An investigation of immune system disorder as a "marker" for anomalous dominance

Geschwind and Galaburda (1987) proposed that immune disorder (ID) susceptibility, along with left handedness and familial sinistrality (FS), is a "marker" for anomalous dominance. The theory predicts lesser left lateralization for language processes, lessened left hemisphere abilities, and enhanced right hemisphere abilities. We assessed language laterality (dichotic consonant vowel task) and performances on spatial and verbal tasks. Subjects were 128 college students. The factors of handedness, sex, FS, and immune disorder history (negative or positive) were perfectly counterbalanced. Left-handers were significantly less lateralized for language and scored lower than right-handers on the spatial tasks. Females scored lower on mental rotation than males, but performed comparably to males on the spatial relations task. The only effect of ID was by way of interaction with FS on both spatial tasks--subjects who were either negative or positive on both FS and ID status factors scored significantly higher than subjects negative for one but positive for the other factor. A speculative explanatory model for this interaction was proposed. The model incorporates the notion that FS and ID factors are comparably correlated, but in opposite directions, with hormonal factors implicated by other research as relevant for spatial ability differences. Finally, no support for the "anomalous dominance" hypothesis predictions was found.     

Speech dominance and handedness in the normal human

Spectral analysis was used to measure the coherence or similarity of form between occipital and temporal evoked potentials. In both right- and left-handers, coherence was greater in the left hemisphere for click stimuli and in the right hemisphere for flash stimuli. Similar asymmetries occurred in left but not right speech dominant patients whose speech lateralization has been determined by the intracarotid amytal test. Right-handers and males, however, showed significantly larger amplitudes of auditory responses in the right hemisphere. Left-handers and females reversed this pattern. It was concluded that within a basically left speech dominant organization, males and right-handers would emphasize the verbal, temporal structure of auditory information and the nonverbal, spatial structure of visual information. Females and left-handers would tend to reverse this emphasis.     

Women who excel on a spatial task: proposed genetic and environmental factors

A "bent twig" model which incorporates Annett's genetic handedness theory with an environmental component predicted characteristics of college women likely to excel on a mental rotation task. Those likely to have the necessary combination of genetic potential and prior experiences are right-handed women with non-right-handed relatives who rate themselves high in spatial experiences. This subgroup significantly outperformed all other groups of right-handed women on the Vandenberg Mental Rotation Test. This study provides support for the view that family handedness and spatial experiences are important factors influencing mental rotation ability in women.     

Mental rotation and handedness: differences in object-based and egocentric transformations

This study investigates mental rotation performance of right- and left-handers in object-based and egocentric mental rotation tasks using human body stimuli with an outstretched arm in front and back view. Previous literature suggests that right-handers show a slightly better mental rotation performance than left-handers. 42 participants, 14 left-handers and 28 right-handers, completed a mental rotation task with object-based and egocentric transformation of a human figure which was displayed either in front or back view. The main result was a three-way interaction between the factors “kind of transformation”, “handedness” and “view” in a way, that right-handers show significantly faster reaction times then left-handers in front view object-based transformations because of the additional in-depth rotation for front view stimuli. This difference disappeared in egocentric tasks due to the modification of onés own perspective to solve the task. The results of this study show that right-handers not generally outperform left-handers in mental rotation tasks but only if more cognitive resources are needed.     

Intellectual differences in relation to personal and family handedness

Right, mixed and left-handed college students were given the complete WAIS, and a series of cognitive factor tests. Results showed left- and mixed-handed individuals to have a significantly lower full scale I.Q. than right-handers. There was no difference between the mixed and left-handers. In all three handedness groups, subjects with a positive family history of sinistrality had a lower full scale I.Q. than did subjects without left-handed relatives. Neither handedness nor family history differentially affected the Verbal or Performance subscales, nor did they have a significant effect on scores in the other cognitive tests. These results are discussed with respect to Levy's theory of hemispheric specialization, and to the role of inheritance and brain damage in the causation of left- and mixed-handedness.     

Skill, strength, handedness, and fatigue

Thirty male subjects, 20 of whom were self-classified left-handers and 10 right-handers, were tested on a grip-strength task and a handwriting task with each hand, both under normal conditions and in a situation of induced experimental fatigue. On the basis of questionnaire scores, the left-handers were sub-divided into two groups comprising the 10 most left-handed and the 10 least left-handed subjects. The test of grip strength showed a small but significant deterioration in performance of both hands from fatigue. With the handwriting task, a similar significantly adverse effect of fatigue was recorded for all groups as well as a large significant difference in performance between the preferred and nonpreferred hands under normal conditions, which decreased under fatigue. An explanation of these differential effects is discussed in terms of the greater efficiency of the preferred hand in the highly developed skill of handwriting.     

Individual differences in spatial relation processing: effects of strategy, ability, and gender

Numerous studies have focused on the distinction between categorical and coordinate spatial relations. Categorical relations are propositional and abstract, and often related to a left hemisphere advantage. Coordinate relations specify the metric information of the relative locations of objects, and can be linked to right hemisphere processing. Yet, not all studies have reported such a clear double dissociation; in particular the categorical left hemisphere advantage is not always reported. In the current study we investigated whether verbal and spatial strategies, verbal and spatial cognitive abilities, and gender could account for the discrepancies observed in hemispheric lateralization of spatial relations. Seventy-five participants performed two visual half field, match-to-sample tasks (Van der Ham, van Wezel, Oleksiak, & Postma, 2007; Van der Ham, Raemaekers, van Wezel, Oleksiak, and Postma, 2009) to study the lateralization of categorical and coordinate relation processing. For each participant we determined the strategy they used in each of the two tasks. Consistent with previous findings, we found an overall categorical left hemisphere advantage and coordinate right hemisphere advantage. The lateralization pattern was affected selectively by the degree to which participants used a spatial strategy and by none of the other variables (i.e., verbal strategy, cognitive abilities, and gender). Critically, the categorical left hemisphere advantage was observed only for participants that relied strongly on a spatial strategy. This result is another piece of evidence that categorical spatial relation processing relies on spatial and not verbal processes.     

The influence of handedness on profile and line drawing directionality in children,young, and older normal adults

One hundred twenty-two normal subjects--children, young and older adults (77 right-handers and 45 left-handers)--performed two drawing tasks in order to study their directionality trends. The first task consisted of drawing the profile of a face and in the second task subjects had to link two points in order to draw a line. The analysis of the drawing directionality revealed a significant effect of the age when right-handers drew profiles whereas this effect reached significance in left-handed subjects only when drawing lines. Left- and right-handers' performances across the two tasks were found to significantly differ. Results are discussed in terms of hemispheric and environmental factors.     

Spatial and Selective Attention in the Cerebral Hemispheres in Depression, Mania, and Schizophrenia

Two tachistoscopic tests examining distinct aspects of attention were administered to normal subjects and patients with depression, mania, and schizophrenia. The first examined spatial attentional bias using happy-sad chimeric faces, known to elicit a perceptual bias to the left side of space in normal right-handers provided the right cerebral hemisphere is intact. The second used a lateralized version of the Stroop task, a traditional test of selective attention. Normals showed the expected leftward perceptual bias but showed equivalent susceptibility to the Stroop effect in both visual fields. As previously demonstrated with chimeric faces viewed in free vision, depression and mania were associated with weak and strong biases respectively with schizophrenics showing no bias to either side of space. The relationship between perceptual bias, as assessed by reaction time and absolute performance and the Stroop effect, showed differences according to diagnosis. This may be interpreted as evidence for the dissociability of attentional processes as well as lateralized differences in the pattern of cerebral activation in affective disorders and schizophrenia. The independence of performance variables on these tests in the schizophrenic group points to severe neuropsychological dysfunction.     

Persisting apraxia in two left-handed, aphasic patients with right-hemisphere lesions

Apraxia usually follows a left hemisphere lesion in right-handers with left hemisphere speech representation. Apraxia following a right hemisphere lesion in left-handers is rare, however, and not well documented in the literature. Two left-handed patients are described in whom apraxia and aphasia followed a right hemisphere lesion. Both the apraxic and the aphasic deficits improved but were still demonstrable 6 weeks following the infarct. The data are consistent with those for right-handers with left hemisphere lesions in suggesting some overlap of anatomical structures for the control of speech and praxis.     

Sexual orientation and handedness in men and women: a meta-analysis

Recent findings suggest that sexual orientation has an early neurodevelopmental basis. Handedness, a behavioral marker of early neurodevelopment, has been associated with sexual orientation in some studies but not in others. The authors conducted a meta-analysis of 20 studies that compared the rates of non-right-handedness in 6,987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) participants. Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men (20 contrasts) and women (9 contrasts) were 34% and 91%, respectively. The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation. The authors discuss 3 possibilities: cerebral laterality and prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability.     

Sex and handedness differences in EEG measures of hemispheric specialization

EEG alpha asymmetry was studied in 90 normal adults: right-handed, left-handed, and ambidextrous, male and female. Recordings were made from homologous central, parietal, and occipital leads, referenced to vertex, while subjects engaged in writing, speaking, reading, listening to speech, singing, and block design construction. These data confirm our previous findings that alpha asymmetry is task-dependent and extend them to a broader range of tasks, subjects, and leads. Among right-handers significant differences were found between the language tasks and the musical and spatial tasks: the $\text{R}\text{L}$ alpha ratio is higher in the language tasks. In addition, significant ordering of $\text{R}\text{L}$ alpha ratios was found among the language tasks themselves: WRITE å SPEAK > READ > LISTEN. No one “verbal” task can be considered representative of all language behaviors. Task differences in asymmetry were greater at the central than at the parietal leads, and no differences were found at the occiput. Differences among the handedness groups were found in $\text{R}\text{L}$ alpha ratio in specific tasks, in the relationship among tasks, and in alpha power level. Non-right-handers showed less task-dependent asymmetry. On some measures ambidexters appear to be a distinct group, not simply representing the middle range of a left-handed/right-handed continuum. Reversal of the “expected” right-handed pattern (SPEAK $\text{R}\text{L}$ ratio > BLOCKS $\text{R}\text{L}$ ratio) was seen in 10% of right-handers, and in 36% of left-handers, particularly among left-handed females (46%), suggesting a possible sex difference among non-right-handers. No sex difference was found among right-handers on any task with any measure at any lead.     

A lateralization of function approach to sex differences in spatial ability: a reexamination

The current study assessed the lateralization of function hypothesis (Rilea, S. L., Roskos-Ewoldsen, B., & Boles, D. (2004). Sex differences in spatial ability: A lateralization of function approach. Brain and Cognition, 56, 332–343) which suggested that it was the interaction of brain organization and the type of spatial task that led to sex differences in spatial ability. A second purpose was to evaluate explanations for their unexpected findings on the mental rotation task. In Experiment 1, participants completed the Water Level, Paper Folding, and mental rotation tasks (using an object-based or self-based perspective), presented bilaterally. Sex differences were only observed on the Water Level Task; a right hemisphere advantage was observed on Water Level and mental rotation tasks. In Experiment 2, a human stick figure or a polygon was mentally rotated. Men outperformed women when rotating polygons, but not when rotating stick figures. Men demonstrated a right hemisphere advantage when rotating polygons; women showed no hemisphere differences for either stimulus. Thus, hemisphere processing, task complexity, and stimulus type may influence performance for men and women across different spatial measures.     

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.     

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.     

利手与内隐左右空间情感效价关系的眼动研究

为探明手动作流畅性和情感材料呈现空间在不同利手者左右空间情感偏好中的关系,本研究将情绪Stroop范式和眼动测量相结合,通过反应速度和眼动数据将动作流畅性和空间情感注意偏向相分离,并考察其交互作用。结果发现右利手个体的反应速度存在优势手效应,不同利手者在使用左手时表现出对优势手同侧空间的内隐情感偏好,表明右利手个体的反应速度存在优势手流畅性的主导作用,手动作流畅性和内隐空间情感偏好的作用可以分离。     

Familial handedness and spatial ability: a study with Chinese students aged 14-24

This study tested Annett's right-shift theory on spatial ability with two samples from China. The Vandenberg Mental Rotation Test (MRT), Edinburgh Handedness Inventory, and Family Handedness Questionnaire were administered to 266 high school students and 297 undergraduates. We found very few r++ or r-- among Chinese students. Most Chinese are either moderately right-handed or ambidextrous. Consistent with Casey's finding, we found using different methods to classify handedness leads to different conclusions. However, we did not find the effect of familial handedness that Casey found. Visual strategy is related to success on the MRT but handedness is not.     

Differential visual field-interhemispheric transfer: can it explain sex and handedness differences in lateralization?

104 men and women were tested for visual field-hemispheric transfer of spatial information on a dot-localization task. Right-handed subjects showed significant improvement when stimuli were presented to the left visual field of the right hemisphere (LVF-RH) after practice on the same task presented to the right visual field of the left hemisphere (RVF-LH) first. No improvement was found when the task was presented in the reverse order (LVF-RH first followed by RVF-LH). It was concluded that, for right-handers, transfer of spatial information to the right hemisphere is facilitated while transfer to the left hemisphere is inhibited. Left-handed subjects demonstrated no significant improvement in either condition, suggesting inhibition or lack of transfer of spatial information in either direction. No sex differences were found in either right-handed or left-handed subjects. The findings suggest that there may be different mechanisms underlying the similarities in functional lateralization of women and left-handers.     

Familial handedness and its relation to spatial ability following strategy instructions

This study compared subjects from right-handed families with subjects from nonrighthanded families in their ability to solve a mental-rotation task when instructed to use one of two different spatial strategies. All subjects completed a pretest Vandenberg. Next, one of the following procedures was presented prior to administering the Vandenberg posttest: Group 1 was given mental-rotation instructions, Group 2 was given spatial-orientation instructions, and Group 3 (control group) was given no special directions. For familial right-handers, no condition effects were found. In contrast, familial nonright-handers benefited significantly from mental-rotation instructions when compared both to their own control group and to familial right-handed subjects given the same instructions. However, with orientation instructions, the familial nonright-handers showed significantly less posttest improventnt than their control group. These results suggests familial non-rright-handers may be stronger in ability to use one spatial strategy, transformation of mental images, and weaker on a second, reorientation in relation to left-right cues. The educational and research implications of these findings are discussed.     

Visuospatial competency, handedness, and cerebral dominance

The present study addressed the question of Levy's (1974, Psychobiological implications of bilateral assymetry. In S. Dimond &; J. G. Beaumont, Hemispheric function in the human brain, NY: Halstead. Pp. 121–183.) proposal that left handers would have lowered spatial skills relative to verbal skills. In the first part of the study, performance on the PMA (visuospatial subtest) and WAIS Block Design subtest were compared between right and left handed high school and college samples. No support could be found for deficient visuo-spatial performance in the left handers. In the second part of the experiment, no relative impairment of visuospatial skills was found when subjects were classified into predicted speech dominance groups on the basis of a dichotic listening task and/or a visual half-field task. An extreme groups comparison of the most left dominant and most right dominant groups again yielded no significant differences in visuo-spatial performance. Finally, the relationship between degree of speech lateralization and visuo-spatial skills was examined. Only partial support for differences in cerebral organization for speech in left handers was found in the college sample.