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.     

Motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task

The issue of handedness has been the topic of great interest for researchers in a number of scientific domains. It is typically observed that the dominant hand yields numerous behavioral advantages over the non-dominant hand during unimanual tasks, which provides evidence of hemispheric specialization. In contrast to advantages for the dominant hand during motor execution, recent research has demonstrated that the right hand has advantages during motor planning (regardless of handedness), indicating that motor planning is a specialized function of the left hemisphere. In the present study we explored hemispheric advantages in motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task. Replicating previous findings, both motor planning and execution was influenced by object end-orientation congruency. In addition, although motor planning (i.e., end-state comfort) was not influenced by hand or handedness, motor execution differed between left and right hand, with shorter object transport times observed for the left hand, regardless of handedness. These results demonstrate that the hemispheric advantages often observed in unimanual tasks do not extend to discrete bimanual tasks. We propose that the differences in object transport time between the two hands arise from overt shifting visual fixation between the two hands/objects.     

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.     

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).     

Development of unimanual versus bimanual task performance in an isometric task

Sixty-three children between 5 and 12 years of age and 15 adults performed a unimanual and a bimanual isometric force task. The performance of the preferred hand in the unimanual task was compared to the performance of the preferred hand in the bimanual task. It was hypothesized that in the bimanual task the absolute error will be higher, there will be more irregularity and the participants will need more time due to the additional effort from the central nervous system, especially with respect to the communication between the hemispheres. Furthermore, in younger children bimanual force variability was expected to be higher due to developmental aspects concerning callosal maturation and attention. It was found that with respect to force generation the preferred hand was not affected by bilateral isometric force generation, but with respect to force regulation it was. The coefficient of variation (CV) of the force was 34% larger in the bimanual task as compared to the unimanual task. For the time to target force, the increase was 28%. With repetition of the trials the CV decreased in the bimanual task, but only in the youngest age group. During development there was no change in absolute error, yet there was a major reduction in force variability in the bimanual task. It is suggested that improvement in interhemispheric communication and in the ability to focus attention plays a role in the decrease in variability with age.     

Hand preferences in unimanual and bimanual feeding by wild vervet monkeys (Cercopithecus aethiops)

Lateral preference was examined in spontaneous feeding actions in 2 troops of wild vervet monkeys (Cercopithecus aethiops). Processing of 4 foods (termites, leaf shoots, sugarcane, and fruit) was studied. Actions included unimanual reaching to moving objects, operating from an unstable posture, and coordinated bimanual processing. Between 19 and 31 subjects were available, according to the task. In 2 tasks, laterality of 2 independent stages was measured separately, giving 6 measures in all. On 4 of these measures, most monkeys were ambipreferent, and only a few showed significant hand preferences. Only for termite feeding and detaching material from fruits did the majority show significant lateralization; no tasks elicited exclusive use of 1 hand. Preference appeared labile, because in 2 tasks, population trends reversed with increasing age. No population trends to left or right were found; instead, these monkeys showed ambilaterality, with lateralization associated with task complexity.     

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.     

Subliminal priming and effects of hand dominance

In the masked priming paradigm, motor responses to targets are influenced by previously presented subliminal primes, and are guided by facilitatory and inhibitory mechanisms that depend on prime-target compatibility/duration. In this study, we evaluate subliminal-driven priming in right- and left-handers during unimanual as well as bimanual tasks. The data from the unimanual tasks confirmed that prime-target compatibility affects performance as a function of prime-target duration. In a bimanual setting, the preferred hand benefitted from facilitation in both handedness groups whereas the non-preferred hand showed a positive priming effect only in left-handers. This denotes that left-handers are more susceptible to response activation of either hand. In addition, inhibitory priming had a stronger effect on the non-preferred than preferred hand, independent of handedness group. Overall, the findings suggest that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions.     

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.     

Effects of S-R and R-R compatibility on bimanual movement time

Bimanual asymmetrical movements are generally found to be slower than symmetrical movements but asymmetrical movement normally involves visual separation of targets which might account for the effect. By using a system in which the subject controls two cursors on an oscilloscope screen by moving two levers the S-R relationship on either hand can be reversed, thus providing an asymmetrical movement task without visual separation of targets. Movement times for five right-handed subjects were recorded on four unimanual and six bimanual conditions varying with respect to both S-R and R-R compatibility. In the unimanual conditions, the left hand was found to be as fast as the right when the opposite S-R relationship was used. In the bimanual tasks visual separation of targets was a relatively minor factor movement time being strongly influenced by S-R compatibility and to a lesser degree by R-R compatibility. The results suggest that compatibility, rather than being a property of a single central channel, differs, as between the two cerebral hemispheres.     

Hand preferences and hand ability in congenitally blind children

Congenitally blind and sighted blindfolded children between the ages of 6 and 14 years were tested for hand preference with performance tasks. There were no differences between the groups in direction or degree of hand preference. The degree of handedness increased with age and was essentially linear though the blind seemed to be somewhat less lateralized at the younger ages.

When the same groups were required to match three-dimensional bricks for height, depth, breadth, and volume, no hand advantages were found for either group. Both groups of children improved in their accuracy of spatial discriminations with age.

Further, the degree of lateralization on the handedness task did not relate to ability on the tactile task or to differences between the right and left hands on the tactile task. Thus, there is no effect of blindness on tactile matching ability nor is there an effect of the hand used in the task.     

Visuospatial reaching preferences of common marmosets (Callithrix jacchus): an assessment of individual biases across a variety of tasks

Using multiple measures of hand preference, the authors investigated lateralization at an individual level in 21 common marmosets. Despite showing group biases for sensory and communication functions, these same marmosets did not show a group bias in direction of lateralized hand use. Hand preferences were recorded on four novel reaching tasks requiring different levels of visual guidance and postural control. As found for simple food holding (with the same subjects), they displayed strong individual hand preferences but no group bias indicative of handedness. The strength of hand preference was influenced by task demands: stronger preferences were expressed when subjects adopted a suspended posture, and when "successful" versus "unsuccessful" foraging strategies were compared. Comparisons between visuospatial reaching and simple food holding preferences also revealed that half of the subjects displayed a division of function between the hands/hemispheres; subjects displayed opposing preferences in simple and visuospatial reaching, which would be beneficial for the performance of coordinated bimanual tasks. Given the apparent absence of a selective advantage for handedness, the authors suggest that hand preferences may reflect hemispheric dominance of other cognitive domains (i.e., temperament).     

Multiple measures of hand-use lateralization in the ring-tailed lemur (Lemur catta)

Evaluated a free-ranging matriline of 13 ring-tailed lemurs (Lemur catta) from videotaped records for lateralized hand use with 2 tasks and 4 measures: food reaching, feeding posture, duration of food holding, and manipulation of food between mouth and hand while eating. Binomial z scores determined 7 lemurs to be left preferent in reaching, 3 right, and 3 ambipreferent. Ideographic analyses suggested possible sex-linked and early experience twin effects. When compared to right and ambipreferent lemurs, left reach preferent lemurs used the left hand more but bimanuals grasped less in food holding and also engaged in less hand-mouth food manipulation. The tendency to manipulate food was not correlated with bimanual holding but was inversely related to left hand holding and directly related to right hand holding. These patterns are discussed as possible precursors of human bimanual manipulation.     

Kinematic parameters of hand movement during a disparate bimanual movement task in children with unilateral Cerebral Palsy

Children with unilateral Cerebral Palsy (uCP) experience problems performing tasks requiring the coordinated use of both hands (bimanual coordination; BC). Additionally, some children with uCP display involuntary symmetrical activation of the opposing hand (mirrored movements). Measures, used to investigate therapy-related improvements focus on the functionality of the affected hand during unimanual or bimanual tasks. None however specifically address spatiotemporal integration of both hands. We explored the kinematics of hand movements during a bimanual task to identify parameters of BC. Thirty-seven children (aged 10.9 ± 2.6 years, 20 male) diagnosed with uCP participated. 3D kinematic motion analysis was performed during the task requiring opening of a box with their affected- (AH) or less-affected hand (LAH), and pressing a button inside with the opposite hand. Temporal and spatial components of data were extracted and related to measures of hand function and level of impairment. Total task duration was correlated with the Jebsen–Taylor Test of Hand Function in both conditions (either hand leading with the lid-opening). Spatial accuracy of the LAH when the box was opened with their AH was correlated with outcomes on the Children’s Hand Use Experience Questionnaire. Additionally, we found a subgroup of children displaying non-symmetrical movement interference associated with greater movement overlap when their affected hand opened the box. This subgroup also demonstrated decreased use of the affected hand during bimanual tasks. Further investigation of bimanual interference, which goes beyond small scaled symmetrical mirrored movements, is needed to consider its impact on bimanual task performance following early unilateral brain injury.     

Maternal cradling bias in baboons: The first environmental factor affecting early infant handedness development?

The most emblematic behavioral manifestation of human brain asymmetries is handedness. While the precise mechanisms behind the development of handedness are still widely debated, empirical evidences highlight that besides genetic factors, environmental factors may play a crucial role. As one of these factors, maternal cradling behavior may play a key role in the emergence of early handedness in the offspring. In the present study we followed 41 Papio anubis infants living in social groups with their mother for which direction (e.g., left- or right-arm) and degree of maternal cradling-side bias were available from a previous published study. We assessed hand preferences for an unimanual grasping task at three developmental stages: (A) 0–4, (B) 4—6, and (C) 9–10 months of age. We found that individual hand preferences for grasping exist as soon as the first months of age, with a population-level left-handedness predominance, being stable until 6 months; to wit the period during which juveniles are mainly carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later in the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age), are less dependent from the maternal cradling bias and less consistent with the earlier developmental stages, especially in infants initially cradled on the right maternal side. Our findings suggest that the ontogenetic dynamics of the infant's hand preference and its changes might ultimately rely on the degree of infant dependence from the mother across development.     

Experimental field study of hand preference in wild black-horned (<Emphasis Type="Italic">Cebus nigritus</Emphasis>) and white-faced (<Emphasis Type="Italic">Cebus capucinus</Emphasis>) capuchins: evidence for individual and species differences

In this experimental field investigation, we compare the degree to which wild capuchins in Brazil (Cebus nigritus) and Costa Rica (Cebus capucinus) exhibit individual- and population-level handedness during three visually-guided tasks. These tasks required reaching to remove a large leaf covering a hidden food reward, seizing the food reward, and manipulating a tool (pulling a wooden dowel) in order to obtain access to an embedded food reward. Studies in some populations of captive capuchins indicate evidence for both individual hand preferences and population-level handedness. In this study, six of eight wild C. capucinus and six of seven wild C. nigritus exhibited a significant hand preference during individual tasks, but no individual exhibited a consistent preference across all three tasks. Task-specialization, or the tendency for most individuals in the same group or population to use the same hand to accomplish a particular task, also was evaluated. Cebus nigritus showed a significant bias toward the use of the right hand in removing the leaf. Although the number of individual capuchins in both species that manipulated the dowels was limited (N = 7), each individual that manipulated the dowels in eight or more instances had a positive handedness index, suggesting a greater use of the right hand to accomplish this task. Overall, our results provide preliminary support for individual- and population-level handedness in wild capuchin monkeys.     

Development of lateral asymmetry in the perception of sequentially touched fingers

In order to investigate lateral asymmetry in tactile perception, two or four fingers of normal primary school children were touched sequentially. Stimulation was either unimanual or bimanual and either verbal or nonverbal responses were required. Right hand advantage was demonstrated subsequent to uni- and bimanual stimulation in both the verbal and nonverbal response conditions. Neither an age nor a sex effect on laterality was found. Right hand advantage was affected by direction of stimulation in the bimanual condition. Left hemispheric dominance was argued to be related to the temporal nature of the tasks.     

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.     

Bimanual interference in children performing a dual motor task

The present study addressed the development of bimanual interference in children performing a dual motor task, in which each hand executes a different task simultaneously. Forty right-handed children (aged 4, 5-6, 7-8 and 9-11years, ten in each age group) were asked to perform a bimanual task in which they had to tap with a pen using the non-preferred hand and simultaneously trace a circle or a square with a pen using the preferred hand as quickly as possible. Tapping and tracing were also performed unimanually. Differences between unimanual and bimanual performance were assessed for number of taps, length of tap trace and mean tracing velocity. It was assumed that with increasing age, better bimanual coordination would result in better performance on the dual task showing less intermanual interference. The results showed that tapping and tracing performance increased with age, unimanually as well as bimanually, consistent with developmental advancement. However, the percentage of intermanual interference due to bimanual performance was not significantly different in the four age groups. Although performing the dual task resulted in mutual intermanual interference, all groups showed a significant effect of tracing shape. More specifically, all age groups showed a larger percentage decrease in tracing velocity when performing the circle compared to the square in the dual task. The present study reveals that children as young as four years are able to coordinate both hands when tapping and tracing bimanually.     

Bimanual coordination dynamics in poststroke hemiparetics

Poststroke hemiparetic individuals (n = 9) and a control group (n = 9) completed a frequency-scaled circle-drawing task in unimanual and bimanual conditions. Measures of intralimb spatial and temporal task accuracy and interlimb coordination parameters were analyzed. Significant reductions in task performance were seen in both limbs of the patients and controls with the introduction of bimanual movement. Spatial performance parameters suggested that the 2 groups focused on different hands during bimanual conditions. In the controls, interlimb coordination variables indicated predictable hand dominance effects, whereas in the patient group, dominance was influenced by the side of impairment and prior handedness of the individual. Therefore, in this particular bimanual task, performance improvements in the hemiplegic side could not be elicited. Intrinsic coupling asymmetries between the hands can be altered by unilateral motor deficits.