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PubMed1996

Effects of handedness and script types on visual-field differences in the mental addition task.

The effects of handedness and script types on the difference in performance in a mental addition task by visual field were examined. Right-handers, nonfamilial left-handers, and familial left-handers who were all native speakers of Japanese were asked to add two numbers presented in the visual half-fields tachistoscopically. The two numbers were displayed either to one visual field (left or right visual field) or to the center. The numbers were displayed in Arabic, in Kanji, or in Arabic and Kanji numerals (one in Arabic and the other in Kanji: Mixed stimuli). The subjects were asked to add the two numbers and to state the sum orally. In the right-handers group, a right visual-field advantage was found for the Arabic condition but not for the Kanji or Mixed stimuli. On the other hand, in the nonfamilial and familial left-handers group, no visual-field difference in any of the conditions was found. These findings suggest that pattern of cerebral lateralization for familial and nonfamilial left-handers is the same but it is different from that of right-handers.

Adult↗
PubMed1997

Laterality and handedness in mentally retarded subjects.

In a study of 69 adults with mental retardation, atypical laterality measured on 12 tasks was only partially noted. Distribution of over-all laterality scores was different from that of handedness with more left-handed than left lateralized and more right manual preference among the 43 women.

Adolescent↗
PubMed1999

Sensorimotor performance as a function of eye dominance and handedness.

Performance on a speeded target striking task was significantly associated with eye dominance and handedness for a sample of 30 subjects. They showed the expected higher performance with the dominant hand but also showed an effect of eye of input. Highest performance was obtained with binocular viewing, next best used the dominant eye, and poorest performance the nondominant eye. Effects were additive with no interaction between hand and eye dominance.

Adult↗
PubMed2000

Left-handedness and inheritance of bronchial asthma.

A statistically significant difference in mean laterality quotients of 15 asthmatic and 106 nonasthmatic children showed a coexistence of left-handedness and asthma early in life. It is suggested that this phenomenon is not only a fetal event as the Geschwind-Galaburda hypothesis claims but it is mainly based on maternal line inheritance.

Asthma↗
PubMed2000

Magical ideation and right-sided hemispatial inattention on a spatial working memory task: influences of sex and handedness.

A correlation between magical ideation scores and the size of relative right-sided hemispatial inattention was previously reported for healthy right-handed men performing a tactile line-bisection task. To re-investigate this relation, a computerized version of Corsi's Block-Tapping Test was used to test working memory. In this version, different numbers of cubes are similtaneously displayed on a screen, and after the cubes disappear the subject is asked to designate the cubes' locations on a grid as quickly as possible. 98 healtly medical students were divided into four groups on the basis of their handedness and sex in the following way: right-handed men, right-handed women, nonright-handed men, and nonright-handed women. Each subject performed the test once with the right hand and once with the left hand. Accuracy and Neglect scores were computed for the two hemispaces separately. Also, all subjects filled in the Magical Ideation Scale which asks for hallucination-like experiences and delusion-like beliefs. In all groups a significant right-sided inattention was found when subjects performed with the right hand. Magical Ideation scores were significantly correlated with Neglect in the right hemispace for the right-handed women when the right hand was used. For the nonright-handed men, when the right hand was used, a significant negative correlation between Magical Ideation scores and Neglect scores in the left hemispace was found. Our findings support the previous study in some aspects and suggest that the correlation between hemispatial inattention and proneness to schizotypy in normal subjects is restricted to right-hand performance.

Adult↗
PubMed2001

Handedness and creativity in a sample of homosexual men.

A form concerning handedness, dyslexia, stuttering (self-report), and twinning was included in a study of sexual habits of homosexual men. Questions about interests in music, art, and creative writing were also included. A questionnaire was sent out to male homosexuals. Out of 391 returned forms, 363 were suitable for data processing. Analysis showed 13.9% reported writing with the left hand, 6.5% with stuttering, and 8.6% with dyslexia. The twin incidence was 1.2%. The creativity questions indicated a high music and painting activity. The results confirmed previous studies, showing a left shift in laterality and increased stuttering and dyslexia in the sample.

Adult↗
PubMed2004

Correlations among handedness, eyedness, monocular shifts from binocular focal point, and nonverbal intelligence in university mathematics students.

Relationships among hand preference, nonverbal intelligence, and the monocular shifts of binocular focal point were studied in 33 men and 12 women university mathematics students. Ocular dominance was assessed with the Miles test. The monocular shift of binocular focal point for each eye was assessed with a modified Miles test. Hand preference was assessed on the Edinburg Handedness Inventory. Nonverbal intelligence was assessed with Cattell's Culture Fair Intelligence Test. In a prior study, the percentage of left-eye preference had been reported to be greater for mathematics students than for nonmathematics students. In the present study there were positive correlations between hand preference and the sum of the monocular shifts of two eyes. In addition, there was a negative correlation between nonverbal intelligence and the sum of the monocular shifts of two eyes. As these resultssuggest that the sum of the monocular shifts of two eyes may be related to mathematical ability and nonverbal intelligence, further research with a larger sample including non-mathematics students is needed.

Adolescent↗
PubMed2001

The effect of right or left-handedness on oral hygiene.

It has been shown that there is a strong relation between periodontal diseases and bacterial plaque with clinical and experimental studies. According to scientific data, the best way to protect against the periodontal diseases is to remove bacterial plaque from tooth surface mechanically. To remove bacterial plaque from tooth surface completely, the patient must have good hand skill and motivation in addition to professional treatment. The aim of our study was to examine whether there is a difference between the left-handed who are known as skillful at drawing, geometry, and graphics and the right-handed at oral hygiene check. The study included 28 persons, 12 female and 16 male, ranging in age from 19 to 26. Subjects were divided into two groups according to their right or left hand use. Being right- or left-handed was determined with Edinburgh Handedness Inventory (Oldfield). Both groups were given oral hygiene education with a systematic treatment at the beginning of the study. At the beginning of the study, GI (Silness-Löe) and PI (Quigley-Hein) scores were taken from all subjects. Then, those scores were repeated in the 1st and 3rd month. Received scores were evaluated statistically with Wilcoxon test. While there was no statistical difference between both groups initially p > .05, there was a statistical difference between them in the 1st and 3rd month in favour of the left-handed p < .05. Consequently, it was found that the left-handed were more successful at oral hygiene check than the right-handed.

Adult↗
PubMed1984

Cognitive asymmetries after waking from REM and NONREM sleep: effects of delayed testing and handedness.

The present paper describes two experiments designed to investigate cognitive asymmetry after awakening from REM and NONREM sleep as a function of time after the awakening and handedness. Two groups of 9 right-handed male subjects each participated in the first experiment. Subjects were awakened from REM and NONREM sleep and after 35 min (Group 1), or 75 min (Group 2), tested on a 6-test battery designed to measure cognitive asymmetry. In contrast to our previous findings in subjects tested within 1-2 min after the awakening who showed a significant sleep-stage dependent shift in cognitive asymmetry, the present results did not show significant differences in performance between the two awakening conditions for any of the groups. Two groups of 12 male and 12 female left-handed subjects participated in the second experiment. All subjects were tested within 1-2 min after the awakenings from REM and NONREM sleep on the same 6-test battery as in experiment 1. Also in contrast to our previous findings in right handers, left-handers did not show any consistent shifts in cognitive asymmetry after the awakenings.

Adult↗
PubMed1987

Handedness and psychophysics: weight and roughness.

A sample of 20 men (10 right-handed, 10 left-handed) was selected. Using the method of constant stimuli, the number of correct responses and the differential threshold for weight and roughness for both hands, were studied. The findings were: (1) In the weight test, the number of correct responses was greater and the differential threshold lower in the right-handed than in the left-handed subjects, and the preferred hand was superior to the nonpreferred hand for both groups; (2) In the roughness test, the number of correct responses was greater and the differential threshold lower for the nonpreferred hand. Implications of these findings with regard to our present knowledge of handedness organization are analyzed.

Adult↗
PubMed1989

Cerebral somatosensory potentials evoked by posterior tibial nerve stimulation: lateralization and relation to handedness in left-handed normal subjects.

Somatosensory potentials evoked by stimulation of the right and left posterior tibial nerves were studied in left-handed normal subjects. Hand preference was assessed by the Edinburgh Handedness Inventory; a laterality score (Geschwind score) was calculated for each subject. Hand skill was assessed by the peg moving task. The mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. In the subjects without familial sinistrality, there was no statistically significant difference between the evoked potentials from the right and left sides. In the subjects with familial sinistrality, the mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. There was an inverse relationship between the lateralization quotient (LQ) for the N1 wave and left-hand preference. The amplitudes of the P1, N1, and P2 waves from the right cerebral cortex were positively linearly correlated with left-hand preference. There was an inverse relationship between LQ for the P1 and N1 waves and the right-hand skill. The left-hand skill was not correlated with LQ for the evoked potential. The LQs for the P1 and N1 waves were negatively linearly correlated with the difference between the right and left hand skills (right minus left peg moving times). The amplitudes of the P1 and N1 waves from the left cerebral cortex were found to be inversely related to the right hand skill. There was no relationship between the evoked potential amplitudes from the right cerebral cortex and left hand skill in the total sample. It was concluded that the stronger sensory feedback for the somatomotor foot area within the right cerebral cortex would contribute to left-footedness in left-handers; the asymmetric organization of the somatosensory potentials evoked by stimulation of the right and left PTNs correlates with hand preference and skill, but in an unexpected manner.

Adult↗
PubMed1991

The distribution of paw preference in right-, left-, and mixed pawed male and female cats: the role of a female right-shift factor in handedness.

The distribution of paw preference was studied in male and female cats. Paw preference was assessed by the food reaching test. Of the total sample (N = 109), 54 (49.5%) cats were found to be right-preferent, 44 (40.4%) left-preferent, and 11 (10.1%) ambidextrous. In females (N = 63), 34 cats (54.0%) were right-preferent, 23 (36.5%) left-preferent, and 6 (9.5%) ambidextrous. The proportion of the right-preferents was found to be significantly higher than that for the left-preferents in females as in humans. Of the male cats (N = 46), 20 (43.5%) were right-preferent, 21 (45.7%) left-preferent, and 5 (10.9%) ambidextrous. The proportion of the strongly right-preferent females (44%) was found to be significantly higher than that of the strongly right-preferent males (28%) as in humans. In the right-preferent animals, the incidence of the moderate left-paw use was found to be higher in males than females. There was no significant difference in the proportions of the strongly left-preferent males and females. It was concluded that the U-shaped distribution of paw preference in cats is largely shaped by females and a prominent left-paw use of males. The results provided evidence for a right-biased paw preference in females compared to males, indicating that females may be responsible for the emergence of cerebral lateralization and hand preference in animals and humans. It was tentatively suggested that a female right-shift factor may be required for the emergence of a right-bias in handedness. The absence of this factor would decrease the chance of being right-handed and increase the vulnerability of the developing brain to environmental influences.

Animals↗
PubMed1992

Handedness, dyslexia and twinning in homosexual men.

A study of handedness, dyslexia, stuttering and twinning, was included in a study of sexual habits of homosexual men. A questionnaire was mailed to homosexuals, and 394 forms suitable for data analysis were received. The results showed an increased rate of lefthand writing (17.5% compared to 8-8.4%), and a clear left shift. There were increased occurrence of both stuttering (7.1% compared to 1.6%) and reading difficulties (7.9% compared to 1-3%). The incidence of twins was lower than the population (1.3%). The results confirm earlier attempts to show a left shift in homosexuals, and support Geschwind's hypotheses about etiological factors for both lefthandedness and homosexuality.

Adult↗
PubMed1992

The relation of body height to handedness in male and female right- and left-handed human subjects.

The association between body size and the degree of hand preference was studied in male and female right- and left-handed human subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. In left-handers (total sample), there was a significant, negative linear correlation between the degree of left-hand preference and body height. There was no significant correlation between these parameters if the males and females were considered separately. In right-handers (total sample), body height was found to be significantly and negatively linearly correlated with the degree of right-hand preference. A similar correlation was observed in males without familial sinistrality (FS-) and in FS+ females. There was no significant correlation between these parameters in FS+ right-handed males and FS- right-handed females. It was suggested that hormones affecting body height and brain size such as human growth hormone and testosterone would also contribute to the development of cerebral lateralization.

Adult↗
PubMed1993

Grasp reflex strength from right and left hands is associated with pH stressor from the umbilical arterial blood in human newborns: handedness and sex-related differences.

Grasp reflex and its asymmetry was studied in relation to pH of the umbilical blood in human newborns, to examine whether the degree of acidity in fetal blood (birth stress) is associated with cerebral laterality. Low pH values were considered as an index for birth stress. Grasp-reflex strength was found to be directly related to pH in total sample. There were sex-related differences. Namely, this correlation was true only for female newborns, not for males. Right minus left grasp-reflex strength linearly increased with pH, i.e., low pH values were associated with left-hand dominance, but only in males. The grasp-reflex asymmetry was not related to pH in females. It was concluded that blood pH may be associated with motor asymmetry and motor development in human newborns, but show sex-related differences; female brain seemed to be more sensitive to pH changes than male brain. The results partly supported the Bakan's hypothesis that birth stress may be associated with left-handedness.

Dominance, Cerebral↗
PubMed1996

Functional brain asymmetry, handedness and age characteristics of climacterium in women.

A total of 1985 women aged between 55 and 65 were distributed into two groups (145 left-handers and 1840 right-handers). They were asked to complete a questionnaire on the appearance of menopause, duration of menopausal transition and age of menopause. In left-handed women a significantly earlier appearance of premenopause was established together with a shorter menopause transition and an earlier occurrence of menopause. These results give grounds for a correlation between handedness, functional brain asymmetry, respectively and the genetically determined fading away of ovary steroidogenesis associated with the appearance and progression of the climacterium. In light of the available literature we assume that progressive reduction in ovarian function during climacterium is coupled with possible specific functioning of the hypothalamo-pituitary-gonadal axis, dependent on the type of hemispheric asymmetry.

Aged↗