Alan Searleman

Environmental factors in hand preference formation: Evidence from attempts to switch the preferred hand

We surveyed 650 young adults to assess both their current handedness behaviors and past attempts to shift their hand preference. We found that 73 (11.2%) individuals had experienced hand preference change attempts and 52 (8.0%) had undergone pressure to switch hand preference to the right. The likelihood that an individual had experienced pressure to change hand use was not related significantly to gender or to a number of familial factors. However, the success of the hand change varied with gender; females reported greater success in shifting their handedness.

Subject Variables and Cerebral Organization for Language

The present study investigated the usefulness of a variety of subject variables that have been proposed as having predictive value for determining cerebral organization for language. To accomplish this, a total of 373 subjects (117 left-handers and 256 right-handers) were given 240 trials of a consonant-vowel dichotic listening task to assess direction and degree of language lateralization. Each subject was also classified on the basis of eight subject variables (handedness, strength of handedness, familial sinistrality, writing hand posture, sex, sighting dominance, preferred footedness, and overall laterality). The results of the study indicated that left hemisphere language processing is very pervasive and that most of the subject variables examined were not very useful predictors of language lateralization. In addition, surprisingly, footedness and not handedness was the single best predictor of cerebral organization for language.

Suspected autoimmune disorders and left-handedness: evidence from individuals with diabetes. Crohn's disease and ulcerative colitis.

This study tested the theory that left-handedness is associated with certain disorders that may have an autoimmune aetiology. To accomplish this, we compared the handedness patterns of people with either Type I or Type II diabetes, Crohns disease, or ulcerative colitis with a normal control group. Consistent with earlier findings, a significantly higher incidence of left-handedness was observed in people with either Crohns disease or ulcerative colitis. In addition, there was evidence that males with Type I diabetes were more likely to be left-handed than males with Type II diabetes.

Cognitive Abilities and Left-Handedness: An Interaction between Familial Sinistrality and Strength of Handedness.

Abstract The present study demonstrates that there are substantial differences in cognitive ability between different subsets of left-handers. The verbal and mathematical Scholastic Aptitude Test (SAT) scores of 86 left-handed undergraduates were examined as a function of familial sinistrality, strength of left-handedness, and sex. The results revealed that there was an interaction between familial sinistrality and strength of handedness in terms of aptitude: for the weakly to moderately left-handed there was no relationship between familial sinistrality and performance, whereas for the strongly left-handed a positive history of familial sinistrality (FS+) was associated with significantly lower aptitude when compared with subjects without a history of familial sinistrality (FS−). In addition, the strongly left-handed FS− group was superior to the other three groups, particularly in verbal aptitude.

Relationship between birth order, birth stress, and lateral preferences: a critical review.

Reviews the literature examining the relationship between birth order, birth stress, and lateral preferences in nonclinical samples, with special emphasis on reports since 1971. The review found no evidence to relate birth order position to deviations from right-sidedness for either sex. More direct measures of birth stress indicated that deviations from right-handedness (particularly for male subjects), and also right-eyedness, were statistically related to specific birth stressors. It should be stressed, however, that all the relationships, including the significant ones, were very weak, accounting for less than 1% of the variance. When statistical significance was achieved, it was largely due to the huge sample sizes used in the meta-analyses. Methological and theoretical problems exist in the current literature, and we offer some suggestions to resolve them.

Rate of physical maturation and handedness

Early versus late physical maturation was measured in 713 females and 467 males using the onset of secondary sexual characteristics, age of menarche, and relative body size. Delayed rates of maturation were associated with an increased incidence of left‐handedness in both sexes.

The ontogeny of hemispheric specialization: Evidence from dichotic listening in twins

Abstract To determine if variation in the direction and/or degree of hemispheric asymmetry for speech perception among right handers has a heritable component, 53 monozygotic (MZ) and 35 dizygotic (DZ) right handed, same sex twin pairs were tested with a 240 trial consonant-vowel dichotic listening test. Intraclass correlations for MZ and DZ pairs for handedness and various measures of ear asymmetry, including absolute values, were not significantly different, while MZ pairs showed a significantly higher correlation for overall total correct, a measure unrelated to the laterality scores. Concordance for direction of ear asymmetry alone was not significantly greater among MZ than DZ pairs. These results support the hypothesis that variation in direction and degree of lateralization for speech processing in right handers is non-genetic in origin. A comparison of MZ, DZ, and singleton groups showed all three to be equivalent in terms of mean scores on the laterality and total correct measures, indicating that these twins are not atypical of the general population on these measures. Sex differences as well as effects of familial sinistrality were observed in the twin sample.

Interrelationships among subject variables believed to predict cerebral organization

Abstract A variety of subject variables have been proposed as having predictive value for determining cerebral organization. Subject variables proposed as likely candidates include strength of handedness, familial sinistrality, writing posture, and sex. The present study examined the interrelationships among these variables by means of a questionnaire given to 847 undergraduates.

Birth stress and left-handedness : the rare trait marker model

Publisher Summary This chapter illustrates the operation of the rare trait marker model in the context of a relationship between birth stressors and the appearance of left-handedness. The rare trait marker model is a statistical model that does not rely on any particular mechanism but simply operates on a population in which there is an asymmetrical distribution of traits, with one trait or set of traits rarer than the others. The chapter makes a few simplifying assumptions to demonstrate the operation of this model. The computational procedures might prove to be a good means to estimate the likelihood that left-handedness would result from other manifestations of birth stress. The use of the rare trait marker model produced other outcomes of theoretical interest in the past. Based on the present data set, the relative risk of left-handedness as a function of increasing maternal age is larger for males than females. The data, however, indicate that males and females do not differ qualitatively in terms of their susceptibility to stressors but may differ only in threshold, with females requiring a greater dose to trigger the effects. One unexpected finding of theoretical interest is that the original distribution of right-handedness (R) is similar for both males and females. The operation of birth stressors on the development of handedness appears to be reasonably established.

Personal need for structure, the einstellung task, and the effects of stress

Abstract We examine the relationship between the personality variable of Personal Need for Structure (PNS) and problem solving on the Einstellung water-jar task. The Einstellung task was administered under stressful and nonstressful conditions. Results from 172 participants showed the predicted interaction between PNS and experimentally-induced stress: Participants higher in PNS were more likely to develop a mental set under stressful conditions, while no significant relationship was found between PNS and set development under nonstressful conditions. PNS was not related to perseveration on the Einstellung task, regardless of experimental condition. These findings are consistent with recent research on the importance of contextual activation of personality.