samples with European ethnicities and using the preferred hand for writing as key assessment. Here, we investigated handedness in a sample of Chinese school children in Hong Kong, including 426 singletons and 205 pairs of twins, using both the Edinburgh Handedness Inventory and Pegboard Task.

RESULTS

Based on a binary definition of writing hand, we found a higher prevalence of left-handedness (8%) than what was previously reported in Asian datasets. We found no evidence of increased left-handedness in twins, but our results were in line with previous findings showing that males have a higher tendency to be left-handed than females. Heritability was similar for both hand preference (21%) and laterality indexes (22%). However, these two handedness measures present only a moderate correlation (.42) and appear to be underpinned by different genetic factors.

CONCLUSION

In summary, we report new reference data for an ethnic group usually underrepresented in the literature. Our heritability analysis supports the idea that different measures will capture different components of handedness and, as a consequence, datasets assessed with heterogeneous criteria are not easily combined or compared.

Different laterality indexes are poorly correlated with one another but consistently show the tendency of males and females to be more left- and right-lateralized, respectively

The most common way to assess handedness is based on the preferred hand for writing, leading to a binary (left or right) trait. Handedness can also be assessed as a continuous trait with laterality indexes, but these are not time- and cost-effective, and are not routinely collected. Rarely, different handedness measures are collected for the same individuals. Here, we assessed the relationship of preferred hand for writing with four laterality indexes, reported in previous literature, derived from measures of dexterity (pegboard task, marking squares and sorting matches) and strength (grip strength), available in a range of N = 6664-8069 children from the ALSPAC cohort. Although all indexes identified a higher proportion of individuals performing better with their right hand, they showed low correlation with each other (0.08-0.3). Left handers were less consistent compared to right handers in performing better with their dominant hand, but that varied across indexes, i.e. 13% of left handers performed better with their right hand on marking squares compared to 48% for sorting matches and grip strength. Analysis of sex effects on the laterality indexes showed that males and females tend to be, on all measures, more left- and right-lateralized, respectively. Males were also over-represented among the individuals performing equally with both hands suggesting they had a higher tendency to be weakly lateralized. This study shows that different handedness measures tap into different dimensions of laterality and cannot be used interchangeably. The trends observed across indexes for males and females suggest that sex effects should be taken into account in handedness and laterality studies.

Half a century of handedness research: Myths, truths; fictions, facts; backwards, but mostly forwards

Although most people are right-handed and have language in their left cerebral hemisphere, why that is so, and in particular why about ten per cent of people are left-handed, is far from clear. Multiple theories have been proposed, often with little in the way of empirical support, and sometimes indeed with strong evidence against them, and yet despite that have become modern urban myths, probably due to the symbolic power of right and left. One thinks in particular of ideas of being right-brained or left-brained, of suggestions that left-handedness is due to perinatal brain damage, of claims that left-handers die seven years earlier than right-handers, and of the unfalsifiable ramifications of the byzantine Geschwind-Behan-Galaburda theory. This article looks back over the past fifty years of research on brain asymmetries, exploring the different themes and approaches, sometimes in relation to the author's own work. Taking all of the work together it is probable that cerebral asymmetries are under genetic control, probably with multiple genetic loci, only a few of which are now beginning to be found thanks to very large databases that are becoming available. Other progress is also seen in proper meta-analyses, the use of fMRI for studying multiple functional lateralisations in large number of individuals, fetal ultra-sound for assessing handedness before birth, and fascinating studies of lateralisation in an ever widening range of animal species. With luck the next fifty years will make more progress and show fewer false directions than had much of the work in the previous fifty years.

The relationship between behavioral language laterality, face laterality and language performance in left-handers

Left-handers provide unique information about the relationship between cognitive functions because of their larger variability in hemispheric dominance. This study presents the laterality distribution of, correlations between and test-retest reliability of behavioral lateralized language tasks (speech production, reading and speech perception), face recognition tasks, handedness measures and language performance tests based on data from 98 left-handers. The results show that a behavioral test battery leads to percentages of (a)typical dominance that are similar to those found in neuropsychological studies even though the incidence of clear atypical lateralization (about 20%) may be overestimated at the group level. Significant correlations were found between the language tasks for both reaction time and accuracy lateralization indices. The degree of language laterality could however not be linked to face laterality, handedness or language performance. Finally, individuals were classified less consistently than expected as being typical, bilateral or atypical across all tasks. This may be due to the often good (speech production and perception tasks) but sometimes weak (reading and face tasks) test-retest reliabilities. The lack of highly reliable and valid test protocols for functions unrelated to speech remains one of the largest impediments for individual analysis and cross-task investigations in laterality research.

Attentional Asymmetries during Concurrent Bimanual Performance

An asymmetry of attention was observed when subjects attempted to perform concurrent, relatively independent tasks with the two hands: right-handed subjects performed very much better on a dual task which required them to follow the beat of a metronome with the left while tapping as quickly as they could with the right than with the converse arrangement. It is suggested that attentional strategies which have evolved to allow guidance of interdependent skilled bimanual activities are also used when subjects attempt to perform relatively independent concurrent bimanual movements, which are not observed in the naturally occurring motor repertoire. Thus, interactions between hand, hand preference and nature of task are an important factor in dual task performance.

Tapping Speed Asymmetry in Drummers for Single-Hand Tapping with a Stick

The purpose of this study was to investigate tapping speed asymmetry in 13 right-handed drummers and 13 right-handed nondrummers. The participants executed single-hand tapping with a stick as fast as possible for 10 sec. with the left and right hand. There was no significant difference in the tapping speed of the right hand between the drummers and the nondrummers, whereas in the left hand, the drummers tapped significantly faster than the nondrummers. Drummers showed less tapping speed asymmetry than nondrummers. These results suggest that the tapping speed of the nonpreferred hand progressed nearly to the level of the preferred hand through daily drum training.

Between-hand difference in ipsilateral deactivation is associated with hand lateralization: fMRI mapping of 284 volunteers balanced for handedness

In right-handers (RH), an increase in the pace of dominant hand movement results in increased ipsilateral deactivation of the primary motor cortex (M1). By contrast, an increase in non-dominant hand movement frequency is associated with reduced ipsilateral deactivation. This pattern suggests that inhibitory processes support right hand dominance in right-handers and raises the issues of whether this phenomenon also supports left hand preference in left-handers (LH), and/or whether it relates to asymmetry of manual ability in either group. Thanks to the BIL&GIN, a database dedicated to the investigation of hemispheric specialization (HS), we studied the variation in M1 activity during right and left finger tapping tasks (FTT) in a sample of 284 healthy participants balanced for handedness. An M1 fMRI localizer was defined for each participant as an 8 mm diameter sphere centered on the motor activation peak. RH exhibited significantly larger deactivation of the ipsilateral M1 when moving their dominant hand than their non-dominant hand. In contrast, LH exhibited comparable ipsilateral M1 deactivation during either hand movement, reflecting a bilateral cortical specialization. This pattern is likely related to left-handers’ good performances with their right hand and consequent lower asymmetry in manual ability compared with RH. Finally, inter-individual analyses over the whole sample demonstrated that the larger the difference in manual skill across hands, the larger the difference in ipsilateral deactivation. Overall, we propose that difference in ipsilateral deactivation is a marker of difference in manual ability asymmetry reflecting differences in the strength of transcallosal inhibition when a given hand is moving.

Developmental changes in lateralized inhibition of symmetric movements in children with and without Developmental Coordination Disorder

The present study investigates developmental changes in selective inhibition of symmetric movements with a lateralized switching task from bimanual to unimanual tapping in typically developing (TD) children and with Developmental Coordination Disorder (DCD) from 7 to 10 years old. Twelve right-handed TD children and twelve gender-matched children with DCD and probable DCD produce a motor switching task in which they have (1) to synchronize with the beat of an auditory metronome to produce bimanual symmetrical tapping and (2) to selectively inhibit their left finger's tapping while continuing their right finger's tapping and conversely. We assess (1) the development of the capacity to inhibit the stopping finger (number of supplementary taps after the stopping instruction) and (2) the development of the capacity to maintain the continuing finger (changes in the mean tempo and its variability for the continuing finger's tapping) and (3) the evolution of performance through trials. Results indicate that (1) TD children present an age-related increase in the capacity to inhibit and to maintain the left finger's tapping, (2) DCD exhibits persistent difficulties to inhibit the left finger's tapping, and (3) both groups improve their capacity to inhibit the left finger's movements through trials. In conclusion, the lateralized switching task provides a simple and fine tool to reveal differences in selective inhibition of symmetric movements in TD children and children with DCD. More theoretically, the specific improvement in selective inhibition of the left finger suggests a progressive development of inter-hemispheric communication during typical development that is absent or delayed in children with DCD.

Matching of Movements Made Independently by the Two Arms in Normal Humans

Comparisons were made of voluntary movements of the right and left arms in normal human subjects. A series of movements of different amplitudes, made at the subject' own speed, was performed with one limb. After a rest period, the same series was repeated with the contralateral limb. The relation between movement peak velocity and movement amplitude was linear and was the same for both arms. With repeated testing over periods up to two months, the slope of the peak velocity-amplitude relation decreased during the first week, thereafter remaining unchanged. In a second series of experiments, six normal subjects continuously wore a 1 lb (0.45 kg) weight strapped to their left (non-dominant) forearm for up to 1 week. This resulted in an increase in the slope of the peak-velocity/amplitude relation in this arm. A parallel change occurred in movements made independently by the right (non-loaded) arm. A similar matching of movement performance of the two limbs was seen following removal of the weight. The data is interpreted as proving support for the hypothesis that there is a single movement "command" which is applied to both limbs. The interaction of this command with the limbs which have similar second-order mechanical properties yields similar movements even when they are made independently.

Establishing hand preference: why does it matter?

Hand preference has been associated with psychological and physical well-being, risk of injury, pathological irregularities, longevity, and cognitive function. To determine hand preference, individuals are often asked what hand they use to write with, or what hand is used more frequently in activities of daily living. However, relying only on one source of information may be misleading, given the strong evidence to support a disassociation between self-reported hand preference and outcomes of hand performance assessments. This brief communication is intended to highlight the various methods used to determine hand preference, to discuss the relationship between hand preference inventories and performance measures and to present some recent findings associated with hand preference and musculoskeletal disorders.

Going beyond students: an association between mixed-hand preference and schizotypy subscales in a general population

Research on the sub-clinical condition of schizotypy suggests that it is associated with mixed handedness. To date, however, this research has focussed on undergraduate populations. If the association between schizotypy and mixed-handedness is the result of an underlying neurological trait, it is important to demonstrate that the effect extends to the general population. With this in mind, 699 participants were drawn from a wide community sample. Schizotypy was measured using the Psychosis Proneness Questionnaire and handedness was assessed using the Annett inventory. To avoid the sometimes arbitrary definitions of left-, right- and mixed-handed, regression analyses were used to explore the data. There was no evidence of a difference in schizotypy between individuals with a left- or right-hand preference. People with a mixed-hand preference, however, had higher scores on PER-MAG (Perceptual Aberration and Magical Ideation) and HYP-IMP (Hypomania and Impulsive Non-Conformity) scales (positive traits). No effect was observed for the SAN (Social Anhedonia) and PAN (Physical Anhedonia) scales (negative traits). The nature of the association between schizotypy and handedness observed in the current study is similar to that reported for student populations. The possibility that the association is related to response biases or a biological mechanism is discussed.

Coupling between perception and action timing during sensorimotor synchronization

Time is an important parameter in behaviour, especially when synchronization with external events is required. To evaluate the nature of the association between perception and action timing, this study introduced pitch accented tones during performance of a sensorimotor tapping task. Furthermore, regularity of the pacing cues was modified by small (subliminal) or large (conscious) timing perturbations. A global analysis across the intervals showed that repeated accented tones increased the tap-tone asynchrony in the regular (control) and irregular (subliminal) trials but not in the irregular trials with awareness of the perturbations. Asynchrony variability demonstrated no effect of accentuation in the regular and subliminal irregular trials, whereas it increased in the conscious irregular trials. A local analysis of the intervals showed that pitch accentuation lengthened the duration of the tapping responses, but only in the irregular trials with large timing perturbations. These data underline that common timing processes are automatically engaged for perception and action, although this arrangement can be overturned by cognitive intervention. Overall, the findings highlight a flexible association between perception and action timing within a functional information processing framework.

Intrinsic constraint of asymmetry acting as a control parameter on rapid, rhythmic bimanual coordination: a study of professional drummers and nondrummers

Expert musicians show experience-dependent reduced asymmetry in the structure of motor-related brain areas and in the maximum tapping frequency between the hands. Therefore we hypothesized that a reduced hand-skill asymmetry is strongly related to rapid and rhythmical bimanual coordination and developed a dynamical model including a symmetry-breaking parameter Δω, for human bimanual coordination. We conducted unimanual and bimanual drumming experiments to test the following model predictions. 1) The asymmetry in the maximum tapping frequency is more pronounced in nondrummers than that in drummers. If so, 2) a larger number of phase wanderings (i.e., succession of taps by the same hand), 3) larger SD of the relative phase between the hands (SD ), and 4) larger deviation of mean relative phase (mean ) from 180° would be observed in nondrummers than that in professional drummers during antiphase bimanual drumming at the maximum speed. In a unimanual tapping task, the asymmetry in maximum tapping frequency of nondrummers was more pronounced than that of professional drummers. In a bimanual coordination task, phase wanderings were observed only in nondrummers and SD of the nondrummers is significantly larger than that of professional drummers. On the other hand, there was no significant difference between the mean of the two groups. All these observations were successfully reproduced by changing Δω, which corresponded to the asymmetry in the maximum tapping frequency. These results support the hypothesis indicating that the prominent bimanual coordination pattern emerges spontaneously after a nonspecific change in Δω or symmetry restoration of the nonlinear dynamical systems.

The relationship between hand preference, hand performance, and general cognitive ability

The idea that handedness indicates something about a person's cognitive ability and personality is a perennial issue. A variety of models have been put forward to explain this relationship and predict a range of outcomes from higher levels of cognitive ability in left-handers or moderate right-handers to lower levels of achievement in left- or mixed-handers. We tested these models using a sample (n = 895) drawn from the BRAINnet database (www.brainnet.net). Participants completed a general cognitive ability (GCA) scale and a test of hand preference/performance. Moderate right-handers, as indexed by their performance measures, had higher GCA scores compared with strong left- or right-handers. The performance measure also showed lower levels of GCA for left-handers compared with right-handers. The hand preference data showed little or no association with cognitive ability-perhaps because this measure clusters individuals toward the extremes of the handedness distribution. While adding support to Annett's heterozygous advantage model, which predicts a cognitive disadvantage for strong left- or right-handers, the data also confirm recent research showing a GCA disadvantage for left-handers. Although this study demonstrates that handedness is related to cognitive ability, the effects are subtle and might only be identified in large-scale studies with sensitive measures of hand performance.

Motor cortex and hand motor skills: structural compliance in the human brain

Recent studies in humans and nonhuman primates have shown that the functional organization of the human sensorimotor cortex changes following sensory stimulation or following the acquisition of motor skills. It is unknown whether functional plasticity in response to the acquisition of new motor skills and the continued performance of complicated bimanual movements for years is associated with structural changes in the organization of the motor cortex. Professional musicians, especially keyboard and string players, are a prototypical group for investigating these changes in the human brain. Using magnetic resonance images, we measured the length of the posterior wall of the precentral gyrus bordering the central sulcus (intrasulcal length of the precentral gyrus, ILPG) in horizontal sections through both hemispheres of right-handed keyboard players and of an age- and handedness-matched control group. Lacking a direct in vivo measurement of the primary motor cortex in humans, we assumed that the ILPG is a measure of the size of the primary motor cortex. Left-right asymmetry in the ILPG was analyzed and compared between both groups. Whereas controls exhibited a pronounced left-larger-than-right asymmetry, keyboard players had more symmetrical ILPG. The most pronounced differences in ILPG between keyboard players and controls were seen in the most dorsal part of the presumed cortical hand representation of both hemispheres. This was especially true in the nondominant right hemispheres. The size of the ILPG was negatively correlated with age of commencement of musical training in keyboard players, supporting our hypothesis that the human motor cortex can exhibit functionally induced and long-lasting structural adaptations.

Effect of stick use on rapid unimanual tapping in drummers

Drummers achieve impressive musical performance by using drumsticks. The present study investigated the effect of drumstick use on rapid unimanual tapping performance. 17 drummers tapped a force transducer as fast as possible for 10 sec. with a finger and a drumstick. No significant difference between finger and stick tapping was found for tapping speed and variability of peak force, but there were significant differences in contact time with the tapping surface, mean peak force, and intertap interval variability: Stick tapping had a shorter contact time, a larger peak force, and more stable intertap interval than did finger tapping. Thus, stick use makes it possible to produce a larger impact force and enhances the ability to control timing during rapid manual movement, allowing drummers to play drums powerfully and stably, which is clearly important for the role they have in controlling or enhancing musical rhythm.

Linear versus non-linear measures of temporal variability in finger tapping and their relation to performance on open- versus closed-loop motor tasks: comparing standard deviations to Lyapunov exponents

The nature of temporal variability during speeded finger tapping was examined using linear (standard deviation) and non-linear (Lyapunov exponent) measures. Experiment 1 found that right hand tapping was characterised by lower amounts of both linear and non-linear measures of variability than left hand tapping, and that linear and non-linear measures of variability were often negatively correlated with one another. Experiment 2 found that increased non-linear variability was associated with relatively enhanced performance on a closed-loop motor task (mirror tracing) and relatively impaired performance on an open-loop motor task (pointing in a dark room), especially for left hand performance. The potential uses and significance of measures of non-linear variability are discussed.

An observational method of assessing handedness in children and adults

The current study was performed to assess the WatHand Cabinet Test (WHCT), a newly developed multidimensional observational test of handedness. Because the test is observational, it is ideal for assessing children, as it does not require a high degree of verbal comprehension on the part of the participants. 548 individuals participated in the present study on a voluntary basis. Individuals of varying ages were examined (including 3 to 5, 6, 7, 8, 9, 10, and 11-year-olds, and 19-to 24-year-olds). Each participant was asked to complete the WHCT, the Annett Pegboard (Annett, 1985), and the Waterloo Handedness Questionnaire (WHQ) (M.P. Bryden, 1977). Overall, the total score on the WHCT was significantly correlated with both the WHQ, r = .795, p < .01, and the Annett Pegboard, r = .542, p < .01. Sub-scores measuring skilled performance, bimanual performance, and internal consistency were also examined, as well as performance on the three tests as a function of age. Overall, findings indicate that that the WHCT is a valid test of hand preference in both children and adults. Its ease of use, quick administration, and built-in quantitative sub-scores offer a robust alternative method for measuring hand preference.

How Good People are at Estimating their Own Performance? A Study of the Relationship between Hand Preference and Motor Performance

This article examines the relationship between the awareness of hand preference and hand and foot performance among right-, left- and mixed-handers (n = 224). The hand preference was assessed using a handedness inventory. Hand and foot performances were measured using rapid index finger or toe tapping. A significant interaction between hand preference and the tapping rate indicated that in left-handers, left tapping was faster than right tapping and in right-handers, right tapping was faster than left tapping regardless of effector, finger or toe. The mixed-handers, however, did not show differences between left and right tapping performance. Correlations between performances were highest between hands or between feet. Also, hand performance was more strongly positively associated to foot performance in the mixed- and left-handers than right-handers. Similar inter-limb performance in mixed-handers tends to implicate inconsistent or undeveloped cerebral lateralisation. The results indicate that self-awareness of the pattern of hand use significantly relates to hand and foot performance.

Extent of innate dexterity and ambidexterity across handedness and gender: Implications for training in laparoscopic surgery

BACKGROUND

As innate dexterity is considered one of the important predictors of eventual operative competence, an experimental human factors study was conducted to determine innate dexterity and ambidexterity across handedness and gender.

METHODS

50 medical students (right-handed males, left-handed males, and right-handed females) were recruited as participants in a study designed to assess innate dexterity and degree of ambidexterity for endoscopic manipulations in a validated virtual-reality simulator. All participants performed unilateral and bilateral tasks with both dominant and nondominant hands in random sequence. The outcome measures were execution time, extent of ambidexterity (ambidexterity index), aiming errors, and maximum tissue damage.

RESULTS

Right-handed males exhibited a greater level of ambidexterity than left-handed males (p = 0.02 for path length, p = 0.001 for angular path) and right-handed females (p = 0.01 for path length, p = 0.02 for angular path), and more-efficient task performance as measured by execution time (p = 0.001 for males and p = 0.03 across gender). The task quality when executed by the dominant hand was best in right-handed males (p = 0.001 vs. left-dominant males and p = 0.03 across gender). No significant difference was observed in terms of precision control and fine movements (aiming errors and maximum tissue damage) between the three groups.

CONCLUSIONS

These findings indicate that training surgical curricula in laparoscopic surgery should be more flexible to accommodate the innate differences across handedness and gender.

Task demands affect manual asymmetries in pegboard performance

Previous work by Bryden and Roy (1999) showed a larger performance difference between the hands for placing pegs into holes on the Grooved Pegboard test than for removing pegs from the holes. The authors argued that these data provided evidence of the importance of task demands in manual asymmetries. However the study failed to control for the differing starting positions of the pegs. To clarify this possible confound, the purpose of the current investigation was to determine the influence of starting position on the between-hand performance differences on the Grooved Pegboard Test. To do so, both the start and end positions were manipulated, such that participants moved the pegs from the receptacle to another receptacle or to a set of holes, or participants moved the pegs from a set of holes to a receptacle or another set of holes. A total of 30 right-handed individuals (as classified using the Waterloo Handedness Questionnaire) participated in the experiment, completing five trials with each hand for each of the four conditions. While no significant effects of start position were found, a significant interaction between hand and end position, F(1.29) = 30.85, P<.001, was found for the time to complete the task, where larger differences between the hands, fovouring the right hand, were seen for placing pegs into the holes as opposed to the receptacles. This effect was also found when the data were expressed using a laterality quotient. The results are discussed in terms of the influence of task complexity on manual asymmetries.

Intermanual Differences in movement-related interhemispheric inhibition

Interhemispheric inhibition (IHI) between motor cortical areas is thought to play a critical role in motor control and could influence manual dexterity. The purpose of this study was to investigate IHI preceding movements of the dominant and nondominant hands of healthy volunteers. Movement-related IHI was studied by means of a double-pulse transcranial magnetic stimulation protocol in right-handed individuals in a simple reaction time paradigm. IHI targeting the motor cortex contralateral (IHI(c)) and ipsilateral (IHI(i)) to each moving finger was determined. IHI(c) was comparable after the go signal, a long time preceding movement onset, in both hands. Closer to movement onset, IHI(c) reversed into facilitation for the right dominant hand but remained inhibitory for left nondominant hand movements. IHI(i) displayed a nearly constant inhibition with a trough early in the premovement period in both hands. In conclusion, our results unveil a more important modulation of interhemispheric interactions during generation of dominant than nondominant hand movements. This modulation essentially consisted of a shift from a balanced IHI at rest to an IHI predominantly directed toward the ipsilateral primary motor cortex at movement onset. Such a mechanism might release muscles from inhibition in the contralateral primary motor cortex while preventing the occurrence of the mirror activity in ipsilateral primary motor cortex and could therefore contribute to intermanual differences in dexterity.

Converging evidence of ERD/ERS and BOLD responses in motor control research

In this chapter we summarize findings of our group in which we studied the neural underpinnings of finger tapping control using different methods (functional magnetic resonance imaging: fMRI, electroencephalography: EEG, transcranial magnetic stimulation: TMS, and behavioural experiments). First, we found that maximum finger tapping speed is a matter of training as shown for professional musicians. Secondly, we demonstrated that different finger tapping speeds are accompanied by different hemodynamic responses in the primary hand motor area (M1), the cerebellum and partly in pre-motor areas. With increasing tapping speed there is an increase of hemodynamic response in these areas (rate effect). Thirdly, the effect measured with fMRI is substantiated by rate effects measured by means of task-related power decreases in the upper alpha-band (10-12 Hz) over the primary motor cortex. In case of sequential finger movement learning, we observed decreases in task-related alpha-power in lateral PMC (event-related desynchronization: ERD) and simultaneous alpha-power increases in SMA (event-related synchronization: ERS) that came along with training-induced increases in movement rate. This pattern is discussed in relation to the "focal ERD/surround ERS" phenomenon suggested by Pfurtscheller and Lopes da Silva. Finally, we demonstrated that finger tapping speed was slowed by selectively inhibiting the primary hand motor area using TMS. Taken together, these studies demonstrate on the basis of converging evidence that the primary hand motor area is the basic control centre for controlling the movement parameter tapping speed. However, the neural efficiency to control finger tapping speed (as measured with hemodynamic responses or ERD/ERS patterns) is a matter of training.

The advantage of a decreasing right-hand superiority: The influence of laterality on a selected musical skill (sight reading achievement)

In this study, the unrehearsed performance of music, known as 'sight reading', is used as a model to examine the influence of motoric laterality on highly challenging musical performance skills. As expertise research has shown, differences in this skill can be partially explained by factors such as accumulated practise and an early start to training. However, up until now, neurobiological factors that may influence highly demanding instrumental performance have been widely neglected. In an experiment with 52 piano students at a German university music department, we could show that the most challenging musical skill, sight reading (which is characterized by extreme demands on the performer's real time information processing), is positively correlated with decreasing right-hand superiority of performers. Laterality was measured by the differences between left and right-hand performance in a speed tapping task. SR achievement was measured using an accompanying task paradigm. An overall superiority of 22% for non-right-handed pianists was found. This effect is gender-related and stronger in non-right-handed males (r(24) = -0.49, p<0.05) than in non-right-handed females (r(28) = -0.16, p>0.05). We conclude that non-right-handed motoric laterality is associated with neurobiological advantages required for sight reading, an extremely demanding musical subskill.

Drawing on either side of the brain

Although both the cerebral laterality of processing visual information and human drawing skill have long been sources of investigation, there is not much empirical work combining the two. In this study, an attempt was made to explore if known different specialisations of the two cerebral hemispheres could help in predicting qualities of drawings produced by each hand. For this purpose, an amateur artist who is able to draw with either the left or the right hand produced a series of realistic drawings of 3D objects. Then 28 participants rated the drawings for several predetermined perceptual and aesthetic properties. The participants judged drawings made with the left hand as superior to those made with the right hand. Given that the right hemisphere controls the left hand, we suggest that this hand might also benefit from the more direct access to lateralised areas that are involved in the processing aspects of visual information and spatial properties (e.g., depth and shading). These perceptual processes may thus play an important role in the ability to draw realistic depictions of objects.

Postural Stability and Hand Preference as Constraints on One-Handed Catching Performance in Children

Effects of postural state and hand preference as constraints on 1-handed catching performance were investigated in different ability groups of children aged 9-10 years. On the basis of pretest data, the authors classified 48 participants into groups of good, intermediate, and poor catchers (n = 16 in each) and asked them to perform 1-handed catches with their preferred and nonpreferred hands while standing and sitting. The good catchers' performance was not affected by the imposed postural constraints but did improve when they used the preferred hand. A similar effect of hand preference was evident in the intermediate and poor catchers, but there was also an effect of postural constraint. Independent of hand preference, intermediate catchers' performance while seated improved significantly compared with that during standing. For poor catchers, there was an interaction between hand preference and posture; significant improvement was evident only when they used the preferred hand in the sitting condition. The finding that manipulation of posture and hand preference affected performance outcomes indicates that perceptual skill is not the only influence on catching performance in children. Manipulation of those key constraints may facilitate the acquisition of catching skill, but more research is needed to determine the permanence of those effects.

Are there pre-existing neural, cognitive, or motoric markers for musical ability?

Adult musician's brains show structural enlargements, but it is not known whether these are inborn or a consequence of long-term training. In addition, music training in childhood has been shown to have positive effects on visual-spatial and verbal outcomes. However, it is not known whether pre-existing advantages in these skills are found in children who choose to study a musical instrument nor is it known whether there are pre-existing associations between music and any of these outcome measures that could help explain the training effects. To answer these questions, we compared 5- to 7-year-olds beginning piano or string lessons (n=39) with 5- to 7-year-olds not beginning instrumental training (n=31). All children received a series of tests (visual-spatial, non-verbal reasoning, verbal, motor, and musical) and underwent magnetic resonance imaging. We found no pre-existing neural, cognitive, motor, or musical differences between groups and no correlations (after correction for multiple analyses) between music perceptual skills and any brain or visual-spatial measures. However, correlations were found between music perceptual skills and both non-verbal reasoning and phonemic awareness. Such pre-existing correlations suggest similarities in auditory and visual pattern recognition as well a sharing of the neural substrates for language and music processing, most likely due to innate abilities or implicit learning during early development. This baseline study lays the groundwork for an ongoing longitudinal study addressing the effects of intensive musical training on brain and cognitive development, and making it possible to look retroactively at the brain and cognitive development of those children who emerge showing exceptional musical talent.

Finger tapping, handedness and grey matter amount in the Rolando's genu area

The morphology of the central sulcus (CS), at the level of the hand primary motor cortex, has been shown to be related to hand preference and skill. Differences in the cerebral functional organisation of left and right-handers have been described, notably with respect to hemispheric specialisation, which might cause the neural substrate of hand dominance or skill to differ between the two groups. Here, we further explored the relationship between the anatomical variability of the central sulcus and hand skill in two groups of young male subjects differing by handedness (n = 56 right-handers and n = 55 left-handers). Grey matter volume (GMV) in the upper region of the central sulcus was estimated with Voxel Based Morphometry, using a probabilistic region of interest approach, while hand motor skill was measured with the finger tapping test. No significant anatomical differences could be evidenced between the two hand preference groups, a rightward hemispheric asymmetry being observed in both samples. However, multiple regression analyses showed that, in the right-handed group, the maximum tapping rate of the right hand correlated positively with the left central sulcus GMV, but negatively with the right. Similar analyses showed that, in left-handers, the maximum tapping rate of the non-dominant right hand was strongly correlated with the GMV of the ipsilateral CS but not significantly with that of the contralateral CS. These results may be due to differences in the organisation of motor systems between these two groups, possibly concerning a left hemispheric specialisation for fast repetitive movements in right-handers, which would be different in left-handers.

Measuring handedness: a validation study of Bishop's reaching card test

The aim of the study was the validation of Bishop's reaching card test (Bishop et al., 1996) in a French population. Annett's peg-moving test (1985) and the Purdue pegboard (Tiffin, 1948) were also used to assess manual performance. Subgroups of left- and right-handers were established according to manual preference as measured by Annett's questionnaire (1985). A sample of 260 adults was tested, including 158 self-professed right-handers, 77 self-professed left-handers, and 25 self-professed ambidextrous people. The three manual performance tests and the questionnaire presented good metric qualities (homogeneity, test-retest reliability). However the constitution of subgroups of laterality (in particular left-handers) as a function of manual preference could not be validated by classic tasks, or by Bishop's test, which is supposed to combine features of both preference and performance. Moreover the link between performance and preference was weak. Both evaluations should be used to produce a complete pattern of laterality for each participant.