左利手及其形成机制:生理、病理及心理学的视角

与右利手相比,左利手在人口中占少数,并且具有明显的性别差异,男性比女性多。左利手有时会表现出认知缺陷,同时在某些领域也具有优势。左利手形成机制比较复杂,既有遗传影响,也有生理、病理方面的原因,可能的因素包括早期脑损伤,各种出生风险因素,以及孕期激素水平等,还具有深刻的心理、社会根源。     

On the left hand of time

The present experiment examined the effects of sex and handedness on the perception of brief intervals up to 20 s in duration. In order to obtain participants with sufficiently high scores on a scale of handedness, we screened 1,276 people; the process yielded 16 men and 16 women eligible for testing. In an empty production procedure, each person estimated 4 intervals of 1, 3, 7, and 20 s, respectively, using both their preferred and nonpreferred hands to provide recorded responses. The order of presentation was randomized across participants but yoked across the sexes in each of the respective handedness subgroups. Results indicated significant effects for handedness in conjunction with the hand used to make the respective response. The pattern of these interactive effects differed between male and female participants, however. These results are discussed in terms of a hemispheric account of interval timing control and potential sex difference in hemispheric specialization.     

Spatial ability and handedness

The relationship between preferred handedness and spatial visualization was examined for 124 female and 229 male undergraduate students. Handedness and spatial ability were used in the design as continuous variables. Other variables examined were sex of subject and family history of sinistrality. Spatial ability was found to be systematically related to measured handedness, familial left-handedness, and sex of subject. Males outperformed females at all levels of handedness. The lowest performance was obtained by subjects who were either extremely left-handed or extremely right-handed. The highest scores were obtained by individuals with left-handed relatives and whose handedness scores were in the range considered mixed or slightly right-handed. The results suggest that decreased hemispheric specialization is associated with increased spatial ability.     

Sex differences and handedness in hemispheric lateralization of tactile-spatial functions

Sex differences in spatial processing and handedness were studied with a tactile-spatial task in 27 male and 29 female right-handed undergraduate students in psychology. Subjects were asked to identify amorphous shapes to investigate possible male right-hemisphere specialization for spatial functions and bilateral representation among the women. The Annett handedness questionnaire estimated extent of right-handedness. Subjects were classified by major, and women by phase of menstrual cycle. Analysis shows significantly more right-handedness in women and ambidexterity in men. Over-all, men do not perform significantly better than women, although men outperform women with their left hands when handedness is covaried. Within sex, no difference is seen between left and right hand scores for men, but women perform significantly better with right than left hands. Further analyses suggest men appear right-hemisphere dominant for this task whereas women show left-hemisphere dominance. Analyses of hormonal data support recent research, in that for women on the pill there is a trend to perform worse than all other groups. Engineering students perform significantly better than all other majors.     

Handedness and stuttering: A dead horse?

A handedness questionnaire was administered to 446 stutterers and a control group. No significant male/female or stutterer/control effects were found, although both males and stutterers tended to be less right handed. The slight sex effect in handedness is consistent with previously reported studies and with cerebral structural and functional asymmetries.     

Sex and eyedness in a sample of Turkish high school students

The relationship of sex with eyedness was examined in 176 boys and 129 girls ages 15 to 21 years (M = 16.9 yr., SD = 1.8) in Turkish high schools. Sex was significantly associated with handedness; the rate of left-handedness was 10.8% in boys and 2.3% in girls and was not related to eyedness. Rate of left-eyedness in the sample was 7.9% for boys and 8.5% for girls. One may wonder whether eyedness shows a reverse sex effect, less than handedness, but methods of measurement must be compared.     

Handedness of handedness researchers.

This study tested the hypothesis that laterality and handedness researchers are more likely than other researchers to be left-handed. A questionnaire assessing hand preference was sent to authors of articles which either dealt with handedness (N = 50) or other aspects of laterality (N = 100) or did not concern laterality (N = 50). The proportion of left-handers was highest in the handedness group (12.9%) and lowest in the non-laterality group (5.0%), but this difference did not reach significance.     

An evaluation of evidence for innate sex differences in linguistic ability

A female superiority in verbal ability is reported on many tests. It has been hypothesized that the female brain is more functionally symmetrical for language then the male, and that this is the cause of the alleged superiority. Recent research has suggested that factors other than sex are involved: handedness, age of maturity, and endocrine influences. It is not yet clear whether, despite its biological correlates, the female superiortiy is innate.     

Handedness and sex differences in hemispheric asymmetry

A study was designed to assess the contributions of the factors of sex and familial history to cerebral dominance, where cerebral dominance was inferred from laterality on a dichotic listening task. The 144 subjects were selected from a larger sample on the basis of handedness, sex, and familial history of sinistrality, and tested on a task involving the dichotic presentation of CV syllables. Analysis of the data indicated that in female subjects, the presence of familial sinistrality increased the likelihood that they present atypical left-ear superiorities, while in males the converse was the case. Moreover, there was a significant sex difference overall, such that males were more clearly lateralized than females. A review of other dichotic listening studies provided support for the reliability of this sex difference for dichotic tasks using verbal material. A review of the clinical literature indicated that the hypothesis of a sex difference is at least tenable and merits further investigation. However, the possibility that there is a sex difference in the cognitive strategy used in dichotic listening cannot be ruled out.     

A note on Corballis (1997) and the genetics and evolution of handedness: developing a unified distributional model from the sex-chromosomes gene hypothesis

A unified, quantitative model for sex, twin, parent, and grandparent influences on handedness is presented. Recent research modeling the evolutionary development of genetic mechanisms for the transmission of handedness on the basis of genotype fitness has appeared to lead to the conclusion that a handedness gene cannot be located on the sex chromosomes. It is shown in this article, however, that this conclusion is not of general validity. The sex-chromosomes hypothesis is developed further, and it is demonstrated that a wide-ranging, detailed, and parsimonious account of the distribution of handedness is obtained when left-handedness is assumed to be associated recessively, and with low penetrance, with genetic variation located on the X chromosome.     

Corpus callosum size is linked to dichotic deafness and hemisphericity, not sex or handedness

Individuals differ in the number of corpus callosum (CC) nerve fibers interconnecting their cerebral hemispheres by about threefold. Early reports suggested that males had smaller CCs than females. This was often interpreted to support the concept that the male brain is more "lateralized" or "specialized," thus accounting for presumed male predominance in mathematics, as well as for aggressive behavior. Ultimately, meta-analyses of these many reports found no significant overall sex differences in inter-cerebral information carrying capacity. Here, using quantitative MRI, we found the midline CC area of 113 subjects was significantly correlated, not with handedness or sex, but with dichotic deafness, and even more so with redefined hemisphericity, the latter accounting for over 19% of CC variability. That is, both dichotic hearing and right brain-oriented individuals of either sex had significantly larger CCs than dichotically deaf or left brain-oriented persons. Thus, current traditions of brain laterality and gender may benefit from revisions that include redefined hemisphericity.     

Sex and ear differences in spontaneous and click-evoked otoacoustic emissions in young adults

Effects of sex and handedness on the production of spontaneous and click-evoked otoacoustic emissions (OAEs) were explored in a non-hearing impaired population (ages 17-25 years). A sex difference in OAEs, either produced spontaneously (spontaneous OAEs or SOAEs) or in response to auditory stimuli (click-evoked OAEs or CEOAEs) has been reported in infants and children, but healthy young adults seldom have been the target of study. In the current data, a robust sexual dimorphism was confirmed, with women producing more numerous and stronger SOAEs, and CEOAEs with greater response amplitude compared to men. A right-ear advantage was found for the number of SOAEs produced and, in women, for SOAE power. Although handedness did not moderate the ear asymmetry in production, exploratory analyses revealed that departures from strong right hand preference were associated in the present sample with reduced numbers or strengths of OAEs. The results are discussed with respect to differential exposure to androgens during prenatal development.     

Evaluation of some tasks used for specifying handedness and footedness

Healthy men (n = 42) and women (n = 45) who were right-handed and men (n = 21) and women (n = 20) who were left-handed were studied. Men's mean age was 21.1 +/- 3.5 yr. and women's 20.7 +/- 3.1 yr. These students in various faculties reported they were right- or left-handed. Then their hand and foot preferences (handedness and footedness) were ascertained by asking each of the subjects to perform 11 tasks for handedness and 9 tasks for footedness. A discriminate function analysis test showed that each of the 11 tasks used for assessing their self-reported handedness was significant, but, of the 9 tasks used for assessing self-reported footedness, only 7 were significant. Strength of the hand or foot played no role in reports of handedness or footedness. A combination of four tasks, such as pulling a door, pushing a door, holding an object, and hammering a nail, on which the maximum number of subjects performed with the right or left hand, depending upon their self-reported handedness, would be ideal for ascertaining handedness. A combination of three tasks, namely, kicking a football, pushing an object with the foot, and stamping on the ground, would be ideal for ascertaining footedness.     

Handedness and sex differences in selective interference of verbal and spatial information

The purpose of this experiment was to investigate handedness and sex differences with regard to the way verbal and spatial information is coded in selective-interference tasks. Left- and right-handed males and females were required to recall both letters and their positions in a matrix under three different kinds of interpolated conditions: visual, auditory, and noninterpolated activities. The results indicated that the selective-interference effect differed in right- and left-handers, whereas there were no differences by sex. Identity information had a dual encoding for both handedness groups, but it was relatively more biased toward visual encoding in left-handers than in right-handers; position information, however, was predominantly visually encoded--and to the same extent--in both handedness groups. These findings were interpreted as supporting the view that the differences in coding manner of right- and left-handers are related to differences in their hemispheric specialization.     

A new method of administering the Grooved Pegboard Test: performance as a function of handedness and sex

The purpose of the present study was twofold: first to examine the influences of sex and handedness on manual performance on the Grooved Pegboard Test; and secondly to provide normative data for two versions (Place and Remove tasks) of the Grooved Pegboard Test, as previous work (Bryden & Roy, 1999) had suggested that the Remove task of the Grooved pegboard may provide a purer measure of motor speed of the two hands than the standard administration of the Grooved Pegboard Test. One hundred and fifty-three (47 males and 106 females) participants completed the Grooved Pegboard Test. Individuals performed the standard version of the Grooved Pegboard Test (Place task) and a novel version of the test (Remove task). In the standard version, participants were timed on their speed for placing the pegs, while in the novel version they were timed on their speed for removing the pegs. Results confirmed previously noted hand and sex differences in the Place task of the Grooved Pegboard Test, as well as the lack of effect of handedness on performance (Bornstein, 1995; Ruff & Parker, 1993). Significant performance differences between the hands were also noted for the Remove task. Findings also indicated that the Remove task was sensitive to sex and handedness effects.     

Predicting spatial ability from hemispheric ‘non-verbal’ lateralisation: Sex,handedness and task differences implicate encoding strategy effects

Left- and right-handed males and females were given a divided visual field delayed form recognition task and three tests of visuospatial ability of varying degrees of complexity [(a) AH4 diagrammatic section, using 2-D items testing non-verbal reasoning; (b) Revised Minnesota Paper Form Board, using 2-D items testing simple spatial ability; (c) Differential Aptitude Test Space Relations, using 3-D items testing spatial manipulation]. Females of both handedness groups were left hemisphere dominant for the recognition task; males displayed no hemisphere difference. Only the most complex visuospatial test discriminated between groups, both left- right-handed males were superior to their female counterparts. There were no handedness effects for either laterality or spatial ability. Since it was also possible in some cases to predict spatial ability from laterality within sex/handedness groups, the findings were discussed in terms of the contribution of both structural and encoding factors to individual and group differences in laterality and cognitive abilities.     

Sex differences in coincidence-anticipation timing (CAT): a review

Coincidence-anticipation timing (CAT) is the ability to judge when a moving stimulus will arrive at a target. 43 articles were reviewed which investigated sex differences in this skill. Performance was typically recorded as one or more of three error measures, absolute error (AE), constant error (CE), and variable error (VE). Despite many null findings, it is argued that the evidence for a male advantage is strong, particularly for AE and VE. 10 parameters typically associated with CAT studies were analyzed (e.g., knowledge of results, number of trials, stimulus duration, and stimulus speed), but none differentiated clearly between the presence and absence of the sex difference. However, when the mean AE score was used as a measure of task difficulty, a male advantage was reliably associated with lower values of AE (easier tasks) and null findings with higher values (more difficult tasks). An attempt to compare sex difference findings from Bassin timer and real-world tasks was thwarted by the lack of studies using real-world tasks. Given little evidence for the influence of socialization on sex differences in CAT, it is suggested that the difference may have originated from the evolutionary selection of women for gathering and men for hunting.     

Development of the infant's hand preference for visually directed reaching: Preliminary report of a longitudinal study

The development of hand preference in infancy was investigated longitudinally by using a visually-directed reaching task. Thirty-two infants, equally divided into groups of familial right- and left-handed boys and girls, were tested every 3 weeks from 24 to 39 weeks of age and once again at 52 weeks. Group trends for the development of hand preference were differentiated by familial handedness and sex of the infant. At all ages, test object position (to the infant's right or left) strongly influenced the hand used for reaching. Marked variability both between and within infants demonstrated an instability of early hand preference, an effect that could be appreciated fully only with a prospective longitudinal design. The results thus suggest that the development of hand preference for reaching is highly variable, discontinuous, and related to the interaction of sex and familial handedness.     

Influences of handedness and gender on the grooved pegboard test

We studied performance on the Grooved Pegboard Test upon repeated trials and transfer of training between the hands in the first trial. The classification of handedness was based on the writing hand. We employed three trials for each hand and two different protocols for the order in which the hands started the test. For the three trials combined, women were faster than men. From the first to the second trial, there was an improvement in performance for both sexes. Within the first trial, sex differences reached significance and the protocol interacted with handedness. In this trial, only left-handed men were found to benefit from previous opposite-hand performance. It is speculated that a larger corpus callosum in left-handed men allows for the greater transfer of training between the hands.     

Is the handedness gene on the X chromosome? Comment on Jones and Martin (2000).

G. V. Jones and M. Martin (2000) argued, contrary to M. C. Corballis (1997), that a gene for handedness might plausibly be located in homologous, noncombining regions of the X and Y chromosomes. The specific model they proposed is unlikely to be correct, but a case can be made for an X-linked gene that has no homologue on the Y chromosome and that is subjected to X-inactivation in females. An X-linked gene predicts no overall sex difference in the incidence of left-handedness; the slight preponderance of left-handers among males might then be attributed to a higher incidence of pathologically induced left-handedness.