Do "right-armed" lefthanders have different lateralization of motor control for the proximal and distal musculature?

Expertise- and Tempo-Related Performance Differences in Unimanual Drumming

BACKGROUND

High-speed drumming requires precise control over the timing, velocity, and magnitude of striking movements.

AIM

To examine effects of tempo and expertise on unaccented repetitive drumming performance using 3D motion capture.

METHODS

Expert and amateur drummers performed unimanual, unaccented, repetitive drum strikes, using their dominant right hand, at five different tempi. Performance was examined with regard to timing variability, striking velocity variability, the ability to match the prescribed tempo, and additional variables.

RESULTS

Permutated multivariate analysis of variance (PERMANOVA) revealed significant main effects of tempo (p < .001) and expertise (p <.001) on timing variability and striking velocity variability; low timing variability and low striking velocity variability were associated with low/medium tempo as well as with increased expertise. Individually, improved precision appeared across an optimum tempo range. Precision was poorest at maximum tempo (400 hits per minute) for precision variables.

CONCLUSIONS

Expert drummers demonstrated greater precision and consistency than amateurs. Findings indicate an optimum tempo range that extends with increased expertise.

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.

DOES DYSLEXIA DEVELOP FROM LEFT-EYE DOMINANCE?

The purpose of this theoretical analysis and synthesis is to indicate how left-eye sighting dominance may lead to reading failure through dysfunctional right hemisphere letter encoding. Differing compensatory strategies are postulated to lead to outcomes that include the development of the phonologically impaired and phonologically proficient subtypes of dyslexia as well as specific spelling disability. Evidence is presented indicating that these disorders might be prevented by delaying the introduction of letter writing until the age of 8 years. Early childhood speech categorization in children genetically at-risk of developing dyslexia is also considered from this perspective. Convergent support for this premature writing hypothesis is provided by a comparison with the development of the left-hand inverted writing posture.

Lateral preference patterns as possible correlates of successfully switched left hand writing: Data and a theory

Left-handers often have had to contend with pressure to switch their preferred writing hand and shift attempt reports are common, especially among older adult left-handers. Three groups of left-handers can be defined by combining two variables, writing hand side and the report of a rightward hand preference shift attempt. The three groups are, first, right hand writers who report a rightward shift (successfully shifted left-handers); second, left hand writers who report a rightward shift attempt (unsuccessfully shifted left-handers); and, finally, left hand writers who do not report a rightward shift attempt. The underlying mechanisms that determine the success or failure of a handwriting shift attempt remain unclear. The present study examined the history of attempts to switch the preferred writing hand in a sample of 1277 adults aged 65 to 100 years of age. Older adults are well suited to participate in such a study because pressure to switch hand preference was especially severe for those who grew up in the early part of the 20th century; reports of rightward shift attempts are more common in this age group than among younger adults. Our results suggest that the three groups of left-handers, distinguished by the presence or absence of a shift history report and writing hand side, can also be distinguished from each other on the basis of their overall lateral preference profiles (the sides of hand, foot, eye, and ear preferences). Left hand writers, with and without reports of a rightward shift history, showed stronger left side lateralisation patterns when compared to right hand writers who reported a rightward switch (the successfully shifted left-handers).

Eye-dominance, Writing Hand, and Throwing Hand

Handedness and eye-dominance are undoubtedly associated statistically, although a previous meta-analysis has found that the precise relationship is difficult to explain, with about 35% of right-handers and 57% of left-handers being left eye dominant. Of particular difficulty to genetic or other models is that the proportions are distributed asymmetrically around 50%. The present study asked whether this complicated pattern of association occurred because, following Peters, it is necessary to divide right-and left-handers into consistent handers (who write and throw with the same hand) and inconsistent handers (who write and throw with opposite hands). In an analysis of 10,635 subjects from questionnaire studies, 28.8% of left-handers and 1.6% of right-handers by writing were inconsistent for throwing. Our results also showed that writing hand and throwing hand both relate independently to eyedness, that throwing hand is somewhat more strongly associated with eyedness, and that the awkward asymmetry around 50% is now removed, 24.2% of consistent right-handers being left eye dominant compared with 72.3% of consistent left-handers, and 55.4% of inconsistent right-handers compared with 47.0% of inconsistent left-handers. We conclude that eyedness is phenotypically secondary to writing and throwing handedness. In our discussion we note that eyedness runs in families, we present new data suggesting that writing hand and throwing hand are co-inherited, and we argue that further data are now required to model properly the associations of writing hand, throwing hand, and eyedness, as well as probably also footedness and language dominance.

Unimanual and Bimanual Simultaneous Fingertapping in Schoolchildren: Developmental Aspects and Hand Preference-related Asymmetries

Computerised analysis of finger tapping was performed in 233 normal 5- to 12-year-old children whose hand preference was assessed with six demonstration actions. Performance with both hands became more rapid with age when tapping unimanually or simultaneously in phase with two hands as quickly as possible. There were no differences between the sexes. Performance with both hands also acquired more tapping regularity with age during unimanual tapping, whereas only the left hand did so during bimanual tapping. There was no age effect on the dexterity (speed) difference between unimanually tapping hands, nor on the relative time lag and the degree of synchrony between the hands in bimanual tapping. The degree of synchrony, however, becomes more stable in older children. The more righthanded children are, the faster the right hand is in unimanual tapping, and the more the right hand is ahead of the left hand during bimanual tapping. However, there is a right shift for both of these variables which makes them poor predictors of hand preference. These results suggest that there is a strong bias towards the right hand in complete righthanders as well as--to a lesser extent--in all others, which might be connected to the leading role of the left hemisphere for the performance aspects of hand motor function under study.

Kissing right? On the consistency of the head-turning bias in kissing

The present study investigated the consistency of the head-turning bias in kissing. In particular we addressed what happens if a person who prefers to kiss with the head turned to the right kisses a person who prefers to kiss with the head turned to the left. To this end, participants (N=57) were required to kiss a life-sized doll's head rotated in different orientations that were either compatible or incompatible with the participants' head-turning preference. Additionally, participants handedness, footedness, and eye preference was assessed. Results showed that a higher percentage of participants preferred to kiss with their head turned to the right than to the left. In addition, the right-turners were more consistent in their kissing behaviour than left-turners. That is, with the doll's head rotated in an incompatible direction, right-turners were less likely to switch their head to their non-preferred side. Since no clear relationships between head-turning bias and the other lateral preferences (i.e., handedness, footedness, and eye preference) were discerned, the more consistent head-turning bias among right-turners could not be explained as deriving from a joint pattern of lateral preferences that is stronger among individuals with rightward as compared to individuals with leftward lateral preferences.

Cortical lateralization of bilateral symmetric chin movements and clinical relevance in tumor patients—A high field BOLD–FMRI study

Although unilateral lesion studies concerning the opercular part of primary motor cortex report clinically severe motor deficits (e.g. anarthria, masticatory paralysis), functional lateralization of this area has not yet been addressed in neuroimaging studies. Using BOLD-FMRI, this study provides the first quantitative evaluation of a possible cortical lateralization of symmetric chin movements (rhythmic contraction of masticatory muscles) in right-handed healthy subjects and presurgical patients suffering tumorous lesions in the opercular primary motor cortex. Data were analyzed according to "activation volume" and "activation intensity". At group level, results showed a strong left-hemispheric dominance for chin movements in the group of healthy subjects. In contrast, patients indicated dominance of the healthy hemisphere. Here, a clinically relevant dissociation was found between "activation volume" and "activation intensity": Although "activation volume" may be clearly lateralized to the healthy hemisphere, "activation intensity" may indicate residual functionally important tissue close to the pathological tissue. In these cases, consideration of BOLD-FMRI maps with the exclusive focus on "activation volume" may lead to erroneous presurgical conclusions. We conclude that comprehensive analyses of presurgical fMRI data may help to avoid sustained postoperative motor deficits and dysarthria in patients with lesions in the opercular part of primary motor cortex.

Lateral preference profiles and right shift attempt histories of consistent and inconsistent left-handers

Differences in abilities and preferences exist between left-handers who both write and throw with their left hands (consistent left-handers) and those who write with their left hand but prefer to throw with their right (inconsistent left-handers). It is also known that many left-handers are pressured to switch to right-hand writing, and that these pressures can lead to a right shift attempt. The present study is the first to explore the joint effects of the consistent/inconsistent left-handedness dichotomy, right shift attempt history, and lateral preference profiles. Testing 379 Canadian adults between the ages of 18 and 94 indicated that, while both types of left-handers were equally likely to experience a right shift attempt, the inconsistent left-handers were more likely to successfully switch to right-hand writing. Further analyses revealed that throwing hand was more associated than writing hand with the direction of sidedness for a lateral preference index based upon eye, foot, and ear preferences. More specifically, right-hand throwers were much more likely to have a rightward lateral preference score than were left-hand throwers, regardless of current preferred writing hand. Overall, the results support an hypothesis that the left-handers who are least likely to submit to rightward switch pressures are those with the strongest, most consistent left-sided lateral preference profile.

Can I twist your arm? The influence of target orientation on the magnitude of the right-hand advantage

Controversy exists concerning whether handedness is a unidimensional trait or a multidimensional trait. However, researchers espousing the view that handedness is multidimensional are in disagreement regarding what the dimensions are that underlie handedness. Healey, Liederman, and Geschwind (1986) have provided some evidence that the type of musculature utilised (i.e., proximal versus distal) may be an underlying factor in determining handedness. The present research attempted to test this notion by examining the effects of target orientation on the relative performance of the two hands, using a peg-moving task. Target orientation was examined by utilising key-shaped pegs that fit securely into key-shaped holes. The results showed that the presence of target orientation increased the preferred-hand advantage. It is considered that this increased advantage for the right hand may be due to the hemispheric control of proximal versus distal musculature suggested by Geschwind and Galaburda (1985).

Manual asymmetries in reaching movement control. II: Study of left-handers

Two experiments performed with left-handed subjects investigated how the manual asymmetries and hemispheric specialization involved in visuo-manual coordination are associated with handedness. Pro and retroactive processes involved in rapid movement control were analyzed according to the different movement parameters to be controlled, similar to studies performed with right-handers (Boulinguez, Nougier and Velay, 2001). Manual performances and kinematic properties of reaching movements showed that the left and right hands of left-handers behaved in the same way as the left and right hands of right-handers. Results are discussed in the light of the independence of handedness and other forms of cerebral dominance in sensori-motor information processing involved in hand movements.

Manual asymmetries in reaching movement control. I: Study of right-handers

Two experiments investigated manual asymmetries in the control of rapid reaching movements according to the movement parameters to be controlled. Single- and double-step reaching movements were performed by right-handed subjects with both hands. Pro and retroactive processes involved in rapid movement control were investigated. Manual performances and kinematic properties of hand movements showed that various forms of hemispheric specialization were involved in sensori-motor information processing. It was shown that the effects of hemispheric specialization were specific to the task constraints, that is, to the various operations involved in movement control.

Predicting hand preference with performance on motor tasks

Handedness may be defined as preference or hand-differences in task performance. The strength and significance of the relationship between hand preference and hand performance asymmetries have been contested. To evaluate this relationship, we administered the Edinburgh Handedness Inventory and measured asymmetries in finger tapping, Purdue Pegboard, and grip strength in 30 subjects who prefer their right hand and 30 subjects who prefer their left hand. Hand asymmetries in finger tapping, Purdue Pegboard, and grip strength each predicted hand preference scores. However, a multiple regression equation best predicted hand preference by using performance of each task. Hand asymmetries in finger tapping correlated strongly with asymmetries in Purdue Pegboard performance, but neither of these asymmetries correlated strongly with asymmetries in grip strength. These findings indicate that hand preference and asymmetries in motor proficiency are strongly related, but suggest that preference and proficiency for different aspects of motor performance may be independently lateralized.

Performance on a mirror-drawing task by non-right-handers

Left-, mixed-, and right-handed (each n = 10, N = 30) adolescent boys who were classified on the basis of a hand preference inventory performed a mirror-drawing task with a bilateral transfer of a skill paradigm. Participants' hand preference and the magnitude of bilateral transfer of skill were assessed in terms of errors committed and time taken to complete the mirror-drawing task. Mixed-handed participants exhibited significantly less habit interference for mirror drawing, and they performed the task significantly faster than the left-handers did; the group difference was not significant for the frequency of errors committed. These groups did not differ in terms of the magnitude of bilateral transfer of skill; the trend, however, showed that the transfer of skill was minimum in mixed-handers. These findings extend the theory that mixed-handed participants' inability to transfer motor skill from one hand to the other could be attributable to their lack of a clear pattern of lateralization. Their ability to perform well either at initial or later trials may be a function of less interference from their normal motor habits.

Considering handedness in studies involving manual control

With studies of motor behavior that feature manual control, it is suggested that the methodology used to select subjects in reference to handedness be reviewed. This suggestion is in view of the recommendation that simply asking subjects to identify their writing hand is inadequate to define handedness. Complementing this are recent findings in neuroscience indicating differences, at times significant, in information-processing behavior based on handedness classification. A brief review of recently published studies in two prominent outlets for motor behavior research confirms that most reports provide minimal (and sometimes no) information regarding handedness and the method used for assessment. Recommendations for addressing the problem include using an acceptable preference inventory, selecting only those subjects with strong lateral characteristics, and briefly describing the methodology used for the reviewing audience.

A behavioral measure of hand preference as opposed to hand skill

Twenty-five self-professed left-handers and 21 self-professed right-handers were given a variety of performance tests to assess handedness, along with a preference inventory and a dichotic listening test of language lateralization. The performance tests included the Annett pegboard task, that Tapley and Bryden dot-filling tasks, and two procedures, the long pegboard and long dots tasks, that were intended to assess the point in space at which a particular unimanual movement became sufficiently awkward for one to shift to the other hand. All four of these performance tests differentiated between left-handers and right-handers, although the differences between handedness groups were somewhat larger when handedness was defined in terms of the preference inventory rather than on the basis of self-report. When the difference between preferred and non-preferred hands was examined, the best predictor of hand preference was the long pegboard task. Such a finding is consistent with the view that the long pegboard provides a behavioral measure of hand preference, while the pegs and dots tasks are more closely linked to specific skills. In addition, the correlations between individual preference items and the dichotic right-ear advantage suggest that language lateralization is related to rather different handedness measures than those usually used to define handedness. This finding would suggest that handedness and language lateralization are determined by somewhat different mechanisms.

Hand performance of French children on a finger-tapping test in relation to handedness, sex, and age

Hand performance and laterality scores on a unimanual tapping test were studied in relation to age, sex, and handedness in a sample of 209 French children. Each child performed three trials with each hand. Older children were faster, but differences between hands were not related to age. Right-handed girls were more lateralized than right-handed boys. Left- and right-handers could be differentiated more clearly by tapping speed than by variability of tapping. A subsample of 36 right-handers were retested to estimate reliability. The coefficients were high, especially when using the mean of trials as the dependent variable. Correlations between performance on the tapping task and another test of hand-efficiency (dot-filling task) were low.