Moving What Is Seen: Arm Visibility Modulates Infants’ Manual Preference

Measuring infant handedness reliably from reaching: A systematic review

Researchers have utilized reaching paradigms to measure infant handedness for more than a century. However, methods vary widely. Recent research has identified that the number of trials used in assessment is critical with the recommendation that at least 15 trials are necessary to reliably classify infants into handedness categories via statistical cutoffs. As a first step towards establishing best practices for the field, we identified, categorized, and synthesized findings according to trial number from studies that utilized reaching to index handedness in infants across the first two years of life using PRISMA guidelines. Database searches were conducted in PsycINFO, PubMed, and Ovid MEDLINE®. All articles published through May 2018 were included. Additional records were identified through other sources. After removing duplicates, 1,116 records were screened using the online software program Abstrackr. Of these records, 125 full-text articles were further assessed for eligibility, and 87 articles were included in the qualitative synthesis. Results revealed that the majority of papers published since 1890 (70%) do not meet the 15-trial minimum criterion for statistically reliable measurement of infant handedness. Broad themes from articles meeting the measurement criterion and implications for future research are discussed.

A historical, systematic review of handedness origins

Handedness ontogenesis is still under debate in science. This systematic review analyzed articles regarding the theories and basis of handedness formation, highlighting the historical knowledge path that this literature underwent. Cochrane Library, LILACS, Web of Sciences, Science Direct and PubMed databases were searched. This review included review studies with handedness as the main topic. Only papers written in English with analyses exclusively in neurotypical humans (any age range) were included. Different approaches (genetic, neural, social, and behavioural) were reviewed in light of growing evidence, summarizing the current state of the art. Genetic and environmental/social impacts are common points in most of the reviews, each given more or less importance, depending on the author and theory proposed. Multifactorial, developmental approaches to handedness formation seem to be the most up to date view of the phenomenon. Different control mechanisms between hemisphere and neural asymmetries are also contributing factors to handedness formation.

Transient Motor Asymmetry Among Infants With Congenital Torticollis-Description, Characterization, and Results of Follow-Up

AIM

The purpose of this study was to assess the prevalence of transient functional motor asymmetry in infants with congenital postural torticollis.

METHODS

This was a retrospective review of the medical records of infants with postural torticollis. We analyzed epidemiological, obstetric, perinatal data, physical therapy, physician assessments, and clinical follow-up for two years after diagnosis.

RESULTS

Of 173 children, 44 (25.4%, 95% confidence interval = 19.5 to 32.4) demonstrated functional asymmetry. Demographic and obstetrical data did not differ between the asymmetry/nonasymmetry groups. Delayed motor development (P = 0.01) and plagiocephaly (P = 0.032) were more common in infants with motor asymmetry. No difference was observed in the frequency of referral for further neurological diagnosis between the group with functional asymmetry and that without asymmetry. Among the 44 patients with functional asymmetry, 78% depicted no evidence of torticollis by age two years, and the motor asymmetry had disappeared in 82%.

CONCLUSION

Benign, transient functional motor asymmetry occurred in a quarter of infants with congenital postural torticollis. Transient motor delay was also significantly more common in the asymmetry group. In most instances, motor asymmetry and motor delay disappeared by age two years. Plagiocephaly was more common in the asymmetry group. Clinician awareness of this transient asymmetry may have avoided unnecessary diagnostic tests in these infants.

Attentional asymmetries - cause or consequence of human right handedness?

It is well established that the vast majority of the population favors their right hand when performing complex manual tasks. However, the developmental and evolutionary underpinnings of human manual asymmetries remain contentious. One often overlooked suggestion is that right handedness may stem from an asymmetrical bias in attention, with the right hand being allocated more attentional resources during bimanual tasks than the left hand (Peters, 1981). This review examines the evidence for attentional asymmetries during a variety of bimanual tasks, and critically evaluates the explanatory power of this hypothesis for explaining the depth and breadth of individual- and population-level manual asymmetries. We conclude that, while the attentional bias hypothesis is well-supported in adults, it requires further validation from a developmental perspective to explain the full breadth of adult manual laterality.

Modulation of manual preference induced by lateralized practice diffuses over distinct motor tasks: age-related effects

In this study we investigated the effect of use of the non-preferred left hand to practice different motor tasks on manual preference in children and adults. Manual preference was evaluated before, immediately after and 20 days following practice. Evaluation was made with tasks of distinct levels of complexity requiring reaching and manipulation of cards at different eccentricities in the workspace. Results showed that left hand use in adults induced increased preference of that hand at the central position when performing the simple task, while left hand use by the children induced increased preference of the left hand at the rightmost positions in the performance of the complex task. These effects were retained over the rest period following practice. Kinematic analysis showed that left hand use during practice did not lead to modification of intermanual performance asymmetry. These results indicate that modulation of manual preference was a consequence of higher frequency of use of the left hand during practice rather than of change in motor performance. Findings presented here support the conceptualization that confidence on successful performance when using a particular limb generates a bias in hand selection, which diffuses over distinct motor tasks.