Reduced asymmetry in motor skill learning in left-handed compared to right-handed individuals

Hemispheric specialization for motor control influences how individuals perform and adapt to goal-directed movements. In contrast to adaptation, motor skill learning involves a process wherein one learns to synthesize novel movement capabilities in absence of perturbation such that they are performed with greater accuracy, consistency and efficiency. Here, we investigated manual asymmetry in acquisition and retention of a complex motor skill that requires speed and accuracy for optimal performance in right-handed and left-handed individuals. We further determined if degree of handedness influences motor skill learning. Ten right-handed (RH) and 10 left-handed (LH) adults practiced two distinct motor skills with their dominant or nondominant arms during separate sessions two–four weeks apart. Learning was quantified by changes in the speed–accuracy tradeoff function measured at baseline and one-day retention. Manual asymmetry was evident in the RH group but not the LH group. RH group demonstrated significantly greater skill improvement for their dominant-right hand than their nondominant-left hand. In contrast, for the LH group, both dominant and nondominant hands demonstrated comparable learning. Less strongly-LH individuals (lower EHI scores) exhibited more learning of their dominant hand. These results suggest that while hemispheric specialization influences motor skill learning, these effects may be influenced by handedness.     

Asymmetric division of labor in human skilled bimanual action: the kinematic chain as a model

This article presents a tentative theoretical framework for the study of asymmetry in the context of human bimanual action. It is emphasized that in man most skilled manual activities involve two hands playing different roles, a fact that has been often overlooked in the experimental study of human manual lateralization. As an alternative to the current concepts of manual preference and manual superiority-whose relevance is limited to the particular case of unimanual actions-the more general concept of lateral preference is proposed to denote preference for one of the two possible ways of assigning two roles to two hands. A simple model describing man's favored intermanual division of labor in the model are the following. 1) The two hands represent two motors, that is, decomplexity is ignored in the suggested approach. 2) In man, the two manual motors cooperate with one another as if they were assembled in series, thereby forming a kinematic chain: In a right-hander allowed to follow his or her lateral preferences, motion produced by the right hand tends to articulate with motion produced by the left. It is suggested that the kinematic chain model may help in understanding the adaptive advantage of human manual specialization.     

The influence of a hand preference for acquiring objects on the development of a hand preference for unimanual manipulation from 6 to 14 months

Development of hand preferences for unimanual manipulation of objects was explored in 90 infants (57 males) tested monthly from 6 to 14 months. From a larger sample of 380 infants, 30 infants with a consistent left hand preference for acquiring objects were matched for sex and development of locomotion skills with 30 infants with a consistent right hand preference for acquisition and 30 with no preference. Although frequency of unimanual manipulations increased during 6–14 month period, infants with a hand preference for acquisition did more object manipulations than those without a preference for acquisition. Multilevel modeling of unimanual manipulation trajectories for the three hand-preference groups revealed that hand preferences for unimanual manipulation become more distinctive with age, and the preference is predicted by the hand preference for object acquisition. Infants with a right and left hand preference for object acquisition develop a right and left (respectively) hand preference for unimanual manipulation. However, the majority of infants at each month do not exhibit hand preferences for unimanual manipulation that are unlikely to occur by chance, even by 14 months. The results are consistent with a cascading theory of handedness development in which early preferences (i.e., for acquisition) are transferred to later developing preferences (i.e., for unimanual manipulation).     

Unimanual performance across the age span

The purpose of the current investigation was to examine the age-related changes in the performance of the two hands on the Annett pegboard (Annett, 1970). The current study was part of a large-scale study investigating the development of unimanual and bimanual performance. Three hundred and two right-handed individuals participated in the present study, comprising five different age groups (3-5 year olds, 6 and 7 year olds, 8 and 9 year olds, 10-12 year olds, and 19-24 year olds). All participants completed the Waterloo Handedness Questionnaire and the standard Annett pegboard. Analyses revealed significant overall performance differences between the hands, as expected, where the right hand was significantly faster than the left hand. Additionally, significant performance differences between the hands were noted as a function of age. More specifically, the adults showed a much smaller performance difference between the hands than the other age groups. The results are discussed in light of current theories of the development of hand preference and manual asymmetry.     

Posture and target location effects on manual preference

Twenty-nine right-handed participants made unimanual movements to 5 target locations while standing and while balancing on a rocker platform. Manual preference was affected by target location (p < .001; manual preference tended to be concordant with target hemispace) and posture (p < .05; responses from the rocker platform were associated with a lower level of right-hand responding). A location by posture interaction (p < .05) indicated that the effect of posture was present only for targets in left hemispace; the right hand was used less frequently in the rocker condition than simple standing. Manual preference is viewed as a process of response selection motivated by an effort to minimize neural processing and mechanical costs.     

The development of hand preference in children: The effect of task demands and links with manual dexterity

Lateralisation of hand preference and manual dexterity are known to develop over childhood, while in adulthood strength of hand preference has been shown to interact with extrinsic task demands. Some evidence exists to suggest that strength of hand preference and motor skill may be related. In the current study a handedness inventory, midline crossing (QHP) and peg-moving tasks were used to investigate: (1) the development of hand preference between 4 and 11 years; (2) whether extrinsic task demands affect strength of hand preference, and (3) whether strength of hand preference was associated with manual dexterity. Younger children (4–5 years) showed weak hand preference in comparison to older children (8–11 years), and extrinsic task demands influenced willingness to cross the body’s midline with the preferred hand. Age and peg-moving speed were associated with midline crossing in certain task conditions. Overall, results suggest a coupling between manual dexterity and brain maturation in typical development.     

Hand preference and performance on unimanual and bimanual tasks in capuchin monkeys (Cebus apella)

Patterns of manual preference and the extent to which preference provided a benefit in performance (movement time) were evaluated in 7 young adult capuchin monkeys (Cebus apella). Directions of preference were inconsistent within individual animals across home-cage activities, unimanual, and bimanual experimental tasks. Preferences were more strongly expressed in the experimental tasks than in the home cage. A left bias in the population for prehension, predicted by recent theories, was not evident in any setting. Movement time was moderately negatively correlated with degree of preference within experimental tasks. The benefit to performance conferred by lateral preference was not dependent on whether the right or left hand was preferred. Lateralization of prehension appears to be a flexible process in these monkeys, which can result in quickly realized benefits in some conditions.     

The acquisition of bimanual coordination is mediated by anisotropic coupling between the hands

The present study was designed to test two predictions from the coupled oscillator model of multifrequency coordination. First, it was predicted that multifrequency tasks that match the inherent manual asymmetry (i.e., the preferred hand assigned to the faster tempo) would be easier to learn than tasks that do not match the inherent dynamics (i.e., the non-preferred hand assigned to the faster tempo). Second, in the latter case acquisition of the multifrequency coordination would involve a reorganisation of the coupling dynamics such that the faster hand would exert a greater influence on the slower hand than vice versa. Sixteen right-handed volunteers received extensive training on a 2:1 coordination pattern involving a bimanual forearm pronation-supination task. Participants were randomly assigned to one of two groups: 1L:2R in which the preferred right hand performed the higher frequency, or 2L:1R in which the non-preferred left hand performed the higher frequency. The dynamic stability of the patterns was assessed by the ability of participants to maintain the coordination pattern as movement frequency was increased. Changes in the directional coupling between the hands was assessed by transition pathways and lead-lag relationship evident in a 1:1 anti-phase frequency-scaled coordination task performed prior to and following three practice sessions of the 2:1 task. The predicted differential stability between the multifrequency patterns was evident in the initial acquisition sessions but by the end of training the two patterns evidenced equivalent stability. Unexpectedly, for both groups the fast hand displayed greater variability in amplitude and movement frequency than the slow hand perhaps reflecting anchoring afforded to the slow hand by synchronising movement endpoints with the auditory pacing metronome. Analysis of pre- to post-training changes to the coupling dynamics in the 1:1 anti-phase task support the hypothesis that acquisition of the 2L:1R pattern involved reorganisation of the inherent dynamics.     

Development of hand preferences in marmosets (Callithrix jacchus) and effects of aging

The authors investigated the development of unimanual hand use and hand preferences during feeding in 15 marmosets (Callithrix jacchus), ages birth to 51-70 months. Bimanual hand use was common at 1-2 months, but by 5-8 months unimanual holding had developed and so had significant hand preferences. Half of the marmosets preferred to pick up and take food to the mouth with the left hand, and half preferred the right hand. Individuals maintained the same hand preference at all ages examined. Significant relationships were also found between the postures adopted during feeding and the direction of hand preferences displayed by juvenile marmosets. There was a positive correlation between increased suspension and increased left-hand preference, and a negative correlation between increased feeding in a tripedal posture and increased left-hand preference. These results are discussed in terms of motor development and hemispheric specialization.     

Lateral asymmetries in the development of the overarm throw

Lateral asymmetries of manual, pedal, and ocular preferences, and motor asymmetry in the performance of the forceful overarm throw were analyzed in 71 children aged 4 to 10 years old. Performance with each side of the body was assessed on the basis of qualitative analysis, as proposed by M. A. Roberton and L. Halverson (1984) for identification of developmental stages by components of the task. Lateral preference was indicated by the frequency the children used the right or the left side of their body to carry out different manual, pedal, and ocular tasks. The overarm throw movement pattern was developed with both sides of the body but at different levels. Development of the nondominant side lagged behind that of the dominant side at all ages; a significant asymmetry in performance detected in the 4-year-olds was stable up to the age of 10 years. Indices of asymmetry for lateral preference and performance were found to be specific because no consistent correlations were observed among them throughout the age periods studied. Those results show the multidimensional character of human laterality and imply a property of motor development that prevents asymmetry of performance from increasing because of unilateral practice.     

Asymmetric haptic function and manual motor efficiency in blind children aged 6 to 14

Forty-eight congenitally blind children aged 6 to 14 were asked to discriminate and recognize Braille characters unimanually and to perform unimanual motor tasks which tested tapping ability and grip-strength. Haptic and motor efficiency scores increased with age, but no specific relationships were found between ipsilateral haptic and motor scores. Exploring Braille characters was faster in bimanual than unimanual conditions, but right-hand scores did not differ from left-hand scores. The role of blindness in manual functional asymmetry is discussed.     

Unimanual tapping during concurrent articulation: examining the role of cortical structures in the execution of programmed movement sequences

Three experiments were conducted to examine effects of speech on concurrent unimanual tapping. Experiments 1 and 2 involved the manual tapping of a short burst of preprogrammed responses with or without concurrent articulation. Results of these experiments showed no effects of speech articulation on the concurrent execution of programmed manual movement sequences. In Experiment 3, subjects continuously tapped for 15 sec, again, with or without concurrent speech articulation. The results showed that articulation affected the speed of concurrent manual responses with larger interference for right hand tapping than for left hand tapping. Additional analysis of the tapping variability revealed equivalent effects of concurrent articulation on the timing of repetitive right and left hand tapping. Kinsbourne's Functional Cerebral Distance Principle was used to interpret these results. Within this framework, the present findings indicate that functionally distinct processes control speech articulation and the execution of programmed manual movement sequences.     

A developmental analysis of the relationship between hand preference and performance: II. A performance-based method of measuring hand preference in children

The present study describes a performance-based method of measuring hand preference in children. Three aspects of handedness were considered to be important in developing the paradigm (a) overall hand preference across a number of tasks, (b) consistency of hand use and, (c) the use of the preferred hand in a bimanual task. The new paradigm, termed the WatHand Box Test (WBT), requires participants to perform a variety of unimanual tasks such as, using a hammer, tossing a ball, and opening a lock with a key. To determine the validity of the WBT and examine the developmental trends in hand preference, eighty right-handed children and adults (ages 3-4, 6-7, 9-10, and 18-24 years) performed the WBT. First, the WBT was found to correlate significantly with scores on a standard hand preference questionnaire for the adults. As well, significant developmental trends were noted in hand preference as measured by the WBT. Most specifically, three- and four-year-olds had significantly lower scores on the WBT indicating a less stable pattern of hand preference than in the other three age groups.     

Is handedness just response bias?

Although most people prefer to use the right hand for unimanual tasks, it is unknown whether handedness arises from response bias. Whether it does is a question inspired by signal detection theory. We drew on the framework of signal detection theory to assess bias and sensitivity in hand choice by asking right-handers to choose between two tasks—one performed with the left hand, and one performed with the right. For some participants, the left-hand task stayed constant while the right-hand task was varied. For other participants, the right-hand stayed constant while the left-hand task was varied. We reasoned that if hand preference only reflected bias, participants would choose the generally preferred hand to the same degree, regardless of whether its task was constant or varied. Our participants followed this strategy only to some extent, suggesting that bias and sensitivity both contribute to hand preference.     

The distribution and development of handedness for manual gestures in captive chimpanzees (Pan troglodytes)

This article describes the distribution and development of handedness for manual gestures in captive chimpanzees. Data on handedness for unimanual gestures were collected in a sample of 227 captive chimpanzees. Handedness for these gestures was compared with handedness for three other measures of hand use: tool use, reaching, and coordinated bimanual actions. Chimpanzees were significantly more right-handed for gestures than for all other measures of hand use. Hand use for simple reaching at 3 to 4 years of age predicted hand use for gestures 10 years later. Use of the right hand for gestures was significantly higher when gestures were accompanied by a vocalization than when they were not. The collective results suggest that left-hemisphere specialization for language may have evolved initially from asymmetries in manual gestures in the common ancestor of chimpanzees and humans, rather than from hand use associated with other, non-communicative motor actions, including tool use and coordinated bimanual actions, as has been previously suggested in the literature.     

Impact of Handedness Consistency on Bimanual and Unimanual Continuous Movements

Bimanual coordination is an essential human function requiring efficient interhemispheric communication to produce coordinated movements. Previous research suggests a “bimanual advantage” phenomenon, where completing synchronized bimanual tasks results in less variability than unimanual tasks. Additionally, of hand dominance has been shown to influence coordinated performance. The present study examined the bimanual advantage in individuals with consistent and inconsistent handedness. It was predicted that participants with consistent handedness would not display a bimanual advantage unlike those with inconsistent handedness. Fifty-six young adults completed a finger-tapping paradigm in five conditions: unimanual tapping with either left or right hand, in-phase bimanual tapping, and out-of phase bimanual tapping led by either left or right hand. Results were not consistent with the hypothesis that participants with consistent handedness displayed the “bimanual advantage”. However, the “bimanual advantage” was not evident for the inconsistent handers when the temporal consistency was measured with either the left or right hand only. Overall, the “bimanual advantage” may be dependent upon consistency of hand preference, as well as the direction of hand dominance.     

Behavioral asymmetries of psychomotor performance in rhesus monkeys (Macaca mulatta): a dissociation between hand preference and skill.

Hand preferences were recorded for 35 rhesus monkeys (Macaca mulatta) as they manipulated a joystick in response to 2 computerized tasks. These preferences were then used to contrast 8 left- and 10 right-handed subjects on performance measures of hand skill. Individual hand preferences were found, but no significant population asymmetry was observed across the sample. However, the performance data reveal substantial benefits of right-handedness for joystick manipulation, as this group of monkeys mastered the 2 psychomotor tasks significantly faster than did their left-handed counterparts. The data support earlier reports of a right-hand advantage for joystick manipulation and also support the importance of distinguishing between hand preference and manual performance in research on functional asymmetries.     

Asymmetric control of force and symmetric control of timing in bimanual finger tapping

An experiment was conducted to examine the control of force and timing in bimanual finger tapping. Participants were trained to produce both unimanual (left or right hand) and bimanual finger-tapping sequences with a peak force of 200 g and an intertap interval (ITI) of 400 ms. During practice, visual force feedback was provided pertaining to the hand performing the unimanual tapping sequences and to either the dominant or the nondominant hand in the bimanual tapping sequences. After practice, the participants produced the learned unimanual and bimanual tapping sequences in the absence of feedback. In those trials the force produced by the dominant (right) hand was significantly larger than that produced by the nondominant (left) hand, in the absence of a significant difference between the ITIs produced by both hands. Furthermore, after unilateral feedback had been provided of the force produced by the nondominant hand, the force output of the dominant hand was significantly more variable than that of the nondominant hand. In contrast, after feedback had been provided of the force produced by the dominant hand, the variability of the force outputs of the two hands did not differ significantly. These results were discussed in the light of both neurophysiological and anatomical findings, and were interpreted to imply that the control of timing (in bimanual tasks) may be more tightly coupled in the motor system than the control of force.     

Pathological left-handedness and familial sinistrality in relation to degree of mental retardation

The relationship between personal and familial hand preference and mental retardation was examined. Six unimanual tasks were performed by 232 subjects within four mental retardation severity groups. Family handedness histories were obtained. Right hand preference varied inversely with severity of mental retardation. The handedness of mentally retarded groups at the different functional levels paralleled, but tended much more to the sinistral, than that of the corresponding parent groups. The parent-proband handedness correlations were largely insignificant, especially in lower functioning groups. The findings support both pathological left-handedness theory and an association between brain damage causing mental retardation and familial sinistrality.     

Bimanual reaching across the hemispace: Which hand is yoked to which?

When both hands perform concurrent goal-directed reaches, they become yoked to one another. To investigate the direction of this coupling (i.e., which hand is yoked to which), the temporal dynamics of bimanual reaches were compared with equivalent-amplitude unimanual reaches. These reaches were to target pairs located on either the left or right sides of space; meaning that in the bimanual condition, one hand's contralateral (more difficult) reach accompanied by the other hand's ipsilateral (easier) reach. By comparing which hand's difficult reach was improved more by the presence of the other hand's easier ipsilateral reach, we were able to demonstrate asymmetries in the coupling. When the cost of bimanual reaching was controlled for the contralateral reaching left hand's performance was improved, suggesting that the left hand is yoked to the right during motor output. In contrast, the right hand showed the greatest improvements for contralateral reaching in terms of reaction time, pointing toward a dominant role for the left hand in the processes prior to movement onset. The results may point toward a mechanism for integrating the unitary system of attention with bimanual coordination.