Evidence for general right-, mixed-, and left-sidedness in self-reported handedness, footedness, eyedness, and earedness, and a primacy of footedness in a large-sample latent variable analysis

Does the Fraternal Birth Order Effect Influence Handedness?

The fraternal birth order effect (FBOE) is the phenomenon whereby the probability that a man has a same-sex sexual orientation in adulthood increases with each biological older brother. Several studies have found evidence that the FBOE is limited to right-handed men, and left-handed men do not show an FBOE. Recent debates about the appropriate methods for quantifying the FBOE center on distinguishing the FBOE from other effects, such as the female fecundity effect (FFE), whereby mothers more prone to bearing gay sons are also more fecund. The FBOE and FFE are confounded in that a real FFE will result in data consistent with the FBOE under some analyses. Here, we applied some recent proposed analytic methods for the FBOE to the property of handedness. A straightforward application of Khovanova's technique to the binary trait of handedness yielded support for a fraternal birth order effect consistent with the maternal immune hypothesis, in that the ratios of handedness differed between men with one older brother only, and men with one younger brother only, while no such effect was seen in women. This effect was not seen, however, when the confounding effects of parental age were controlled for. Models including factors to simultaneously test multiple posited effects find significant female fecundity effects, as well as paternal age and birth order effects on handedness in men, but no FBOE. The effects seen in women were different, with no fecundity or parental age effects, but birth order and sex of older siblings had effects. We conclude, based on this evidence, that many of the factors thought to contribute to sexual orientation in men may also have an influence on handedness, and further note that parental age is a potential confound which may be overlooked by some analyses of the FBOE.

Significant gender-specific difference in brain lateralization of schizophrenia patients assessed by new combined foot dominance scale

Objective

Reduced hemispheric asymmetry has been identified as a potential risk factor for schizophrenia, characterized by diminished brain lateralization and a lack of dominance in the left hemisphere. Moreover, there is growing evidence of disrupted connectivity between various cortical regions. This study aimed to investigate gender differences in left-footedness as a potential biological marker for neuronal dysontogenesis in individuals with schizophrenia and control subjects.

Materials and methods

A New Combined Foot Dominance Scale (14 foot tests), comprising a Modified Chapman & Chapman Subscale (10 foot tests) and a Complex Tasks Subscale (four foot tests) was administered as performance tasks in 180 subjects [98 schizophrenia patients with mean age 34.45 years (SD = 15.67, range 23-79) for men and 42.20 years (SD = 11.38, range 21-63) for women and 82 controls with a mean age 34.70 years (SD = 16,82, range 18-79) for men and 44.50 years (SD = 10.73, range 23-67)]. As our data are not continuous and lacks normal distribution, the non-parametric Mann-Whitney test was used for comparing categorical data.

Results

The mean left-footedness, as assessed by the New Combined Foot Dominance Scale, is significantly higher in individuals with schizophrenia compared to control subjects. Our findings from inter-gender comparisons reveal that female schizophrenia patients exhibit a significantly greater average left-footedness than female control subjects, while in males no such a statistical significant difference is detected.

Conclusion

Left foot dominance is higher in patients with schizophrenia than in control subjects and women contribute significantly more to this difference.

Cross-Cultural Adaptation of the Arabic Version of the Waterloo Footedness Questionnaire-Revised to Assess Footedness in Arabic-Speaking Adults

PURPOSE

 The goal of this research is to translate and analyze the psychometric properties of the Arabic version of the Waterloo Footedness Questionnaire-Revised (WFQ-R).

MATERIALS AND METHODS

Two native Arabic speakers created separate forward translations, which were then merged. Two different multilingual translators were used to translate it back into English from the synthetic version. Experts were gathered for a discussion on how to improve the localization and adaptation processes. A group of specialists was convened to analyze the localization and modification procedures. We now have the Arabic version of the WFQ-R which is "WFQ-R-Ar". Two hundred and ninety Arabic-speaking adults over the age of 18 were surveyed to evaluate the WHQ-R-Ar's characteristics (internal consistency, test-retest reliability, and construct validity).

RESULTS

 The WFQ-R-Ar had no collisions with the ground or the sky. The factor analysis showed that the construct validity of the WFQ-R-Ar was dependent on a single factor. The WFQ-R-Ar also has excellent internal consistency, with a Cronbach's alpha of 0.93. The reliability of the examinations was examined, and it was found to have an intraclass correlation value of 0.94.

CONCLUSION

 The WFQ-R-Ar may be relied on to provide accurate results when used to evaluate footedness in Arabic-speaking society.

Both direction and degree of handedness as influential factors in rumination

There is contradictory evidence on the influence of handedness on depression and anxiety. However, few studies have investigated the relationship between handedness and rumination, which is robustly associated with both depression and anxiety. This study aimed to examine the influence of direction and consistency of handedness on rumination, considering four different classifications of handedness. The study sample included 406 participants (282 females) who attended an online survey and answered a demographic questionnaire, the Edinburgh Handedness Inventory, the Ruminative Response Scale, and the second edition of the Beck Depression Inventory. Considering four different classifications of handedness, a series of one-way ANOVAs was conducted to investigate any differences between the handedness groups. Besides, linear regression models were used to predict depression or rumination scores among the whole study sample, left-handers, and right-handers. Consistency of handedness predicted rumination among right-handers (but not left-handers), with a direct association between consistency and brooding/total rumination scores. Also, consistent left-handers and consistent right-handers showed higher brooding scores than inconsistent right-handers. Overall, the results supported the significant influence of both direction and consistency of handedness on individual differences in rumination and suggested consistent- and left-handedness as perpetuating factors for ruminative response style.

Unintentional force drifts in the lower extremities

We explored the phenomenon of unintentional force drift seen in the absence of visual feedback during knee extension contractions in isometric conditions. Based on the importance of knee extensors for the anti-gravity function, we hypothesized that such force drifts would be slower and smaller compared to those reported for the upper extremities. We also explored possible effects of foot dominance and gender on the force drifts. Young healthy persons produced isometric knee extension contractions to different levels, ranging from 15 to 25% of maximal voluntary contraction force, with the help of visual feedback, and then, the visual feedback was turned off. Force change over the time interval without visual feedback was quantified. In the absence of visual feedback, force drifted to smaller magnitudes. The drift magnitude expressed in percent of the initial force magnitude was smaller for smaller initial force levels, ranging between 8 and 15% of the initial force for the initial force magnitude of 15% and 25% of maximal voluntary contraction force. The time exponent of the force drift was independent of the initial force magnitude and was, on average, 6.45 s. There were no significant effects of foot dominance or gender, although the male subjects tended to show stronger scaling of the drift magnitude with the initial force level compared to the female subjects. The results show that unintentional force drift is a common phenomenon across limbs and muscle groups. This conclusion fits the theory of control with spatial referent coordinates and the general tendency of all natural systems to drift to states with lower potential energy.

The development of hand, foot, trunk, hearing, and visual lateral preference throughout the lifespan

This research investigated the developmental process of five lateral preference dimensions (hand, foot, trunk, hearing, and visual preference). A total of 1236 volunteers participated in this study, divided into five age groups: 07-12 (n = 247); 13-17 (n = 234); 18-30 (n = 227); 31-60 (n = 225); and 61-90 years old (n = 303). Lateral preference was assessed via questionnaire with the Global Lateral Preference Inventory. By assessing the degree and direction of lateral preference in different ages, our results revealed a pattern of lateralization strengthening with aging in all the analyzed dimensions. We also verified significant correlation between hand preference and the other dimensions for all age groups, but correlation was stronger in the 7-12 group for all correlation pairs. Our results lead to the suggestion of an underlying general lateralization process in early ages (7-12 years old) followed by specific developmental trajectories of each preference dimension (13 years forward), likely startled by hemisphere and functional specialization related to innate developmental patterns of neural structures and social/environmental influences.

Consistency of limb preference across unimanual feeding, bipedal locomotion, and social grooming in golden snub-nosed monkeys (Rhinopithecus roxellana)

The golden snub-nosed monkey (Rhinopithecus roxellana) is a typical arboreal group-living Old World primate. While limb preference has been extensively studied in this species, limb preference consistency has not yet been explored. Here, based on 26 R. roxellana adults, we investigated whether individuals exhibit consistent motor biases in manual- (e.g., unimanual feeding and social grooming) and foot-related (e.g., bipedal locomotion) tasks and whether limb preference consistency is influenced by increased social interactions during social grooming. Results showed no consistency in the direction or strength of limb preference among tasks, except for lateral strength in handedness for unimanual feeding and footedness in the initiation of locomotion. Population-level foot preference was only found among right-handers. Marked lateral bias was found in unimanual feeding, indicating that it may be a sensitive behavioural measure for assessing manual preference, especially for provisioned populations. This study not only improves our understanding of the relationship between hand and foot preference in R. roxellana but also reveals potential differential hemispheric regulation of limb preference and the influence of increased social interaction on handedness consistency.

The Simon Effect Asymmetry for Left- and Right-Dominant Persons

When participants respond to a task-relevant stimulus attribute by pressing a left or right key with the respective index finger, reaction time is shorter if task-irrelevant left-right stimulus location corresponds to that of the response key than if it does not. For right-handers, this Simon effect is larger for right-located than left-located stimuli; for left-handers this Simon-effect asymmetry is reversed. A similar asymmetry has been found for right-footers pressing pedals with their feet. For analyses that separate stimulus- and response-location factors, these asymmetries appear as a main effect of response location, with responses being faster with the dominant effector. If the Simon-effect asymmetry is strictly a function of effector dominance, it should reverse for left-footers responding with their feet. In Experiment 1, left-dominant persons showed faster responses with the left than right hand but with the right than left foot, a finding consistent with prior research on tapping actions. Right-dominant persons also showed the right-foot asymmetry but, unexpectedly, not the typical asymmetry with hand responses. To evaluate whether hand-presses yield results distinct from finger-presses, in Experiment 2 participants performed the Simon task with finger-presses and hand-presses. The opposing asymmetries for right- and left-dominant persons were evident for both response modes. Our results are consistent with the view that the Simon effect asymmetry is primarily due to differences in effector efficiency, usually but not always favoring the dominant effector.

Bilateral Training Improves Agility and Accuracy for Both Preferred and Non-Preferred Legs in Young Soccer Players

As laterality of the lower limbs is regarded as a relevant influence on soccer performance, we assessed whether a bilateral training program for both the preferred leg (PL) and non-preferred leg (NPL) would improve soccer players' lateral asymmetry, agility, and accuracy. Sixty right-foot-dominant young soccer players were randomly assigned to either an experimental group (EXP) that underwent bilateral training or a control group (CONT) that performed their usual training schedule without bilateral exercise. We assessed the players' lateral asymmetries before and after training on four soccer skill tasks: a zigzag test with and without a ball, a receiving and direct volley-shooting accuracy test, and a passing accuracy test. Results showed post-test versus pre-test performance improvements for the EXP group on the index of technical skills and agility (p < .001). A post-hoc analysis further revealed a pre-test to post-test performance improvement on shooting and passing accuracy with both legs only for the EXP group (p < .001). These results support the role of bilateral practice in improving lateral asymmetries, agility, and accuracy.

Does Orthodontic Treatment Change the Preferred Chewing Side of Patients with Malocclusion?

Whether orthodontic treatment can change the preferred chewing side (PCS) is unknown. This study examined (1) if the PCS changes after orthodontic treatment and (2) which factors contribute to this change. Two hundred fifty patients who visited the orthodontic clinic at Tokyo Medical and Dental University Hospital between 2017 and 2020 were included in the study. Mandibular kinesiograph (MKG) was taken at pre- and post-treatment, and PCS was determined. Patients who showed a change in PCS to the opposite side and those who showed no change in PCS at post-treatment were pooled into the PCS-changed and PCS-unchanged groups, respectively. The demographic, clinical, and cephalometric parameters were compared between the groups. Significant factors associated with changes in were of age < 20 years at the beginning of orthodontic treatment (odds ratio (OR), 2.00), maximum lateral mandibular movement to PCS ≥ 10.0 mm at pre-treatment (OR, 6.51), and change in occlusal canting of ≥1.0° (OR, 2.72). The predicted probability of change in PCS was 13.2%, 36.0%, and 67.5% for no factor, one factor, and two factors associated with PCS change, respectively. Orthodontic treatment may change PCS due to patient age, maximum lateral mandibular movement to PCS, and change in occlusal canting.

Waterloo Handedness Questionnaire: Cross-Cultural Adaptation and Psychometric Properties of the Arabic Version

Handedness is one of the most studied behavioural predictors of cerebral lateralization. Assessing handedness is often essential in neuropsychology and motor behaviour research. Thus, it is important that self-reported assessment tools for determining handedness are available in multiple languages for different cultures. The purpose of the present study was to conduct a translation and cross-cultural adaptation of the Waterloo Handedness Questionnaire into the Arabic language and to assess its psychometric properties. Two independent forward translations were performed by two native Arabic speakers and then synthesized into one version. The synthesized version was backtranslated into English by two independent bilingual translators. An expert committee was formed to review the translation and adaptation process. A final Arabic version of the WHQ was obtained, the WHQ-Ar. Two hundred and ninety adult Arabic speakers were recruited to participate in the study and investigate the properties of the WHQ-Ar. Results showed that the WHQ-Ar had no floor or ceiling effect. For construct validity, results of factor analysis revealed that the WHQ-Ar had two dimensions. Further, the WHQ-Ar had excellent internal consistency with Cronbach′s alpha = 0.93. For test-retest reliability, intraclass correlation coefficient score was 0.94. The Bland-Altman plot showed acceptable agreement between test and retest scores. Therefore, the WHQ-Ar is a valid, reliable tool and ready for use among the Arabic-speaking population for determining handedness.

Elite Tennis Players Experiencing High-Arched Supination and Cuboids Dropped Foot Syndromes in Daily Normal Gait

Many studies have focused on the plantar pressure characteristics of specific movements and footwork in tennis. However, little research has been conducted for exploring the foot characteristics among tennis professionals' daily habitual paces. This study aims to examine the pressure profiles associated with foot posture and balance abilities of elite tennis players during normal gait to understand how foot loading patterns result from habitual paces that may be derived from intensive tennis training and competition. A cross-sectional comparative study is conducted on 95 male college elite tennis players (mean age: 20.2 ± 1.2 years) and 100 male recreational tennis players (mean age: 19.8 ± 0.9 years). Bipedal plantar pressure distributions (PPDs) associated with arch index (AI) and centers of gravity balance are explored through the plantar pressure device. The foot posture is estimated to determine the rearfoot postural alignment. During the midstance phase of walking with a normal gait, the bipedal AI values of the elite group are significantly lower, indicating that they have high-arched feet. Additionally, the elite group experienced higher PPDs at the lateral regions of their longitudinal arches and heels and relatively lower PPDs at the medial portions of both feet. Rearfoot postural alignment resonance analysis of the PPDs suggests that the elite group experienced foot supination associated with cuboid dropped. Moreover, the right foot bears heavier centers of gravity balance in the present study. The elite tennis players in the study are categorized as having high-arched supination with cuboids dropped when performing daily habitual paces. This finding warrants further investigation into the correlation between possible injuries and daily habitual paces that may result from tennis' intensive training and competition.

Lateralization Direction, Strength, and Consistency in Juvenile and Adolescent Idiopathic Scoliosis: A Case Control Pilot Study

The aim of this study was to assess the hypothesis that functional laterality features are associated with scoliosis incidence. The study included 59 patients with radiologically confirmed idiopathic scoliosis (mean age 13 years, 41 girls and 18 boys) and 55 controls (mean age 10.5 years, 38 girls and 17 boys). Side dominance was determined by the Lateral Preference Inventory. Direction, strength, and consistency of lateral dominance was obtained. Continuous data were compared by Student’s t-test or U Mann-Whitney test where appropriate. Categorical data were compared by chi-squared test and Fisher’s exact test. Groups were significantly different in terms of age (p < 0.001) and dependent variables: height (p < 0.001) and weight (p < 0.001). Lateralization analysis showed some trends, but the results obtained were not statistically significant. Statistical significance of lateralization direction are respectively: for hand (p = 0.364); leg (p = 0.277); eye (p = 0.804); ear (p = 0.938); number of right/left sided participants p = 0.492; p = 0.274; p = 0.387; p = 0.839, and right/mixed/left sided participants p = 0.930; p = 0.233; p = 0.691; p = 0.804. For laterality consistency depending on definition used, p = 0.105; p = 0.108; p = 0.380. The relationship between scoliosis and laterality is not a simple causal relationship and needs further investigation.

The Handedness Index Practical Task (HI20): An economic behavioural measure for assessing manual preference

ABSTRACTBecause self-report hand preference measures are limited to investigating cognitive aspects of manual laterality, valid, easy-to-administer and economic behavioural methods are needed for capturing the motoric component of handedness. Therefore, this study introduces the Handedness Index Practical Task (HI₂₀) and tests it in a sample of 206 students (M_age = 23.79 years, SD_age = 3.01 years), half of whom were self-specified left-handers. After confirming good reliabilities at the subscale and total scale levels, k-means cluster analysis allowed an empirically based partitioning of test subjects into left- (n = 72), mixed- (n = 23) and right-handers (n = 111). To validate this categorization and the HI₂₀ index, data were compared with the Edinburgh Handedness Inventory (EHI), EHI-short, HI₂₂ and hand grip strength. The congruency between the HI₂₀ clusters and alternative categorizations ranged from 95.6% to 84.0%, while the clusters explained large portions of variance in grip strength differences. The HI₂₀ sub- and total scores showed strong correlations with other measures of lateral preference. Altogether, the freely available HI₂₀ emerges as a reliable and valid alternative for behavioural handedness assessment, whose power lies in explaining differential hand use patterns and enabling fine-grained examinations of handedness.

The enigma and implications of brain hemispheric asymmetry in neurodegenerative diseases

The lateralization of the human brain may provide clues into the pathogenesis and progression of neurodegenerative diseases. Though differing in their presentation and underlying pathologies, neurodegenerative diseases are all devastating and share an intriguing theme of asymmetrical pathology and clinical symptoms. Parkinson’s disease, with its distinctive onset of motor symptoms on one side of the body, stands out in this regard, but a review of the literature reveals asymmetries in several other neurodegenerative diseases. Here, we review the lateralization of the structure and function of the healthy human brain and the common genetic and epigenetic patterns contributing to the development of asymmetry in health and disease. We specifically examine the role of asymmetry in Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, and interrogate whether these imbalances may reveal meaningful clues about the origins of these diseases. We also propose several hypotheses for how lateralization may contribute to the distinctive and enigmatic features of asymmetry in neurodegenerative diseases, suggesting a role for asymmetry in the choroid plexus, neurochemistry, protein distribution, brain connectivity and the vagus nerve. Finally, we suggest how future studies may reveal novel insights into these diseases through the lens of asymmetry.

Harnessing the Fifth Element of Distributional Statistics for Psychological Science: A Practical Primer and Shiny App for Measures of Statistical Inequality and Concentration

Although distributional inequality and concentration are important statistical concepts in many research fields (including economics, political and social science, information theory, and biology and ecology), they rarely are considered in psychological science. This practical primer familiarizes with the concepts of statistical inequality and concentration and presents an overview of more than a dozen useful, popular measures of inequality (including the Gini, Hoover, Rosenbluth, Herfindahl-Hirschman, Simpson, Shannon, generalized entropy, and Atkinson indices, and tail ratios). Additionally, an interactive web application (R Shiny) for calculating and visualizing these measures, with downloadable output, is described. This companion Shiny app provides brief introductory vignettes to this suite of measures, along with easy-to-understand user guidance. The Shiny app can readily be used as an intuitively accessible, interactive learning and demonstration environment for teaching and exploring these methods. We provide various examples for the application of measures of inequality and concentration in psychological science and discuss venues for further development.

Human Lateralization, Maternal Effects and Neurodevelopmental Disorders

In humans, behavioral laterality and hemispheric asymmetries are part of a complex biobehavioral system in which genetic factors have been repeatedly proposed as developmental determinants of both phenomena. However, no model solely based on genetic factors has proven conclusive, pushing towards the inclusion of environmental and epigenetic factors into the system. Moreover, it should be pointed out that epigenetic modulation might also account for why certain genes are expressed differently in parents and offspring. Here, we suggest the existence of a sensitive period in early postnatal development, during which the exposure to postural and motor lateral biases, expressed in interactive sensorimotor coordination with the caregiver, canalizes hemispheric lateralization in the “typical” direction. Despite newborns and infants showing their own inherent asymmetries, the canalizing effect of the interactive context owes most to adult caregivers (usually the mother), whose infant-directed lateralized behavior might have been specifically selected for as a population-level trait, functional to confer fitness to offspring. In particular, the case of the left-cradling bias (LCB; i.e., the population-level predisposition of mothers to hold their infants on the left side) represents an instance of behavioral trait exhibiting heritability along the maternal line, although no genetic investigation has been carried out so far. Recent evidence, moreover, seems to suggest that the reduction of this asymmetry is related to several unfavorable conditions, including neurodevelopmental disorders. Future studies are warranted to understand whether and how genetic and epigenetic factors affect the lateralization of early mother-infant interaction and the proneness of the offspring to neurodevelopmental disorders.

The Bias toward the Right Side of Others Is Stronger for Hands than for Feet

As shown by a series of previous studies, ambiguous human bodies performing unimanual or unipedal actions tend to be perceived more frequently as right-handed or right-footed rather than left-handed or left-footed, which indicates a perceptual and attentional bias toward the right side of others’ body. However, none of such studies assessed whether the relative strength of such a bias differs between the upper and lower limbs. Indeed, given that the prevalence of right-handedness is slightly larger than that of right-footedness, and given that hands provide more information than feet as regards both communicative and aggressive acts, it is plausible that the bias toward the right side of human bodies should be stronger for the hand than for the foot. We performed three experiments in each of which participants had to indicate the rotating direction (revealing the perceived handedness/footedness) of ambiguous human figures with either one limb (arm or leg) or two limbs (one arm and the contralateral leg) extended. The hypothesized advantage of the right hand over the right foot was found in both the second and the third experiment.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

A large-scale estimate on the relationship between language and motor lateralization

Human language is dominantly processed in the left cerebral hemisphere in most of the population. While several studies have suggested that there are higher rates of atypical right-hemispheric language lateralization in left-/mixed-handers, an accurate estimate of this association from a large sample is still missing. In this study, we comprised data from 1,554 individuals sampled in three previous studies in which language lateralization measured via dichotic listening, handedness and footedness were assessed. Overall, we found a right ear advantage indicating typical left-hemispheric language lateralization in 82.1% of the participants. While we found significantly more left-handed individuals with atypical language lateralization on the categorical level, we only detected a very weak positive correlation between dichotic listening lateralization quotients (LQs) and handedness LQs using continuous measures. Here, only 0.4% of the variance in language lateralization were explained by handedness. We complemented these analyses with Bayesian statistics and found no evidence in favor of the hypothesis that language lateralization and handedness are related. Footedness LQs were not correlated with dichotic listening LQs, but individuals with atypical language lateralization also exhibited higher rates of atypical footedness on the categorical level. We also found differences in the extent of language lateralization between males and females with males exhibiting higher dichotic listening LQs indicating more left-hemispheric language processing. Overall, these findings indicate that the direct associations between language lateralization and motor asymmetries are much weaker than previously assumed with Bayesian correlation analyses even suggesting that they do not exist at all. Furthermore, sex differences seem to be present in language lateralization when the power of the study is adequate suggesting that endocrinological processes might influence this phenotype.

The Pen Is Not Always Mightier: Different Ways of Measuring Handedness With the Edinburgh Handedness Inventory Yield Different Handedness Conclusions

Although consistency of handedness (the strength of dominant hand preference) is increasingly recognized as an important individual difference, there are questions about how to best measure it. A recent meta-analysis showed that researchers have often failed to report details of responses and response formats to handedness test items. In addition to measuring handedness direction (i.e., left versus right handedness), there can be utility to dichotomizing the Edinburgh Handedness Inventory (EHI) into consistent and inconsistent dominant handedness, despite controversy over the best means of doing so. In this study, we performed a discriminant function analysis of EHI items to determine which items best predicted handedness consistency versus handedness direction. Although the same discriminant function accounted for most of the variance for both dependent measures, writing and drawing EHI items were the strongest predictors of handedness direction and combing and opening jars items were the strongest predictors of handedness consistency. As different items on the EHI predicted these different handedness dimensions, we discuss the implications of dichotomizing EHI items into both relevant dimensions for both biological and environmental theories of the basis of handedness and for future handedness research.

Prevalence and heritability of handedness in a Hong Kong Chinese twin and singleton sample

BACKGROUND

Left-handedness prevalence has been consistently reported at around 10% with heritability estimates at around 25%. Higher left-handedness prevalence has been reported in males and in twins. Lower prevalence has been reported in Asia, but it remains unclear whether this is due to biological or cultural factors. Most studies are based on samples with European ethnicities and using the preferred hand for writing as key assessment. Here, we investigated handedness in a sample of Chinese school children in Hong Kong, including 426 singletons and 205 pairs of twins, using both the Edinburgh Handedness Inventory and Pegboard Task.

RESULTS

Based on a binary definition of writing hand, we found a higher prevalence of left-handedness (8%) than what was previously reported in Asian datasets. We found no evidence of increased left-handedness in twins, but our results were in line with previous findings showing that males have a higher tendency to be left-handed than females. Heritability was similar for both hand preference (21%) and laterality indexes (22%). However, these two handedness measures present only a moderate correlation (.42) and appear to be underpinned by different genetic factors.

CONCLUSION

In summary, we report new reference data for an ethnic group usually underrepresented in the literature. Our heritability analysis supports the idea that different measures will capture different components of handedness and, as a consequence, datasets assessed with heterogeneous criteria are not easily combined or compared.

Using Mobile EEG to Investigate Alpha and Beta Asymmetries During Hand and Foot Use

The Edinburgh Handedness Inventory (EHI) and the Waterloo Footedness Questionnaire (WFQ) are two of the most widely used questionnaires to assess lateralized everyday behavior in human participants. However, it is unclear to what extent the specific behavior assessed in these questionnaires elicit lateralized neural activity when performed in real-life situations. To illuminate this unresolved issue, we assessed EEG alpha and beta asymmetries during real-life performance of the behaviors assessed in the EHI and WFQ using a mobile EEG system. This methodology provides high ecological validity for studying neural correlates of motor behavior under more naturalistic conditions. Our results indicate that behavioral performance of items of both the EHI and WFQ differentiate between left- and right-handers and left- and right-footers on the neural level, especially in the alpha frequency band. These results were unaffected by movement parameters. Furthermore, we could demonstrate that neural activity elicited specifically during left-sided task performance provides predictive power for the EHI or WFQ score of the participants. Overall, our results show that these prominent questionnaires not only distinguish between different motor preferences on the behavioral level, but also on the neurophysiological level. Furthermore, we could show that mobile EEG systems are a powerful tool to investigate motor asymmetries in ecologically valid situations outside of the laboratory setting. Future research should focus on other lateralized behavioral phenotypes in real-life settings to provide more insights into lateralized motor functions.

Leg dominance as a risk factor for femoroacetabular impingement syndrome

One etiological factor of femoroacetabular impingement syndrome (FAIS) is high impact athletics involving deep hip flexion, axial loading and jumping during skeletal development. Previous work has established that there is physiologic asymmetry of the lower limbs regarding function, with the dominant limb being primarily responsible for propulsion and kicking while the non-dominant limb is responsible for stability and planting. The authors hypothesize that the dominant limb will be more likely to undergo hip arthroscopy for symptomatic FAIS. Four hundred and sixty-nine patients at a single surgical center who underwent primary or revision hip arthroscopy for cam-type FAIS were identified. Patients were asked to identify their dominant lower extremity, defined as the lower extremity preferred for kicking. Sixty patients who indicated bilateral leg dominance were excluded. It was assumed that with no association between limb dominance and the need for surgery, the dominant side would have surgery 50% of the time. Enrichment for surgery in the dominant limb was tested for using a one-sample test of proportions, determining whether the rate differed from 50%. The enrichment for surgery on the dominant side was 57% (95% confidence interval 52–62%) which was significantly different from the rate expected by chance (50%), P = 0.003. No other significant differences were noted between groups. Limb dominance appears to be an etiological factor in the development of cam-type FAIS. Patients are more likely to undergo arthroscopic treatment of FAIS on their dominant lower extremity, although the non-dominant lower extremity frequently develops FAIS as well.

Hand Preference and Performance in Basketball Tasks

The aims of this study were to develop and validate an instrument to quantitatively assess the handedness of basketballers in basketball tasks (Basketball Handedness Inventory, BaHI) and to compare it with their handedness in daily activities by the Edinburgh Handedness Inventory (EHI). The participants were 111 basketballers and 40 controls. All subjects completed the EHI and only basketballers filled in the BaHI. To validate the BaHI, a voluntary subsample of basketballers repeated the BaHI. Exploratory and confirmatory factor analyses supported a two-factor model. Our results show that: (i) Handedness score (R) in daily actions did not differ between basketball players (R by EHI = 69.3 ± 44.6) and the control group (R by EHI = 64.5 ± 58.6); (ii) basketballers more frequently favored performing certain sport tasks with the left hand or mixed hands (as highlighted by R by BaHI = 50.1 ± 47.1), although their choice was primarily the right hand in everyday gestures; and (iii) this preference was especially true for athletes at the highest levels of performance (R by BaHI of A1 league = 38.6 ± 58.3) and for those playing in selected roles (point guard's R = 29.4 ± 67.4). Our findings suggest that professional training induces handedness changes in basketball tasks. The BaHI provides a valid and reliable measure of the skilled hand in basketball. This will allow coaches to assess mastery of the ball according to the hand used by the athlete in the different tasks and roles.

Footedness related differences in femoral bone mineral density in elderly women with osteoporosis

Purpose: The presumed link between lateralized habitual motor activity and bilateral skeletal asymmetry, as result of bone functional adaptation, is the basis for inferences about bone mineral distribution; consequently, bone loss and osteoporosis. As there is no research connecting directly footedness with osteoporosis, the present study was designed to investigate their relation, in elderly women with osteoporosis.Methods: A sample of 420 white, Caucasian race women, older than 65 years, with previous diagnosis of osteoporosis, was recruited for the study. Finally, 164 women met the inclusion criteria and participated. The femoral neck and total hip bone mineral density (BMD) differences between right and left hips of 105 right-footed and 59 non-right-footed women, and the between footedness groups differences of the above right-left BMD differences, were measured with Dual-energy X-ray Absorptiometry (DXA).Results: In right-footers, total hip right-left BMD differences were statistically significant, favoring left femur [t(104) = -2.79, p < .01, two tailed]. In non-right-footers, femoral neck right-left BMD differences were statistically significant, favoring right femur [t(58) =2.025, p < .05, two tailed]. Femoral neck and total hip right-left BMD differences of right- versus non-right-footed women were statistically insignificant.Conclusion: The dominance of the right lower limb had an asymmetric effect on left total hip BMD, while non-right-footedness favored right femoral neck BMD. The findings highlighted the influence of load bearing effects of the body weight and muscle contractions on femoral BMD. We noted a possible association between footedness and BMD, as a result of bone functional adaptation.

No Evidence That Lateral Preferences Predict Individual Differences in the Tendency to Update Mental Representations: A Replication-Extension Study

A growing body of evidence suggests that inconsistent hand preference is indicative of an increased disposition to update one’s beliefs upon exposure to novel information. This is attributed to a facilitated exchange of information between the two brain hemispheres among inconsistent handers, compared to consistent handers. Currently available studies provide only indirect evidence for such an effect, were mostly based on small sample sizes, and did not provide measures of effect size. Small sample size is a major factor contributing to low replicability of research findings and false-positive results. We thus attempted to replicate Experiment 1 of Westfall, Corser and Jasper (2014), which appears to be representative of research on degree of handedness and belief updating in terms of the employed methods. We utilized data from a sample more than 10 times the size (N = 1243) of the original study and contrasted the commonly applied median-split technique to classify inconsistent and consistent handers with an empirically grounded classification scheme. Following a replication-extension approach, besides handedness, footedness was also explored. Only one out of 12 chi-squared tests reached significance and supported the original hypothesis that inconsistent handers stay with, or switch more often from, the status quo than consistent handers, depending on the valence of novel information. A small-telescopes analysis suggested that the original study had too low analytic power to detect its reported effect reliably. These results cast doubt on the assumption that inconsistent and consistent-handers differ in the tendency to update mental representations. We discuss the use of the median-split technique in handedness research, available neuroscientific evidence on interhemispheric interaction and inconsistent handedness, and venues of future research.

A Cortical Pathogenic Theory of Parkinson's Disease

In Parkinson's disease, the progressive neurodegeneration of nigrostriatal dopaminergic neurons in the substantia nigra pars compacta (SNc) is associated with classic motor features, which typically have a focal onset. Since a defined somatotopic arrangement in the SNc has not been recognized, this focal motor onset is unexplained and hardly justified by current pathogenic theories of bottom-up disease progression (Braak's hypothesis, prionopathy). Here we propose that corticostriatal activity may represent a critical somatotopic "stressor" for nigrostriatal terminals, ultimately driving retrograde nigrostriatal degeneration and leading to focal motor onset and progression of Parkinson's disease. As a pathogenic mechanism, corticostriatal activity may promote secretion of striatal extracellular alpha-synuclein, favoring its pathological aggregation at vulnerable dopaminergic synapses. A similar pathogenic process may occur at corticofugal projections to the medulla oblongata and other vulnerable structures, thereby contributing to the bottom-up progression of Lewy pathology. This cortical pathogenesis may co-exist with bottom-up mechanisms, adding an integrative top-down perspective to the quest for the factors that impinge upon the vulnerability of dopaminergic cells in the onset and progression of Parkinson's disease.

Associations of Bisexuality and Homosexuality with Handedness and Footedness: A Latent Variable Analysis Approach

Non-right-handedness appears to be more common among bisexuals and homosexuals than among heterosexuals, which might be indirect evidence of effects of prenatal androgen exposure. Current data suggest higher prenatal testosterone levels among bisexual and homosexual women, but are inconclusive for men. This study examined the association between sexual orientation and non-right-handedness for sex differences and whether higher rates of mixed-handedness, rather than left-handedness, might be the driving factor. This allowed for more specific tests regarding the predictions of two competing theories of prenatal androgen exposure, the Geschwind-Galaburda theory and the callosal hypothesis, than in previous research. Being a potentially better indicator of cerebral lateralization than handedness, associations with footedness were also explored. To counter inconsistencies and shortcomings of previous research, we utilized two large discovery and replication datasets (ns = 2368 and 1565) and applied latent variable analysis to reliably classify lateral preferences (i.e., handedness, footedness). This maximized the statistical conclusion validity and allowed for direct tests of replicability. Sexual orientation was differentially associated with lateral preferences among men and women. Associations among women were consistent with predictions of the Geschwind-Galaburda theory, whereas among men they were consistent with predictions of the callosal hypothesis. The results were further consistent with models of homosexuality that suggest a role of parental epigenetic marks on sexually dimorphic fetal development. Research efforts should be increased with regard to footedness and epigenetic theories of homosexuality.

Factor analysis of the Home Handedness Questionnaire: Unimanual and role differentiated bimanual manipulation as separate dimensions of handedness

Questionnaires are commonly used to measure handedness. However, popular measures do not capture hand preference by skill type, thus reducing handedness to a single dimension. An exception is the Home Handedness Questionnaire (HHQ), an action-based measure developed initially for children, which measures skills across two dimensions of handedness: unimanual actions and role differentiated bimanual manipulation (RDBM). The goal of the current study was to confirm the factor structure of the HHQ in a large sample of adults (N = 1051). A secondary goal was to measure RDBM hand preference in adults. To further validate the HHQ, participants also completed the Edinburgh Handedness Inventory (EHI). Confirmatory factor analysis verified the two-factor structure of the HHQ, and a one-factor solution was replicated for the EHI. Individuals that were classified as consistent on the EHI had stronger preferences for unimanual and RDBM hand use on the HHQ. Right hand patterning was reduced for RDBM compared to unimanual on the HHQ, and the EHI. The HHQ was found to be reliable and valid against the EHI. The HHQ offers researchers a tool to examine individual differences across manual skills that comprise the neuropsychological phenomenon handedness, and to more broadly examine laterality patterns with respect to cognition.

Hand and foot preference in two cultures

Adult participants from India and France were requested to respond to hand and foot preference questionnaires. The items of the questionnaires assessed the choice of the preferred hand and foot on a scale that ranged from extreme left preference through no preference to extreme right preference. Results showed that both groups were more right lateralized for hand actions, whereas foot preferences were less right lateralized and spread across extreme right preference to no preference on the laterality index continuum for men and women. As compared to requiring large numbers for consistency in hand preferences across geographical regions, trends in the lateralization of hand and foot preferences may be consistently obtained with smaller samples. The study reveals the existing difference in lateral preferences between the upper and lower limbs that is sustained regardless of culture or geographical location and indicates the need for further investigation to know why the lower limbs are less lateralized than the upper limbs.

Effects of side-dominance on knee joint proprioceptive target-matching asymmetries

AIMS

Right- and left-side-dominant individuals reveal target-matching asymmetries between joints of the dominant and non-dominant upper limbs. However, it is unclear if such asymmetries are also present in lower limb's joints. We hypothesized that right-side-dominant participants perform knee joint target-matching tasks more accurately with their non-dominant leg compared to left-side-dominant participants.

METHODS

Participants performed position sense tasks using each leg by moving each limb separately and passively on an isokinetic dynamometer.

RESULTS

Side-dominance affected (p < 0.05) knee joint absolute position errors only in the non-dominant leg but not in the dominant leg: right-side-dominant participants produced less absolute position errors (2.82° ± 0.72°) with the non-dominant leg compared to left-side-dominant young participants (3.54° ± 0.33°).

CONCLUSIONS

In conclusion, right-side-dominant participants tend to perform a target-matching task more accurately with the non-dominant leg compared to left-side-dominant participants. Our results extend the literature by showing that right-hemisphere specialization under proprioceptive target-matching tasks may be not evident at the lower limb joints.

Joint assessment of handedness and footedness through latent class factor analysis

Recently, some studies have demonstrated the effectiveness of two latent variable approaches in which hand preferences are analysed using either latent class methods or latent class factor (LCF) methods. The main aims of this study are: (i) to establish whether these approaches are adequate for assessing footedness, (ii) to evaluate their appropriateness when hand and foot preferences are jointly analysed, and (iii) to measure the association between handedness and footedness based on the examined latent variable models. To this end, a dataset providing information about the limb used to perform ten hand actions and three foot movements by 2236 young Italian sportspeople is analysed. The first aim is pursued through an exploratory analysis of the observed foot preferences; according to this analysis, footedness patterns are adequately described by two latent levels of footedness. As far as the second aim is concerned, a confirmatory analysis of foot and hand preferences is carried out; the best fit to the dataset is obtained using a two-dimensional LCF model with four latent levels of handedness and two latent levels of footedness. Finally, the association between handedness and footedness resulting from the employed methods is remarkably lower than that registered in other studies.

Footedness Is Associated With ADHD Symptoms in the Adult General Population

OBJECTIVE

Mixed-handedness among children has recently been proposed as a marker of neurodevelopmental disorder and ADHD. This study expanded this initial evidence to the questions of whether mixed-handedness as well as mixed-footedness are similarly associated with ADHD among adults.

METHOD

Self-reported ADHD symptoms, handedness, footedness, and current depression and anxiety were assessed in a large, heterogeneous general population sample ( N = 2,592). Latent variable analysis was used to investigate the structure and measurement properties of ADHD symptoms, the dimensionality of footedness, and the classification of lateral preferences.

RESULTS

Mixed-footedness was associated with probable ADHD (odds ratio [OR] = 1.76 [1.07, 2.89], p = .026). Left- and mixed-footedness were associated with higher inattention and impulsivity scores.

CONCLUSION

Developmental continuities of the associations of mixed lateral preferences with ADHD from child to adult age seem to exist. In particular, mixed-footedness, rather than mixed-handedness, appears to be an ADHD marker among adults.

Behavioural lateralization in domestic pigs (Sus scrofa)-variations between motor functions and individuals

Motor lateralization is hypothesized to depend on the complexity of the motor function, but it might at the same time reflect hemispheric dominance within an individual across motor functions. We investigated possible motor lateralization patterns in four motor functions of different complexity (snout use in a manipulative task, foot use in two-stepping tasks and tail curling) in the domestic pig, a tetrapod species relevant as farm animal but also as a model in human neuroscience. A significant majority of our sample showed individual biases for manipulation with their snout and for curling their tail. Interestingly, the tail curling was lateralized towards the right at the population level and showed stronger lateralization patterns than the snout. Using a cluster analysis with combined tail and snout laterality, we identified groups of individuals with different lateralization patterns across motor functions that potentially reflect the individuals' hemispheric dominance. To conclude, our results suggest that pigs show lateralization patterns that depend on the motor function and on the individual. Such individual lateralization patterns might have broader implications for animal personality and welfare. Our study lays the methodological groundwork for future research on laterality in pigs.

Is crossed laterality associated with academic achievement and intelligence? A systematic review and meta-analysis

Over the last century, sporadic research has suggested that people whose hand, eye, foot, or ear dominances are not consistently right- or left-sided are at special risk of suffering academic difficulties. This phenomenon is known as crossed laterality. Although the bulk of this research dates from 1960's and 1970's, crossed laterality is becoming increasingly popular in the area of school education, driving the creation of several interventions aimed at restoring or consolidating lateral dominance. However, the available evidence is fragmentary. To determine the impact of crossed laterality on academic achievement and intelligence, we conducted a systematic review and meta-analysis of articles published since 1900. The inclusion criteria for the review required that studies used one or more lateral preference tasks for at least two specific parts of the body; they included a valid measure of crossed laterality; they measured the impact of crossed laterality on academic achievement or intelligence; and they included participants between 3 and 17 years old. The final sample included 26 articles that covered a total population of 3578 children aged 5 to 12. Taken collectively, the results of these studies do not support the claim that there is a reliable association between crossed laterality and either academic achievement or intelligence. Along with this, we detected important shortcomings in the literature, such as considerable heterogeneity among the variables used to measure laterality and among the tasks utilized to measure the outcomes. The educational implications of these results are discussed.

Foot-preference underlies bite-scar asymmetry in the gecko Ptyodactylus guttatus

Scar-asymmetry may reflect brain laterality because scar location may reflect behaviour when being attacked. This has been studied in a few organisms, but never in lizards. Wild geckos (Ptyodactylus guttatus) from Israel were examined for bite-scar numbers and their lateral asymmetry. Social status was documented in the field before capture. Foot-preference, for either the right (R-footed) or left (L-footed) hind leg was determined in six trials for each gecko on adults captured in Jerusalem. I studied 48 geckos: 15 R-footed, 6 ambidextrous and 9 L-footed females; 6 R-footed, 3 ambidextrous and 9 L-footed males. Adults showed significantly more bite-scars than juveniles. The proportion of L-footed males mirrored that of R-footed females. Ambidextrous and L-footed geckos had a higher social status. In males, R-footed individuals had more bite-scars on the right side of the body, while L-footed individuals had more on the left side. R-footed females had more bite-scars on the right side, while L-footed females had bite-scars equally on both sides. Bite-scar asymmetry correlated with hind-leg preference, clearly reflecting brain laterality. Since all ambidextrous males had high social status, that may be the driving factor behind the females' different bite-scar pattern.

Handedness and schizotypy: The potential effect of changing the writing-hand

Mixed-handedness, which has been associated with schizotypy in recent studies, might exist for at least two different reasons: it is innate or it has been forced. We examined whether the association between mixed-handedness and schizotypy differs depending on its source. We enrolled 3485 college students in Taiwan. We used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess schizotypy, and the Annett Hand Preference Questionnaire to assess handedness. Two ways of classifying handedness were examined: the three-way classification based on Annett's categories and mixed- vs. non-mixed-handedness based on Degree of Handedness. Both mixed-handedness groups showed higher positive schizotypy scores. Among mixed handers, those who had been required to change their writing hand from left to right had higher positive schizotypy scores. Being forced to change writing hand seemed to be related to a higher level of schizotypy. The potential effect of the social pressure against using the left hand for writing is discussed.

Footedness Is Associated with Self-reported Sporting Performance and Motor Abilities in the General Population

Left-handers may have strategic advantages over right-handers in interactive sports and innate superior abilities that are beneficial for sports. Previous studies relied on differing criteria for handedness classification and mostly did not investigate mixed preferences and footedness. Footedness appears to be less influenced by external and societal factors than handedness. Utilizing latent class analysis and structural equation modeling, we investigated in a series of studies (total N > 15300) associations of handedness and footedness with self-reported sporting performance and motor abilities in the general population. Using a discovery and a replication sample (ns = 7658 and 5062), Study 1 revealed replicable beneficial effects of mixed-footedness and left-footedness in team sports, martial arts and fencing, dancing, skiing, and swimming. Study 2 (n = 2592) showed that footedness for unskilled bipedal movement tasks, but not for skilled unipedal tasks, was beneficial for sporting performance. Mixed- and left-footedness had effects on motor abilities that were consistent with published results on better brain interhemispheric communication, but also akin to testosterone-induced effects regarding flexibility, strength, and endurance. Laterality effects were only small. Possible neural and hormonal bases of observed effects need to be examined in future studies.

Evidence of Sex-Linked Familial Transmission of Lateral Preferences for Hand, Foot, Eye, Ear, and Overall Sidedness in a Latent Variable Analysis

This study investigated the familial transmission of handedness, footedness, eyedness, earedness, and of underlying sidedness in a sample of adults (n = 592 families; 1528 individuals in total), using multi-item inventories and probabilistic methods for preference classification. Our results corroborate three classes of lateral preferences and of sidedness each, right, mixed, and left. Consistent with genetic studies, we obtained evidence of parent-of-origin and sex-of-children effects, suggesting important roles of maternal mixed preferences and of paternal left preferences. Further, parental age at conception predicted mixed preferences in the child. We recommend a trichotomous classification of lateral preferences also in future studies, and to intensify research into the genetic bases of footedness, eyedness and earedness.

Starting off on the right foot: strong right-footers respond faster with the right foot to positive words and with the left foot to negative words

Recent studies have provided evidence for an association between valence and left/right modulated by handedness, which is predicted by the body-specificity hypothesis (Casasanto, 2009) and also reflected in response times. We investigated whether such a response facilitation can also be observed with foot responses. Right-footed participants classified positive and negative words according to their valence by pressing a key with their left or right foot. A significant interaction between valence and foot only emerged in the by-items analysis. However, when dividing participants into two groups depending on the strength of their footedness, an interaction between valence and left/right was observed for strong right-footers, who responded faster with the right foot to positive words, and with the left foot to negative words. No interaction emerged for weak right-footers. The results strongly support the assumption that fluency lies at the core of the association between valence and left/right.