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PubMed1981

Ear asymmetry in an auditory spatial Stroop task as a function of handedness.

A reaction-time (RT) experiment was carried out in which five groups consisting of subjects with various degrees of left and right handedness, participated. The words left and right were presented binaurally, one at a time, either to the left or to the right side, implying four presentation modes. The two interfering presentation modes are regarded as Stroop tasks. Two reaction conditions were applied in separate sessions; 1. reacting to the perceived location, and 2. reacting to the content of the word. With specific hypotheses concerning cerebral dominance for verbal functions in right-handed subjects, but considerably less clear anticipations with respect to left-handers, we obtained an interaction between side of presentation, Stroop effect and handedness. The results are discussed in terms of the relation between the conceptualization of space and cerebral dominance.

Adolescent↗
PubMed1982

Effects of sex, handedness, stimulus and visual field on "mental rotation".

Shepard's mental rotation paradigm (e.g. Shepard and Metzler, 1971) was modified to allow tachistoscopic presentation of stimuli at varying angles of orientation (0 degrees to 180 degrees) in the right and left visual fields. Thirty male and thirty female subjects divided into three handedness groups (right-handers, non-familial and familial left-handers) judged whether a stimulus was a standard form or its mirror image. In general response times for correct judgements (RTc) increased monotonically as a function of angle of orientation though the curves tended to be negatively accelerated rather than linear. Right-handers showed a slower rate of increase in RTc as a function of angle than either left-handed group. Mean RTc and the rate of increase in RTc were equivalent for the two sexes and for the two visual fields. Both mean RTcs and on the rate of increase in RTc varied as a function of the stimulus. Error rates also increased monotonically as a function of angle of orientation. No sex or handedness differences in error rates were found. However, errors increased significantly less rapidly when stimuli were presented in the left visual field. It is argued that right hemisphere specialization for spatial processing minimizes the rate of increase in errors. The present failure to find sex differences may be of interest and it is argued that rapid presentation of stimuli results in subjects setting maximum and minimum response times. Within this relatively restricted "bandwith" of response times males and females may perform spatial tasks equally efficiently. Some confirmation for this hypothesis vs. an alternative based upon differences in hemispheric organization was found in a second experiment.

Adolescent↗
PubMed1984

Handedness, sex and intelligence.

On the basis of data from a large and representative population (N = 1880), we have now had the opportunity to examine the relationships that have been claimed to exist between handedness, sex, and the patterning of intellectual abilities, as these are reflected in performance on the Wechsler Adult Intelligence Scale--Revised (Wechsler, 1981). Such relationships had previously been studied using rather small samples of men and women. Our analyses show a reliable, if negligible, effect of sex on these test results, but no effect of handedness.

Adult↗
PubMed1984

Body perception and somatic discomfort in relation to right- versus left-handedness.

Multiple studies analyzed differences in body perception and body complaints between right- and left-handed subjects. Both male and female samples were included. The findings indicated that the left-handed exceeded the right-handed in feelings of body security and degree of body boundary differentiation. In addition, handedness was shown to be linked with different modes of distributing attention to the major sectors of one's body. An adequate explanation of the link between handedness and body perception is not at present available.

Adolescent↗
PubMed1986

Is there a link between handedness and hypersensitivity?

Data from the National Child Development Study were analysed to test the hypothesis of a link between left-handedness and certain immune diseases. Allergies, eczema, psoriasis, and asthma showed no association with handedness in this sample.

Adolescent↗
PubMed1988

Testosterone levels, handedness and sex ratio at birth.

Geschwind has hypothesized that levels of androgens in utero affect postnatal laterality preferences, high levels being associated with left-handedness of offspring. I have hypothesized that high parental androgen levels at the time of conception are associated with subsequent male births. However, left-handed parents seem to produce an excess of female, not male, offspring. This finding could be reconciled with the two hypotheses if individuals who were exposed to high levels of androgens in utero had low circulating levels in adulthood. Some evidence for this loophole is reviewed here. Lyster & Lloyd (1987, J. theor. Biol. 126, 125) have reported that (consistent with the hypotheses) index left-handed men have an excess of brothers; but, contrary to the hypotheses, index left-handed women have an excess of sisters. Accordingly these authors proposed that left-handedness in females is associated not with high levels of androgen in utero, but with a "sensitivity" to it. If such sensitivity were associated with low androgen levels, it might explain an excess of sisters among the sibs of left-handed women. It is shown here that evidence in agreement with this hypothesis (though not discriminating between it and Geschwind's) suggests that the sex ratios of offspring of LH male x RH female and of RH male x LH female matings, are both low.

Family↗
PubMed2001

Handedness, criminality, and sexual offending.

A very large database was used to investigate whether men with a history of criminality and/or sexual offending have a higher incidence of nonright-handedness (NRH) relative to a control sample of nonoffender men. The sample (N>8000) comprised interviews by investigators at the Kinsey Institute for Sex and Reproduction in Indiana. The general offender group and a subsample of sex offenders (e.g. pedophiles) had a significantly higher rate of NRH relative to the control (nonoffender) men. In addition, evidence was found that the general criminality/NRH relationship might result from increased educational difficulties that some nonright-handers experience. In contrast, education was unrelated to the handedness/pedophilia relationship, suggesting that there may be a different mechanism underlying the handedness/pedophile relationship than the handedness/(general) criminality relationship. Finally, as a cautionary note, it is stressed that the effects are small and that NRH should not be used as a marker of criminality.

Adult↗
PubMed2002

Drawing and identifying objects in relation to semantic category and handedness.

We investigated whether the directionality of different objects and participants' handedness affected drawing and visual object identification performance. In Experiment 1, 190 participants were asked to draw 246 pictures of objects belonging to different semantic categories. Results showed a preferential direction (leftward, rightward, or frontal view) for most of pictures. In Experiment 2, the directionality patterns found in Experiment 1 were verified in a visual identification task. Sixty participants were requested to identify pictures presented leftward or rightward. For some categories, the speed of responses was greater for pictures having the directionality assessed in the previous experiment. The effect of handedness emerged for two categories of objects (animals and vehicles) characterised by two properties: asymmetry and motion. Findings were discussed in relation to the Motor Image Theory on the isomorphism between motor (drawing) and visual (identification) processes.

Adult↗
PubMed1997

Image generation and handedness: is the hemi-imagery method valid for studying the hemisphere imagery generation process?

The validity of the proposal by Shuren et al. (Neuropsychologia, 1996, 34, 491-492) that there is some relation between handedness and hemi-imagers was investigated by means of the hemi-imagery test. Two-hundred and two subjects were asked to image one-half of an object and to report which half (left or right) they saw. The analyses, based on criteria identical to those of Shuren et al., did not replicate their findings that subjects were more likely to image the right half of objects than the left, and that right handers are right hemi-imagers. Rather, our subjects were more inclined to image the left half than the right, and no relation between handedness score and right hemi-imagers was found. It is suggested that the reading habits of the different cultures of the groups of subjects may account for this discrepancy.

Adolescent↗
PubMed1998

Footedness is a better predictor than is handedness of emotional lateralization.

A tremendous amount of experimental work has attempted to identify reliable behavioural predictors of cerebral lateralization. Preferred handedness has been the most popular predictor, but some recent reports suggest that preferred footedness may serve as a more accurate predictor of functional laterality, especially in the left-handed population. The present study sought to test this claim by selectively recruiting individuals with either 'crossed' lateral preferences (right-handed and left-footed or left-handed and right-footed) or 'uncrossed' lateral preferences (right-handed and right-footed or left-handed and left-footed). Lateralization of emotional perception was assessed with two blocks of the dichotic Emotional Words Test (EWT), and lateral preference for both handedness and footedness was assessed using self-report questionnaires. Ear advantage on the dichotic task varied significantly with preferred foot (P=0.003), but not with preferred hand. Cerebral lateralization may be more related to footedness than to other lateral preferences.

Adult↗
PubMed1999

P300, handedness, and corpus callosal size: gender, modality, and task.

The P300 event-related potential (ERP) was elicited in left- and right-handed young adult male and female subjects (n = 20/group), with auditory and visual stimulus modalities from single-stimulus and oddball tasks. P300 amplitude was larger across all conditions for left- compared to right-handed subjects at anterior and central electrode sites. P300 latency was shorter across all conditions for left- compared to right-handers. Task type did not affect the ERP handedness differences. Male and female subjects demonstrated comparable ERP handedness effects, although smaller P300 components were obtained for males compared to females. When considered in the context of previously reported corpus callosal size differences for left- vs. right-handed and male vs. female participants, the findings suggest that the P300 reflects callosal size and inter-hemispheric transmission efficacy.

Acoustic Stimulation↗
PubMed1998

The AEP T-complex to synthesised musical tones: left-right asymmetry in relation to handedness and hemisphere dominance.

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory 'musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and 'musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.

Acoustic Stimulation↗
PubMed2002

Gender and handedness effects on hedonicity of laterally presented odours.

The effect of lateral presentation of odours on the hedonic evaluation is reported using a range of different substances. The hypothesis that hedonic evaluation of odours depends on stimulated nostril and on gender and handedness is tested using psychophysical methodology. A total of 51 untrained subjects evaluated 16 substances with different hedonic valences. Each odour substance was presented to the subjects four times, twice at each nostril using a balanced experimental design. Effects of gender and handedness, and interactions, are observed. Some parallels with the perception of visual emotional stimuli are suggested. Hedonic processing of odour stimuli is concluded to be an emotional, rather than an analytical task.

Affect↗
PubMed2003

The valence-specific laterality effect in free viewing conditions: The influence of sex, handedness, and response bias.

The right hemisphere has often been viewed as having a dominant role in the processing of emotional information. Other evidence indicates that both hemispheres process emotional information but their involvement is valence specific, with the right hemisphere dealing with negative emotions and the left hemisphere preferentially processing positive emotions. This has been found under both restricted (Reuter-Lorenz & Davidson, 1981) and free viewing conditions (Jansari, Tranel, & Adophs, 2000). It remains unclear whether the valence-specific laterality effect is also sex specific or is influenced by the handedness of participants. To explore this issue we repeated Jansari et al.'s free-viewing laterality task with 78 participants. We found a valence-specific laterality effect in women but not men, with women discriminating negative emotional expressions more accurately when the face was presented on the left-hand side and discriminating positive emotions more accurately when those faces were presented on the right-hand side. These results indicate that under free viewing conditions women are more lateralised for the processing of facial emotion than are men. Handedness did not affect the lateralised processing of facial emotion. Finally, participants demonstrated a response bias on control trials, where facial emotion did not differ between the faces. Participants selected the left-hand side more frequently when they believed the expression was negative and the right-hand side more frequently when they believed the expression was positive. This response bias can cause a spurious valence-specific laterality effect which might have contributed to the conflicting findings within the literature.

Affect↗
PubMed2001

Dermatoglyphic fluctuating asymmetry and atypical handedness in schizophrenia.

Atypical handedness and dermatoglyphic abnormalities are hypothesized to reflect a neurodevelopmental disturbance in schizophrenia. Developmental instability, indexed by dermatoglyphic fluctuating asymmetry (FA), reflects the degree to which an individual's ontogenetic program is maintained and provides a useful framework in which to consider atypical handedness in schizophrenia. Thirty patients diagnosed with schizophrenia were compared with 37 matched healthy controls on levels of dermatoglyphic FA, a demonstration task determining hand preference and a test of relative hand skill. Multivariate analyses established that patients demonstrated greater FA and more atypical hand skill compared with controls. In patients, but not in controls, there was a strong positive association between a measure of FA and a measure of atypical hand skill, suggesting that these markers of neurodevelopmental disturbance are related in schizophrenia. On a measure of hand preference, patients were more likely than controls to be classified as mixed handed than either right or left handed. Results from the present study support the conjecture of greater developmental instability in schizophrenia affecting neurodevelopmental processes, including those conferring manual dominance.

Adult↗
PubMed1999

Genetic models for handedness, brain lateralization, schizophrenia, and manic-depression.

There has been a long-standing debate to explain the complex correlation of development of human hand preference with brain lateralization, and occasionally, the correlation of both lateralizations with psychiatric disorders. A major unanswered question in this debate is whether nature (i.e., genetics) or nurture (environment/culture) controls the development of these attributes of human behavior. Simple genetic models have failed to satisfactorily explain the mode of inheritance of psychotic disorders as well as of the handedness trait. This paper advances several hypothetical and testable genetic models to explain the complex inheritance of these traits. In one model, brain lateralization is proposed to result from nonrandom segregation of the 'Watson' and 'Crick' strands of a particular chromosome, causing hemisphere lateralization, and that a gene, designated RGHT (for right), is further proposed to be responsible for the distribution of DNA chains to specific hemispheres. Accordingly, dominant, familially inherited schizophrenia and bipolar disorders are postulated to result from chromosomal rearrangements disrupting strand segregation, while sporadic cases are proposed to occur at increased frequencies in individuals with the recessive handedness genotype. Finally, discordance in monozygotic twins is suggested to occur due to developmental differences in brain lateralization in twins of the recessive genotype. Psychotic disorders are suggested to be due to developmental anomalies of cerebral asymmetry.

Bipolar Disorder↗
PubMed1999

Eye development: Notch lends a handedness.

The arrangement of photoreceptors in the ommatidia of the Drosophila compound eye is polarized, having a handedness or chirality. Notch signalling helps determine this handedness, first by establishing a signalling center at the eye equator, and second by mediating a choice between two photoreceptor fates

Animals↗
PubMed1997

The epidemiology of left-handedness in a hospital population.

PURPOSE: We evaluated the association between left-handedness (LH) and age, education, cigarette smoking, alcohol consumption, and disease status in a case-control study of 8801 hospitalized patients with cancer and those with other conditions. METHODS: Subjects were interviewed in person using a structured questionnaire that contained detailed sections of lifestyle behaviors. RESULTS: The overall prevalences of LH were 7.6% among men and 6.5% among women. Among both sexes LH declined with increasing age (P < 0.05). After adjustment for age, the following associations were observed. Men had a higher risk of LH than women. The prevalence of LH was lower in ever-married subjects compared with never-married subjects (odds ratio [OR] for men, 0.7; 95% confidence intervals [CI], 0.5-0.9; for women, OR, 0.5; 95% CI, 0.3-0.9). Among men, the prevalence of LH was not associated with race, years of education, smoking status, or levels of alcohol consumption. The risk of LH was elevated in men diagnosed with fractures as compared with all other male patients (OR, 2.4; 95% CI, 1.3-6.7). Among women, LH was not associated with race, smoking, or hormonal and reproductive factors, but LH was more common among female high-school and college graduates and among self-reported alcoholics. The odds ratio of LH was significantly lower in women with breast cancer (OR, 0.3; 95% CI, 0.1-0.7). CONCLUSIONS: The increased risk of serious injuries in LH is not a result of higher alcohol use. Handedness might be an important factor in the safe use of industrial equipment.

Adult↗