Cluster analysis reveals at least three, and possibly five distinct handedness groups

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.

Notational Analysis of Wheelchair Paralympic Table Tennis Matches

Paralympic table tennis is the third largest paralympic sport for the number of players. Performance analysis was conducted for the rally duration and interval and impact of serve, whilst none investigated the shots distribution among classes of physical impairment. Therefore, the purpose of this study was to conduct a notational analysis of international competitions in relation to the wheelchair classes. Five matches for each wheelchair class (C1-to-C5) were evaluated from 20 elite male right-handed players. Both players for each match were analyzed for the following performance indicators: strokes type, the area of ball bouncing, and the shots outcome. Backhand shots were the most used technique for all classes. The most used strokes for C1 players were backhand and forehand drive and backhand lob, while for C5 players they were backhand and forehand push and backhand topspin. Similar shots distribution was registered for C2-to-C5 players. The central and far-from-the-net zone was mainly reached by the serve for all classes. Errors shots were similar in all classes, whilst winning shots were more frequent in C1. The current notational analysis provided a meaningful performance modelling of indicators for coaches and athletes that can be used to design training programs for each class.

Comparative Analysis of Lateral Preferences in Patients With Resistant Schizophrenia

BACKGROUND

Schizophrenia is a chronic brain disorder of diverse etiology and clinical presentation. Despite the expansion of treatment methods, between 30 and 50% of cases remain resistant to treatment. In patients with schizophrenia, specifics in the dominant lateralization in the brain function have been discovered. This gave a reason to seek the relation between functional lateralization and the effect of treatment.

METHODS

Of the 105 people observed with schizophrenia, 45 (42.9%) were treatment resistant, and 60 (57.1%) were considered responders. We compared functional lateralization (hand, foot, and eye) between the two groups. Handedness was ascertained by using the Edinburgh Handedness Inventory. The assessment was made at 12 weeks of treatment.

RESULTS

Of all patients with schizophrenia, 41.89% have mixed lateralization, 53.34% are right winged, and 4.76% of the patients are left winged. Resistance of the symptoms shows that 26 (57.78%) are cross-dominated, 18 (40%) are right winged, and 1 (2.22%) is left winged. In patients with clinical remission, 18 (30%) are of mixed dominance, 38 (63.33%) are right winged, and 4 (6.66%) are left winged. From the results for the separate lateralization of the hand, foot, and eye, we found a significant difference only in terms of the dominance of the eye. In 44 (41.9%) of the patients, we found dominance of the left eye. In patients with resistance, the percentage established by us is higher-at 26 (57.8%). These results indicate that the increased percentage of mixed dominance in patients with schizophrenia is mainly due to left-sided lateralization of the eye, especially in those with resistance to treatment.

CONCLUSION

We find an increased number of patients with cross-dominance left eye dominance in patients with schizophrenia. Cross-dominance and left eye dominance are associated with a higher probability of symptom resistance than other forms of lateralization (left-handed or right-handed). The high percentage of cross-dominance is due to the high percentage of left-sided dominance of the eye.

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 Role of the Non-Playing Hand during Topspin Forehand in Table Tennis

Theoretical tutorials and the scientific literature do not provide information on the proper use of the non-playing hand in table tennis. This study aimed to evaluate the course of the movement in the joints of the non-playing limb during a table tennis topspin forehand stroke (played after a backspin ball) and to determine the inter-individual movement variability. The study involved 12 male table tennis players (178.7 ± 5.5 cm, 70.0 ± 6.6 kg, 23 ± 3 y) at a competitive level. The participants performed one topspin forehand as a response to a backspin ball. Kinematics were measured using an Inertial Motion Unit–MR3 myoMuscle Master Edition system. Changes in the angles of the upper limb joints (with particular emphasis on the non-playing hand) during the forehand topspin were analyzed. A novel method of normalized function of variance was used to characterize areas of high/low variability of movement. Most of the movements in the joints of the non-playing limb were performed symmetrically to the playing one, especially in the hitting phase. A rapid change of direction characterizes these movements, just before or during the hitting phase, which may indicate a supportive, ‘driving’ character for these movements. High inter-individual variability for the duration of the entire movement cycle in both limbs was observed; higher in the non-playing limb. This perhaps indicates a greater degree of individualization on the non-playing side.

Left-handers know what's left is right: Handedness and object affordance

We live in a right-hander's world. Although left-handers become accustomed to using right-handed devices, an underlying preference for objects that afford the dominant hand could remain. We employed eye tracking while left- and right-handed participants viewed advertisements for everyday products. Participants then rated aesthetic appeal, purchase intention, and perceived value. Left-handed participants found advertisements for products that more easily afforded them action to be more aesthetically appealing. They also indicated greater future purchase intention for products that were oriented towards the left hand, and gave these products a higher perceived value. Eye tracking data showed that object handles attracted attention, and were also able to retain participants' attention. Further, across multiple eye movement measures, our data show that participant eye movements were altered by the orientation of the handle, such that this side of the image was examined earlier and for longer, regardless of handedness. Left-handers' preferences might be stronger because they are more aware of object orientation, whereas right-handers do not experience the same difficulties. These findings highlight intrinsic differences in the way in which we perceive objects and our underlying judgments about those products, based on handedness.

Lower Limb Maneuver Investigation of Chasse Steps Among Male Elite Table Tennis Players

Background and objectives: The popularity of table tennis has increased globally. As a result, the biomechanical movement patterns in the lower limb during table tennis have attracted extensive attention from coaches, scientists and athletes. The purpose of this study was to compare the differences between the long and short chasse steps in table tennis and evaluate risk factors related to injuries in the lower limb. Materials and Methods: Twelve male elite athletes performed forehand topspin strokes with long and short chasse steps in this study, respectively. The kinematics data of the lower-limb joints were measured by a Vicon motion analysis system. The electromyograms (EMG) of six lower-limb muscles were recorded using a myoelectricity system. Results: The key findings were that the angle change rate of the ankle in the long chasse step was faster with a larger range of motion (ROM) in the coronal and transverse planes. The hip was also faster in the sagittal and transverse planes but slower in the coronal plane compared with the short chasse step. In addition, the vastus medialis (VM) was the first activated muscle in the chasse step. Conclusions: The hip and ankle joints in the long chasse step and the knee joint in the short chasse step have higher susceptibility to injury. Moreover, tibialis anterior (TA), vastus medialis (VM) and gastrocnemius (GM) should be sufficiently stretched and warmed prior to playing table tennis. The results of this study may provide helpful guidance for teaching strategies and providing an understanding of potential sport injury mechanisms.

Home and Community-Based Service Use by Vulnerable Older Adults

Purpose of the Study

The purpose of this study was to identify different types of clients who use home and community-based services.

Design and Methods

Enrollment characteristics of 76 clients at risk of nursing home placement and Medicaid spend-down who were enrolled in the Virginia Community Living Program were analyzed. Two-step cluster analysis identified 4 groups of service users.

Results

Enabling resources (caregiver relationship to participant, participant living arrangement, and length of time caregiver provided assistance to participant) and disability type (physical, cognitive, traumatic brain injury, or other) differentiated the client groups. Groups differed on average service cost per day and likelihood of nursing home placement if services were not provided.

Implications

Findings point to the value of having practitioners assist vulnerable clients in tailoring services to meet different care needs and the need for refining policies guiding home and community-based care.

Left preference for sport tasks does not necessarily indicate left-handedness: sport-specific lateral preferences, relationship with handedness and implications for laterality research in behavioural sciences

In the elite domain of interactive sports, athletes who demonstrate a left preference (e.g., holding a weapon with the left hand in fencing or boxing in a ‘southpaw’ stance) seem overrepresented. Such excess indicates a performance advantage and was also interpreted as evidence in favour of frequency-dependent selection mechanisms to explain the maintenance of left-handedness in humans. To test for an overrepresentation, the incidence of athletes' lateral preferences is typically compared with an expected ratio of left- to right-handedness in the normal population. However, the normal population reference values did not always relate to the sport-specific tasks of interest, which may limit the validity of reports of an excess of ‘left-oriented’ athletes. Here we sought to determine lateral preferences for various sport-specific tasks (e.g., baseball batting, boxing) in the normal population and to examine the relationship between these preferences and handedness. To this end, we asked 903 participants to indicate their lateral preferences for sport-specific and common tasks using a paper-based questionnaire. Lateral preferences varied considerably across the different sport tasks and we found high variation in the relationship between those preferences and handedness. In contrast to unimanual tasks (e.g., fencing or throwing), for bimanually controlled actions such as baseball batting, shooting in ice hockey or boxing the incidence of left preferences was considerably higher than expected from the proportion of left-handedness in the normal population and the relationship with handedness was relatively low. We conclude that (i) task-specific reference values are mandatory for reliably testing for an excess of athletes with a left preference, (ii) the term ‘handedness’ should be more cautiously used within the context of sport-related laterality research and (iii) observation of lateral preferences in sports may be of limited suitability for the verification of evolutionary theories of handedness.

Differences between left- and right-handers in approach/avoidance motivation: influence of consistency of handedness measures

Hand preference is often viewed as a troublesome variable in psychological research, with left-handers routinely excluded from studies. Contrary to this, a body of evidence has shown hand preference to be a useful variable when examining human behavior. A recent review argues that the most effective way of using handedness as a variable, is a comparison between individuals who use their dominant hand for virtually all manual activities (consistent handers) versus those who use their other hand for at least one activity (inconsistent handers). The authors contend that researchers should only focus on degree of handedness rather than direction of preference (left versus right). However, we argue that the field suffers from a number of methodological and empirical issues. These include a lack of consensus in choice of cut-off point to divide consistent and inconsistent categories and importantly a paucity of data from left-handers. Consequentially, researchers predominantly compare inconsistent versus consistent right-handers, largely linked to memory, cognition and language. Other research on response style and personality measures shows robust direction of handedness effects. The present study examines both strength and direction of handedness on self-reported behavioral inhibition system (BIS) and behavioral activation system (BAS) scores, using evidence from a large (N = 689) dataset including more than 200 left-handers. There were degree of handedness effects on BIS and BAS-Fun Seeking, but effects are largely driven by differences between consistent left-handers and other groups. Choice of cut-off point substantively influenced results, and suggests that unless a suitable sample of left-handers is included, researchers clarify that their degree of handedness effects are applicable only to right-handers. We concur that strength of hand preference is an important variable but caution that differences related to consistency may not be identical in right and left-handers.

Effects of saccadic bilateral eye movements on episodic and semantic autobiographical memory fluency

Performing a sequence of fast saccadic horizontal eye movements has been shown to facilitate performance on a range of cognitive tasks, including the retrieval of episodic memories. One explanation for these effects is based on the hypothesis that saccadic eye movements increase hemispheric interaction, and that such interactions are important for particular types of memory. The aim of the current research was to assess the effect of horizontal saccadic eye movements on the retrieval of both episodic autobiographical memory (event/incident based memory) and semantic autobiographical memory (fact based memory) over recent and more distant time periods. It was found that saccadic eye movements facilitated the retrieval of episodic autobiographical memories (over all time periods) but not semantic autobiographical memories. In addition, eye movements did not enhance the retrieval of non-autobiographical semantic memory. This finding illustrates a dissociation between the episodic and semantic characteristics of personal memory and is considered within the context of hemispheric contributions to episodic memory performance.

Left-handedness in professional and amateur tennis

Negative frequency-dependent effects rather than innate predispositions may provide left-handers with an advantage in one-on-one fighting situations. Support mainly comes from cross-sectional studies which found significantly enhanced left-hander frequencies among elite athletes exclusively in interactive sports such as baseball, cricket, fencing and tennis. Since professional athletes' training regimes continuously improve, however, an important unsolved question is whether the left-handers' advantage in individual sports like tennis persists over time. To this end, we longitudinally tracked left-hander frequencies in year-end world rankings (men: 1973-2011, ladies: 1975-2011) and at Grand Slam tournaments (1968-2011) in male and female tennis professionals. Here we show that the positive impact of left-handed performance on high achievement in elite tennis was moderate and decreased in male professionals over time and was almost absent in female professionals. For both sexes, left-hander frequencies among year-end top 10 players linearly decreased over the period considered. Moreover, left-handedness was, however, no longer seems associated with higher probability of attaining high year-end world ranking position in male professionals. In contrast, cross-sectional data on left-hander frequencies in male and female amateur players suggest that a left-handers' advantage may still occur on lower performance levels. Collectively, our data is in accordance with the frequency-dependent hypothesis since reduced experience with left-handers in tennis is likely to be compensated by players' professionalism.

Establishing hand preference: why does it matter?

Hand preference has been associated with psychological and physical well-being, risk of injury, pathological irregularities, longevity, and cognitive function. To determine hand preference, individuals are often asked what hand they use to write with, or what hand is used more frequently in activities of daily living. However, relying only on one source of information may be misleading, given the strong evidence to support a disassociation between self-reported hand preference and outcomes of hand performance assessments. This brief communication is intended to highlight the various methods used to determine hand preference, to discuss the relationship between hand preference inventories and performance measures and to present some recent findings associated with hand preference and musculoskeletal disorders.

Inconsistent vs consistent right-handers' performance on an episodic memory task: evidence from the California Verbal Learning Test

Inconsistent handedness is associated with better memory performance on episodic memory tasks than consistent handedness. The present study further explored this difference in memory related to handedness by administering a measure that is used in clinical settings to assess different aspects of long-term memory. The results indicated that inconsistent right-handed individuals recalled and recognised more words on the California Verbal Learning Test-II than consistent right-handed individuals. Inconsistent right-handers also showed better performance than consistent right-handers on measures of source recognition. The results of this study further extend the effects of handedness on memory to the clinical setting because the CVLT-II is a measure used extensively in clinical neuropsychology.

A classification of handedness using the Annett Hand Preference Questionnaire

The Annett Hand Preference Questionnaire (AHPQ) was administered to a sample of 352 randomly selected individuals from the general community to examine the reproducibility of its handedness classification and to evaluate its model-based reliability and convergent validity. Latent class analysis showed that the eight categories of hand preferences could not be justified on statistical grounds. Instead, three broad handedness classes adequately accommodated the variety of handedness patterns: 'consistent right' (66.0%), 'consistent left' (9.8%) and 'inconsistent or mixed' (24.2%). Confirmatory factor analysis not only showed that the AHPQ is reliable and has solid convergent validity, but also the measurement properties of the AHPQ could be further improved by eliminating a few items from the scale. The implications of these findings are discussed, and it is suggested that questionnaire requires modification, possibly by replacing obsolete items such as 'sweeping' and 'shovelling' with modern manual activities, such as 'typing SMS messages' and 'using a remote control'.

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).

Description and Validation of a Flexible and Broadly Usable Handedness Questionnaire

Empirical evidence is provided which shows that handedness questionnaires should: (a) comprise items that cover skilled and unskilled activities; (b) be sufficiently long to capture a ''mass effect'' of variability in lateral preferences over a range of items; and (c) allow graded answer options for individual items rather than forced left/right choices. When using questionnaires that meet these criteria, it is possible to establish significant correlations between hand preference and performance even within a group of right-handers. In addition, such questionnaires are flexible enough to accommodate a great variety of handedness classification schemes.

An observational method of assessing handedness in children and adults

The current study was performed to assess the WatHand Cabinet Test (WHCT), a newly developed multidimensional observational test of handedness. Because the test is observational, it is ideal for assessing children, as it does not require a high degree of verbal comprehension on the part of the participants. 548 individuals participated in the present study on a voluntary basis. Individuals of varying ages were examined (including 3 to 5, 6, 7, 8, 9, 10, and 11-year-olds, and 19-to 24-year-olds). Each participant was asked to complete the WHCT, the Annett Pegboard (Annett, 1985), and the Waterloo Handedness Questionnaire (WHQ) (M.P. Bryden, 1977). Overall, the total score on the WHCT was significantly correlated with both the WHQ, r = .795, p < .01, and the Annett Pegboard, r = .542, p < .01. Sub-scores measuring skilled performance, bimanual performance, and internal consistency were also examined, as well as performance on the three tests as a function of age. Overall, findings indicate that that the WHCT is a valid test of hand preference in both children and adults. Its ease of use, quick administration, and built-in quantitative sub-scores offer a robust alternative method for measuring hand preference.

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.

The divided visual field paradigm: Methodological considerations

The divided visual field methodology has been used to examine a wide variety of lateralised processes. When conducting such studies it is important to employ a number of strict controls in order to maximise the effectiveness of the paradigm for examining the processing of stimuli by each hemisphere. The use of these controls is discussed in this paper. The following issues are discussed: selection of participants; methods of fixation control; presenting stimuli unilaterally; methods of responding; and measures that can be taken. The use of the divided visual field paradigm to examine interhemispheric cooperation is also discussed. Employing the recommended controls provides an effective and relatively easy method of examining the role of each hemisphere in the processing of stimuli.

Asymmetries of cortical shape: Effects of handedness, sex and schizophrenia

Some evidence suggests that sex, handedness and disease processes associated with schizophrenia affect the magnitude and/or direction of structural brain asymmetries. There are mixed findings, however, on how these factors influence cerebral torque, when torque is assessed with linear or volumetric measurements. We obtained MRI data from 67 healthy (30 males, 10 non-dextrals) and 84 schizophrenia subjects (60 males; 16 non-dextrals) and applied cortical pattern matching to spatially relate and compare differences in the surface morphology of the two cerebral hemispheres at high spatial resolution. Asymmetry indices, computed at thousands of matched hemispheric locations, were used to examine effects of sex, handedness and schizophrenia on hemispheric shape asymmetries while controlling for age and the other factors. Highly significant and discriminative right-frontal and left parietal-occipital surface expansions and protrusions (petalias) were mapped within groups. Although hemispheric shape asymmetries appeared less pronounced within female non-dextrals, asymmetry indices were not shown to differ significantly across sex, hand preference or diagnosis, or to reveal interactions of handedness with sex or diagnosis. Our 3D maps of spatially detailed anterior and posterior hemispheric shape asymmetries reflect subtle geometric distortions in hemispheric surface morphology that cannot be characterized with 2D or volumetric methods. Inter-individual variations in hemispheric torque appear minimally influenced by sex, dextrality or disease status. Biological factors driving language dominance or other lateralized brain functions dissociable from handedness, may more closely relate to hemispheric shape asymmetries, while the lateralization of other discrete brain regions may be more influenced by sexually dimorphic factors or by schizophrenia pathophysiology.

Mixed handedness is associated with the Disorganization dimension of schizotypy in a young male population

Within the ASPIS (Athens Study of Psychosis Proneness and Incidence of Schizophrenia) we sought out to examine in accordance with previous reports if a deviation from dextrality is associated with an augmented endorsement of self rated schizotypal personality traits in a large population of 1129 young male army recruits. Schizotypal traits were assessed using the Schizotypal Personality Questionnaire and hand preference membership was determined by applying stringent criteria derived from the Annett Handedness Questionnaire and the Porac-Coren questionnaire of lateral preferences. By adopting three different definitions of hand preference membership, we confirmed an association between mixed handedness and increased schizotypal personality traits, and in particular with Disorganization schizotypy that encompasses aspects of self perceived difficulties in verbal communication. Non-verbal cognitive ability, as indexed by measurement of non-verbal IQ, sustained attention and working memory was not associated with hand preference. We argue that a deviation from normal cerebral lateralization, as indexed by mixed handedness, is associated with mild sub clinical language dysfunction, rather than non-verbal cognitive ability, and this might be relevant to the expression of psychosis phenotype.

Handedness as a major determinant of functional cradling bias

Cradling is an interactive activity, involving a manual component that is very often an integral part of cradling. Cradling, while doing something else with the free hand, is referred to here as functional cradling. This study examined the relationship between a person's handedness and what arm he or she prefers to use when functionally cradling a baby doll that resembles a newborn infant. A total of 765 participants took part in the experiment, 403 women and 362 men, between the ages of 4 and 86 years. Left- and mixed-handers were actively recruited. The sample consisted of 64.3% right-handed, 24.7% mixed-handed, and 11.0% left-handed participants. The results showed a clear tendency for participants to cradle in their non-dominant arm (p < .001). Furthermore, this tendency increased with age and it was present in both sexes, although significantly stronger in women than in men. On the other hand, experience with young children through younger siblings and/or being a parent did not increase the likelihood to cradle in the non-dominant arm. It is concluded that humans have a clear functional cradling preference for the non-dominant arm because this enables the dominant arm to engage in other tasks. This might also explain why previous studies have reported a universal left cradling bias because a right-handed majority (intuitively) keeps the dominant hand free when cradling.

Schizotypy and mixed-handedness revisited

Although some previous studies assert that an association between schizotypy and loss of hand dominance is well established, the prevailing use of student populations, small effect sizes and arbitrariness of handedness classification suggest that this tentative association merits further investigation. The association of schizotypy and loss of hand dominance was examined using four samples. The first comprised 353 randomly selected individuals from the general community, the second comprised 131 screened volunteers participating as control subjects in a family study of schizophrenia, the third included 97 full siblings of schizophrenia patients, and the fourth consisted of 176 schizophrenia patients from the same study. The samples of screened volunteers and nonpsychotic siblings were used to replicate results from the community sample and to test the hypothesis that an increase in genetic liability is related to the association of schizotypal traits and mixed handedness. The results demonstrated that mixed handedness and schizotypy traits were unrelated in the representative sample from the community. This finding was replicated in the sample of screened volunteers, while siblings of schizophrenia patients showed a trend in the direction of the hypothesised relationship. In contrast, there was an expected significant but low in magnitude association between loss of hand dominance and the Schizotypal Personality Questionnaire factor of Cognitive Perceptual Dysfunction in schizophrenia patients.

Handedness, footedness, and language laterality: evidence from Wada testing

A total of 37 candidates for temporal lobe resection for epilepsy completed the Lateral Dominance Examination, a self-report instrument that measures hand and foot preference. Questionnaire results were compared with speech dominance, which had been determined by Intracarotid Sodium Amytal Procedure. Footedness was as good as handedness as a predictor of language laterality.

Evaluation of empirical methods and methodological foundations of human left-handedness

The methodological and empirical foundations underlying the theories on human left-handedness are examined, including the definition and classification of left-handedness, its relation to pathology, and the results on family, adoption, and twin research. It is argued that major research findings on left-handedness are based on inadequate empirical methods, and the concrete definitions and assessment procedures do not meet validity and reliability criteria. This also casts doubt on the relationship between left-handedness and pathology reported in the literature. Furthermore, findings from family, adoption, and twin studies do not allow interpretation of possible direct genetic contributions to explaining left-handedness. It is concluded that the methodological limitations of a causal explanation should encourage an examination of the epistemological and methodological premises of theory formulation. The functional method and a theoretical framework based on early childhood experiences and the neural plasticity of the brain may be more appropriate for the selection of empirical methods in research of human left-handedness.

Categorization and validation of handedness using latent class analysis

BACKGROUND

A view that handedness is not a dichotomous, i.e. left-right, phenomenon is shared by majority of researchers. However, there are different opinions about the exact number of hand-preference categories and criteria that should be used for their classification.

OBJECTIVES

This study examined hand-preference categories using the latent class analysis (LCA) and validated them against two external criteria (i.e. hand demonstration test and a series of arbitrary cut-off points).

METHOD

The Edinburgh Handedness Inventory was applied to 354 individuals randomly selected from the general population, and the obtained data were analysed using the LatentGOLD software.

RESULTS

Three discrete hand-preference clusters were identified, i.e. left-, right- and mixed-handed category. Further subdivision of hand-preference clusters resulted in a non-parsimonious subcategorization of individuals. There was a good agreement between the LCA-based classification and classification based on hand-preference demonstration tests. The highest agreement between the LCA model and the different types of arbitrary classification criteria ranged between 0 ± 50 and 0 ± 70 of the laterality quotient.

CONCLUSIONS

The study findings supported the view that handedness is not a bimodal phenomenon. However, definitions and subcategorizations of mixed-handedness using the cut-off points that are outside of the recommended range may lead to misclassification of cases. It is hoped that the categorization and validation of handedness developed in the context of this study will make future research in this area less dependent on arbitrary values and criteria.

The effects of hand preference side and hand preference switch history on measures of psychological and physical well-being and cognitive performance in a sample of older adult right-and left-handers

Claims have been made that left-handedness often arises from pathological causes, and that owing to this underlying pathology, the presence of sinistrality may entail disadvantages for both the length and quality of life. A prime implication of these claims is that left-handers, as a group, should display signs of poorer fitness than right-handers. This poorer fitness might take the form of an increased incidence of illnesses and/or accidents. In addition, it might also be predicted that left-handers would experience a psychological and, perhaps, cognitive quality of life that is inferior to that of right-handers. In the present study, we measured a large sample (N=1277) of older adults on four indexes of lateral preference (hand, foot, eye, and ear), on whether or not they experienced pressure to switch their preferred writing hand, and variables related to psychological well-being, physical health, and cognitive performance. The results revealed that the presence of left hand writing, in isolation, did not predict decreases in quality of life factors; however, in conjunction with left-handed writing, the presence of a hand preference switch report was shown to be important. In particular, one subset of left-handers-those who attempted to change their preferred writing hand but were unsuccessful-was found to have a lower quality of psychological and physical well-being on multiple measures.

Hand preference side and its relation to hand preference switch history among old and oldest-old adults

The last 10 years of research on adult hand preference patterns have generated a controversy over the meaning of the difference in the incidence rates of left- and right-hand preference in older adult samples (> 60 years old) when compared to samples of younger individuals (< 30 years old). Age differences in hand preference prevalence often are studied with large, cross-sectional age samples; however, with 1 notable exception (Gilbert & Wysocki, 1992), these large samples frequently are dominated numerically by individuals below the age of 45 years. This study reports on hand preference data from a sample of 1,277 individuals between the ages of 65 and 100 years. Overall, the participants in this sample displayed an incidence of 93.1% right preference versus 6.9% left preference. However, the occurrence of age differences in right-hand use when the oldest-old adults (> 73 years old) were compared to the others in this sample were only apparent for writing hand preference. Variation in hand preference prevalence was related to whether an individual reported a history of attempts to switch preference toward the right side. These findings support the view that age-related variations in hand preference prevalence are best explained by a number of factors, the interaction of which is still not well understood (Hugdahl, Satz, Mitrushina, & Miller, 1993; Hugdahl, Zaucha, Satz, Mitrushina, & Miller, 1996).

The effect of finger-movement speed of the dominant and the subdominant hand on cerebellar activation: A functional magnetic resonance imaging study

We studied the effects of different speeds of unimanual and bimanual movements on functional magnetic resonance signal changes in the cerebellum. Six healthy consistently right-handed subjects were scanned at rest and while executing a sequential finger-to-thumb-opposition task either unimanually (left or right hand) or bimanually. Movement frequency was paced by an auditory signal at rates of either 1 or 3 Hz. Significant frequency-dependent blood oxygen level-dependent signal increases were demonstrated ipsilaterally and contralaterally in the intermediate and lateral portions of the anterior cerebellum for bimanual movements and for unimanual movements with the subdominant hand. There was only a weak frequency-dependent effect for unimanual movements performed with the dominant hand. In addition, signals were stronger on the right intermediate zone of the anterior cerebellum for movements involving the right (dominant) hand while there was stronger activity on the left cerebellar hemisphere for movements involving the left (subdominant) hand. Taken together, these results suggest that rate and movement task effects on cerebellar activation are differentially sensitive to subdominant and dominant hand movements.

Performance Asymmetries in Computer Mouse Control of Right-Handers, and Left-Handers with Left- and Right-Handed Mouse Experience

Precision and general computer mouse aiming performance by right-handers (RH-RM) and left-handers with right-handed mouse experience (LH-RM) and by left-handers with left-handed mouse experience (LH-LM) were compared. A number of performance measures, such as reaction time, time to reach a target, time to click on target, and cursor trajectory, were analyzed. Superficially, specific hand experience seemed to dictate performance asymmetries, but a closer look revealed interactions between hand preference and hand performance. That finding has implications for theories of handedness. In addition, precision and general directional aiming with the mouse cursor showed a clear right hand superiority in reaction time in both RH-RM and LH-RM subjects, whereas LH-LM subjects showed no lateral asymmetries. Finally, the overall time taken for the task, averaged across groups and conditions, favored the experienced hand by some 180 ms. In practical terms, that is not a large difference, especially because the difference will be reduced with practice. Thus, the use of the inexperienced hand can be advocated when there is a need to forestall or ameliorate repetitive stress in the experienced hand.

Judgments of the duration of visually marked empty time intervals: linking perceived duration and sensitivity

The capability of subjects to categorize (as short or long) visually marked empty time intervals was investigated in three experiments. Two visual signals, located 18 degrees to the left (L) and to the right (R) of a fixation point in the visual field, established four marking conditions, two unilaterally presented (L-L and R-R) and two bilaterally presented (L-R and R-L). In Experiments 1 and 2, the results show that discrimination is better with unilateral sequences than with bilateral sequences and that the perceived duration is longer with an L-R than with an R-L sequence. In addition, Experiment 2 shows that, in comparison with a condition in which Markers 1 and 2 remain identical for a complete session, varying the markers from trial to trial does not decrease discrimination. Also, Experiment 2 shows that discrimination is better when both visual markers are presented at fovea than it is in the unilateral conditions. Experiment 3 shows that bilateral intervals are perceived as being longer and are better discriminated than are intervals marked by an intermodal sequence (auditory-visual or visual-auditory). The general discussion reports the implications of having different perceived duration and sensitivity levels, in various marker-type conditions, for an internal-clock hypothesis. Some implications of these results for a lateralized-timer hypothesis are also discussed.

Environmental influences in hand preference: an African point of view

In order to examine further the role of cultural and environmental factors in human manual preference, two surveys were undertaken in students from Ivory Coast and Sudan. In the first study (Abidjan, Ivory Coast) 382 secondary students, ages 12 to 22, answered a 20-item manual preference questionnaire. The observed frequency of left-hand preference was 7.9%, with very low left-hand use among the 18-22 age group (1%) and high among the 12-15 age group (14%). In the second study (Khartoum, Sudan) 759 undergraduates, ages 18 to 33, answered a 25-item questionnaire. The observed frequency of left manual preference was 5%. Subjects were also asked to indicate any pressure to change hand for writing, eating, or other manual activities and, in the second study, any upper limb injury which temporarily rendered the subject unable to use his (her) preferred hand. Report of an upper limb injury in the past was related to mixed (or inconsistent) hand preference. In both studies, the target activity against left-hand use was eating. These results show that cultural and environmental factors could change "natural" hand preference in three ways: (i) by changing the hand used for only one activity (e.g., eating), with no change for other familiar unimanual activities; (ii) by reducing the degree of hand preference; (iii) by changing the overall preferred hand, generally reducing the prevalence of left-handedness. The design of handedness studies should allow these possibilities to be distinguished.

The Specificity of Motor Skill and Manual Asymmetry: A Review of the Evidence and Its Implications

Results of investigations on gaining control of limb movements are reviewed, and their contribution to understanding the development of manual asymmetries is discussed in relation to the discrimination and programming of appropriate neuromuscular resources. An examination of the relevant evidence on number and types of manual asymmetries recorded provides strong grounds for concluding that where asymmetries occur, they simply represent a further example of the well-documented activity-specific nature of motor skills and of the extremely lengthy periods of learning or experience needed for their acquisition and perfection. This specificity of motor skill and manual asymmetry also readily accounts for most of the discrepancy usually reported between assessments of hand preference and performance differences between hands, because these alternative measures of handedness have rarely employed the same range or variety of tasks.

What is the role of the corpus callosum in intermanual transfer of motor skills? A study of three cases with callosal pathology

Intermanual transfer for a skilled motor task was studied in two patients with total callosal agenesis, and one with an acquired partial callosal lesion and clinical evidence for disturbed transfer of motor signals. Patients had to draw meaningless figures with one upper extremity (original learning, OL) and to reproduce their mirror-reversals thereafter with the other side (transfer learning, TL). Both directions of intermanual transfer were tested in two conditions, that is, between either proximal or distal muscle groups. Transfer was evaluated by comparing OL and TL performance at the same effector. The main variable of interest was movement time during the first eight trials of OL and TL. All three patients displayed a significant benefit for transfer from the dominant to the non-dominant hand but not vice versa during proximal motor activity. When compared with the performance of healthy subjects tested in almost identical conditions in a previously reported study, the proximal transfer behavior was found to be similar for all patients and the normal group. Although patients exhibited no significant benefit for distal transfer, their non-dominant-to-dominant distal transfer was above the normal range. The similar transfer pattern of the patients and healthy subjects when using proximal musculature suggests that proximal transfer may be subserved by identical extracallosal pathways, most probably by the ipsilaterally descending motor systems. Since non-dominant-to-dominant distal transfer was found to be disadvantageous in healthy subjects, the patients' relative superiority in this condition may reflect missing callosal influences of an inhibitory nature.

Frequency-dependent maintenance of left handedness in humans

The percentage (10-13%) of left handedness in human has apparently not changed since the Neolithic. Left handedness is heritable and appears to be repeatedly associated with some reduced fitness components; the persistence of left handedness implies that left handers have a fitness advantage in some situations. We propose that left handers have a frequency-dependent advantage in fights and for that reason a fitness advantage. To test this hypothesis, left handedness frequencies in the general population and in sporting individuals (both students and the sporting elite) have been compared, as sporting performance is likely to be a good indicator of fighting abilities. The higher proportion of left-handed individuals in interactive sports (reflecting some fighting elements), reaching 50% in some sports categories, but not in noninteractive sports, is consistent with the fighting hypothesis. The greater frequency of left handedness in males than in females is also consistent with this hypothesis, as male-male fights are universally more frequent than other combinations. The frequency-dependent advantage in fights of left handers might explain the stability of left handedness.

Between-limb asynchronies during bimanual coordination: effects of manual dominance and attentional cueing

Whereas previous studies on interlimb coordination have mainly underscored the ubiquitous tendency to synchronize the motions of the limbs, the present experiment revealed a small, but distinct, interlimb asynchrony or phase offset, i.e. the dominant limb led the non-dominant limb during the production of bimanual circle drawing. This asynchrony was clearly evident in the majority of right-handers, but not in left-handers. Moreover, attentional cueing affected the size of the asynchrony. Instructions to visually monitor the dominant limb or non-dominant limb strengthened and weakened the phase offset, respectively. A multifactorial neural account is proposed to underly the temporal asynchrony.

Morphological asymmetries of motoneurons innervating upper extremities: clues to the anatomical foundations of handedness?

Handedness is one of the main issues in laterality research and is known to be related to a large number of morphological asymmetries of the central nervous system. However, the main focus of previous studies were cerebral structures, which ignored the spinal cord as the most distal neural entity innervating the muscles of the extremities. We analyzed morphometrically motoneurons from segments innervating the arms and hands and compared them with motoneurons of segments that innervated the upper trunk. We found an asymmetry with larger motoneuron perikaryas on the right side of the spinal cord in segments innervating the upper limbs. To our knowledge this is the first time a morphological asymmetry on single-cell-level was shown in the spinal cord of man. The possible relation of this cellular asymmetry to the origins of handedness is discussed.