A sinister plot? Facts, beliefs, and stereotypes about the left-handed personality

The Perceived Handism Discrimination Scale (PHDS): Development and factor analysis

While discrimination based on race, gender, and other factors is well-documented, the discrimination faced by left-handed individuals is often overlooked. To address this gap, a study developed the Perceived Handism Discrimination Scale (PHDS) to assess how left-handed people perceive discrimination related to their hand preference. The original questionnaire consisted of 20 items using a 7-point Likert scale and was evaluated by experts using Lawshe's methodology. After refinement, the scale was reduced to 12 items, and further analysis through Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) with two separate samples (n=200 each) led to a final scale of 10 items clustered around two significant factors: cultural and individual dimensions of perceived handism discrimination. The PHDS demonstrated good psychometric properties, including reliability and statistical significance in factor analyses. However, the fit of the assumptions underlying EFA and CFA was not ideal, suggesting that further refinement is needed. Despite this, the PHDS represents a valuable tool for identifying perceived handism discrimination, ultimately aiming to inform policies that mitigate its effects in society.

Does Hand-Predominance Have a Predominant Influence on Craniofacial Asymmetric and Anthropometric Analysis in Preadolescences?

BACKGROUND

Although the human body generally exhibits bilateral symmetry, achieving perfect symmetry is exceedingly uncommon. During preadolescent development, a face that approximates symmetry is considered both aesthetically and functionally ideal. This study aimed to investigate the relationship between craniofacial traits and hand predominance, using three-dimensional (3D) stereophotogrammetry to discern whether facial soft-tissue characteristics are correlated with hand preference.

MATERIALS AND METHODS

The study involved children aged 9 and 10 years who were free from any diagnosed craniofacial anomalies. Three-dimensional stereophotogrammetry was conducted to analyze their facial morphology, and 37 distinct anatomical landmarks were manually identified using a MATLAB-developed program.

RESULTS

A total of 188 Taiwanese children participated in the study. All participants were healthy, with a mean age of 9.79 years. Among them, 93.1% (175) were right-hand predominant, and 6.9% (13) were left-hand predominant. There were no significant differences in linear parameters or facial asymmetry between right-hand-predominant and left-hand-predominant participants (p > 0.05). However, a consistent trend toward right laterality, especially in the right lateral frontal region of the cranium, was observed, as illustrated by heat maps of the average three-dimensional model.

CONCLUSIONS

The study found no association between facial morphology and hand predominance. A normal asymmetry with a rightward tendency was noted in children aged 9 to 10 years, which was particularly notable in the lateral frontal region of the head.

Left-hand preference in visual artists: A pre-registered observational study on Instagram

The notion of an increased incidence of left handers among architects and visual artists has inspired both scientific theory building and popular discussion. However, a systematic exploration of the available publications provides, at best, modest evidence for this claim. The present preregistered observational study was designed to reinvestigate the postulated association by examining hand preference of visual artists who share their artistic activities as short video clips ("reels") on the social media platform Instagram. Determining individual hand preference based on five reels for each of N = 468 artists, we identified 42 (8.97%) left handers, suggesting an incidence which is below but statistical comparable to the 10.6% expected for the general population (χ2 = 1.30; p = .25; Cohen's w = 0.05). Also, we did not find any support for the notion that the art created by left-handed artists is of higher quality than art of right handers, as no difference in public endorsement or interest were observed (reflected by the number of likes per post or account followers). Taken together, we do not find any support for difference in artistic engagement or quality between left and right handers.

Age, but not hand preference, is related to personality traits in common marmosets (Callithrix jacchus)

The proximate mechanisms underlying animal personalities, i.e. consistent inter-individual differences in behaviour, are a matter of discussion. Brain lateralization, expressed as the preferred use of the contralateral limb, has been suggested as one of these mechanisms. In this study, we measured a proxy of brain lateralization in captive common marmosets (N = 28) by testing hand preference in a simple food-reaching task and evaluated personality by coding a wide range of behaviours observed in daily situations. We explored the links between personality and both direction and strength of hand preference, as well as age and sex, using linear models. Principal component analysis revealed that the stable behavioural variables were organized in three personality dimensions: Agreeableness, Extraversion and Neuroticism. Regarding hand preference, 14 individuals were left-handed, seven were right-handed and seven were ambilateral. Contrary to our predictions, we did not find any relationship between personality scores and hand preference or sex. Instead, age was a significant predictor of personality scores, with older individuals being more agreeable and less extraverted. The link between brain lateralization and personality seems to be equivocal and dependent on personality and brain lateralization assessment methods. Further examinations of other proximate mechanisms, such as physiology or (epi)genetics, may elucidate what drives personality variation in common marmosets.

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.

Do cerebral motivational asymmetries mediate the relationship between handedness and personality?

Handedness has long been tied to personality, but detailed explanations for the association are lacking. Importantly for purposes of theory development, measures of approach and withdrawal associated with Big Five personality traits have also been traced back to activity in brain areas that relate to handedness. Specifically, increased right-hemisphere frontal activity appears to be linked to both withdrawal motivation and left/inconsistent-handedness, while increased left-hemisphere frontal activity is associated with approach motivation and right/consistent-handedness. Cerebral motivational asymmetries therefore present one plausible mechanism by which approach and withdrawal motivation could mediate the relationship between handedness and personality. We tested this possibility in a large online study (N = 499) in which participants completed multiple survey measures. Results indicated that approach/withdrawal motivation partially accounts for relationships between handedness and personality.

Success of Hand Movement Imagination Depends on Personality Traits, Brain Asymmetry, and Degree of Handedness

Brain-computer interfaces (BCIs), based on motor imagery, are increasingly used in neurorehabilitation. However, some people cannot control BCI, predictors of this are the features of brain activity and personality traits. It is not known whether the success of BCI control is related to interhemispheric asymmetry. The study was conducted on 44 BCI-naive subjects and included one BCI session, EEG-analysis, 16PF Cattell Questionnaire, estimation of latent left-handedness, and of subjective complexity of real and imagery movements. The success of brain states recognition during imagination of left hand (LH) movement compared to the rest is higher in reserved, practical, skeptical, and not very sociable individuals. Extraversion, liveliness, and dominance are significant for the imagination of right hand (RH) movements in "pure" right-handers, and sensitivity in latent left-handers. Subjective complexity of real LH and of imagery RH movements correlates with the success of brain states recognition in the imagination of movement of LH compared to RH and depends on the level of handedness. Thus, the level of handedness is the factor influencing the success of BCI control. The data are supposed to be connected with hemispheric differences in motor control, lateralization of dopamine, and may be important for rehabilitation of patients after a stroke.

Psychometric properties of the Spanish version of the Edinburgh Handedness Inventory in a sample of Chilean undergraduates

An individual's nervous and cognitive systems are lateralized, and handedness represents a behavioral manifestation of such organization. Therefore, accurately and reliably measuring handedness has repercussion on our understanding of both the human brain and cognition. The Edinburgh Handedness Inventory (EHI) is the most frequently used instrument to measure handedness both in clinical practice and research. We assessed the psychometric properties of the Spanish version of the EHI in a sample of 348 Chilean university students by confirmatory factor analysis. Cronbach's alpha and composite reliability were calculated to evaluate the internal consistency and reliability of the EHI, while the average variance extracted was estimated to evaluate its convergent validity. A 10-item unifactorial structure was confirmed, with factor loadings ≥0.50, showing excellent goodness-of-fit indicators, very high internal consistency and adequate composite reliability and convergent validity. Socio-demographic variables (sex, area of residence and belonging to an indigenous people or community) did not significantly modulate the EHI scores. Overall, by using this validated version of the EHI to accurately and reliably measure handedness in the greater Spanish population, researchers will be able to produce robust data to tackle the still open questions of lateralization in human cognitive and neural architecture.

Human motor cortical organization is influenced by handedness

Although there is some evidence that handedness is associated with structural and functional differences in the motor cortex, findings remain inconclusive. Here, we evaluated whether handedness influences the location, size and overlap of the cortical representations of upper limb muscles across hemispheres in right- versus left-handed individuals. Using transcranial magnetic stimulation, the cortical representations of abductor pollicis brevis, flexor carpi radialis and biceps brachii muscles were mapped bilaterally with a 6 by 5 grid space. Results indicate that right-handers had more lateral and posterior representations in the non-dominant hemisphere as well as greater overall cortical territory compared to left-handers. Right- and left-handers did not differ in the extent of overlap between muscle representations. Our findings suggest that human motor cortical organization of upper limb muscles is indeed influenced by handedness, specifically with regard to the location of non-dominant cortical muscle representations and the size of cortical territory dedicated to upper limb muscle representations.

Is self-report a valid measure of unimanual object-based task performance?

Hand preference is commonly measured via self-report using instruments known as handedness inventories. These instruments query which hand subjects use to perform unimanual object-based tasks and also the consistency of usage. Scores reveal which hand people report using most (i.e., which hand is preferred). Some people report highly consistent usage of their preferred hand while others report relatively inconsistent usage. These reports are often assumed to be accurate descriptions of people's actual behavior, but empirical evidence concerning their validity is surprisingly scant. In the present research, subjects completed a handedness inventory on which higher scores indicated more consistent usage of the preferred hand. After a brief filled interval, subjects performed tasks listed on the inventory, spontaneously choosing which hand to use for each task. Subjects who scored higher on the inventory used the preferred hand more often. Subjects were then timed while performing the tasks as fast as they could with each hand. Subjects were faster when using their preferred hand and the magnitude of the preferred hand advantage was positively correlated with self-reported consistency. These results support the validity of inventory scores by showing that they are related to spontaneous hand choice and manual fluency when performing inventory tasks.

Handedness predicts Conservative-Republican preference and eliminates relations of Big Five personality to political orientation using the 48 contiguous American states as analytical units

The two present nomothetic studies focused on the period from 1996 to 2012 to determine relations between handedness and political orientation using the 48 contiguous American states as analytical units. The estimated percentage of left-handers in each state operationally defined handedness. A composite measure of Conservative-Republican preference was created from CBS/New York Times/Gallup polls of state resident conservatism and the percent in each state voting Republican in each presidential election from 1996 to 2012. Study 1 showed that state levels of left-handedness correlated to an extremely high degree with Conservative-Republican preference (r = -.80). As well, with common demographic differences between states reflected in socioeconomic status, White population percent, and urban population percent controlled through multiple regression, handedness still accounted for an additional 37.2% of the variance in Conservative-Republican preference. Study 2 found that each of the Big Five personality variables correlated significantly with handedness and with Conservative-Republican preference, but in the opposite direction. Furthermore, Study 2 demonstrated quite surprisingly that all Big Five personality relations to Conservative-Republican preference were eliminated when handedness was controlled in multiple regression equations. For all regression equations, the global Moran's I test specifically developed for detecting residual spatial autocorrelation indicated no significant spatial autocorrelation.

Forelimb preferences in human beings and other species: multiple models for testing hypotheses on lateralization

Functional preferences in the use of right/left forelimbs are not exclusively present in humans but have been widely documented in a variety of vertebrate and invertebrate species. A matter of debate is whether non-human species exhibit a degree and consistency of functional forelimb asymmetries comparable to human handedness. The comparison is made difficult by the variability in hand use in humans and the few comparable studies conducted on other species. In spite of this, interesting continuities appear in functions such as feeding, object manipulation and communicative gestures. Studies on invertebrates show how widespread forelimb preferences are among animals, and the importance of experience for the development of forelimb asymmetries. Vertebrate species have been extensively investigated to clarify the origins of forelimb functional asymmetries: comparative evidence shows that selective pressures for different functions have likely driven the evolution of human handedness. Evidence of a complex genetic architecture of human handedness is in line with the idea of multiple evolutionary origins of this trait.

Singled Out as the Effect to be Explained

The description and explanation of intergroup differences tend to be framed in terms of how nonnormative (untypical and/or stigmatized) groups differ from normative groups rather than vice versa. Three experiments examined how this affects group members’ collective self-esteem. Single participants felt worse about being single when they read (Study 1) or wrote (Study 2) about how singles differ from coupled people than when they read or wrote about how coupled people differ from singles—although they mentioned more positive aspects of being single under the former comparative framing. In Study 3, left-handed participants indicated lower private collective self-esteem after writing about how left-handers differ from right-handers than after writing about how right-handers differ from left-handers. Thus, regardless of the specific characteristics that the comparison focused on, being marked as different and having to explain one’s group identity negatively affected members of nonnormative, but not members of normative groups.