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Background This study investigated the impact of handedness on a common spatial abilities task, the mental rotation task (MRT). The influence of a right-handed world was contrasted with people’s embodied experience with their own hands by testing both left- and right-handed people on an MRT of right- and left-hand stimuli. An additional consideration is the influence of matching the shape of the hand stimuli with the proprioception of one’s own hands. Two orthogonal hypothesis axes were crossed to yield four competing hypotheses. One axis contrasted (i) embodied experience versus (ii) world knowledge; the other axis contrasted (a) the match between the visual image of a hand on the screen and one’s own hand versus (b) the resemblance of the shape outline information from the hand stimuli with the proprioception of one’s own hands. Results Among people with mixed handedness, right-handers performed more accurately for left-hand stimuli, while left-handers had a trend for higher accuracy for right-hand stimuli. For people with extreme handedness, right-handers outperformed left-handers. Regardless of group, there was no significant variation in performance for left-hand stimuli, with only right-hand stimuli producing significant variation. Conclusions No hypothesis fully aligned with all the data. For left-hand stimuli, the consistent performance across groups does not provide support for embodied experience, while world knowledge might influence all groups similarly. Alternatively, the within-group variation for mixed-handed people supports embodied experience in the hand MRT, likely processed through visual-proprioceptive integration.

Establishing whether handedness is exogenously determined can help explain the relationship between handedness and various health and economic outcomes. It can also ensure the use of handedness as an instrument in empirical applications. Using data from the Korean National Health and Nutrition Examination Survey and the National Health and Nutrition Examination Survey in the United States, I investigate the exogeneity of children's handedness by examining the determinants of mixed-handedness. In the analysis using Korean data, parents' age, parents' non-right-handedness, and family income influence the likelihood of children's mixed-handedness. In the U.S. data analysis, however, none of the child and family characteristics, except being Asian, predict the likelihood of mixed-handedness. These results suggest that mixed-handedness, further handedness cannot be generalized as exogenous and is a race-specific characteristic.

One of the major reasons why the scientific community is so interested in understanding hemispheric asymmetries is the fact that several neurodevelopmental and psychiatric disorders have been associated with atypical lateralization (e.g., mixed handedness or right-hemispheric language lateralization). Understanding the ontogenetic determinants of hemispheric asymmetries may be helpful in understanding why some individuals are affected by such disorders while others are not. Moreover, hemispheric asymmetries can have a major impact on patient outcome in neurological disorders with asymmetric lesion distribution such as Parkinson’s disease. Therefore, understanding the differential cognitive capabilities of the two hemispheres is an integral part in the diagnosis and therapy of such disorders. In this chapter, the evidence for atypical lateralization in a number of different neurodevelopmental, psychiatric, and neurological disorders is reviewed, and the implications of these findings are discussed.

Previous research reported that non-right-handers display a less sex-congruent stereotyped sex-role identity (i.e., women portray themselves as more masculine, men as more feminine) than right-handers. However, classification of handedness was based on arbitrary criteria and did not distinguish between left-handedness and mixed-handedness among non-right-handers. We present data from two large and independent middle-European samples, a discovery (n = 7658) and a replication (n = 5062) sample. Using latent class analysis for handedness classification, it is shown that mixed-handedness, rather than left-handedness, is the driving factor underlying associations between handedness and sex-role identity. We discuss our findings with regard to the Geschwind–Galaburda theory of cerebral lateralization and the need to evaluate the contribution of sexual orientation on this association in future research.

The aim of the present study is twofold. First, we tested the view that individuals who do not develop a typically strong behavioral laterality are distributed differentially among the two genders across age. Second, we examined whether left handedness and mixed handedness are associated with an elevated risk of some developmental or cognitive deficits. A special recruitment procedure provided norms of the Rey-Osterrieth Complex Figure (ROCF) copy from large samples of left-handed ( ) and mixed-handed ( ) compared to right-handed ( ) schoolchildren and adults ( ). This graphic task was considered as reflective of the growth of visual-spatial skills and impairment at copying as a developmental risk. Subjects’ hand preference was assessed by the Edinburgh Handedness Inventory. Data analysis indicated that (1) the trend towards consistent right handedness is sex related. Girls are clearly ahead of boys in this lateralization process, and boys are overrepresented in mixed-handed subjects. The greater prevalence of mixed-handed boys compared to girls decreases with age. (2) Performance on drawing the ROCF varies according to age and handedness groups. Mixed-handed subjects scored worse in all age groups. The results are discussed in relation to the hormonal-developmental, neuropathological, and learning theories of lateralization.

Positive schizotypy is associated with non-right-handedness, which includes left- and mixed-handedness. However, because the underlying mechanisms might be different, it is important to examine whether both left- and mixed-handedness are associated with a high incidence of schizotypy. During 2009-2010, we used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess 1315 undergraduate students in Taiwan for schizotypy and the Annett handedness questionnaire to assess handedness. Among the three-way classifications based on Annett's grouping, the fully left-handed group appeared to have the lowest score of positive schizotypy; next was the fully right-handed group and then the mixed-handed. Among the three-way classifications driven from cluster analysis, mixed-handers showed highest score of positive schizotypy. When handedness was treated continuously, both direction (e.g., Hand Preference Index) and consistency (e.g., Either hand use score) indicators were significantly correlated with schizotypy. The results of regression analyses showed that the quadratic handedness measure were negatively associated with schizotypy. The results remained similar after correcting for social pressure on left-handedness. In conclusion, the relationship between schizotypy and mixed-handedness appears to be cross-cultural. The dichotomous classification of handedness, right- vs. non-right-handedness, appears to be insufficient. Additional studies on the distinct mechanisms of mixed- and left-handedness are warranted.

Left-handers have survived as a minority for thousands of years. This suggests a left-hander survival advantage that compensates for any potential left-hander deficits. Left- and right-handers have similar personalities, similar verbal and spatial abilities and do not differ much when making career choices although left-handed males earn higher wages than their right-handed counterparts. The advantage that left-handed athletes appear to have in certain sports is best explained by the numbers imbalance between left- and right-handers in a sport rather than by inherent left-hander superiority based on specialized brain mechanisms. Left-handers have many opportunities to practice and compete against right-handers, particularly in interactive sports like boxing, fencing, and tennis. They can develop tactical skills that give them an advantage over their right-handed opponents. Competition against left-handers is more infrequent for right-handers so they do not have the same opportunities to develop these strategic benefits. Right-handers who shift to left-handed sports performance can achieve high levels of proficiency while remaining right-handed for everyday activities. This suggests a left side rather than a left-hander advantage in sports performance.

Research indicates that there are individual differences in the flexibility and ease with which one retrieves and uses concepts stored in memory. Based on prior research suggesting that mixed-handedness is associated with greater cognitive flexibility, it was hypothesised that mixed-handers have access to a relatively diffuse associative network, where link strengths for closely related and distantly related concepts are not as disparate as in the case of strong-handers. This idea was explored using ambiguous words for stimuli, as ambiguous words are known to have both strong (concepts related via dominant meaning) and weak associates (concepts related via subordinate meaning). Consistent with the prediction, mixed-handers showed equal ease in accessing both strongly and weakly related concepts. In Experiment 1 mixed-handers exhibited equivalent priming for dominant and subordinate associates, while strong-handers exhibited priming for dominant associates only. In Experiment 2 ratings of strength of association for dominant versus subordinate associates were examined. Mixed-handedness was associated with lesser disparity of dominant and subordinate association ratings.

Aim:The main aim of this study was to describe the relationship between right-handed, left-handed and mixed-handed adults with intellectual disability and their success in vocational training courses.Method:A total of 71 research participants in Iran with moderate and severe intellectual disability were chosen and their hand preferences were determined by means of a hand preference test.Results:The results showed that the research participants who were right-handers or left-handers were significantly more successful than those participants who were mixed-handers. There was a significant relationship between left or right handedness and success in job training (chi2= 11.490, df = 2, p = 0.003). Left-handers were statistically more successful in job training programmes than their mixed-hander counterparts (chi2= 9.252, df = 1, p = 0.002).A similar difference was found between right-hander and mixed-hander groups (chi2= 9.047, df = 1, p = 0.003). The difference between left and right handers in job training was not statistically significant (chi2= 0.227, df = 1, p = 0.634).Conclusion:Hand preference could be an important consideration in the vocational rehabilitation assessment and evaluation of people with intellectual disabilities. Training programmes may need to be tailored to suit an individual according to handedness, particularly with those who are mixed-handers.

Hand preference was studied in 2 groups of children—children with musical ability and children without musical ability—to examine whether particular markers that may connect with handedness patterns, such as bias away from dextrality or mixed-handedness, stabilize during childhood and are associated with musical ability. Children were administered the Edinburgh Handedness Inventory to determine levels of right, left, and mixed handedness. Results demonstrated no differences in hand preference between both cohorts of children, suggesting the relative independence of musical ability and handedness. However, the inclusion of handedness as a motor marker for musical ability in children in conjunction with other preexisting neurocognitive factors cannot be entirely discounted.

OBJECTIVE: Problems with language and symptoms of attention-deficit/hyperactivity disorder (ADHD) in childhood and adolescence are often strongly linked to low scholastic performance. Early recognition of children who are at increased risk is necessary. Our objective was to determine whether mixed-handedness, which is associated with atypical cerebral laterality, is associated with language, scholastic, and ADHD symptoms in childhood and adolescence. METHODS: Prospective data come from the Northern Finland Birth Cohort 1986, a longitudinal, population-based birth cohort with assessments when children were 7 to 8 and 16 years of age (N = 7871). Teacher, parent, and/or adolescent reports were used to assess language difficulties, scholastic performance, and mental health, including ADHD symptoms. RESULTS: Mixed-handed children, relative to right-handed, had approximately a twofold increase in odds of having difficulties with language and scholastic performance at the age of 8 years. Eight years later, as 16-year-olds, adolescents had twofold increase in odds concerning difficulties in school with language and with ADHD symptoms. Mixed-handed children were more likely to have scores indicating probable psychiatric disturbance, including ADHD symptoms. As adolescents, mixed-handed children with previous behavioral problems were at considerably higher risk for scoring within the range of probable ADHD-inattention or ADHD-combined case. Mixed-handedness was associated with greater symptom severity in children and adolescents (P = .01) concerning psychiatric disturbance and ADHD inattention but not ADHD hyperactivity. CONCLUSIONS: The results indicate that mixed-handed children have a greater likelihood of having language, scholastic, and mental health problems in childhood and that these persist into adolescence. Thus, these results suggest that mixed-handedness, particularly in the presence of difficulties, could aid in the recognition of children who are at risk for stable problems. Additional research is needed to understand the connections between neural substrates related to atypical cerebral asymmetry, mixed-handedness, and mental health problems including ADHD symptoms.

Atypical handedness has been repeatedly reported in schizophrenia, with quantitative review of evidence showing an increase of non-right-handedness in patients diagnosed with schizophrenia. Mixed-handedness is also higher among non-clinical people scoring high on questionnaires aimed at measuring psychosis-proneness. However, the greatest part of information on non-clinical samples came from samples collected in North America or in the UK: differences by countries in the socio-cultural pressure to use the right hand could influence the results. In this study 604 Italian non-clinical participants (248 males, 41.1%; 356 females, 58.9%; mean age = 34.5 ± 11.9) completed the Annett Hand Preference Questionnaire (HPQ), the General Health Questionnaire (GHQ), and the Peters et al. Delusions Inventory (PDI). In the sample, 527 subjects (87.3%) were classified on the HPQ as right-handed, 53 (8.8%) were classified as mixed-handed, and 24 (4.0%) were classified as left-handed. Mixed-handed scored statistically higher on the PDI than the right-handed and left-handed, but right-handed and left-handed did not differ from each other on a statistical ground. The difference by handedness was specific for PDI, since scores on the GHQ-12 did not differ by handedness group. The links between mixed-handedness and psychosis-proneness in non-clinical samples are a reliable finding, deserving further investigation as a model for the risk of schizophrenia.

Contains fulltext : 55343.pdf (Publisher’s version ) (Closed access) Atypical lateralization, as indicated by mixed-handedness, has been related to diverse psychopathologies. Maternal prenatal stress has recently been associated with mixed-handedness in the offspring. In the present study, this relationship was investigated further in a prospective, methodologically comprehensive manner. Stress levels were determined three times during pregnancy by means of questionnaires and measurements of cortisol levels. The handedness of 110 6-y-old children (48 boys) was determined by independent observers. Mixed handedness was defined as using the opposite hand for one or more of the tested activities. Logistic regression analysis showed that more maternal daily hassles in late pregnancy and maternal mixed-handedness increased the chance of mixed-handedness in the offspring. In contrast, more pregnancy-related fear in late pregnancy and a longer duration of gestation were associated with a smaller chance of being mixed-handed. Prenatal stress measured during the first two periods of pregnancy or determined by cortisol was not related to mixed-handedness in the offspring. In conclusion, reported and physiologic measures of prenatal stress in a moderately stressed pregnant population were only partly related to offspring mixed-handedness. 5 p.

This study evaluated the degree of mixed-handedness in predominantly right-handed Vietnam combat veteran twins and their identical, combat-unexposed cotwins. The "high-risk" cotwins of combat veterans with combat-related posttraumatic stress disorder (PTSD) had more mixed-handedness (i.e., less right-handedness) than the "low-risk" cotwins of combat veterans without PTSD. Self-reported combat exposure in combat-exposed twins was a mediator of the association between handedness in their unexposed cotwins and PTSD in the twins themselves. We conclude that mixed-handedness is a familial risk factor for combat-related PTSD. This risk may be mediated in part by a proclivity for mixed-handed soldiers and Marines to experience heavier combat.

The new meta-analysis by Hirnstein & Hugdahl[1][1] shows that schizophrenia is robustly associated with non-right-handedness and thus makes a strong case for genetic links between schizophrenia, brain lateralisation and handedness. The association was obtained meta-analytically for psychometrically

International audience; Weak and absent hand preferences have often been associated with developmental disorders or with cognitive functioning in the typical population. The results of different studies in this area, however, are not always coherent. One likely reason for discrepancies in findings is the diversity of cut-offs used to define ambidexterity and mixed right- and mixed left-handedness. Establishing and applying a common criterion would constitute an important step on the way to producing systematically comparable results. We thus decided to try to identify criteria for classifying individuals ambidextrous, mixed right- or left-handed or strong right- or left-handed. For that purpose, we first administered a handedness questionnaire to 716 individuals and performed multiple correspondence analyses to define handedness groups. Twenty-four participants were categorized as ambidextrous (3.3%), as opposed to mixed (29.2%) and strong (56%) right-handers, and to mixed (9.1%) and strong (2.4%) left-handers. We then compared this categorization with laterality index (LI)-based categories using different cut-offs and found that it was most correlated with LI cut-offs at -90, -30, +30 and +90, successively delimiting strong left-handedness, mixed left-handedness, ambidexterity (-30 to +30), mixed right-handedness and strong right-handedness. The characteristics of ambidextrous and lateralized individuals are also compared.

Recent studies suggest that mixed-handedness is a risk factor for posttraumatic stress disorder (PTSD). This study examined whether mixed-handed veterans with combat-related PTSD respond more poorly to psychosocial treatment. Consistency of hand preference was assessed in 150 Vietnam combat veterans with PTSD using the Edinburgh Handedness Inventory (R. C. Oldfield, 1971). Growth modeling analyses using Mplus (L. K. Muthen & B. Muthen, 2002) identified that PTSD veterans with mixed-handedness reported significantly less treatment improvement on the PTSD Checklist (F. W. Weathers, B. T. Litz, D. S. Herman, J. A. Huska, & T. M. Keane, 1993) than did veterans with consistent handedness. These data suggest that mixed-handedness is associated with poorer PTSD treatment response. Several possible explanations for this finding are discussed.

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.

There is still considerable discussion of whether schizophrenia is a lateralized brain disorder. In fact, schizophrenic patients appear to exhibit a shift away from dexterity, as confirmed by the majority of the 23 publications dealing with this question (14 positive, seven null, two paradoxical). However, quite a few of these positive studies have distinguished between left-handedness and mixed-handedness (MH), thus lacking specificity. Whereas prior studies failed to specify schizophrenic MH, we could observe a significant relationship between strong MH and schizophrenia in male patients in a relatively small group due to sex differentiation and accurate application of Annett's hand preference questionnaire.

Mixed-handedness was reported indicative of schizotypy, relevant to psychosis and schizophrenia. However, studies suffered from validity threats and did not systematically investigate associations with footedness. Moreover, there is a dearth of studies in the general population and it is currently untested whether widely used self-report scales measure schizotypy in a comparable way in student and community samples. The present study used two large and independent community and student samples (total N2800) and utilized latent class analysis (LCA) for the classification of handedness and footedness. Psychometric properties and measurement equivalence of the Schizotypal Personality Questionnaire-Brief form (SPQ-B) in the two samples were also examined. We found that mixed-handedness (6% prevalence), but also much more common mixed-footedness (25% prevalence), was specifically and similarly associated with higher schizotypy in both samples, Cohen d=0.15-0.18. Findings indicate that schizotypal traits in conjunction with mixed lateral preferences are thus more prevalent in the overall population than previously assumed, and that footedness may be the more relevant predictor of schizotypy than handedness. Findings are further consistent with evidence on neurodevelopmental instability, but also epigenetic mechanisms involving the sex chromosomes, regarding possible common causes of both mixed-handedness and psychosis-relevant traits.

Differences in assessment and classification procedures of many mixed-handedness studies have made comparison of findings difficult. In the present study, “narrow” and “broad” definitions of mixed-handedness were investigated using the Annett Handedness Questionnaire in patients with schizophrenia ( n = 68), panic disorder ( n = 62), borderline personality disorder ( n = 35), heroin addiction ( n = 54), and mental retardation ( n = 33) in comparison with 944 controls. According to the “narrow” definition of mixed-handedness, an excess of mixed-handedness was observed in patients with borderline personality disorder and mental retardation. An excess of nonmixed-handedness was found in patients with panic disorder. According to the “broad” definition of mixed-handedness, an excess of mixed-handedness was observed in patients with mental retardation, in the total sample of psychiatric patients ( n = 252), and in the schizophrenic patients. Thus, we can conclude that different mixed-handedness definitions can be associated with different results. Furthermore, we suggest that the neurotic part of the present psychopathology spectrum tends to be related to an excess of normal or nonmixed-handedness, and the psychotic as well as the organic portion is associated with an excess of mixed-handedness. regardless of the definition of mixed-handedness used.

In the present investigation, we addressed the relation between manual preference and performance. A total of 52 right-handers and 48 left-handers were tested for manual proficiency and preferences using a range of tasks. Self-professed right-and left-handers showed greater preference for, and superior performance with, the preferred hand. Left-handers use their nonpreferred hand more often and in some instances are more skilled with it than right-handers. There was a subgroup of persons with mixed handedness, who identified themselves as left-handed, wrote with the left hand, and were more skilled with the left hand on dot-filling, but who were otherwise right-handed. Overall, the data indicated that a complete description of handedness will only be provided by careful consideration of the nature of the preference and performance measures one uses.

Fifty seven deaf and 71 hearing children were administered a 32-item Waterloo Handedness Questionnaire. The deaf children, in comparison to hearing children, were found to be weakly right-handed in terms of their hand preference with a relatively high incidence of mixed handedness.

The present study examined the link between schizotypal personality traits and manual hand preference for ‘skilled’ and ‘less skilled’ tasks in a non-clinical sample of college students. The results are consistent with previous findings regarding the higher proportion of non-right handedness among college students who score high on the Schizotypal Personality Questionnaire (SPQ), a self-report measure of schizotypal traits. A significant correlation between hand preference for ‘skilled’ tasks and particular schizotypal traits associated with cognitive—perceptual deficits was noted. The analyses also indicate that unlike schizophrenic patients who exhibit a higher incidence of mixed handedness for ‘less skilled’ tasks (see Nelson, Satz, Green & Cicchetti, 1993), individuals who score high on the SPQ exhibit a higher incidence of non-right handedness for ‘skilled’ tasks. Examination of the stability of non-right handedness over time in this population indicates that at least some of the schizotypes did not maintain their non-right handedness upon retesting, supporting the role of situational variables on lateral dominance in this population.

Increased rates of nonright-handedness have been reported in schizophrenia, but a clear distinction has not been made between left- and mixed-handedness. Handedness preferences in 96 patients fulfilling DSM-III criteria for schizophrenia and 43 normal comparison subjects were assessed with the Edinburgh Handedness Inventory. A 100% criterion was used to establish left- and right-handedness. Results were analyzed with mantel-Haenszel odds ratios adjusted for age and sex. The schizophrenic group showed a significant increase in the proportion of mixed-handers compared with the normal group. There was no increase in pure left-handedness in the schizophrenic relative to the normal group. Mixed-handedness in the schizophrenic patients was significantly associated with chronicity of illness. Mixed-handed patients were less likely to have a family history of psychotic illness than patients with strong right- or left-handedness. The results indicate a neurodevelopmental rather than a genetic origin for anomalous lateralization in schizophrenia.

The hand preference of psychosis-prone college students was examined in two separate studies using the Annett Handedness Questionnaire. The first sample, subjects who completed the Perceptual Aberration and Magical Ideation scales ( n =895), confirmed Chapman and Chapman's (1987a) report of greater mixed handedness in psychosis-prone college students. The second sample, 214 college students who completed the Schizotypal Personality Questionnaire (SPQ), did not support Kim, Raine, Triphon and Green's (1992) findings of a correlation between mixed handedness and certain SPQ scales. The results of the current study are discussed in light of Overby's (1993) failure to replicate Chapman and Chapman's (1987a) study. The possible role of task conditions, skilled vs simple, in the emergence of atypical handedness in psychosis-prone college students is discussed.

The present study was designed to examine patterns of handedness across tasks (i.e., those requiring less vs. greater skill) and over time (initially and 1 month later) in 72 schizophrenic patients and 105 normal controls. Two important methodologic advances were introduced: (1) two handedness tasks, varying in skill level (simple vs. complex); and (2) the addition of a retest on both tasks, 1 month later. Results show a higher incidence (43%) of mixed handedness in the schizophrenic sample than in normal controls (14.3%) on tasks requiring less precision in performance. Similar results were obtained when schizophrenic patients were retested 1 month later, R 1 =.88. When the more demanding set of tasks was presented, the frequency of mixed handed schizophrenics dropped by 50% at initial testing. Despite these findings, there was no evidence for stability of change over time. For example, each of the most extreme shifters at Time 1 was fully lateralized 1 month later.

Magical ideation has been shown to be related to measures of hand preference, in which those with mixed handedness exhibit higher levels of magical ideation than those with either consistent left- or right-handedness. It is unclear whether the relation between magical ideation and hand preference is the result of a bias in questionnaire-taking behaviour or of some neuropsychological concomitant of cerebral specialization. We sought to replicate this finding and further investigate how magical ideation is related to other measures of laterality, including handedness based on finger-tapping performance, and cerebral asymmetries for language, spatial judgment, and face processing as revealed by fMRI. Creative achievement was also assessed by questionnaire and correlated with magical ideation and the other measures. Magical ideation and creativity were positively correlated, and both were negatively correlated with absolute hand preference but not with hand performance or with any of the cerebral asymmetries being assessed. The results do not support the notion that the observed association between magical ideation, creativity and hand preference has a neuropsychological explanation based on reduced cerebral lateralization.

Mixed-handedness, which may reflect atypical brain laterality, has been linked to a number of medical conditions as well as prenatal stress.The aim of the study was to examine whether infertility or infertility treatment was associated with an increased risk of mixed-handedness in children. STUDY DESIGN, SUBJECTS AND OUTCOME MEASURES: We used data from three population-based birth cohorts in Denmark: the Aalborg-Odense Birth Cohort (1984-1987), the Aarhus Birth Cohort (1990-1992) and the Danish National Birth Cohort (1996-2002) (N=7728, 5720 and 29486, respectively). Data on time to pregnancy and infertility treatment were collected during pregnancy. Handedness was reported in a follow-up questionnaire when the children were at least 7years old. Children were categorized as mixed-handed if their mothers reported that they used both hands equally.Children born after infertility treatment, particularly intrauterine insemination, had a higher risk of being mixed-handed compared to children of fertile couples with a time to pregnancy/=12months (odds ratio 1.41, 95% confidence interval 1.09-1.82). Children of couples with unplanned pregnancies, particularly after an oral contraceptives failure, were also more likely to be mixed-handed. There was no association between a long waiting time to pregnancy and mixed-handedness in children.Children born after infertility treatment, particularly intrauterine insemination, and children exposed to oral contraceptives during early gestation may have a higher risk of being mixed-handed.

Although footedness is closely associated with handedness, accurate prevalence rates of contralateral footedness in right- and left-handed populations were previously unavailable to researchers studying the relationship between phenotypic and hemispheric asymmetries. We collected preference data from 2081 Brazilian children and adolescents, and relate the prevalence of crossed hand/foot preferences to values reported elsewhere in the literature. In our samples, about 4% of the dextrals and 33% of the sinistrals exhibited a contralateral kicking preference. This is in close agreement with the weighted means from our analysis of 19 papers in the literature, which yields 4.0% left-footed kicking in dextrals and 33.5% right-footed kicking in sinistrals. These values are in marked contrast to the 50% figure for right-footed kicking in sinistrals as given by MacNeilage and colleagues (1988, 1991). Among Brazilians with mixed handedness, there was a substantial increase in incongruent footedness. Male consistent right- and left-handers showed a higher prevalence of cross-footed preferences in their kicking preference than females. The sex difference in dextrals was attributed to a training effect in soccer-related activities, and to a sampling bias in sinistrals.

Numerous previous studies have reported on handedness differences among schizophrenics, as well as in normal subjects who are high in ''schizotypal'' traits, and hence putatively at risk for schizophrenia. Results have varied, but there is evidence of a shift away from dextrality, especially consistent among schizotypal individuals. Using both a conventional three-category and Annett's seven-category classification of handedness, we re-examined the question in 681 general population subjects assessed for schizotypy. The three-category analysis confirmed previous findings of increased schizotypy in mixed-handers. However, the more fine-grained analysis showed that, although mild degrees of mixed handedness were indeed associated with increased schizotypy, this trend was reversed in the most mixed-handed subjects whose schizotypy scores did not differ significantly from right-handers. Independently of our work, this subgroup of mixed-handers are also reported to show superior intellectual function, especially on some spatial tasks. We concluded that previous studies of schizophrenia and schizotypy have failed to distinguish different reasons for shifts from dextrality. It is argued that the latter's association with schizophrenia might come about through exogenous, neurodevelopmental, influences, whereas some-possibly genetically basedforms of mixed handedness could reflect a variety of cerebral organisation that protects against, rather than enhances, the risk for mental disorder.

Mentally retarded and age-matched normal controls with no history of parental sinistrality were examined for their handedness with the Waterloo Handedness Questionnaire (Singh & Bryden, 1994). Normal controls showed a clear rightward bias, with the effect being significantly higher for skilled as compared to unskilled hand items. Mentally retarded subjects showed mixed handedness with a nonsignificant difference in performance between skilled and unskilled hand items.

Previous research found that mixed handers (i.e., those that are more ambidextrous) were more likely than strong handers to update their beliefs (Niebauer, Aselage, & Schutte, 2002). It was assumed that this was due to greater degrees of communication between the two cerebral hemispheres in mixed handers. Niebauer and Garvey (2004) made connections between this model of updating beliefs and metacognitive processing. The current work proposes that variations in interhemispheric interaction (as measured by degree of handedness) contribute to differences in consciousness, specifically when consciousness is used in rumination versus the metacognitive task of self-reflection. Using the Rumination-Reflection Questionnaire (Trapnell & Campbell, 1999), predictions were supported such that strong handedness was associated with self-rumination; whereas, mixed handedness was associated with increased self-reflection p values

Hand preference was measured in a total group of 71 ELBW children to determine patterns of hand preference at 4 and 6 years, possible aetiological factors leading to handedness, and whether left or non right hand preference were markers for intellectual, motor, temperament or behavioural differences. At both 4 and 6 years the prevalence of left handedness was increased, though this prevalence changed over the period of the study. Results supported brain injury as one mechanism leading to increased left hand preference, though this process did not adequately explain this increase. Possible reasons for this and the apparent change in prevalence with time are examined. Mixed handedness at 4 years was associated with lower intellectual abilities though otherwise children were similar in motor skills, temperament and behaviour independent of hand preference category.

The purpose of the study was to replicate findings of an earlier study of fourth grade boys manifesting mixed handedness with a sample. Among 32 mixed-handed boys in Grades 6 to 8, the right-handed writer, left-handed thrower group obtained low spelling scores (Normal Curve Equivalent Scores) on the California Achievement Test significantly more frequently than the left-handed writer, right-handed thrower group. These findings are consistent with data for Grade 4 boys in the earlier study. Findings strengthen the hypotheses that mixed handedness is not a unitary neuropsychological entity and that boys who write with the right hand and throw with the left hand might be at risk for certain academic deficits.

Publisher Summary This chapter reviews the literature related to handedness and criminality. There is a general support for the hypothesis that left- and mixed-handers are somewhat more prone toward criminality than right-handers. The chapter presents various theoretical explanations for why such a relationship should exist. The most plausible explanations for a handedness–criminality relationship seem to be based upon the knowledge about how the two hemispheres differentially respond to stimuli both cognitively and emotionally. There is considerable support for the hypothesis that left- and mixed-handers are slightly more likely to engage in crime than right-handers, at least among males. Research suggests that the most reasonable explanations for why even a modest relationship should exist between handedness and criminality are neurologically based. Such explanations have focused on differences in how the two hemispheres respond to incoming stimuli. Compared to the left hemisphere, the right hemisphere appears to be (1) less capable of handling language and other forms of logical–serial thought, (2) more emotional, especially with reference to negative emotions, and (3) may be less motivated by social influences than by self-interest. The chapter offers a theoretical model that suggests that three identifiable parts of the brain are altered by being exposed to sex hormones, one of which is the neocortex.

SummaryThe relationship between hand preference, age, and developmental functioning was examined in 70 autistic patients. Unilateral or mixed handedness appeared to be stabilized by the age of five years. Patients with established hand lateralization tended to function better in all developmental areas including intelligence, language, and visuospatial abilities. It is a tenable hypothesis that the presence or absence of hand lateralization by age five may be an important predictor of outcome in autism.

Contralateral limb bud graftings were performed on tadpoles of the anuran Bufo bufo . The anteroposterior axis was inverted while the larvae were at stage IV or V (e.g., between 22–30 days after fertilization). Eighty-four tadpoles were operated on, 10 of which were used as controls. At anterior or posterior location 104 supernumerary structures developed in toto . They were collected and whole-mount examined after being stained with Alcian blue. They were further prepared for serial sectioning, mounting, and staining with hematoxylin and eosin. The majority of these supernumerary structures were found to be normal limbs of the stump handedness in agreement with all models and experiments on the urodeles axolotl and newt. However, some of the structures were clearly abnormal: double symmetric or of mixed handedness. This result is consistent with a prediction of a hierarchical polar coordinate model. The fact that no such structures have been found in the experiments on the urodeles may be due to the expected low probability for their appearance and the fact that only few such limbs have been sectioned and analyzed as yet.

Normal Curve Equivalent Scores on subtests of the California Achievement Test for mixed-handed children, 52 boys and 58 girls from Grades 3 and 4, who are right- and left-handed writers, indicate no differences by handedness in girls, but among the mixed-handed fourth grade boys, those who wrote right-handed scored lower on Study Skills than the boys who wrote left-handed.

SummaryA new series of patients with personality disorders has provided an opportunity to extend to both sexes an earlier finding that personality disordered women tend to be mixed handed. Eighty-one subjects completed Annett's handedness questionnaire. The frequency of mixed hand preference in both sexes was similar to that found in the previous study, though deviations from consistent preference were small and dependent on the method used to classify handedness. The hysterical, antisocial and explosive personality types were particularly likely to have mixed handedness. These associations were reflected in small but significant trends among several psychometric variables.

SUMMARY Previous studies have indicated a high proportion of left-handers in association with a variety of handicaps. In the present study of 203 children with myelomeningocele and hydrocephalus, a statistically significant high incidence of left and mixed handedness has been found in comparison with the control group of 200 normal children. In both groups there was a marked decline in the percentage of mixed handers between the ages of five and six years. The mixed handers (i.e. those who showed no specific hand preference in a simple drawing and writing test) exhibited significantly lower verbal IQS on the wise, substantially lower reading attainment, and they were more likely to have the upper limit of their myelomeningocele in the thoracic vertebrae. The latter finding suggests that handedness is not only determined by cortical factors but may also be influenced by asymmetrical motor or sensory dysfunction due to lesion of the thoracic cord. The findings are not inconsistent with the suggested practice of teaching mixed handers to achieve a definite hand preference, but further prospective studies are needed to substantiate this suggestion. In the cases of the left-handed children in both groups, other researchers have already emphasised the need for appropriate instruction, particularly when they are learning to write. RESUME Preference manuelle chez les enfants avec myelomeningocele et hydrocephalic Des etudes precedentes ont indique une proportion elevee de gauchers dans divers types de handicaps. Dans l'etude presente de 203 enfants avec myelomeningocele et hydrocephalic, une frequence elevee de gauchers et d'ambidextres a ete trouvee, signiflcativement plus elevee que dans un groupe controle de 200 enfants normaux. Dans les deux groupes, on a note un declin marque du pourcentage d'ambidextres entre les âges de cinq et six ans. Les ambidextres, c'est a dire les sujets ne montrant pas de preference manuelle dans un dessin simple et un test d'ecriture, avaient un score signiflcativement plus bas a l'echelle verbale du wise et des resultats substantiellement plus faibles en lecture; par ailleurs, ils avaient moins de chances que la limite superieure de leur myelomeningocele soit situee au niveau des vertebres dorsales. Ce dernier fait indique que la predominance manuelle n'est pas seulement determinee par des facteurs corticaux mais peut aussi etre influencee par des troubles asymetriques moteurs ou sensoriels dus a une lesion de la moelle epiniere. Ces donnees ne sont pas en contradiction avec la suggestion pratique d'orienter les ambidextres vers une preference manuelle mais d'autres etudes prospectives sont necessaires pour consolider cette suggestion. Dans le cas des gauchers, spina bifida ou normaux, d'autres chercheurs ont deja insiste sur la necessite d'instructions appropriees particulierement lors de l'apprentissage de la lecture. ZUSAMMENFASSUNG Handdominanz bei Kindern mit Myelomeningocele und Hydrocephalus Fruhere Untersuchungen haben bei verschiedenen Behinderungen einen hohen Prozentsatz an Linkshandern beschrieben. Bei der vorliegenden Arbeit sind von 203 Kindern mit Myelomeningocele und Hydrocephalus sehr viele links- oder beidhandig und zwar statistisch mehr als in einer Kontrollgruppe von 200 gesunden Kindern. Bei beiden Gruppen fand sich ein deutlicher Ruckgang des Prozentsatzes der beidhandigen Kinder in der Altersgruppe von funf bis sechs Jahren. Die beidhandigen Kinder, d.h. die, die bei einfachen Zeichen- und Schreibtests keine Handdominanz zeigten, erreichten einen deutlich niedrigeren IQ in der Verbalskala des WISC; erheblich niedrigere Leistungen im Lesen; sie hatten meistens eine sehr hoch sitzende Myelomeningocele im Thoraxbereich. Der letzte Befund spricht dafur, das die Handdominanz nicht nur durch cortikale Faktoren bestimmt wird. Sie kann moglicherweise audi durch Lasionen im Bereich des thorakalen Ruckenmarkes bedingte einseitige motorische oder sensorische Dysfunktionen beeinflust werden. Die Befunde bestatigen die Empfehlung, beidhandige Patienten auf eine Handdominanz umzuschulen, es sind jedoch weitere Untersuchungen erforderlich, um dies zu belegen. Fur die Linkshander unter den Kindern mit Spina bifida und den gesunden Kindern haben andere Wissenschaftler bereits betont, das eine entsprechende Schulung, insbesondere in der Phase des schreiben Lernens, von Wichtigkeit ist. RESUMEN Preferencia manual en ninos con mielomeningocele e hidrocefalia Estudios previos han mostrado una elevada proporcion de preferencia zurda manual en asociacion con una variedad de minusvalias. En el presente estudio de 203 ninos con mielomeningocele e hidrocefalia, se ha hallado una marcada incidencia de preferencia manual izquierda y mixta, siendo la incidencia estadisticamente significativa en comparacion con un grupo de 200 ninos normales. En ambos grupos habia una marcada disminucion en el porcentaje de preferencias manuales mixtas entre los cinco y seis anos. Los ninos con preferencia manual mixta es decir, aquellos que no mostraban ninguna preferencia especifica en un simple test de dibujo y escritura, tenian un CI verbal significativamente mas bajo en el WISC, un nivel para la lectura substancialmente mas bajo, y tenian una tendencia a tener el limite superior de su mielomeningocele en las vertebras toracicas. El ultimo hallazgo sugiere que la preferencia manual esta determinada no solo por factores corticales, sino que tambien puede ser influida por una disfuncion asimetrica motriz o sensitiva consecutiva a una lesion de la medula toracica. Los hallazgos no estan en contradiccion con la sugerencia de que los que tienen una lateralidad mixta deben ser ensenados para conseguir una preferencia manual definida, pero se necesitan estudios mas amplios para substanciar esta sugerencia. Otros investigadores han resaltado tambien la necesidad de dar una instruccion apropiada a los ninos zurdos normales o con espina bifida, sobre todo cuando aprenden a escribir.

Eight hundred psychiatric patients and eight hundred controls completed a handedness preference questionnaire. There was no significant difference in handedness between the two samples, but, contrary to some previous reports, excess of sinistrality was not associated with male sex. The distribution of handedness was similar in neurotics and controls, but among psychotics in general there was a higher proportion of fully right-handed subjects. Among schizophrenics there was a significantly higher proportion of left-handed writers among males than females. There were relatively few left-handed writers of either sex among patients with affective psychosis. Female patients with personality disorders had a significantly higher proportion of mixed handedness than controls. The findings are considered in relation to suggestions that functional psychoses may be associated with asymmetrical cerebral dysfunction, and that poorly lateralized function may be related to anomalous psychological development.