Handedness and Hemispheric Asymmetry in the Control Of Movements

This study investigated the influence of hemispheric specialization of function on the motor performance of the hands. Right-handed (n=17), ambidextral (n=21), and ambisinistral (n=12) subjects performed Fitts' (1954) reciprocal tapping task under two conditions with each hand. Conditions had the same index of difficulty but differed in movement precision. The left hand of righthanders was superior in the condition requiring the greatest amount of preprogramming. Conversely, the right hand was not superior in the condition having the greatest demand for feedback control. For ambidextrals, left-hand superiority in the relatively preprogrammed condition was also revealed. Ambisinistrals showed no significant difference between conditions with either hand. The results partially support the hypothesis that the motor performance of the hands mirrors the dominant processing mode of their contralateral hemisphere. Failure to find supportive evidence in ambisinistrals is consistent with the contention that they lack hemispheric specialization of function.     

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.     

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.     

Sequential motor ability of left-handed inverted and non-inverted writers

Left-handed female subjects, categorized as using an inverted (LI) (n=7) or non-inverted (LN) (n=7) writing posture, were compared on performance of a motor task. Task parameters were manipulated to create four conditions varying in demand for sequential processing. Based on previously observed group differences in the direction and extent of hemispheric lateralization, non-inverted writers were predicated to exhibit superior left hand performance. An analysis of variance substantiated a performance superiority by the LN writers, however, post hoc analysis indicated the difference to exist only at the highest level of task difficulty. Analysis of right-hand performance revealed a significant group difference in favor of the LN writers and a group-by-sequential processing demand interaction. This interaction indicated that the decrement in performance of LI writers, relative to LN writers, increased systematically with increases in task demands for sequential processing. Since previous research indicated that inverted writers exhibit less hemispheric specialization of function, it is concluded that this bilateral representation is associated with an overall reduction in sequential processing ability.     

The effect of unilateral hand contractions on psychophysiological activity during motor performance: Evidence of verbal-analytical engagement

ObjectivesConscious engagement in movement control can influence motor performance. In most cases, the left hemisphere of the brain plays an important role in verbal-analytical processing and reasoning, so changes in the balance of hemispheric activation may influence conscious engagement in movement. Evidence suggests that unilateral hand contractions influence hemispheric activation, but no study has investigated whether there is an associated effect of hand contractions on verbal-analytical processing during motor performance. This study utilized psychophysiological (and behavioural) measures to examine whether pre-performance unilateral hand contraction protocols change verbal-analytical engagement during motor performance.DesignA repeated measures crossover design was employed.MethodsTwenty-eight participants completed three hand contraction protocols in a randomised order: left-, right- and no-hand contractions. Electroencephalography (EEG) measures of hemispheric asymmetry were computed during hand contractions. A golf putting task was conducted after each protocol. EEG connectivity between sites overlying the left verbal-analytical temporal region (T7) and the motor planning region (Fz) was computed for the 3 sec prior to movement initiation. Additionally, electrocardiography (ECG) and electromyography (EMG) signals were analysed 6 sec prior to movement initiation until 6 sec after. Golf putting performance (distance from the target) and putter swing kinematics were measured.ResultsContralateral hemisphere activity was revealed for the left-hand and right-hand contraction conditions. During motor planning, the left-hand contraction protocol led to significantly lower T7-Fz connectivity, and the right-hand contraction protocol led to significantly higher T7-Fz connectivity than the other conditions. EMG, ECG and kinematic measures did not differ as a function of condition. Importantly, T7-Fz connectivity mediated the relationship between hand squeezing and motor performance (distance from the target).ConclusionThe EEG results suggest that pre-performance unilateral hand contractions influence the extent of verbal-analytical engagement during motor planning, which in turn influences motor performance. However, the hand contractions did not influence cardiac activity, muscle activity or kinematics.     

Lateralized lexical decision in schizophrenia: hemispheric specialization and interhemispheric lexicality priming

Reports of left-hemisphere dysfunction and abnormal interhemispheric transfer in schizophrenia are mixed. The authors used a unified paradigm, the lateralized lexical decision task, to assess hemispheric specialization in word recognition, hemispheric error monitoring, and interhemispheric transfer in male, right-handed participants with schizophrenia (n=34) compared with controls (n=20). Overall, performance and error monitoring were worse in patients. However, patients like controls showed left-hemisphere superiority for lexical processing and right-hemisphere superiority for error monitoring. Only patients showed selective-interhemispheric lexicality priming for accuracy, in which performance improved when the lexical status of target and distractor stimuli presented to each hemifield was congruent. Results suggest that schizophrenia is associated with impaired monitoring and with increased interhemispheric automatic information transfer rather than with changed hemispheric specialization for language or error monitoring.     

Speech fluency and hand performance on a sequential tapping task in left- and right-handed stutterers and nonstutterers

The purpose of this study was to examine hemispheric functioning in right- and left-handed stutterers and nonstutterers using tasks that require concurrent speech and unimanual sequential tapping activity. Twenty adult stutterers (15 right-handers and 5 left-handers) and 20 adult nonstutterers (15 right-handers and 5 left-handers) performed four experimental tasks: tapping, tapping-spontaneous speech, tapping-reading, and tapping-singing. Subjects performed each task for 120 sec (8 trials of 15 sec per trial), alternating tapping hands after each trial.Results indicated that subjects' speech and manual performance were hindered by the concurrent motor activities and that stutterers demonstrated more interference than the nonstutterers. In addition, the tapping-spontaneous speech task resulted in the greatest interfering condition. Results suggest that both intrahemispheric competition and interhemispheric integration processes are involved in the regulation of speech and motor activities. Moreover, the possibility exists that a key difference between stutterers and nonstutterers may be linked to the degree to which these activities are synchronized.     

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.     

Increases in language lateralization in normal children as observed using magnetoencephalography

Previous functional magnetic resonance imaging (fMRI) studies investigating hemispheric dominance for language have shown that hemispheric specialization increases with age. We employed magnetoencephalography (MEG) to investigate these effects as a function of normal development. In sum, 22 healthy children aged 7-16 years were investigated using two language tasks: a verb-generation (VG) task and a vowel-identification (VI) task. Significant hemispheric differences were found for both tasks in cerebral language areas using oscillatory MEG spectral analyses, confirming the MEG's ability to detect hemispheric specialization for language in children. Additionally, a significant increase of this lateralization as a function of age was observed for both tasks. As performance in the VI task showed no correlation with age, this increase seems to be unrelated to performance. These results confirm an increase in hemispheric specialization as a function of normal brain maturation.     

The nature of hemispheric specialization for prosody perception

Recent evidence suggests a relative right-hemispheric specialization for emotional prosody perception, whereas linguistic prosody perception is under bilateral control. It is still unknown, however, how the hemispheric specialization for prosody perception might arise. Two main hypotheses have been put forward. Cue-dependent hypotheses, on the one hand, propose that hemispheric specialization is driven by specialization for the non-prosody-specific processing of acoustic cues. The functional lateralization hypothesis, on the other hand, proposes that hemispheric specialization is dependent on the communicative function of prosody, with emotional and linguistic prosody processing being lateralized to the right and left hemispheres, respectively. In the present study, the functional lateralization hypothesis of prosody perception was systematically tested by instructing one group of participants to evaluate the emotional prosody, and another group the linguistic prosody dimension of bidimensional prosodic stimuli in a dichotic-listening paradigm, while event-related potentials were recorded. The results showed that the right-ear advantage was associated with decreased latencies for an early negativity in the contralateral hemisphere. No evidence was found for functional lateralization. These findings suggest that functional lateralization effects for prosody perception are small and support the structural model of dichotic listening.     

Sex Differences in Perception: Exploring the Integration of Sensory Information with Respect to Vision and Proprioception

Inter- and intra-modal matching by right hand preferred Norwegian adults were tested using a matching task. The task required them to locate target pins visually, proprioceptively or in combination, while matching was always carried out without vision. When combined scores for both hands were analysed, the females showed superior performance in the intra-modal matching condition. For both groups, when the scores for the two hands were treated separately, superior performance was obtained in using the right hand to match under the visual condition. The only significant sex difference relative to hand preference was that the females matched the target more accurately with the right hand in the intra-modal matching condition. These findings are discussed relative to inter-hemispheric processing     

An effect of spatial-temporal association of response codes: understanding the cognitive representations of time

The present study addresses the question of how such an abstract concept as time is represented by our cognitive system. Specifically, the aim was to assess whether temporal information is cognitively represented through left-to-right spatial coordinates, as already shown for other ordered sequences (e.g., numbers). In Experiment 1, the task-relevant information was the temporal duration of a cross. RTs were shorter when short and long durations had to be responded to with left and right hands, respectively, than with the opposite stimulus-response mapping. The possible explanation that the foreperiod effect (i.e., shorter RTs for longer durations) is greater with right than with left hand responses is discarded by results of Experiment 2, in which right and left hand responses alternated block-wise in a variable foreperiod paradigm. Other explanations concerning manual or hemispheric asymmetries may be excluded based on the results of control experiments, which show that the compatibility effect between response side and cross duration occurs for accuracy when responses are given with crossed hands (Experiment 3), and for RTs when responses are given within one hand (Experiment 4). This pattern suggests that elapsing time, similarly to other ordered information, is represented in some circumstances through an internal spatial reference frame, in a way that may influence motor performance. Finally, in Experiment 5, the temporal duration was parametrically varied using different values for each response category (i.e., 3 short and 3 long durations). The compatibility effect between hand and duration was replicated, but followed a rectangular function of the duration. The shape of this function is discussed in relation to the specific task demands.     

Bimanual tapping of a syncopated rhythm reveals hemispheric preferences for relative movement frequencies

In bimanual multifrequency tapping, right-handers commonly use the right hand to tap the relatively higher rate and the left hand to tap the relatively lower rate. This could be due to hemispheric specializations for the processing of relative frequencies. An extension of the double-filtering-by-frequency theory to motor control proposes a left hemispheric specialization for the control of relatively high and a right hemispheric specialization for the control of relatively low tapping rates. We investigated timing variability and rhythmic accentuation in right handers tapping mono- and multifrequent bimanual rhythms to test the predictions of the double-filtering-by-frequency theory. Yet, hemispheric specializations for the processing of relative tapping rates could be masked by a left hemispheric dominance for the control of known sequences. Tapping was thus either performed in an overlearned quadruple meter (tap of the slow rhythm on the first auditory beat) or in a syncopated quadruple meter (tap of the slow rhythm on the fourth auditory beat). Independent of syncopation, the right hand outperformed the left hand in timing accuracy for fast tapping. A left hand timing benefit for slow tapping rates as predicted by the double-filtering-by-frequency theory was only found in the syncopated tapping group. This suggests a right hemisphere preference for the control of slow tapping rates when rhythms are not overlearned. Error rates indicate that overlearned rhythms represent hierarchically structured meters that are controlled by a single timer that could potentially reside in the left hemisphere.     

One year after ischemic stroke: Changes in leg movement path stability in a speed–accuracy task but no major effects on the hands

First year after the stroke is essential for motor recovery. The main motor control strategy (i.e., faster movement production at the expense of lower movement accuracy and stability, or greater movement accuracy and stability at the expense of slower movement) selected by poststroke patients during a unilateral speed–accuracy task (SAT) remains unclear. We aimed to investigate the poststroke (12 months after stroke) effects on the trade-off between movement speed and accuracy, and intraindividual variability during a motor performance task. Healthy right-handed men (n = 20; age ∼ 66 years) and right-handed men after ischemic stroke during their post rehabilitation period (n = 20; age ∼ 69 years) were asked to perform a simple reaction task, a maximal velocity performance task and a SAT with the right and left hand, and with the right and left leg. In the hand movement trial, reaction time and movement velocity (V_max) in the SAT were slower and time to V_max in the SAT was longer in the poststroke group (P < .01). In the leg movement trial, poststroke participants reached a greater V_max in the SAT than the healthy participants (P < .01). The greatest poststroke effect on intraindividual variability in movements was found for movement path in the SAT, which was significantly greater in the legs than in the hands. Poststroke patients in the first year after stroke mainly selected an impulsive strategy for speed over hand and leg motor control, but at the expense of lower movement accuracy and greater variability in movement.     

Focus of attention and automaticity in handwriting

This study investigated the nature of automaticity in everyday tasks by testing handwriting performance under single and dual-task conditions. Item familiarity and hand dominance were also manipulated to understand both cognitive and motor components of the task. In line with previous literature, performance was superior in an extraneous focus of attention condition compared to two different skill focus conditions. This effect was found only when writing with the dominant hand. In addition, performance was superior for high familiarity compared to low familiarity items. These findings indicate that motor and cognitive familiarity are related to the degree of automaticity of motor skills and can be manipulated to produce different performance outcomes. The findings also imply that the progression of skill acquisition from novel to novice to expert levels can be traced using different dual-task conditions. The separation of motor and cognitive familiarity is a new approach in the handwriting domain, and provides insight into the nature of attentional demands during performance.     

Manual behavior, lateralization of manual skills and cognitive performance of preschool children

Direction and degree of manual specialization (functional asymmetry between the hands) on a pegboard task, and fine motor ability (total number of pegs inserted) of both hands were correlated with verbal and visuospatial performances for 47 preschool children. No significant differences were found between right-, and left-, and mixed-handers even though the best motor skills were shown by the 6 mixed-handed subjects, who also had the highest scores on cognitive tasks. Verbal and visuospatial performances were not correlated with degree or direction of manual specialization. They were instead correlated with the level of motor ability of both hands. Motor maturation should be viewed, then, as a process that implies a richer motor performance of both hands and could be interpreted as a more specific diagnostic parameter than the traditional indices of handedness in cognitive fields.     

Hemispheric specialization for speech perception in language deficient kindergarten children

Twenty right-handed kindergarten children with superior language skills and twenty with deficient language skills (as defined by performance on an elicited sentence repetition task) were tested (1) for hemispheric specialization for speech perception with a dichotic CV syllable task and (2) for relative manual proficiency by means of a battery of hand tasks. Reading readiness and aspects of other cognitive abilities were also assessed. The superior children evidenced a mean right-ear advantage of 14.5%, which is consistent with normal values reported by other investigators using the same stimuli. The language deficient group evidenced essentially no mean ear advantage (0.5) with half of these subjects exhibiting left-ear superiority. The findings suggest relationships among cerébral dominance, language proficiency (including reading readiness), and general cognitive functioning.     

Behavioral and physiological findings of gender differences in global-local visual processing

Hemispheric asymmetries in global-local visual processing are well-established, as are gender differences in cognition. Although hemispheric asymmetry presumably underlies gender differences in cognition, the literature on gender differences in global-local processing is sparse. We employed event related brain potential (ERP) recordings during performance of a global-local reaction time task to compare hemispheric asymmetries and processing biases in adult men (n=15) and women (n=15). Women responded more quickly to local targets while men did not differentially respond to hierarchical stimuli. ERP data indicated that women had P100 responses that were selectively lateralized to the left hemisphere in response to local targets and N150 responses that were smaller for global targets. They also had P300 responses that were greater following local stimuli. The physiological data demonstrate that male-female performance differences arise from biologically based differences in hemispheric asymmetry. Findings are discussed in the context of existing literature regarding gender differences, hemispheric specialization, and the role of stimulus characteristics.     

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.     

Visual versus kinesthetic mental imagery: Efficacy for the retention and transfer of a closed motor skill in young children

The main purposes of this study were (a) to compare the effects of mental imagery combined with physical practise and specific physical practise on the retention and transfer of a closed motor skill in young children; (b) to determine the mental imagery (visual vs. kinesthetic), which is the most efficient for retention and transfer of a closed motor skill; and (c) to verify the relationship between movement image vividness and motor performance. As for the secondary purpose, it was to compare the effects of gender on motor learning. Participants (n = 96) were selected from 3 primary schools. These participants were divided into 6 groups and submitted to different experimental conditions. The experimental task required the participants to throw, with the nondominant hand (left hand), a ball toward a target composed of 3 concentric circles. The results demonstrated that performance obtained by the mental imagery (visual or kinesthetic) combined with physical practise group was, during the retention phase, equivalent to that produced by the specific physical practise group but significantly superior during the transfer of closed motor skill. These results showed the potential benefits of mental imagery as a retention strategy intended for motor skills and performance enhancement. Such results could be explained by the similarity of 3 principal functional evidences shared by mental and physical practise: behavioural, central, and peripheral (as suggested by Holmes & Collins, 2001). (PsycINFO Database Record (c) 2008 APA, all rights reserved).