Cerebral laterality as assessed by hand preference measures and developmental stuttering

Hand Preference in Stuttering: Meta-Analyses

Reduced hemispheric asymmetries, as well as their behavioral manifestation in the form of atypical handedness (i.e., non-right, left-, or mixed-handedness), are linked to neurodevelopmental disorders, such as autism spectrum disorder, and several psychiatric disorders, such as schizophrenia. One neurodevelopmental disorder that is associated with reduced hemispheric asymmetries, but for which findings on behavioral laterality are conflicting, is stuttering. Here, we report a series of meta-analyses of studies that report handedness (assessed as hand preference) levels in individuals who stutter (otherwise healthy) compared to controls. For this purpose, articles were identified via a search in PubMed, Scopus, and PsycInfo (13 June 2023). On the basis of k = 52 identified studies totaling n = 2590 individuals who stutter and n = 17,148 controls, five random effects meta-analyses were conducted: four using the odds ratio [left-handers (forced choice); left-handers (extreme); mixed-handers; non-right-handers vs. total)] and one using the standardized difference in means as the effect size. We did not find evidence of a left (extreme)- or mixed-handedness difference or a difference in mean handedness scores, but evidence did emerge, when it came to left-handedness (forced-choice) and (inconclusively for) non-right-handedness. Risk-of-bias analysis was not deemed necessary in the context of these meta-analyses. Differences in hand skill or strength of handedness could not be assessed as no pertinent studies were located. Severity of stuttering could not be used s a moderator, as too few studies broke down their data according to severity. Our findings do not allow for firm conclusions to be drawn on whether stuttering is associated with reduced hemispheric asymmetries, at least when it comes to their behavioral manifestation.

Family History of Stuttering among Kurdish Children Who Stutter Near the Age of Onset

Background

The family history of stuttering is one of the most important factors for the prediction of recovery from stuttering. There is a high controversy about the rate of positive family history of stuttering among people who stutter (PWS). In the present study, the family history of stuttering in the first-, second-, and third-degree relatives was investigated among a group of Kurdish children who stuttered (CWS) close to the onset of the disorder.

Materials and Methods

One hundred and seventy-two CWS, including 46 females (24.60%) aged 2-5 years (mean age: 3.71 years, SD = 0.75) were consecutively recruited. They were first examined close to the onset of the stuttering. Data about current and former stuttering among first-, second-, and third-degree relatives were collected using interviews with both parents. Data was described and analyzed by independent sample t test or Chi-square.

Results

Among 172 CWS (mean age: 3.71 years, SD = 0.75), 119 (69.20%) reported a family history of stuttering. According to the result, the most family history of stuttering was reported among third-degree relatives (32.60%). Sixty-five participants (37.80%) reported just one relative with stuttering. CWS with a positive family history of stuttering had no significant difference with CWS without a positive family history of stuttering in sex (P = 0.48) and age of stuttering onset (P = 0.96).

Conclusion

The rate of positive family history of stuttering among Kurdish CWS is similar to previously reported data in the same age group. There was no significant association of family history of stuttering with sex and age on the onset of the disorder.

Hand preference and Mathematical Learning Difficulties: New data from Greece, the United Kingdom, and Germany and two meta-analyses of the literature

Increased rates of atypical handedness are observed in neurotypical individuals who are low-performing in mathematical tasks as well as in individuals with special educational needs, such as dyslexia. This is the first investigation of handedness in individuals with Mathematical Learning Difficulties (MLD). We report three new studies (N = 134; N = 1,893; N = 153) and two sets of meta-analyses (22 studies; N = 3,667). No difference in atypical hand preference between MLD and Typically Achieving (TA) individuals was found when handedness was assessed with self-report questionnaires, but weak evidence of a difference was found when writing hand was the handedness criterion in Study 1 (p = .049). Similarly, when combining data meta-analytically, no hand preference differences were detected. We suggest that: (i) potential handedness effects require larger samples, (ii) direction of hand preference is not a sensitive enough measure of handedness in this context, or that (iii) increased rates of atypical hand preference are not associated with MLD. The latter scenario would suggest that handedness is specifically linked to language-related conditions rather than conditions related to cognitive abilities at large. Future studies need to consider hand skill and degree of hand preference in MLD.