Patterns of handedness and footedness in switched and nonswitched Brazilian left-handers: cultural effects on the development of lateral preferences.

In Western societies most left-handers who are pressured to write with the right hand resist the pressure. Searleman and Porac (2001, 2003) studied North American participants and proposed that mixed left-handers, more so than consistent left-handers, would be likely to successfully acquire right-handed writing skills on a long-term basis. In accordance with their two-phenotype hypothesis, the majority of switched left-handers (SLH) in their studies exhibited right-sided asymmetries on other handedness tasks such as throwing, and, in addition, tended to be right-footed.

A cross-cultural comparison of pressures to switch left-hand writing: Brazil versus Canada.

Attempts to switch left-hand preferences towards the right side are socialisation practices found in many countries (Perelle & Ehrman, 1994). Although researchers acknowledge that pressures against left-hand use contribute to the cross-cultural fluctuations in the prevalence of left- versus right-hand preference, there has been little systematic cross-cultural study of how these pressures are applied, and who are the major agents applying the pressures to change. Our study explored specific rightward conversion practices and the results of these practices among individuals from two countries.

Deriving estimates of contralateral footedness from prevalence rates in samples of Brazilian and non-Brazilian right- and left-handers.

Although footedness is closely associated with handedness, accurate prevalence rates of contralateral footedness in right- and left-handed populations were previously unavailable to researchers studying the relationship between phenotypic and hemispheric asymmetries. We collected preference data from 2081 Brazilian children and adolescents, and relate the prevalence of crossed hand/foot preferences to values reported elsewhere in the literature. In our samples, about 4% of the dextrals and 33% of the sinistrals exhibited a contralateral kicking preference.

Footedness across the age span among Brazilian right- and left-handers.

Previous cross-sectional surveys have reported a decreasing prevalence of left-footedness with increasing age. Bell and Gabbard attributed this pattern to a developmental process wherein the right hemisphere ages earlier than the left, leading to a decline in left-footedness among older individuals. A major flaw in this hypothesis is that age-related data were derived exclusively from right-handed samples.

Mean mortality among Brazilian left- and right-handers: modification or selective elimination?

Many surveys report a higher incidence of left-handedness in younger than in older cohorts, and explanations for this phenomenon have centred around two rival hypotheses. The modification hypothesis attributes this trend to secular differences in the social tolerance of left-handed preferences, whereas the elimination hypothesis contends that left-handers have a shorter life-span than right-handers do, and hence are infrequent in the population above age 70. In order to evaluate these two hypotheses, data were collected on 513 decedents from kin informants.