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PubMed1977

Left-handedness.

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Cerebral Cortex↗
PubMed1997

[Tonal dichotic listening: discriminatory value between left and right handedness and between sexes].

INTRODUCTION: The dichotic hearing test consists of simultaneous stimulation of right and left ears with different messages, allowing analysis of the better or worse selective integration of these messages. MATERIAL AND METHODS: With the latest techniques, the tonal dichotic test is applied by listening to a sample of 90 persons, ages from between 20 and 50 years without antecedents of otologic, neurologic nor psiquiatric disorders, valuing their discriminative and dominant capacity for lateral hearing. RESULTS: The test is chosen effectively arranging the persons by their stereophonic capacity, like something adding but is as not as their simple biaural hearing capacity is, it is found an average capacity of hearing of the 79.856% in the left ear while there is only in 74.856% of in the right ear, which represents a dominance or increased value for the left ear. CONCLUSIONS: Separating within the general sample the right-handed (60 persons) from the left-handed (30 persons), there is not found any meaningful differences neither concerning capacity of discrimination nor of dominance. Separating them by sexes (58 women and 32 men) no meaningful differences are found either in discriminative capacity or in dominance.

Adult↗
PubMed2004

Measurement of lateral preferences and schizophrenia: results of the Edinburgh High-Risk Study and methodological issues.

The assessment and measurement of handedness has varied across studies, limiting the comparability of results. Data from the Edinburgh High Risk for Schizophrenia Study were analyzed to investigate the effect of different methods of assessment and scoring of hand preferences on the prevalence of handedness type and on between-group differences in handedness. Handedness was measured using both the Edinburgh Handedness Inventory and the Annett Handedness Scale in 143 subjects at high risk for schizophrenia, 31 control subjects, and 27 patients with a first episode of schizophrenia. Hand preferences were identified through demonstration of items and by verbal report. No group differences were found, although the prevalence of hand preferences changed substantially depending on the definition used. Significant correlations with socio-demographic factors were found in some instances, but these correlations depended on the definition of handedness. No sex differences were identified. The magnitude of group differences remained similar, although the prevalence of handedness types varied greatly with changes in definition of handedness. Care should be taken in correlation studies to avoid spurious relationships between handedness and other factors. To allow for comparability of results across studies, researchers should adopt a standard definition of handedness.

Adolescent↗
PubMed2004

An X-linked three allele model of hand preference and hand posture for writing.

This paper describes a genetic model of hand preferences for writing and for handwriting posture (HWP). The challenge of devising an X-linked model for these aspects of human handedness was posed by the results of a large family handedness study (McKeever, 2000) that showed evidence of such linkage. Because X-linkage for handedness has been widely regarded as untenable, the prospects for developing such a model were not initially encouraging, but ultimately a viable model did suggest itself. Family studies of handedness and leading theories of handedness are briefly described, as is some of the research on HWP motivated by the theory of Levy and Nagylaki (1972). It is argued that there is evidence that HWP reflects a biological dictate and not just individual "choices" or "adaptations" to writing in a left-to-right direction with the left hand. The model proposes that inverted handwriting posture is not necessarily highly related to speech and language lateralities of sinistrals, but that it reveals an interhemispheric mediation of writing. It is hypothesised that it reflects a specialisation of the left angular gyrus (with some possible extension into the supramarginal gyrus) for the storage of movement and timing sequences of cursive writing, and right hemisphere motor programming of the motor output of writing. It is also argued that no family handedness study conducted to date is adequate for testing the predictions of extant handedness theories, and the often wide variations between the results of family handedness studies are noted. It is suggested that fMRI studies could definitively test the HWP hypotheses of the model and that the hypothesis of X-linkage could be tested definitively should studies of the human genome identify a gene for handedness.

Chromosomes, Human, X↗
PubMed1999

Incidences of asymmetries for the palmar grasp reflex in neonates and hand preference in adults.

It was hypothesized that adult handedness might be predicted from the neonatal grasp reflex. Grasp reflex was measured from right and left hand (10 trials for each hand) in neonates. According to significance for the difference between the mean grasp reflex strength from the right and left hands, the subjects were designated as right-, left-, and mixed-handers. Adult hand preference was assessed by Edinburgh Handedness Inventory. The percentage of left-handedness (8.3%) in neonates coincided with adult left-handedness (6.3-9.2%). The percentage of consistent right-hand preference in adults coincided with percentage of right-handedness in neonates (25.7%). The high percentage of neonatal mixed-handedness was similar to that to be expected from the right shift model of hand preference. It was concluded that left-handedness and consistent right-handedness may be determined prenatally, under genetic and/or hormonal control, and that a large majority of neonatal handedness, mixed-handers, might change their hand preference in favor of right-handed-ness under socio-cultural and developmental influences of speech centres.

Adult↗
PubMed1977

An anthropological perspective on the evolution and lateralization of the brain.

The purpose of this paper is to review the anthropological evidence relating to the cultural determinants of the right-hand first postaulted by Hertz in his classic study. Also a genetic/cultural conformity model of handedness is presented that postulates that the incidence of handedness in a society is held to result both from the genetic expression of handedness interacting with cultural pressures towards conformity. The evolutionary basis for the hemispheric functional organization into cognitive and perceptual hemispheric functions is discussed in terms of "right-handed dominant homozygotes, DD," "heterozygotes, DR," mixed-handers, and "left-handed recessive homozygotes, RR." The cross-cultural distribution of handedness provides support for this model since the more conforming agriculturalists as measured by the Asch Test have a significantly lower incidence of left-handedness (0.59%, 1.5% and 3.4%), while the more permissively socialized Eskimo and Arunta hunters, who are seen to be more independent on the Asch Test, have 11.3% and 10.5% left-handers, respectively. Also, due to the greater pressures for females to conform in agricultural societies, the incidence of female left-handedness in agricultural societies is 0% out of 330 female Ss, with 3.8%, 0.79%, and 2.5% in agricultural males, as contrasted with the Eskimo hunters who have 12.5% left-handed males and 10.3% left-handed females, showing no significant sex difference. A further Hong Kong-English study also supports the genetic/cultural conformity model with a significantly lower incidence of Hong Kong Chinese left-handers (RR: male = 2.7%, and female = 4.2%). The next section, concerned with the neonatal sex-hormone differentiation and lateralization processes, provides a neuropsychologic theory relating to spatial and linguistic skills that is relevant to the following section, which deals with relationships between laterality and cognitive style. The results are also presented for the Alaskan Eskimo in relation to hand, eye, auditory dominance and cognitive style. The analysis of Eskimo fixed-versus mixed-laterality data also confirms, as predicted, that both within and across a modality (e.g., right hand/right eye/right ear) fixed right-dominance Eskimo Ss are more field-independent than mixed-dominance Ss, while the fixed left-dominance Ss are the most field-dependent and have lower spatial skills. The discussion section reviews the papers relating to the genetic/conformity model of handedness, as well as laterality and cognitive style. The evolutionary adaptive significance of sex differences in gonadal differentiation and lateralization of the brain on spatial and linguistic skills are also reviewed. The conclusions are concerned with the implications for biosocial theory and the rapidly changing incidence of left-handedness due to accompanying changes in cultural pressures both within and across cultures.

Adult↗
PubMed1988

The relationship between nonverbal intelligence and Geschwind scores in left-handed subjects.

Under psycho motor hypothesis, the relationship between left-handedness and nonverbal intelligence was studied in left-handed male and female subjects. Handedness was assessed by the Edinburgh Handedness Questionnaire; Geschwind scores (GS) were calculated for each subject. A GS of - 100 indicated consistent left-handedness. Spatial reasoning (nonverbal intelligence) was assessed by the Cattle's Culture Fair Intelligence Test. In the male and female subjects, the IQs increased for GSs from weak up to moderate left-handedness (GSs: -5 to -60), and decreased from moderate up to strong left-handedness (GSs: -60 to -100) linearly; the regression coefficient were found to be statistically significant. Weak-, and strong left-handedness both were associated with lowest scores; the highest scores were found in the subjects with moderate left-handedness (GSs: -55 to -65). It was concluded that the prerequisite for well-developed spatial reasoning should be two-sided development of the brain instead of one-sided dominance, and well functioning parallel processing between two cerebral hemispheres.

Adult↗
PubMed2002

Sinistrality in schizophrenia.

UNLABELLED: Sinistrality characterized by an excess of non-right handedness has been reported in schizophrenic patients. Two factors, sex and kind of evaluation of handedness have contributed to major discrepancies across studies. AIM: The hypothesis tested was that schizophrenic patients show a sinistral shift in handedness compared to controls taking into account the sex and using a continuum scoring system for evaluating handedness. METHODS: Seventy-three (73.1% males) schizophrenic patients (DSMIV) and 81 (64.2% males) controls were evaluated with the Edinburgh Handedness Inventory (EHI [Neuropsychologia, 9 (1971) 97]). RESULTS: The EHI score mean difference between patients with schizophrenia and control group was not significant when sex was taken into account. CONCLUSION: Schizophrenic patients taken as a whole did not show a sinistral shift in handedness even if the sex and the continuum score for handedness were considered.

Adult↗
PubMed2003

Anatomical and behavioural asymmetries in right and left handers from India.

A biometric study of the right and left limb size and functional-behavioural measures, such as, strength of the hand and the foot, foot-eye-ear preferences, asymmetries in visual acuity and audiometry, asymmetries in taste and smell perceptions was made in a sample of Indian students to find out the interrelationships between the above parameters. Healthy adult male (n = 42), females (n = 45) right handers, and, male (n = 21), female (n = 20) left handers were studied. In each, 8 measurements of each of the limbs were taken, and the strength of the hands and feet determined. Hand and foot preferences were determined through 11 and 9 tasks respectively. Dominance in the eye, ear, taste and smell were ascertained by various tests. Right or left handedness and right footedness were clearly discernible but left footedness was indistinct. Right handedness was associated with dominant right upper limb and left handedness was associated with dominant left upper limb. Only right handers showed a dominant corresponding lower limb. Eyedness was related to handedness in males. Earedness and taste were associated with handedness in females. Smell had no relationship with handedness in both sexes. There was no interrelationship between handedness, footedness, eyedness, earedness, taste and smell.

Audiometry↗
PubMed1998

Is forced dextrality an explanation for the fall in the prevalence of sinistrality with age? A study in northern England.

OBJECTIVES: The fall in the prevalence of left handedness with age has been attributed to either premature mortality or a cohort effect of forced dextrality. Evidence for forced dextrality was sought to differentiate between these competing theories. DESIGN: 6097 Edinburgh handedness inventories were used to calculate laterality quotients (LQ) with and without the questions relating to writing and drawing. These questions might be expected to be most influenced by forced dextrality. SETTING: The study was performed in a small industrial town in Lancashire, UK. PARTICIPANTS: Using the British family practitioner service where over 95% of the population are registered with a general practitioner a response rate of 82.17% was obtained with respect to the Edinburgh Inventory. RESULTS: Questions about writing and drawing on the Edinburgh Inventory contributed to the positivity (right handedness) of the mean LQ, but equally across the ages. When a negative LQ was used to define left handedness the prevalence of left handedness fell from 11.2% at age 15 to 4.4% at age 70. Removal of the questions about writing and drawing caused the prevalence of left handedness to fall from 10.5% at age 15 to 4.95% at age 70. CONCLUSIONS: Less than 20% of the fall in the prevalence of left handedness was accounted for by questions relating to writing and drawing. The fall in the prevalence of sinistrals in older age groups is not adequately explained by cohort effects of forced dextrality on the writing hand.

Adolescent↗
PubMed1993

Mental rotation, mental representation, and flat slopes.

The "mental rotation" literature has studied how subjects determine whether two stimuli that differ in orientation have the same handedness. This literature implies that subjects perform the task by imagining the rotation of one of the stimuli to the orientation of the other. This literature has spawned several theories of mental representation. These theories imply that mental representations cannot be both orientation-free and handedness-specific. We present four experiments that demonstrate the contrary: mental representations can be both orientation-free and handedness-specific. In Experiment 1 we serendipitously discovered a version of R. N. Shepard and J. Metzler's (1971) "mental rotation" task in which subjects accurately discover the handedness of a stimulus without using "mental rotation," i.e., in which reaction time to compare the handedness of two forms is not a function of the angular disparity between the two forms. In Experiment 2 we generalize this finding to different experimental procedures. In Experiment 3 we replicate this finding with a much larger group of subjects. In Experiment 4 we show that when we preclude the formation of an orientation-free representation by never repeating a polygon, subjects carry out the handedness comparison task by performing "mental rotation."

Adult↗
PubMed1994

A behavioral measure of hand preference as opposed to hand skill.

Twenty-five self-professed left-handers and 21 self-professed right-handers were given a variety of performance tests to assess handedness, along with a preference inventory and a dichotic listening test of language lateralization. The performance tests included the Annett pegboard task, that Tapley and Bryden dot-filling tasks, and two procedures, the long pegboard and long dots tasks, that were intended to assess the point in space at which a particular unimanual movement became sufficiently awkward for one to shift to the other hand. All four of these performance tests differentiated between left-handers and right-handers, although the differences between handedness groups were somewhat larger when handedness was defined in terms of the preference inventory rather than on the basis of self-report. When the difference between preferred and non-preferred hands was examined, the best predictor of hand preference was the long pegboard task. Such a finding is consistent with the view that the long pegboard provides a behavioral measure of hand preference, while the pegs and dots tasks are more closely linked to specific skills. In addition, the correlations between individual preference items and the dichotic right-ear advantage suggest that language lateralization is related to rather different handedness measures than those usually used to define handedness. This finding would suggest that handedness and language lateralization are determined by somewhat different mechanisms.

Dichotic Listening Tests↗